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    <H1 CLASS="centered">A CATECHISM OF THE STEAM ENGINE</H1>

    <H2 CLASS="centered">IN ITS VARIOUS APPLICATIONS TO MINES, MILLS, STEAM
    NAVIGATION, RAILWAYS, AND AGRICULTURE.</H2>

    <H2 CLASS="centered">WITH</H2>

    <H2 CLASS="centered">PRACTICAL INSTRUCTIONS FOR THE MANUFACTURE AND
    MANAGEMENT OF ENGINES OF EVERY CLASS.</H2>

    <H3 CLASS="centered">BY</H3>

    <H3 CLASS="centered">JOHN BOURNE, C.E.</H3>

    <P CLASS="centered" STYLE="font-style: italic">NEW AND REVISED
    EDITION.</P>

    <P>&nbsp;</P>

 
    <H3 CLASS="subhead">PREFACE TO THE FOURTH EDITION.</H3>

    <P>For some years past a new edition of this work has been called for,
    but I was unwilling to allow a new edition to go forth with all the
    original faults of the work upon its head, and I have been too much
    engaged in the practical construction of steam ships and steam engines
    to find time for the thorough revision which I knew the work required.
    At length, however, I have sufficiently disengaged myself from these
    onerous pursuits to accomplish this necessary revision; and I now offer
    the work to the public, with the confidence that it will be found
    better deserving of the favorable acceptation and high praise it has
    already received. There are very few errors, either of fact or of
    inference, in the early editions, which I have had to correct; but
    there are many omissions which I have had to supply, and faults of
    arrangement and classification which I have had to rectify. I have also
    had to bring the information, which the work professes to afford, up to
    the present time, so as to comprehend the latest improvements.</P>

    <P>For the sake of greater distinctness the work is now divided into
    chapters. Some of these chapters are altogether new, and the rest have
    received such extensive additions and improvements as to make the book
    almost a new one. One purpose of my emendations has been to render my
    remarks intelligible to a tyro, as well as instructive to an advanced
    student. With this view, I have devoted the first chapter to a popular
    description of the Steam Engine--which all may understand who can
    understand anything--and in the subsequent gradations of progress I
    have been careful to set no object before the reader for the first
    time, of which the nature and functions are not simultaneously
    explained. The design I have proposed to myself, in the composition of
    this work, is to take a young lad who knows nothing of steam engines,
    and to lead him by easy advances up to the highest point of information
    I have myself attained; and it has been a pleasing duty to me to smooth
    for others the path which I myself found so rugged, and to impart, for
    the general good of mankind, the secrets which others have guarded with
    so much jealousy. I believe I am the first author who has communicated
    that practical information respecting the steam engine, which persons
    proposing to follow the business of an engineer desire to possess. My
    business has, therefore, been the rough business of a pioneer; and
    while hewing a road through the trackless forest, along which all might
    hereafter travel with ease, I had no time to attend to those minute
    graces of composition and petty perfection of arrangement and
    collocation, which are the attribute of the academic grove, or the
    literary parterre. I am, nevertheless, not insensible to the advantages
    of method and clear arrangement in any work professing to instruct
    mankind in the principles and practice of any art; and many of the
    changes introduced into the present edition of this work are designed
    to render it less exceptionable in this respect. The woodcuts now
    introduced into the work for the first time will, I believe, much
    increase its interest and utility; and upon the whole I am content to
    dismiss it into circulation, in the belief that those who peruse it
    attentively will obtain a more rapid and more practical acquaintance
    with the steam engine in its various applications, than they would be
    likely otherwise to acquire.</P>

    <P>I have only to add that I have prepared a sequel to the present
    work, in the shape of a Hand-Book of the Steam Engine, containing the
    whole of the rules given in the present work, illustrated by examples
    worked out at length, and also containing such useful tables and other
    data, as the engineer requires to refer to constantly in the course of
    his practice. This work may be bound up with the &quot;Catechism,&quot;
    if desired, to which it is in fact a Key.</P>

    <P>I shall thankfully receive from engineers, either abroad or at home,
    accounts of any engines or other machinery, with which they may become
    familiar in their several localities; and I shall be happy, in my turn,
    to answer any inquiries on engineering subjects which fall within the
    compass of my information. If young engineers meet with any difficulty
    in their studies, I shall be happy to resolve it if I can; and they may
    communicate with me upon any such point without hesitation, in whatever
    quarter of the world they may happen to be.</P>

    <P>JOHN BOURNE.<BR>
    9 BILLITER STREET,<BR>
    LONDON,<BR>
    <EM>March 1st, 1856</EM>.</P>

    <H3 CLASS="subhead">PREFACE TO THE FIFTH EDITION.</H3>

    <P>The last edition of the present work, consisting of 3,500 copies,
    having been all sold off in about ten months, I now issue another
    edition, the demand for the work being still unabated. It affords,
    certainly, some presumption that a work in some measure supplies an
    ascertained want, when, though addressing only a limited
    circle--discoursing only of technical questions, and without any
    accident to stimulate it into notoriety,--it attains so large a
    circulation as the present work has reached. Besides being reprinted in
    America, it has been translated into German, French, Dutch, and I
    believe, into some other languages, so that there is, perhaps, not too
    much vanity in the inference that it has been found serviceable to
    those perusing it. I can with truth say, that the hope of rendering
    some service to mankind, in my day and generation, has been my chief
    inducement in writing it, and if this end is fulfilled, I have nothing
    further to desire.</P>

    <P>I regret that circumstances have prevented me from yet issuing the
    &quot;Hand-Book&quot; which I have had for some time in preparation,
    and to which, in my Preface of the last year, I referred. I hope to
    have sufficient leisure shortly, to give that and some other of my
    literary designs the necessary attention. Whatever may have been the
    other impediments to a more prolific authorship, certainly one of them
    has not been the coldness of the approbation with which my efforts have
    been received, since my past performances seem to me to have met with
    an appreciation far exceeding their deserts.</P>

    <P>JOHN BOURNE.</P>

    <P><EM>February 2d, 1857</EM>.</P>

    <H3 CLASS="subhead">PUBLISHERS&#39; NOTICE.</H3>

    <P>In offering to the American public a reprint of a work on the Steam
    Engine so deservedly successful, and so long considered standard, the
    publishers have not thought it necessary that it should be an exact
    copy of the English edition; there were some details in which they
    thought it could be improved, and better adapted to the use of American
    engineers. On this account, the size of the page has been increased to
    a full 12mo, to admit of larger illustrations, which in the English
    edition are often on too small a scale; and some of the illustrations
    themselves have been supplied by others equally applicable, more
    recent, and to us more familiar examples. The first part of Chapter XI,
    devoted in the English edition to English portable and fixed
    agricultural engines, in this edition gives place entirely to
    illustrations from American practice, of steam engines as applied to
    different purposes, and of appliances and machines necessary to them.
    But with the exception of some of the illustrations and the description
    of them, and the correction of a few typographical errors, this edition
    is a faithful transcript of the latest English edition.</P>

    <H3 CLASS="subhead">CONTENTS.</H3>

    <P><A HREF="#a01">Classification of Engines.</A></P>

    <P><A HREF="#a02">Nature and uses of a Vacuum.</A></P>

    <P><A HREF="#a03">Velocity of falling Bodies and Momentum of moving
    Bodies.</A></P>

    <P><A HREF="#a04">Central Forces.</A></P>

    <P><A HREF="#a05">Centres of Gravity, Gyration, and
    Oscillation.</A></P>

    <P><A HREF="#a06">The Pendulum and Governor.</A></P>

    <P><A HREF="#a07">The Mechanical Powers.</A></P>

    <P><A HREF="#a08">Friction.</A></P>

    <P><A HREF="#a09">Strength of materials and Strains subsisting in
    Machines.</A></P>

    <P><A HREF="#ch01">CHAP. I.--GENERAL DESCRIPTION OF THE STEAM
    ENGINE.</A></P>

    <P><A HREF="#b01">The Boiler.</A></P>

    <P><A HREF="#b02">The Engine.</A></P>

    <P><A HREF="#b03">The Marine Engine.</A></P>

    <P><A HREF="#b04">Screw Engines.</A></P>

    <P><A HREF="#b05">The Locomotive Engine.</A></P>

    <P><A HREF="#ch02">CHAP. II.--HEAT, COMBUSTION, AND STEAM.</A></P>

    <P><A HREF="#d01">Heat.</A></P>

    <P><A HREF="#d02">Combustion.</A></P>

    <P><A HREF="#d03">Steam.</A></P>

    <P><A HREF="#ch03">CHAP. III.--EXPANSION OF STEAM AND ACTION OF THE
    VALVES.</A></P>

    <P><A HREF="#ch04">CHAP. IV.--MODES OF ESTIMATING THE POWER AND
    PERFORMANCE OF ENGINES AND BOILERS.</A></P>

    <P><A HREF="#f01">Horses Power.</A></P>

    <P><A HREF="#f02">Duty of Engines and Boilers.</A></P>

    <P><A HREF="#f03">The Indicator.</A></P>

    <P><A HREF="#f04">Dynamometer, Gauges, and Cataract.</A></P>

    <P><A HREF="#ch05">CHAP. V.--PROPORTIONS OF BOILERS.</A></P>

    <P><A HREF="#g01">Heating and Fire Grate Surface.</A></P>

    <P><A HREF="#g02">Calorimeter and Vent.</A></P>

    <P><A HREF="#g03">Evaporative Power of Boilers.</A></P>

    <P><A HREF="#g04">Modern Marine and Locomotive Boilers.</A></P>

    <P><A HREF="#g05">The Blast in Locomotives.</A></P>

    <P><A HREF="#g06">Boiler Chimneys.</A></P>

    <P><A HREF="#g07">Steam Room and Priming.</A></P>

    <P><A HREF="#g08">Strength of Boilers.</A></P>

    <P><A HREF="#g09">Boiler Explosions.</A></P>

    <P><A HREF="#ch06">CHAP. VI.--PROPORTIONS OF ENGINES.</A></P>

    <P><A HREF="#h01">Steam Passages.</A></P>

    <P><A HREF="#h02">Air Pump, Condenser, and Hot and Cold Water
    Pumps.</A></P>

    <P><A HREF="#h03">Fly Wheel.</A></P>

    <P><A HREF="#h04">Strengths of Land Engines.</A></P>

    <P><A HREF="#h05">Strengths of Marine and Locomotive Engines.</A></P>

    <P><A HREF="#ch07">CHAP. VII.--CONSTRUCTIVE DETAILS OF BOILERS.</A></P>

    <P><A HREF="#j01">Land and Marine Boilers.</A></P>

    <P><A HREF="#j02">Incrustation and Corrosion of Boilers.</A></P>

    <P><A HREF="#j03">Locomotive Boilers.</A></P>

    <P><A HREF="#ch08">CHAP. VIII.--CONSTRUCTIVE DETAILS OF
    ENGINES.</A></P>

    <P><A HREF="#k01">Pumping Engines.</A></P>

    <P><A HREF="#k02">Various forms of Marine Engines.</A></P>

    <P><A HREF="#k03">Cylinders, Pistons, and Valves.</A></P>

    <P><A HREF="#k04">Air Pump and Condenser.</A></P>

    <P><A HREF="#k05">Pumps, Cocks, and Pipes.</A></P>

    <P><A HREF="#k06">Details of the Screw and Screw Shaft.</A></P>

    <P><A HREF="#k07">Details of the Paddles and Paddle Shaft.</A></P>

    <P><A HREF="#k08">The Locomotive Engine.</A></P>

    <P><A HREF="#ch09">CHAP. IX.--STEAM NAVIGATION.</A></P>

    <P><A HREF="#m01">Resistance of Vessels in Water.</A></P>

    <P><A HREF="#m02">Experiments on the Resistance of Vessels.</A></P>

    <P><A HREF="#m03">Influence of the size of Vessels upon their
    Speed.</A></P>

    <P><A HREF="#m04">Structure and Operation of Paddle Wheels.</A></P>

    <P><A HREF="#m05">Configuration and Action of the Screw.</A></P>

    <P><A HREF="#m06">Comparative Advantages of Paddle and Screw
    Vessels.</A></P>

    <P><A HREF="#m07">Comparative Advantages of different kinds of
    Screws.</A></P>

    <P><A HREF="#m08">Proportions of Screws.</A></P>

    <P><A HREF="#m09">Screw Vessels with full and auxiliary Power.</A></P>

    <P><A HREF="#m10">Screw and Paddles combined.</A></P>

    <P><A HREF="#ch10">CHAP. X.--EXAMPLES OF ENGINES OF RECENT
    CONSTRUCTION.</A></P>

    <P><A HREF="#p01">Oscillating Paddle Engines.</A></P>

    <P><A HREF="#p02">Direct acting Screw Engine.</A></P>

    <P><A HREF="#p03">Locomotive Engine.</A></P>

    <P><A HREF="#ch11">CHAP. XI.--ON VARIOUS FORMS AND APPLICATIONS OF THE
    STEAM ENGINE.</A></P>

    <P>Governor.</P>

    <P>Donkey Pumps.</P>

    <P>Portable Steam Engines.</P>

    <P>Stationary Engines.</P>

    <P>Steam Fire Engines.</P>

    <P>Steam Excavator.</P>

    <P><A HREF="#ch12">CHAP. XII.--MANUFACTURE AND MANAGEMENT OF STEAM
    ENGINES.</A></P>

    <P><A HREF="#r01">Construction of Engines.</A></P>

    <P><A HREF="#r02">Erection of Engines.</A></P>

    <P><A HREF="#r03">Management of Marine Boilers.</A></P>

    <P><A HREF="#r04">Management of Marine Engines.</A></P>

    <P><A HREF="#r05">Management of Locomotives.</A></P>

    <H2 CLASS="chapter">MECHANICAL PRINCIPLES OF THE STEAM ENGINE.</H2>

    <H4 CLASS="subhead"><A NAME="a01"></A>CLASSIFICATION OF ENGINES.</H4>

    <P>1. <EM>Q.</EM>--What is meant by a vacuum?</P>

    <P><EM>A.</EM>--A vacuum means an empty space; a space in which there
    is neither water nor air, nor anything else that we know of.</P>

    <P>2. <EM>Q.</EM>--Wherein does a high pressure differ from a low
    pressure engine?</P>

    <P><EM>A.</EM>--In a high pressure engine the steam, after having
    pushed the piston to the end of the stroke, escapes into the
    atmosphere, and the impelling force is therefore that due to the
    difference between the pressure of the steam and the pressure of the
    atmosphere. In the condensing engine the steam, after having pressed
    the piston to the end of the stroke, passes into the condenser, in
    which a vacuum is maintained, and the impelling force is that due to
    the difference between the pressure of the steam above the piston, and
    the pressure of the vacuum beneath it, which is nothing; or, in other
    words, you have then the whole pressure of the steam urging the piston,
    consisting of the pressure shown by the safety-valve on the boiler, and
    the pressure of the atmosphere besides.</P>

    <P>3. <EM>Q.</EM>--In what way would you class the various kinds of
    condensing engines?</P>

    <P><EM>A.</EM>--Into single acting, rotative, and rotatory engines.
    Single acting engines are engines without a crank, such as are used for
    pumping water. Rotative engines are engines provided with a crank, by
    means of which a rotative motion is produced; and in this important
    class stand marine and mill engines, and all engines, indeed, in which
    the rectilinear motion of the piston is changed into a circular motion.
    In rotatory engines the steam acts at once in the production of
    circular motion, either upon a revolving piston or otherwise, but
    without the use of any intermediate mechanism, such as the crank, for
    deriving a circular from a rectilinear motion. Rotatory engines have
    not hitherto been very successful, so that only the single acting or
    pumping engine, and the double acting or rotative engine can be said to
    be in actual use. For some purposes, such, for example, as forcing air
    into furnaces for smelting iron, double acting engines are employed,
    which are nevertheless unfurnished with a crank; but engines of this
    kind are not sufficiently numerous to justify their classification as a
    distinct species, and, in general, those engines may be considered to
    be single acting, by which no rotatory motion is imparted.</P>

    <P>4. <EM>Q.</EM>--Is not the circular motion derived from a cylinder
    engine very irregular, in consequence of the unequal leverage of the
    crank at the different parts of its revolution?</P>

    <P><EM>A.</EM>--No; rotative engines are generally provided with a
    fly-wheel to correct such irregularities by its momentum; but where two
    engines with their respective cranks set at right angles are employed,
    the irregularity of one engine corrects that of the other with
    sufficient exactitude for many purposes. In the case of marine and
    locomotive engines, a fly-wheel is not employed; but for cotton
    spinning, and other purposes requiring great regularity of motion, its
    use with common engines is indispensable, though it is not impossible
    to supersede the necessity by new contrivances.</P>

    <P>5. <EM>Q.</EM>--You implied that there is some other difference
    between single acting and double acting engines, than that which lies
    in the use or exclusion of the crank?</P>

    <P><EM>A.</EM>--Yes; single acting engines act only in one way by the
    force of the steam, and are returned by a counter-weight; whereas
    double acting engines are urged by the steam in both directions.
    Engines, as I have already said, are sometimes made double acting,
    though unprovided with a crank; and there would be no difficulty in so
    arranging the valves of all ordinary pumping engines, as to admit of
    this action; for the pumps might be contrived to raise water both by
    the upward and downward stroke, as indeed in some mines is already
    done. But engines without a crank are almost always made single acting,
    perhaps from the effect of custom, as much as from any other reason,
    and are usually spoken of as such, though it is necessary to know that
    there are some deviations from the usual practice.</P>

    <H4 CLASS="subhead"><A NAME="a02"></A>NATURE AND USES OF A VACUUM.</H4>

    <P>6. <EM>Q.</EM>--The pressure of a vacuum you have stated is nothing;
    but how can the pressure of a vacuum be said to be nothing, when a
    vacuum occasions a pressure of 15 lbs. on the square inch?</P>

    <P><EM>A.</EM>--Because it is not the vacuum which exerts this
    pressure, but the atmosphere, which, like a head of water, presses on
    everything immerged beneath it. A head of water, however, would not
    press down a piston, if the water were admitted on both of its sides;
    for an equilibrium would then be established, just as in the case of a
    balance which retains its equilibrium when an equal weight is added to
    each scale; but take the weight out of one scale, or empty the water
    from one side of the piston, and motion or pressure is produced; and in
    like manner pressure is produced on a piston by admitting steam or air
    upon the one side, and withdrawing the steam or air from the other
    side. It is not, therefore, to a vacuum, but rather to the existence of
    an unbalanced plenum, that the pressure made manifest by exhaustion is
    due, and it is obvious therefore that a vacuum of itself would not work
    an engine.</P>

    <P>7. <EM>Q.</EM>--How is the vacuum maintained in a condensing
    engine?</P>

    <P><EM>A.</EM>--The steam, after having performed its office in the
    cylinder, is permitted to pass into a vessel called the condenser,
    where a shower of cold water is discharged upon it. The steam is
    condensed by the cold water, and falls in the form of hot water to the
    bottom of the condenser. The water, which would else be accumulated in
    the condenser, is continually being pumped out by a pump worked by the
    engine. This pump is called the air pump, because it also discharges
    any air which may have entered with the water.</P>

    <P>8. <EM>Q.</EM>--If a vacuum be an empty space, and there be water in
    the condenser, how can there be a vacuum there?</P>

    <P><EM>A.</EM>--There is a vacuum above the water, the water being only
    like so much iron or lead lying at the bottom.</P>

    <P>9. <EM>Q.</EM>--Is the vacuum in the condenser a perfect vacuum?</P>

    <P><EM>A.</EM>--Not quite perfect; for the cold water entering for the
    purpose of condensation is heated by the steam, and emits a vapor of a
    tension represented by about three inches of mercury; that is, when the
    common barometer stands at 30 inches, a barometer with the space above
    the mercury communicating with the condenser, will stand at about 27
    inches.</P>

    <P>10. <EM>Q.</EM>--Is this imperfection of the vacuum wholly
    attributable to the vapor in the condenser?</P>

    <P><EM>A.</EM>--No; it is partly attributable to the presence of a
    small quantity of air which enters with the water, and which would
    accumulate until it destroyed the vacuum altogether but for the action
    of the air pump, which expels it with the water, as already explained.
    All common water contains a certain quantity of air in solution, and
    this air recovers its elasticity when the pressure of the atmosphere is
    taken off, just as the gas in soda water flies up so soon as the cork
    of the bottle is withdrawn.</P>

    <P>11. <EM>Q.</EM>--Is a barometer sometimes applied to the condensers
    of steam engines?</P>

    <P><EM>A.</EM>--Yes; and it is called the vacuum gauge, because it
    shows the degree of perfection the vacuum has attained. Another gauge,
    called the steam gauge, is applied to the boiler, which indicates the
    pressure of the steam by the height to which the steam forces mercury
    up a tube. Gauges are also applied to the boiler to indicate the height
    of the water within it so that it may not be burned out by the water
    becoming accidentally too low. In some cases a succession of cocks
    placed a short distance above one another are employed for this
    purpose, and in other cases a glass tube is placed perpendicularly in
    the front of the boiler and communicating at each end with its
    interior. The water rises in this tube to the same height as in the
    boiler itself, and thus shows the actual water level. In most of the
    modern boilers both of these contrivances are adopted.</P>

    <P>12. <EM>Q.</EM>--Can a condensing engine be worked with a pressure
    less than that of the atmosphere?</P>

    <P><EM>A.</EM>--Yes, if once it be started; but it will be a difficult
    thing to start an engine, if the pressure of the steam be not greater
    than that of the atmosphere. Before an engine can be started, it has to
    be blown through with steam to displace the air within it, and this
    cannot be effectually done if the pressure of the steam be very low.
    After the engine is started, however, the pressure in the boiler may be
    lowered, if the engine be lightly loaded, until there is a partial
    vacuum in the boiler. Such a practice, however, is not to be commended,
    as the gauge cocks become useless when there is a partial vacuum in the
    boiler; inasmuch as, when they are opened, the water will not rush out,
    but air will rush in. It is impossible, also, under such circumstances,
    to blow out any of the sediment collected within the boiler, which, in
    the case of the boilers of steam vessels, requires to be done every two
    hours or oftener. This is accomplished by opening a large cock which
    permits some of the supersalted water to be forced overboard by the
    pressure of the steam. In some cases, in which the boiler applied to an
    engine is of inadequate size, the pressure within the boiler will fall
    spontaneously to a point considerably beneath the pressure of the
    atmosphere; but it is preferable, in such cases, partially to close the
    throttle valve in the steam pipe, whereby the issue of steam to the
    engine is diminished; and the pressure in the boiler is thus
    maintained, while the cylinder receives its former supply.</P>

    <P>13. <EM>Q.</EM>--If a hole be opened into a condenser of a steam
    engine, will air rush into it?</P>

    <P><EM>A.</EM>--If the hole communicates with the atmosphere, the air
    will be drawn in.</P>

    <P>14. <EM>Q.</EM>--With what Velocity does air rush into a vacuum?</P>

    <P><EM>A.</EM>--With the velocity which a body would acquire by falling
    from the height of a homogeneous atmosphere, which is an atmosphere of
    the same density throughout as at the earth&#39;s surface; and although
    such an atmosphere does not exist in nature, its existence is supposed,
    in order to facilitate the computation. It is well known that the
    velocity with which water issues from a cistern is the same that would
    be acquired by a body falling from the level of the head to the level
    of the issuing point; which indeed is an obvious law, since every
    particle of water descends and issues by virtue of its gravity, and is
    in its descent subject to the ordinary laws of falling bodies. Air
    rushing into a vacuum is only another example of the same general
    principle: the velocity of each particle will be that due to the height
    of the column of air which would produce the pressure sustained; and
    the weight of air being known, as well as the pressure it exerts on the
    earth&#39;s surface, it becomes easy to tell what height a column of
    air, an inch square, and of the atmospheric density, would require to
    be, to weigh 15 lbs. The height would be 27,818 feet, and the velocity
    which the fall of a body from such a height produces would be 1,338
    feet per second.</P>

    <H4 CLASS="subhead"><A NAME="a03"></A>VELOCITY OF FALLING BODIES AND
    MOMENTUM OF MOVING BODIES.</H4>

    <P>15. <EM>Q.</EM>--How do you determine the velocity of falling bodies
    of different kinds?</P>

    <P><EM>A.</EM>--All bodies fall with the same velocity, when there is
    no resistance from the atmosphere, as is shown by the experiment of
    letting fall, from the top of a tall exhausted receiver, a feather and
    a guinea, which reach the bottom at the same time. The velocity of
    falling bodies is one that is accelerated uniformly, according to a
    known law. When the height from which a body falls is given, the
    velocity acquired at the end of the descent can be easily computed. It
    has been found by experiment that the square root of the height in feet
    multiplied by 8.021 will give the velocity.</P>

    <P>16. <EM>Q.</EM>--But the velocity in what terms?</P>

    <P><EM>A.</EM>--In feet per second. The distance through which a body
    falls by gravity in one second is 16-1/12 feet; in two seconds, 64-4/12
    feet; in three seconds, 144-9/12 feet; in four seconds, 257-4/12 feet,
    and so on. If the number of feet fallen through in one second be taken
    as unity, then the relation of the times to the spaces will be as
    follows:--</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "The distance through which a body falls by gravity">
      <TR>
        <TD>
          <P>Number of seconds</P>
        </TD>

        <TD>
          <P>1</P>
        </TD>

        <TD>
          <P>2</P>
        </TD>

        <TD>
          <P>3</P>
        </TD>

        <TD>
          <P>4</P>
        </TD>

        <TD>
          <P>5</P>
        </TD>

        <TD>
          <P>6</P>
        </TD>

        <TD>
          <P>&nbsp;</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Units of space passed through</P>
        </TD>

        <TD>
          <P>1</P>
        </TD>

        <TD>
          <P>4</P>
        </TD>

        <TD>
          <P>9</P>
        </TD>

        <TD>
          <P>16</P>
        </TD>

        <TD>
          <P>25</P>
        </TD>

        <TD>
          <P>36</P>
        </TD>

        <TD>
          <P>&amp;c.<BR>
          </P>
        </TD>
      </TR>
    </TABLE>

    <P>so that it appears that the spaces passed through by a falling body
    are as the squares of the times of falling.</P>

    <P>17. <EM>Q.</EM>--Is not the urging force which causes bodies to fall
    the force of gravity?</P>

    <P><EM>A.</EM>--Yes; the force of gravity or the attraction of the
    earth.</P>

    <P>18. <EM>Q.</EM>--And is not that a uniform force, or a force acting
    with a uniform pressure?</P>

    <P><EM>A.</EM>--It is.</P>

    <P>19. <EM>Q.</EM>--Therefore during the first second of falling as
    much impelling power will be given by the force of gravity as during
    every succeeding second?</P>

    <P><EM>A.</EM>--Undoubtedly.</P>

    <P>20. <EM>Q.</EM>--How comes it, then, that while the body falls
    64-4/12 feet in two seconds, it falls only 16-1/12 feet in one second;
    or why, since it falls only 16-1/12 feet in one second, should it fall
    more than twice 16-1/12 feet in two?</P>

    <P><EM>A.</EM>--Because 16-1/12 feet is the average and not the maximum
    velocity during the first second. The velocity acquired <EM>at the
    end</EM> of the 1st second is not 16-1/12, but 32-1/6 feet per second,
    and at the end of the 2d second a velocity of 32-1/6 feet has to be
    added; so that the total velocity at the end of the 2d second becomes
    64-2/6 feet; at the end of the 3d, the velocity becomes 96-3/6 feet, at
    the end of the 4th, 128-4/6 feet, and so on. These numbers proceed in
    the progression 1, 2, 3, 4, &amp;c., so that it appears that the
    velocities acquired by a falling body at different points, are simply
    as the times of falling. But if the velocities be as the times, and the
    total space passed through be as the squares of the times, then the
    total space passed through must be as the squares of the velocity; and
    as the <EM>vis viva</EM> or mechanical power inherent in a falling
    body, of any given weight, is measurable by the height through which it
    descends, it follows that the <EM>vis viva</EM> is proportionate to the
    square of the velocity. Of two balls therefore, of equal weight, but
    one moving twice as fast as the other, the faster ball has four times
    the energy or mechanical force accumulated in it that the slower ball
    has. If the speed of a fly-wheel be doubled, it has four times the
    <EM>vis viva</EM> it possessed before--<EM>vis viva</EM> being
    measurable by a reference to the height through which a body must have
    fallen, to acquire the velocity given.</P>

    <P>21. <EM>Q.</EM>--By what considerations is the <EM>vis viva</EM> or
    mechanical energy proper for the fly-wheel of an engine determined?</P>

    <P><EM>A.</EM>--By a reference to the power produced every half-stroke
    of the engine, joined to the consideration of what relation the energy
    of the fly-wheel rim must have thereto, to keep the irregularities of
    motion within the limits which are admissible. It is found in practice,
    that when the power resident in the fly-wheel rim, when the engine
    moves at its average speed, is from two and a half to four times
    greater than the power generated by the engine in one half-stroke--the
    variation, depending on the energy inherent in the machinery the engine
    has to drive and the equability of motion required--the engine will
    work with sufficient regularity for most ordinary purposes, but where
    great equability of motion is required, it will be advisable to make
    the power resident in the fly-wheel equal to six times the power
    generated by the engine in one half-stroke.</P>

    <P>22. <EM>Q.</EM>---Can you give a practical rule for determining the
    proper quantity of cast iron for the rim of a fly-wheel in ordinary
    land engines?</P>

    <P><EM>A.</EM>--One rule frequently adopted is as follows:--Multiply
    the mean diameter of the rim by the number of its revolutions per
    minute, and square the product for a divisor; divide the number of
    actual horse power of the engine by the number of strokes the piston
    makes per minute, multiply the quotient by the constant number
    2,760,000, and divide the product by the divisor found as above; the
    quotient is the requisite quantity of cast iron in cubic feet to form
    the fly-wheel rim.</P>

    <P>23. <EM>Q.</EM>--What is Boulton and Watt&#39;s rule for finding the
    dimensions of the fly-wheel?</P>

    <P><EM>A.</EM>--Boulton and Watt&#39;s rule for finding the dimensions
    of the fly-wheel is as follows:--Multiply 44,000 times the length of
    the stroke in feet by the square of the diameter of the cylinder in
    inches, and divide the product by the square of the number of
    revolutions per minute multiplied by the cube of the diameter of the
    fly-wheel in feet. The resulting number will be the sectional area of
    the rim of the fly-wheel in square inches.</P>

    <H4 CLASS="subhead"><A NAME="a04"></A>CENTRAL FORCES.</H4>

    <P>24. <EM>Q.</EM>--What do you understand by centrifugal and
    centripetal forces?</P>

    <P><EM>A.</EM>--By centrifugal force, I understand the force with which
    a revolving body tends to fly from the centre; and by centripetal
    force, I understand any force which draws it to the centre, or
    counteracts the centrifugal tendency. In the conical pendulum, or steam
    engine governor, which consists of two metal balls suspended on rods
    hung from the end of a vertical revolving shaft, the centrifugal force
    is manifested by the divergence of the balls, when the shaft is put
    into revolution; and the centripetal force, which in this instance is
    gravity, predominates so soon as the velocity is arrested; for the arms
    then collapse and hang by the side of the shaft.</P>

    <P>25. <EM>Q.</EM>--What measures are there of the centrifugal force of
    bodies revolving in a circle?</P>

    <P><EM>A.</EM>--The centrifugal force of bodies revolving in a circle
    increases as the diameter of the circle, if the number of revolutions
    remain the same. If there be two fly-wheels of the same weight, and
    making the same number of revolutions per minute, but the diameter of
    one be double that of the other, the larger will have double the amount
    of centrifugal force. The centrifugal force of the <EM>same wheel</EM>,
    however, increases as the square of the velocity; so that if the
    velocity of a fly-wheel be doubled, it will have four times the amount
    of centrifugal force.</P>

    <P>26. <EM>Q.</EM>--Can you give a rule for determining the centrifugal
    force of a body of a given weight moving with a given velocity in a
    circle of a given diameter?</P>

    <P><EM>A.</EM>--Yes. If the velocity in feet per second be divided by
    4.01, the square of the quotient will be four times the height in feet
    from which a body must have fallen to have acquired that velocity.
    Divide this quadruple height by the diameter of the circle, and the
    quotient is the centrifugal force in terms of the weight of the body,
    so that, multiplying the quotient by the actual weight of the body, we
    have the centrifugal force in pounds or tons. Another rule is to
    multiply the square of the number of revolutions per minute by the
    diameter of the circle in feet, and to divide the product by 5,870. The
    quotient is the centrifugal force in terms of the weight of the
    body.</P>

    <P>27. <EM>Q.</EM>--How do you find the velocity of the body when its
    centrifugal force and the diameter of the circle in which it moves are
    given?</P>

    <P><EM>A.</EM>--Multiply the centrifugal force in terms of the weight
    of the body by the diameter of the circle in feet, and multiply the
    square root of the product by 4.01; the result will be the velocity of
    the body in feet per second.</P>

    <P>28. <EM>Q.</EM>--Will you illustrate this by finding the velocity at
    which the cast iron rim of a fly-wheel 10 feet in diameter would burst
    asunder by its centrifugal force?</P>

    <P><EM>A.</EM>--If we take the tensile strength of cast iron at 15,000
    lbs. per square inch, a fly-wheel rim of one square inch of sectional
    area would sustain 30,000 lbs. If we suppose one half of the rim to be
    so fixed to the shaft as to be incapable of detachment, then the
    centrifugal force of the other half of the rim at the moment of rupture
    must be equal to 30,000 lbs. Now 30,000 lbs. divided by 49.48 (the
    weight of the half rim) is equal to 606.3, which is the centrifugal
    force in terms of the weight. Then by the rule given in the last answer
    606.3 x 10 = 6063, the square root of which is 78 nearly, and 78 x 4.01
    = 312.78, the velocity of the rim in feet per second at the moment of
    rupture.</P>

    <P>29. <EM>Q.</EM>--What is the greatest velocity at which it is safe
    to drive a cast iron fly-wheel?</P>

    <P><EM>A.</EM>--If we take 2,000 lbs. as the utmost strain per square
    inch to which cast iron can be permanently subjected with safety; then,
    by a similar process to that just explained, we have 4,000 lbs./49.48 =
    80.8 which multiplied by 10 = 808, the square root of which is 28.4,
    and 28.4 x 4.01 = 113.884, the velocity of the rim in feet per second,
    which may be considered as the highest consistent with safety. Indeed,
    this limit should not be approached in practice on account of the risks
    of fracture from weakness or imperfections in the metal.</P>

    <P>30. <EM>Q.</EM>--What is the velocity at which the wheels of railway
    trains may run if we take 4,000 lbs. per square inch as the greatest
    strain to which malleable iron should be subjected?</P>

    <P><EM>A.</EM>--The weight of a malleable iron rim of one square inch
    sectional area and 7 feet diameter is 21.991 feet x 3.4 lbs. = 74.76,
    one half of which is 37.4 lbs. Then by the same process as before,
    8,000/37.4 = 213.9, the centrifugal force in terms of the weight: 213.9
    x 7, the diameter of the wheel = 1497.3, the square root of which, 38.3
    x 4.01 = 155.187 feet per second, the highest velocity of the rims of
    railway carriage wheels that is consistent with safety. 155.187 feet
    per second is equivalent to 105.8 miles an hour. As 4,000 lbs. per
    square inch of sectional area is the utmost strain to which iron should
    be exposed in machinery, railway wheels can scarcely be considered safe
    at speed even considerably under 100 miles an hour, unless so
    constructed that the centrifugal force of the rim will be counteracted,
    to a material extent, by the centripetal action of the arms. Hooped
    wheels are very unsafe, unless the hoops are, by some process or other,
    firmly attached to the arms. It is of no use to increase the dimensions
    of the rim of a wheel with the view of giving increased strength to
    counteract the centrifugal force, as every increase in the weight of
    the rim will increase the centrifugal force in the same proportion.</P>

    <H4 CLASS="subhead"><A NAME="a05"></A>CENTRES OF GRAVITY, GYRATION, AND
    OSCILLATION.</H4>

    <P>31. <EM>Q.</EM>--What do you understand by the centre of gravity of
    a body?</P>

    <P><EM>A.</EM>--That point within it, in which the whole of the weight
    may be supposed to be concentrated, and which continually endeavors to
    gain the lowest possible position. A body hung in the centre of gravity
    will remain at rest in any position.</P>

    <P>32. <EM>Q.</EM>--What is meant by the centre of gyration?</P>

    <P><EM>A.</EM>--The centre of gyration is that point in a revolving
    body in which the whole momentum may be conceived to be concentrated,
    or in which the whole effect of the momentum resides. If the ball of a
    governor were to be moved in a straight line, the momentum might be
    said to be concentrated at the centre of gravity of the ball; but
    inasmuch as, by its revolution round an axis, the part of the ball
    furthest removed from the axis moves more quickly than the part nearest
    to it, the momentum cannot be supposed to be concentrated at the centre
    of gravity, but at a point further removed from the central shaft, and
    that point is what is called the centre of gyration.</P>

    <P>33. <EM>Q.</EM>--What is the centre of oscillation?</P>

    <P><EM>A.</EM>--The centre of oscillation is a point in a pendulum or
    any swinging body, such, that if all the matter of the body were to be
    collected into that point, the velocity of its vibration would remain
    unaffected. It is in fact the mean distance from the centre of
    suspension of every atom, in a ratio which happens not to be an
    arithmetical one. The centre of oscillation is always in a line passing
    through the centre of suspension and the centre of gravity.</P>

    <H4 CLASS="subhead"><A NAME="a06"></A>THE PENDULUM AND GOVERNOR.</H4>

    <P>34. <EM>Q.</EM>--By what circumstance is the velocity of vibration
    of a pendulous body determined?</P>

    <P><EM>A.</EM>--By the length of the suspending rod only, or, more
    correctly, by the distance between the centre of suspension and the
    centre of oscillation. The length of the arc described does not
    signify, as the times of vibration will be the same, whether the arc be
    the fourth or the four hundredth of a circle, or at least they will be
    nearly so, and would be so exactly, if the curve described were a
    portion of a cycloid. In the pendulum of clocks, therefore, a small arc
    is preferred, as there is, in that case, no sensible deviation from the
    cycloidal curve, but in other respects the size of the arc does not
    signify.</P>

    <P>35. <EM>Q.</EM>--If then the length of a pendulum be given, can the
    number of vibrations in a given time be determined?</P>

    <P><EM>A.</EM>--Yes; the time of vibration bears the same relation to
    the time in which a body would fall through a space equal to half the
    length of the pendulum, that the circumference of a circle bears to its
    diameter. The number of vibrations made in a given time by pendulums of
    different lengths, is inversely as the square roots of their
    lengths.</P>

    <P>36. <EM>Q.</EM>--Then when the length of the second&#39;s pendulum
    is known the proper length of a pendulum to make any given number of
    vibrations in the minute can readily be computed?</P>

    <P><EM>A.</EM>--Yes; the length of the second&#39;s pendulum being
    known, the length of another pendulum, required to perform any given
    number of vibrations in the minute, may be obtained by the following
    rule: multiply the square root of the given length by 60, and divide
    the product by the given number of vibrations per minute; the square of
    the quotient is the length of pendulum required. Thus if the length of
    a pendulum were required that would make 70 vibrations per minute in
    the latitude of London, then SQRT(39.1393) x 60/70 = (5.363)^2 = 28.75
    in. which is the length required.</P>

    <P>37. <EM>Q.</EM>--Can you explain how it comes that the length of a
    pendulum determines the number of vibrations it makes in a given
    time?</P>

    <P><EM>A.</EM>--Because the length of the pendulum determines the
    steepness of the circle in which the body moves, and it is obvious,
    that a body will descend more rapidly over a steep inclined plane, or a
    steep arc of a circle, than over one in which there is but a slight
    inclination. The impelling force is gravity, which urges the body with
    a force proportionate to the distance descended, and if the velocity
    due to the descent of a body through a given height be spread over a
    great horizontal distance, the speed of the body must be slow in
    proportion to the greatness of that distance. It is clear, therefore,
    that as the length of the pendulum determines the steepness of the arc,
    it must also determine the velocity of vibration.</P>

    <P>38. <EM>Q.</EM>--If the motions of a pendulum be dependent on the
    speed with which a body falls, then a certain ratio must subsist
    between the distance through which a body falls in a second, and the
    length of the second&#39;s pendulum?</P>

    <P><EM>A.</EM>--And so there is; the length of the second&#39;s
    pendulum at the level of the sea in London, is 39.1393 inches, and it
    is from the length of the second&#39;s pendulum that the space through
    which a body falls in a second has been determined. As the time in
    which a pendulum vibrates is to the time in which a heavy body falls
    through half the length of the pendulum, as the circumference of a
    circle is to its diameter, and as the height through which a body falls
    is as the square of the time of falling, it is clear that the height
    through which a body will fall, during the vibration of a pendulum, is
    to half the length of the pendulum as the square of the circumference
    of a circle is to the square of its diameter; namely, as 9.8696 is to
    1, or it is to the whole length of the pendulum as the half of this,
    namely, 4.9348 is to 1; and 4.9348 times 39.1393 in. is 16-1/12 ft.
    very nearly, which is the space through which a body falls by gravity
    in a second.</P>

    <P>39. <EM>Q.</EM>--Are the motions of the conical pendulum or governor
    reducible to the same laws which apply to the common pendulum?</P>

    <P><EM>A.</EM>--Yes; the motion of the conical pendulum may be supposed
    to be compounded of the motions of two common pendulums, vibrating at
    right angles to one another, and one revolution of a conical pendulum
    will be performed in the same time as two vibrations of a common
    pendulum, of which the length is equal to the vertical height of the
    point of suspension above the plane of revolution of the balls.</P>

    <P>40. <EM>Q.</EM>--Is not the conical pendulum or governor of a steam
    engine driven by the engine?</P>

    <P><EM>A.</EM>--Yes.</P>

    <P>41. <EM>Q.</EM>--Then will it not be driven round as any other
    mechanism would be at a speed proportional to that of the engine?</P>

    <P><EM>A.</EM>--It will.</P>

    <P>42. <EM>Q.</EM>--Then how can the length of the arms affect the time
    of revolution?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig01.png" WIDTH="600" HEIGHT="474" ALT=
    "Fig. 1"></P>

    <P><EM>A.</EM>--By flying out until they assume a vertical height
    answering to the velocity with which they rotate round the central
    axis. As the speed is increased the balls expand, and the height of the
    cone described by the arms is diminished, until its vertical height is
    such that a pendulum of that length would perform two vibrations for
    every revolution of the governor. By the outward motion of the arms,
    they partially shut off the steam from the engine. If, therefore, a
    certain expansion of the balls be desired, and a certain length be
    fixed upon for the arms, so that the vertical height of the cone is
    fixed, then the speed of the governor must be such, that it will make
    half the number of revolutions in a given time that a pendulum equal in
    length to the height of the cone would make of vibrations. The rule is,
    multiply the square root of the height of the cone in inches by
    0.31986, and the product will be the right time of revolution in
    seconds. If the number of revolutions and the length of the arms be
    fixed, and it is wanted to know what is the diameter of the circle
    described by the balls, you must divide the constant number 187.58 by
    the number of revolutions per minute, and the square of the quotient
    will be the vertical height in inches of the centre of suspension above
    the plane of the balls&#39; revolution. Deduct the square of the
    vertical height in inches from the square of the length of the arm in
    inches, and twice the square root of the remainder is the diameter of
    the circle in which the centres of the balls revolve.</P>

    <P>43. <EM>Q.</EM> Cannot the operation of a governor be deduced merely
    from the consideration of centrifugal and centripetal forces?</P>

    <P><EM>A.</EM>--It can; and by a very simple process. The horizontal
    distance of the arm from the spindle divided by the vertical height,
    will give the amount of centripetal force, and the velocity of
    revolution requisite to produce an equivalent centrifugal force may be
    found by multiplying the centripetal force of the ball in terms of its
    own weight by 70,440, and dividing the product by the diameter of the
    circle made by the centre of the ball in inches; the square root of the
    quotient is the number of revolutions per minute. By this rule you fix
    the length of the arms, and the diameter of the base of the cone, or,
    what is the same thing, the angle at which it is desired the arms shall
    revolve, and you then make the speed or number of revolutions such,
    that the centrifugal force will keep the balls in the desired
    position.</P>

    <P>44. <EM>Q.</EM>--Does not the weight of the balls affect the
    question?</P>

    <P><EM>A.</EM>--Not in the least; each ball may be supposed to be made
    up of a number of small balls or particles, and each particle of matter
    will act for itself. Heavy balls attached to a governor are only
    requisite to overcome the friction of the throttle valve which shuts
    off the steam, and of the connections leading thereto. Though the
    weight of a ball increases its centripetal force, it increases its
    centrifugal force in the same proportion.</P>

    <H4 CLASS="subhead"><A NAME="a07"></A>THE MECHANICAL POWERS.</H4>

    <P>45. <EM>Q.</EM>--What do you understand by the mechanical
    powers?</P>

    <P><EM>A.</EM>--The mechanical powers are certain contrivances, such as
    the wedge, the screw, the inclined plane, and other elementary
    machines, which convert a small force acting through a great space into
    a great force acting through a small space. In the school treatises on
    mechanics, a certain number of these devices are set forth as the
    mechanical powers, and each separate device is treated as if it
    involved a separate principle; but not a tithe of the contrivances
    which accomplish the stipulated end are represented in these learned
    works, and there is no very obvious necessity for considering the
    principle of each contrivance separately when the principles of all are
    one and the same. Every pressure acting with a certain velocity, or
    through a certain space, is convertible into a greater pressure acting
    with a less velocity, or through a smaller space; but the quantity of
    mechanical force remains unchanged by its transformation, and all that
    the implements called mechanical powers accomplish is to effect this
    transformation.</P>

    <P>46. <EM>Q.</EM>--Is there no power gained by the lever?</P>

    <P><EM>A.</EM>--Not any: the power is merely put into another shape,
    just as the contents of a hogshead of porter are the same, whether they
    be let off by an inch tap or by a hole a foot in diameter. There is a
    greater gush in the one case than the other, but it will last a shorter
    time; when a lever is used there is a greater force exerted, but it
    acts through a shorter distance. It requires just the same expenditure
    of mechanical power to lift 1 lb. through 100 ft., as to lift 100 lbs.
    through 1 foot. A cylinder of a given cubical capacity will exert the
    same power by each stroke, whether the cylinder be made tall and
    narrow, or short and wide; but in the one case it will raise a small
    weight through a great height, and in the other case, a great weight
    through a small height.</P>

    <P>47. <EM>Q.</EM>--Is there no loss of power by the use of the
    crank?</P>

    <P><EM>A.</EM>--Not any. Many persons have supposed that there was a
    loss of power by the use of the crank, because at the top and bottom
    centres it is capable of exerting little or no power; but at those
    times there is little or no steam consumed, so that no waste of power
    is occasioned by the peculiarity. Those who imagine that there is a
    loss of power caused by the crank perplex themselves by confounding the
    vertical with the circumferential velocity. If the circle of the crank
    be divided by any number of equidistant horizontal lines, it will be
    obvious that there must be the same steam consumed, and the same power
    expended, when the crank pin passes from the level of one line to the
    level of the other, in whatever part of the circle it may be, those
    lines being indicative of equal ascents or descents of the piston. But
    it will be seen that the circumferential velocity is greater with the
    same expenditure of steam when the crank pin approaches the top and
    bottom centres; and this increased velocity exactly compensates for the
    diminished leverage, so that there is the same power given out by the
    crank in each of the divisions.</P>

    <P>48. <EM>Q.</EM>--Have no plans been projected for gaining power by
    means of a lever?</P>

    <P><EM>A.</EM>--Yes, many plans,--some of them displaying much
    ingenuity, but all displaying a complete ignorance of the first
    principles of mechanics, which teach that power cannot be gained by any
    multiplication of levers and wheels. I have occasionally heard persons
    say: &quot;You gain a great deal of power by the use of a capstan; why
    not apply the same resource in the case of a steam vessel, and increase
    the power of your engine by placing a capstan motion between the engine
    and paddle wheels?&quot; Others I have heard say: &quot;By the
    hydraulic press you can obtain unlimited power; why not then interpose
    a hydraulic press between the engines and the paddles?&quot; To these
    questions the reply is sufficiently obvious. Whatever you gain in force
    you lose in velocity; and it would benefit you little to make the
    paddles revolve with ten times the force, if you at the same time
    caused them to make only a tenth of the number of revolutions. You
    cannot, by any combination of mechanism, get increased force and
    increased speed at the same time, or increased force without diminished
    speed; and it is from the ignorance of this inexorable condition, that
    such myriads of schemes for the realization of perpetual motion, by
    combinations of levers, weights, wheels, quicksilver, cranks, and other
    mere pieces of inert matter, have been propounded.</P>

    <P>49. <EM>Q.</EM>--Then a force once called into existence cannot be
    destroyed?</P>

    <P><EM>A.</EM>--No; force is eternal, if by force you mean power, or in
    other words pressure acting though space. But if by force you mean mere
    pressure, then it furnishes no measure of power. Power is not
    measurable by force but by force and velocity combined.</P>

    <P>50. <EM>Q.</EM>--Is not power lost when two moving bodies strike one
    other and come to a state of rest?</P>

    <P><EM>A.</EM>--No, not even then. The bodies if elastic will rebound
    from one another with their original velocity; if not elastic they will
    sustain an alteration of form, and heat or electricity will be
    generated of equivalent value to the power which has disappeared.</P>

    <P>51. <EM>Q.</EM>--Then if mechanical power cannot be lost, and is
    being daily called into existence, must not there be a daily increase
    in the power existing in the world?</P>

    <P><EM>A.</EM>--That appears probable unless it flows back in the shape
    of heat or electricity to the celestial spaces. The source of
    mechanical power is the sun which exhales vapors that descend in rain,
    to turn mills, or which causes winds to blow by the unequal rarefaction
    of the atmosphere. It is from the sun too that the power comes which is
    liberated in a steam engine. The solar rays enable plants to decompose
    carbonic acid gas, the product of combustion, and the vegetation thus
    rendered possible is the source of coal and other combustible bodies.
    The combustion of coal under a steam boiler therefore merely liberates
    the power which the sun gave out thousands of years before.</P>

    <H4 CLASS="subhead"><A NAME="a08"></A>FRICTION.</H4>

    <P>52. <EM>Q.</EM>--What is friction?</P>

    <P><EM>A.</EM>--Friction is the resistance experienced when one body is
    rubbed upon another body, and is supposed to be the result of the
    natural attraction which bodies have for one another, and of the
    interlocking of the impalpable asperities upon the surfaces of all
    bodies, however smooth. There is, no doubt, some electrical action
    involved in its production, not yet recognized, nor understood; and it
    is perhaps traceable to the disturbance of the electrical equilibrium
    of the particles of the body owing to the condensation or change of
    figure which all bodies must experience when subjected to a strain.
    When motion in opposite directions is given to smooth surfaces, the
    minute asperities of one surface must mount upon those of the other,
    and both will be abraded and worn away, in which act power must be
    expended. The friction of smooth rubbing substances is less when the
    composition of those substances is different, than when it is the same,
    the particles being supposed to interlock less when the opposite
    prominences or asperities are not coincident.</P>

    <P>53. <EM>Q.</EM>--Does friction increase with the extent of rubbing
    surface?</P>

    <P><EM>A.</EM>--No; the friction, so long as there is no violent
    heating or abrasion, is simply in the proportion of the pressure
    keeping the surfaces together, or nearly so. It is, therefore, an
    obvious advantage to have the bearing surfaces of steam engines as
    large as possible, as there is no increase of friction by extending the
    surface, while there is a great increase in the durability. When the
    bearings of an engine are made too small, they very soon wear out.</P>

    <P>54. <EM>Q.</EM>--Does friction increase in the same ratio as
    velocity?</P>

    <P><EM>A.</EM>--No; friction does not increase with the velocity at
    all, if the friction over a given amount of surface be considered; but
    it increases as the velocity, if the comparison be made with the time
    during which the friction acts. Thus the friction of each stroke of a
    piston is the same, whether it makes 20 strokes in the minute, or 40:
    in the latter case, however, there are twice the number of strokes
    made, so that, though the friction per stroke is the same, the friction
    per minute is doubled. The friction, therefore, of any machine per hour
    varies as the velocity, though the friction per revolution remains, at
    all ordinary velocities, the same. Of excessive velocities we have not
    sufficient experience to enable us to state with confidence whether the
    same law continues to operate among them.</P>

    <P>55. <EM>Q.</EM>--Can you give any approximate statement of the force
    expended in overcoming friction?</P>

    <P><EM>A.</EM>--It varies with the nature of the rubbing bodies. The
    friction of iron sliding upon iron, has generally been taken at about
    one tenth of the pressure, when the surfaces are oiled and then wiped
    again, so that no film of oil is interposed. The friction of iron
    rubbing upon brass has generally been taken at about one eleventh of
    the pressure under the same circumstances; but in machines in actual
    operation, where a film of some lubricating material is interposed
    between the rubbing surfaces, it is not more than one third of this
    amount or 1/33d of the weight. While this, however, is the average
    result, the friction is a good deal less in some cases. Mr. Southern,
    in some experiments upon the friction of the axle of a grindstone--an
    account of which may be found in the 65th volume of the Philosophical
    Transactions--found the friction to amount to less than 1/40th of the
    weight; and Mr. Wood, in some experiments upon the friction of
    locomotive axles, found that by ample lubrication the friction may be
    made as little as 1/60th of the weight. In some experiments upon the
    friction of shafts by Mr. G. Rennie, he found that with a pressure of
    from 1 to 5 cwt. the friction did not exceed 1/39th of the pressure
    when tallow was the unguent employed; with soft soap it became 1/34th.
    The fact appears to be that the amount of the resistance denominated
    friction depends, in a great measure, upon the nature of the unguent
    employed, and in certain cases the viscidity of the unguent may
    occasion a greater retardation than the resistance caused by the
    attrition. In watchwork therefore, and other fine mechanism, it is
    necessary both to keep the bearing surfaces small, and to employ a thin
    and limpid oil for the purpose of lubrication, for the resistance
    caused by the viscidity of the unguent increases with the amount of
    surface, and the amount of surface is relatively greater in the smaller
    class of works.</P>

    <P>56. <EM>Q.</EM>--Is a very thin unguent preferable also for the
    larger class of bearings?</P>

    <P><EM>A.</EM>--The nature of the unguent, proper for different
    bearings, appears to depend in a great measure upon the amount of the
    pressure to which the bearings are subjected,--the hardest unguents
    being best where the pressure is greatest. The function of lubricating
    substances is to prevent the rubbing surfaces from coming into contact,
    whereby abrasion would be produced, and unguents are effectual in this
    respect in the proportion of their viscidity; but if the viscidity of
    the unguent be greater than what suffices to keep the surfaces asunder,
    an additional resistance will be occasioned; and the nature of the
    unguent selected should always have reference, therefore, to the size
    of the rubbing surfaces, or to the pressure per square inch upon them.
    With oil the friction appears to be a minimum when the pressure on the
    surface of a bearing is about 90 lbs. per square inch. The friction
    from too small a surface increases twice as rapidly as the friction
    from too large a surface, added to which, the bearing, when the surface
    is too small, wears rapidly away.</P>

    <P>57. <EM>Q.</EM>--Has not M. Morin, in France, made some very
    complete experiments to determine the friction of surfaces of different
    kinds sliding upon one another?</P>

    <P><EM>A.</EM>--He has; but the result does not differ materially from
    what is stated above, though, upon the whole, M. Morin, found the
    resistance due to friction to be somewhat greater than it has been
    found to be by various other engineers. When the surfaces were merely
    wiped with a greasy cloth, but had no film of lubricating material
    interposed, the friction of brass upon cast iron he found to be .107,
    or about 1/10th of the load, which was also the friction of cast iron
    upon oak. But when a film of lubricating material was interposed, he
    found that the friction was the same whether the surfaces were wood on
    metal, wood on wood, metal on wood, or metal on metal; and the amount
    of the friction in such case depended chiefly on the nature of the
    unguent. With a mixture of hog&#39;s lard and olive oil interposed
    between the surfaces, the friction was usually from 1/12th to 1/14th of
    the load, but in some cases it was only 1/20th of the load.</P>

    <P>58. <EM>Q.</EM>--May water be made to serve for purposes of
    lubrication?</P>

    <P><EM>A.</EM>--Yes, water will answer very well if the surface be very
    large relatively with the pressure; and in screw vessels where the
    propeller shaft passes through a long pipe at the stern, the stuffing
    box is purposely made a little leaky. The small leakage of water into
    the vessel which is thus occasioned, keeps the screw shaft in this
    situation always wet, and this is all the lubrication which this
    bearing requires or obtains.</P>

    <P>59. <EM>Q.</EM>--What is the utmost pressure which may be employed
    without heating when oil is the lubricating material?</P>

    <P><EM>A.</EM>--That will depend upon the velocity. When the pressure
    exceeds 800 lbs. per square inch, however, upon the section of the
    bearing in a direction parallel with the axis, then the oil will be
    forced out and the bearing will necessarily heat.</P>

    <P>60. <EM>Q.</EM>--But, with, a given velocity, can you tell the limit
    of pressure which will be safe in practice; or with a given pressure,
    can you tell the limit of velocity?</P>

    <P><EM>A.</EM>--Yes; that may be done by the following empirical rule,
    which has been derived from observations made upon bearings of
    different sizes and moving with different velocities. Divide the number
    70,000 by the velocity of the surface of the bearing in feet per
    minute. The quotient will be the number of pounds per square inch of
    section in the line of the axis that may be put upon the bearing. Or,
    if we divide 70,000 by the number of pounds per square inch of section,
    then the quotient will be the velocity in feet per minute at which the
    circumference of the bearing may work.</P>

    <P>61. <EM>Q.</EM>--The number of square inches upon which the pressure
    is reckoned, is not the circumference of the bearing multiplied by its
    length, but the diameter of the bearing multiplied by its length?</P>

    <P><EM>A.</EM>--Precisely so, it will be the diameter multiplied by the
    length of the bearing.</P>

    <P>62. <EM>Q.</EM>--What is the amount of friction in the case of
    surfaces sliding upon one another in sandy or muddy water--such
    surfaces, for example, as are to be found in the sluices of valves for
    water?</P>

    <P><EM>A.</EM>--Various experiments have been made by Mr. Summers of
    Southampton to ascertain the friction of brass surfaces sliding upon
    each other in salt water, with the view of finding the power required
    for moving sluice doors for lock gates and for other similar purposes.
    The surfaces were planed as true and smooth as the planing machine
    would make them, but were <EM>not</EM> filed or scraped, and the result
    was as follows:</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "Friction of sliding surfaces">
      <TR>
        <TD>
          <P>Area of slide rubbing surface.</P>
        </TD>

        <TD>
          <P>Weight or pressure on rubbing surface.</P>
        </TD>

        <TD>
          <P>Power required to move the slide <EM>slowly</EM> in muddy salt
          water, kept stirred up.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Sq. in.</P>
        </TD>

        <TD>
          <P>Lb.</P>
        </TD>

        <TD>
          <P>Lb.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>8</P>
        </TD>

        <TD>
          <P>56</P>
        </TD>

        <TD>
          <P>21.5</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;</P>
        </TD>

        <TD>
          <P>112</P>
        </TD>

        <TD>
          <P>44.<BR>
          </P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;</P>
        </TD>

        <TD>
          <P>168</P>
        </TD>

        <TD>
          <P>65.5</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;</P>
        </TD>

        <TD>
          <P>224</P>
        </TD>

        <TD>
          <P>88.5<BR>
          </P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;</P>
        </TD>

        <TD>
          <P>336</P>
        </TD>

        <TD>
          <P>140.5</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;</P>
        </TD>

        <TD>
          <P>448</P>
        </TD>

        <TD>
          <P>170.75</P>
        </TD>
      </TR>
    </TABLE>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig02.png" WIDTH="600" HEIGHT="285" ALT=
    "Fig. 2. Sketch of Slide. The facing on which the slide moved was similar, but three or four times as long.">
    </P>

    <P>These results were the average of eight fair trials; in each case,
    the sliding surfaces were totally immersed in muddy salt water, and
    although the apparatus used for drawing the slide along was not very
    delicately fitted up, the power required may be considered as a
    sufficient approximation for practical purposes.</P>

    <P>It appears from these experiments, that rough surfaces follow the
    same law as regards friction that is followed by smooth, for in each
    case the friction increases directly as the pressure.</P>

    <H4 CLASS="subhead"><A NAME="a09"></A>STRENGTH OF MATERIALS AND STRAINS
    SUBSISTING IN MACHINES.</H4>

    <P>63. <EM>Q.</EM>--In what way are the strengths of the different
    parts of a steam engine determined?</P>

    <P><EM>A.</EM>--By reference to the amount of the strain or pressure to
    which they are subjected, and to the cohesive strength of the iron or
    other material of which they are composed. The strains subsisting in
    engines are usually characterized as tensile, crushing, twisting,
    breaking, and shearing strains; but they may be all resolved into
    strains of extension and strains of compression; and by the power of
    the materials to resist these two strains, will their practical
    strength be measurable.</P>

    <P>64. <EM>Q.</EM>--What are the ultimate strengths of the malleable
    and cast iron, brass, and other materials employed in the construction
    of engines?</P>

    <P><EM>A.</EM>--The tensile and crushing strengths of any given
    material are by no means the same. The tensile strength, or strength
    when extended, of good bar iron is about 60,000 lbs., or nearly 27 tons
    per square inch of section; and the tensile strength of cast iron is
    about 15,000 lbs., or say 6 3/4 to 7 tons per square inch of section.
    These are the weights which are required to break them. The crushing
    strain of cast iron, however, is about 100,000 lbs., or 44 1/2 tons;
    whereas the crushing strength of malleable iron is not more than 27,000
    lbs., or 12 tons, per square inch of section, and indeed it is
    generally less than this. The ultimate tensile strength, therefore, of
    malleable iron is four times greater than that of cast iron, but the
    crushing strength of cast iron is between three and four times greater
    than that of wrought iron. It may be stated, in round numbers, that the
    tensile strength of malleable iron is twice greater than its crushing
    strength; or, in other words, that it will take twice the strain to
    break a bar of malleable iron by drawing it asunder endways, than will
    cripple it by forcing it together endways like a pillar; whereas a bar
    of cast iron will be drawn asunder with one sixth of the force that
    will be required to break or cripple it when forced together endways
    like a pillar.</P>

    <P>65. <EM>Q.</EM>--What is the cohesive strength of steel?</P>

    <P><EM>A.</EM>--The ultimate tensile strength of good cast or blistered
    steel is about twice as great as that of wrought iron, being about
    130,000 lbs. per square inch of section. The tensile strength of gun
    metal, such as is used in engines, is about 36,000 lbs. per square inch
    of section; of wrought copper about 33,000 lbs.; and of cast copper
    about 19,000 lbs. per square Inch of section.</P>

    <P>66. <EM>Q.</EM>--Is the crushing strength of steel greater or less
    than its tensile strength?</P>

    <P><EM>A.</EM>--It is about twice greater. A good steel punch will
    punch through a plate of wrought iron of a thickness equal to the
    diameter of the punch. A punch therefore of an inch diameter will
    pierce a plate an inch thick. Now it is well known, that the strain
    required to punch a piece of metal out of a plate, is just the same as
    that required to tear asunder a bar of iron of the same area of cross
    section as the area of the surface cut. The area of the surface cut in
    this case will be the circumference of the punch, 3.1416 inches,
    multiplied by the thickness of the plate, 1 inch, which makes the area
    of the cut surface 3.1416 square inches. The area of the point of the
    punch subjected to the pressure is .7854 square inches, so that the
    area cut to the area crushed is as four to one. In other words, it will
    require four times the strain to crush steel that is required to tear
    asunder malleable iron, or it will take about twice the strain to crush
    steel that it will require to break it by extension.</P>

    <P>67. <EM>Q.</EM>--What strain may be applied to malleable iron in
    practice?</P>

    <P><EM>A.</EM>--A bar of wrought iron to which a tensile or compressing
    strain is applied, is elongated or contracted like a very stiff spiral
    spring, nearly in the proportion of the amount of strain applied up to
    the limit at which the strength begins to give way, and within this
    limit it will recover its original dimensions when the strain is
    removed. If, however, the strain be carried beyond this limit, the bar
    will not recover its original dimensions, but will be permanently
    pulled out or pushed in, just as would happen to a spring to which an
    undue strain had been applied. This limit is what is called the limit
    of elasticity; and whenever it is exceeded, the bar, though it may not
    break immediately, will undergo a progressive deterioration, and will
    break in the course of time. The limit of elasticity of malleable iron
    when extended, or, in other words, the tensile strain to which a bar of
    malleable iron an inch square may be subjected without permanently
    deranging its structure, is usually taken at 17,800 lbs., or from that
    to 10 tons, depending on the quality of the iron. It has also been
    found that malleable iron is extended about one ten-thousandth part of
    its length for every ton of direct strain applied to it.</P>

    <P>68. <EM>Q.</EM>--What is the limit of elasticity of cast iron?</P>

    <P><EM>A.</EM>--It is commonly taken at 15,300 lbs. per square inch of
    section; but this is certainly much too high, as it exceeds the tensile
    strength of irons of medium quality. A bar of cast iron if compressed
    by weights will be contracted in length twice as much as a bar of
    malleable iron under similar circumstances; but malleable iron, when
    subjected to a greater strain than 12 tons per square inch of section,
    gradually crumples up by the mere continuance of the weight. A
    cast-iron bar one inch square and ten feet long, is shortened about one
    tenth of an inch by a compressing force of 10,000 lbs., whereas a
    malleable iron bar of the same dimensions would require to shorten it
    equally a compressing force of 20,000 lbs. As the load, however,
    approaches 12 tons, the compressions become nearly equal, and above
    that point the rate of the compression of the malleable iron rapidly
    increases. A bar of cast iron, when at its breaking point by the
    application of a tensile strain, is stretched about one six-hundredth
    part of its length; and an equal strain employed to compress it, would
    shorten it about one eight-hundredth part of its length.</P>

    <P>69. <EM>Q.</EM>--But to what strain may the iron used in the
    construction of engines be safely subjected?</P>

    <P><EM>A.</EM>--The most of the working parts of modern engines are
    made of malleable iron, and the utmost strain to which wrought iron
    should be subjected in machinery is 4000 lbs. per square inch of
    section. Cast iron should not be subjected to more than half of this.
    In locomotive boilers the strain of 4000 lbs. per square inch of
    section is sometimes exceeded by nearly one half; but such an excess of
    strain approaches the limits of danger.</P>

    <P>70. <EM>Q.</EM>--Will you explain in what way the various strains
    subsisting in a steam engine may be resolved into tensile and crushing
    strains; also in what way the magnitude of those strains may be
    determined?</P>

    <P><EM>A.</EM>--To take the case of a beam subjected to a transverse
    strain, such as the great beam of an engine, it is clear, if we suppose
    the beam broken through the middle, that the amount of strain at the
    upper and lower edges of the beam, where the whole strain may be
    supposed to be collected, will, with any given pressure on the piston,
    depend upon the proportion of the length to the depth of the beam. One
    edge of the beam breaks by extension, and the other edge by
    compression; and the upper and lower edges may be regarded as pillars,
    one of which is extended by the strain, and the other is compressed.
    If, to make an extreme supposition, the depth of the beam is taken as
    equal to its length, then the pillars answering to the edges of the
    beam will be compressed, and extended by what is virtually a bellcrank
    lever with equal arms; the horizontal distance from the main centre to
    the end of the beam being one of the arms, and the vertical height from
    the main centre to the top edge of the beam being the other arm. The
    distance, therefore, passed through by the fractured edge of the beam
    during a stroke of the engine, will be equal to the length of the
    stroke; and the strain it will have to sustain will consequently be
    equal to the pressure on the piston. If its motion were only half that
    of the piston, as would be the case if its depth were made one half
    less, the strain the beam would have to bear would be twice as great;
    and it may be set down as an axiom, that the strain upon any part of a
    steam engine or other machine is inversely equal to the strain produced
    by the prime mover, multiplied by the comparative velocity with which
    the part in question moves. If any part of an engine moves with a less
    velocity than the piston, it will have a greater strain on it, if
    resisted, than is thrown upon the piston. If it moves with a greater
    velocity than the piston, it will have a less strain upon it, and the
    difference of strain will in every case be in the inverse proportion of
    the difference of the velocity.</P>

    <P>71. <EM>Q.</EM>--Then, in computing the amount of metal necessary to
    give due strength to a beam, the first point is to determine the
    velocity with which the edge of the beam moves at that point were the
    strain is greatest?</P>

    <P><EM>A.</EM>--The web of a cast-iron beam or girder serves merely to
    connect the upper and lower edges or flanges rigidly together, so as to
    enable the extending and compressing strains to be counteracted in an
    effectual manner by the metal of those flanges. It is only necessary,
    therefore, to make the flanges of sufficient strength to resist
    effectually the crushing and tensile strains to which they are exposed,
    and to make the web of the beam of sufficient strength to prevent a
    distortion of its shape from taking place.</P>

    <P>72. <EM>Q.</EM>--Is the strain greater from being movable or
    intermittent than if it was stationary?</P>

    <P><EM>A.</EM>--Yes it is nearly twice as great from being movable.
    Engineers are in the habit of making girders intended to sustain a
    stationary load, about three times stronger than the breaking weight;
    but if the load be a movable one, as is the case in the girders of
    railway bridges, they make the strength equal to six times the breaking
    weight.</P>

    <P>73. <EM>Q.</EM>--Then the strain is increased by the suddenness with
    which it is applied?</P>

    <P><EM>A.</EM>--If a weight be placed on a long and slender beam
    propped up in the middle, and the prop be suddenly withdrawn, so as to
    allow deflection to take place, it is clear that the deflection must be
    greater than if the load had been gradually applied. The momentum of
    the weight and also of the beam itself falling through the space
    through which it has been deflected, has necessarily to be counteracted
    by the elasticity of the beam; and the beam will, therefore, be
    momentarily bent to a greater extent than what is due to the load, and
    after a few vibrations up and down it will finally settle at that point
    of deflection which the load properly occasions. It is obvious that a
    beam must be strong enough, not merely to sustain the pressure due to
    the load, but also that accession of pressure due to the counteracted
    momentum of the weight and of the beam itself. Although in steam
    engines the beam is not loaded by a weight, but by the pressure of the
    steam, yet the momentum of the beam itself must in every case be
    counteracted, and the momentum will be considerable in every case in
    which a large and rapid deflection takes place. A rapid deflection
    increases the amount of the deflection as well as the amount of the
    strain, as is seen in the cylinder cover of a Cornish pumping engine,
    into which the steam is suddenly admitted, and in which the momentum of
    the particles of the metal put into motion increases the deflection to
    an extent such as the mere pressure of the steam could not produce.</P>

    <P>74. <EM>Q.</EM>--What will be the amount of increased strain
    consequent upon deflection?</P>

    <P><EM>A.</EM>--The momentum of any moving body being proportional to
    the square of its velocity, it follows that the strain will be
    proportional to the square of the amount of deflection produced in a
    specified time.</P>

    <P>75. <EM>Q.</EM>--But will not the inertia of a beam resist
    deflection, as well as the momentum increase deflection?</P>

    <P><EM>A.</EM>--No doubt that will be so; but whether in practical
    cases increase of mass without reference to strength or load will, upon
    the whole, increase or diminish deflection, will depend very much upon
    the magnitude of the mass relatively with the magnitude of the
    deflecting pressure, and the rapidity with which that pressure is
    applied and removed. Thus if a force or weight be very suddenly applied
    to the middle of a ponderous beam, and be as suddenly withdrawn, the
    inertia of the beam will, as in the case of the collision of bodies,
    tend to resist the force, and thus obviate deflection to a considerable
    extent; but if the pressure be so long continued as to produce the
    amount of deflection due to the pressure, the effect of the inertia in
    that case will be to increase the deflection.</P>

    <P>76. <EM>Q.</EM>--Will the pressure given to the beam of an engine in
    different directions facilitate its fracture?</P>

    <P><EM>A.</EM>--Iron beams bent alternately in opposite directions, or
    alternately deflected and released, will be broken in the course of
    time with a much less strain than is necessary to produce immediate
    fracture. It has been found, experimentally, that a cast-iron bar,
    deflected by a revolving cam to only half the extent due to its
    breaking weight, will in no case withstand 900 successive deflections;
    but, if bent by the cam to only one third of its ultimate deflection,
    it will withstand 100,000 deflections without visible injury. Looking,
    however, to the jolts and vibrations to which engines are subject, and
    the sudden strains sometimes thrown upon them, either from water
    getting into the cylinder or otherwise, it does not appear that a
    strength answering to six times the breaking weight will give
    sufficient margin for safety in the case of cast-iron beams.</P>

    <P>77. <EM>Q.</EM>--Does the same law hold in the case of the
    deflection of malleable iron bars?</P>

    <P><EM>A.</EM>--In the case of malleable iron bars it has been found
    that no very perceptible damage was caused by 10,000 deflections, each
    deflection being such as was due to half the load that produced a large
    permanent deflection.</P>

    <P>78. <EM>Q.</EM>--The power of a rod or pillar to resist compression
    becomes very little when the diameter is small and the length
    great?</P>

    <P><EM>A.</EM>--The power of a rod or pillar to resist compression,
    varies nearly as the fourth power of the diameter divided by the square
    of the length. In the case of hollow cylindrical columns of cast iron,
    it has been found, experimentally, that the 3.55th power of the
    internal diameter, subtracted from the 3.55th power of the external
    diameter, and divided by the 1.7th power of the length, will represent
    the strength very nearly. In the case of hollow cylindrical columns of
    malleable iron, experiment shows that the 3.59th power of the internal
    diameter, subtracted from the 3.59th power of the external diameter,
    and divided by the square of the length, gives a proper expression for
    the strength; but this rule only holds where the strain does not exceed
    8 or 9 tons on the square inch of section. Beyond 12 or 13 tons per
    square inch of section, the metal cannot be depended upon to withstand
    the strain, though hollow pillars will sometimes bear 15 or 16 tons per
    square inch of section.</P>

    <P>79. <EM>Q.</EM>--Does not the thickness of the metal of the pillars
    or tubes affect the question?</P>

    <P><EM>A.</EM>--It manifestly does; for a tube of very thin metal, such
    as gold leaf or tin foil, would not stand on end at all, being crushed
    down by its own weight. It is found, experimentally, that in malleable
    iron tubes of the respective thicknesses of .525, .272, and .124
    inches, the resistances per square inch of section are 19.17, 14.47,
    and 7.47 tons respectively. The power of plates to resist compression
    varies nearly as the cube, or more nearly as the 2.878th power of their
    thickness; but this law only holds so long as the pressure applied does
    not exceed from 9 to 12 tons per square inch of section. When the
    pressure is greater than this the metal is crushed, and a new law
    supervenes, according to which it is necessary to employ plates of
    twice or three times the thickness, to obtain twice the resisting
    power.</P>

    <P>80. <EM>Q.</EM>--In a riveted tube, will the riveting be much,
    damaged by heavy strains?</P>

    <P><EM>A.</EM>--It will be most affected by percussion. Long-continued
    impact on the side of a tube, producing a deflection of only one fifth
    of that which would be required to injure it by pressure, is found to
    be destructive of the riveting; but in large riveted structures, such
    as a ship or a railway bridge, the inertia of the mass will, by
    resisting the effect of impact, prevent any injurious action from this
    cause from taking place.</P>

    <P>81. <EM>Q.</EM>--Will the power of iron to resist shocks be in all
    cases proportional to its power to resist strains?</P>

    <P><EM>A.</EM>--By no means. Some cast iron is very hard and brittle;
    and although it will in this state resist compression very strongly,
    it, will be easily broken by a blow. Iron which has been remelted many
    times generally falls into this category, as it will also do if run
    into very small castings. It has been found, by experiment, that iron
    of which the crushing weight per square inch is about 42 tons, will, if
    remelted twelve times, bear a crushing weight of 70 tons, and if
    remelted eighteen times it will bear a crushing weight of 83 tons; but
    taking its power to resist impact in its first state at 706, this power
    will be raised at the twelfth remelting to 1153, and will be sunk at
    the eighteenth remelting to 149.</P>

    <P>82. <EM>Q.</EM>--From all this it appears that a combination of cast
    iron and malleable iron is the best for the beams of engines?</P>

    <P><EM>A.</EM>--Yes, and for all beams. Engine beams should be made
    deeper at the middle than they are now made; the web should be
    lightened by holes pierced in it, and round the edge of the beam there
    should be a malleable iron hoop or strap securely attached to the
    flanges by riveting or otherwise. The flanges at the edges of engine
    beams are invariably made too small. It is in them that the strength of
    the beam chiefly resides.</P>

    <H2 CLASS="chapter"><A NAME="ch01"></A>CHAPTER I.</H2>

    <H3>GENERAL DESCRIPTION OF THE STEAM ENGINE.</H3>

    <H4 CLASS="subhead"><A NAME="b01"></A>THE BOILER.</H4>

    <P>83. <EM>Q.</EM>--What are the chief varieties of the steam engine in
    actual practical use?</P>

    <P><EM>A.</EM>--There is first the single-acting engine, which is used
    for pumping water; the rotative land engine, which is employed to drive
    mills and manufactories; the rotative marine engine, which is used to
    propel steam vessels; and the locomotive engine, which is employed on
    railways. The last is always a high-pressure engine; the others are,
    for the most part, condensing engines.</P>

    <P>84. <EM>Q.</EM>--Will you explain the construction and action of the
    single-acting engine, used for draining mines?</P>

    <P><EM>A.</EM>--Permit me then to begin with the boiler, which is
    common and necessary to all engines; and I will take the example of a
    wagon boiler, such as was employed by Boulton and Watt universally in
    their early engines, and which is still in extensive use. This boiler
    is a long rectangular vessel, with a rounded top, like that of a
    carrier&#39;s wagon, from its resemblance to which it derives its name.
    A fire is set beneath it, and flues constructed of brickwork encircle
    it, so as to keep the flame and smoke in contact with the boiler for a
    sufficient time to absorb the heat.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig03.png" ALIGN="right" WIDTH="400"
    HEIGHT="665" ALT="Fig. 3"></P>

    <P>85. <EM>Q.</EM>--This species of boiler has not an internal furnace,
    but is set in brickwork, in which the furnace is formed?</P>

    <P><EM>A.</EM>--Precisely so. The general arrangement and configuration
    will be at once understood by a reference to the annexed figure (fig.
    3), which is a transverse section of a wagon boiler. The line b
    represents the top of the grate or fire bars, which slope downward from
    the front at an angle of about 25&deg;, giving the fuel a tendency to
    move toward the back of the grate. The supply of air ascends from the
    ash pit through the grate bars, and the flame passes over a low wall or
    bridge, and traverses the bottom of the boiler. The smoke rises up at
    the back of the boiler, and proceeds through the flue F along one side
    to the front, and returns along the other side of the boiler, and then
    ascends the chimney. The performance of this course by the smoke is
    what is termed a wheel draught, as the smoke wheels once round the
    boiler, and then ascends the chimney.</P>

    <P>86. <EM>Q.</EM>--Is the performance of this course by the smoke
    universal in wagon boilers?</P>

    <P><EM>A.</EM>--No; such boilers sometimes have what is termed a split
    draught. The smoke and flame, when they reach the end of the boiler,
    pass in this case through an iron flue or tube, reaching from end to
    end of the boiler; and on arriving at the front of the boiler, the
    smoke splits or separates-- one half passing through a flue on the one
    side of the boiler, and the other half passing through a flue on the
    other side of the boiler--both of these flues having their debouch in
    the chimney.</P>

    <P>87. <EM>Q.</EM>--What are the appliances usually connected with a
    wagon boiler?</P>

    <P><EM>A.</EM>--On the top of the boiler, near the front, is a short
    cylinder, with a lid secured by bolts. This is the manhole door, the
    purpose of which is to enable a man to get into the inside of the
    boiler when necessary for inspection and repair. On the top of this
    door is a small valve opening downward, called the atmospheric valve.
    The intention of this valve is to prevent a vacuum from being formed
    accidentally in the boiler, which might collapse it; for if the
    pressure in the boiler subsides to a point materially below the
    pressure of the atmosphere, the valve will open and allow air to get
    in. A bent pipe, which rises up from the top of the boiler, immediately
    behind the position of the manhole, is the steam pipe for conducting
    the steam to the engine; and a bent pipe which ascends from the top of
    the boiler, at the back end, is the waste-steam pipe for conducting
    away the steam, which escapes through the safety valve. This valve is
    set in a chest, standing on the top of the boiler, at the foot of the
    waste-steam pipe, and it is loaded with iron or leaden weights to a
    point answerable to the intended pressure of the steam.</P>

    <P>88. <EM>Q.</EM>--How is the proper level of the water in the boiler
    maintained?</P>

    <P><EM>A.</EM>--By means of a balanced buoy or float. This float is
    attached to a rod, which in its turn is attached to a lever set on the
    top of a large upright pipe. The upper part of the pipe is widened out
    into a small cistern, through a short pipe in the middle of which a
    chain passes to the damper; but any water emptied into this small
    cistern cannot pass into the pipe, except through a small valve fixed
    to the lever to which the rod is attached. The water for replenishing
    the boiler is pumped into the small cistern on the top of the pipe; and
    it follows from these arrangements that when the buoy falls, the rod
    opens the small valve and allows the feed water to enter the pipe,
    which communicates with the water in the boiler; whereas, when the buoy
    rises, the feed cannot enter the pipe, and it has, therefore, to run to
    waste through an overflow pipe provided for the purpose.</P>

    <P>89. <EM>Q.</EM>--How is the strength of the fire regulated?</P>

    <P><EM>A.</EM>--The draught through the furnaces of land boilers is
    regulated by a plate of metal or a damper, as it is called, which
    slides like a sluice up and down in the flue, and this damper is closed
    more or less when the intensity of the fire has to be moderated. In
    wagon boilers this is generally accomplished by self-acting mechanism.
    In the small cistern pipe, which is called a stand pipe, the water
    rises up to a height proportional to the pressure of the steam, and the
    surface of the water in this pipe will rise or fall with the
    fluctuations in the pressure of the steam. In this pipe a float is
    placed, which communicates by means of a chain with the damper. If the
    pressure of the steam rises, the float will be raised and the damper
    closed, whereas, if the pressure in the boiler falls, the reverse of
    this action will take place.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig04.png" WIDTH="700" HEIGHT="190" ALT=
    "Fig. 4"></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig05.png" ALIGN="right" WIDTH="529"
    HEIGHT="407" ALT="Fig. 5"></P>

    <P>90. <EM>Q.</EM>--Are all land boilers of the same construction as
    that which you have just described?</P>

    <P><EM>A.</EM>--No; many land boilers are now made of a cylindrical
    form, with one or two internal flues in which the furnace is placed. A
    boiler of this kind is represented in Figs. 4 and 5, and which is the
    species of boiler principally used in Cornwall. In this boiler a large
    internal cylinder or flue runs from end to end. In the fore part of
    this cylinder the furnace is placed, and behind the furnace a large
    tube filled with water extends to the end of the boiler. This internal
    tube is connected to the bottom part of the boiler by a copper pipe
    standing vertically immediately behind the furnace bridge, and to the
    top part of the boiler by a bent copper pipe which stands in a vertical
    position near the end of the boiler. The smoke, after passing through
    the central flue, circulates round the sides and beneath the bottom of
    the boiler before its final escape into the chimney. The boiler is
    carefully covered over to prevent the dispersion of the heat.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig06.png" WIDTH="500" HEIGHT="671" ALT=
    "Fig. 6"></P>

    <P>91. <EM>Q.</EM>--Will you describe the construction of the boilers
    used in steam vessels?</P>

    <P><EM>A.</EM>--These are of two classes, flue boilers and tubular
    boilers, but the latter are now most used. In the flue boiler the
    furnaces are set within the boiler, and the flues proceeding from them
    wind backwards and forwards within the boiler until finally they meet
    and enter the chimney. Figs. 6, 7, and 8 are different views of the
    flue boilers of the steamer Forth. There are 4 boilers (as shown in
    plan, Fig. 6), with 3 furnaces in each, or 12 furnaces in all. Fig. 7
    is an elevation of 2 boilers, the one to the right being the front
    view, and that to the left a transverse section. Fig. 8 is a
    longitudinal section through 2 boilers. The direction of the arrows in
    plan and longitudinal section, will explain the direction of the smoke
    current.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig07.png" WIDTH="450" HEIGHT="445" ALT=
    "Fig. 7"></P>

    <P>92. <EM>Q.</EM>--Is this arrangement different from that obtaining
    in tubular boilers?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig08.png" WIDTH="500" HEIGHT="389" ALT=
    "Fig. 8"></P>

    <P><EM>A.</EM>--In tubular boilers, the smoke after leaving the furnace
    just passes once through a number of small tubes and then enters the
    chimney. These tubes are sometimes of brass, and they are usually about
    3 inches in diameter, and 6 or 7 feet long.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig09.png" WIDTH="438" HEIGHT="550" ALT=
    "Fig. 9"></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig10.png" WIDTH="292" HEIGHT="550" ALT=
    "Fig. 10"><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig11.png" WIDTH="292" HEIGHT=
    "550" ALT="Fig. 11"></P>

    <P>Figs. 9, 10, and 11 represent a marine tubular boiler; fig. 9 being
    a vertical longitudinal section, fig. 10 half a front elevation and
    half a transverse section, and fig. 11 half a back elevation and half a
    transverse section near the end. There is a projecting part on the top
    of the boiler called the &quot;steam chest,&quot; of which the purpose
    is to retain for the use of the cylinder a certain supply of steam in a
    quiescent state, in order that it may have time to clear itself of foam
    or spray. A steam chest is a usual part of all marine boilers. In fig.
    9 A is the furnace, B the steam chest, and C the smoke box which opens
    into the chimney. The front of the smoke box is usually closed by doors
    which may be opened when necessary to sweep the soot out of the
    tubes.</P>

    <P>The following are some forms of American boilers:</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig12.png" WIDTH="237" HEIGHT="550" ALT=
    "Fig. 12"><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig13.png" WIDTH="473" HEIGHT=
    "500" ALT="Fig. 13"></P>

    <P>Figs. 12 and 13 are the transverse and longitudinal sections of a
    common form of American marine boiler.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig1415.png" WIDTH="700" HEIGHT="456"
    ALT="Fig. 14 Fig. 15"></P>

    <P>Figs. 14 and 15 are the front and sectional elevation of one of the
    boilers of the U.S. steamer Water Witch.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig16.png" WIDTH="700" HEIGHT="548" ALT=
    "Fig. 16"></P>

    <P>Fig. 16 is a longitudinal section of a boiler of the drop flue
    variety. For land purposes the lowest range of tubes is generally
    omitted, and the smoke makes a last return beneath the bottom of the
    boiler.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig1718.png" WIDTH="750" HEIGHT="460"
    ALT="Fig. 17 Fig. 18"></P>

    <P>Figs. 17 and 18 are the transverse and longitudinal sections of a
    tubular boiler, built in 1837 by R.L. Stevens for the steamboat
    Independence.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig19.png" WIDTH="700" HEIGHT="481" ALT=
    "Fig. 19"></P>

    <P>Fig. 19 is a longitudinal section of a common wood-burning
    locomotive.</P>

    <H4 CLASS="subhead"><A NAME="b02"></A>THE ENGINE.</H4>

    <P>93. <EM>Q.</EM>--The steam passes from the boiler through, the steam
    pipe into the cylinder of the engine?</P>

    <P><EM>A.</EM>--And presses up and down the piston alternately, being
    admitted alternately above and below the piston by suitable valves
    provided for that purpose.</P>

    <P>94. <EM>Q.</EM>--This reciprocating motion is all that is required
    in a pumping engine?</P>

    <P><EM>A.</EM>--The prevailing form of the pumping engine consists of a
    great beam vibrating on a centre like the beam of a pair of scales, and
    the cylinder is in connection with one end of the beam and the pump
    stands at the other end. The pump end of the beam is usually loaded, so
    as to cause it to preponderate when the engine is at rest; and the
    whole effort of the steam is employed in overcoming this preponderance
    until a stroke is performed, when, the steam being shut off, the heavy
    end of the beam again falls and the operation is repeated.</P>

    <P>95. <EM>Q.</EM>--in the double-acting engine the piston is pushed by
    the steam both ways, whereas in the single-acting engine it is only
    pushed one way?</P>

    <P><EM>A.</EM>--The structure and action of a double-acting land engine
    of the kind introduced by Mr. Watt, will be understood by a reference
    to the annexed figure (fig. 20), where an engine of this kind is shown
    in section. A is the cylinder in which a movable piston, T, is forced
    alternately up and down by the alternate admission, to each side, of
    the steam from the boiler. The piston, by means of a rod called the
    piston rod, gives motion to the beam V W, which by means of a heavy
    bar, P, called the connecting rod, moves the crank, Q, and with it the
    fly wheel, X, from which the machinery to be driven derives its
    motion.</P>

    <P>96. <EM>Q.</EM>--Where does the steam enter from the boiler?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig20.png" ALIGN="right" WIDTH="423"
    HEIGHT="550" ALT="Fig. 20"></P>

    <P><EM>A.</EM>--At the steam pipe, B. The throttle valve in that pipe
    is an elliptical plate of metal swivelling on a spindle passing through
    its edge from side to side, and by turning which more or less the
    opening through the pipe will be more or less closed. The extent to
    which this valve is opened or closed is determined by the governor, D,
    the balls of which, as they collapse or expand, move up or down a
    collar on the governor spindle, which motion is communicated to the
    throttle valve by suitable rods and bell-cranks. The governor, it will
    be seen, consists substantially of two heavy balls attached to arms
    fixed upon an upright shaft, which is kept in revolution by means of a
    cord driven by a pulley on the fly wheel shaft. The velocity with which
    the balls of the governor revolve being proportional to that of the fly
    wheel, it will follow, that if by reason of too rapid a supply of
    steam, an undue speed be given to the fly wheel, and therefore to the
    balls, a divergence of the balls will take place to an extent
    corresponding to the excess of velocity, and this movement being
    communicated to the throttle valve it will be partly closed (see fig.
    1), the supply of steam to the engine will be diminished, and the
    velocity of its motion will be reduced. If, on the other hand, the
    motion of the engine is slower than is requisite, owing to a deficient
    supply of steam through B, then the balls, not being sufficiently
    affected by centrifugal force, will fall towards the vertical spindle,
    and the throttle valve, C, will be more fully opened, whereby a more
    ample supply of steam will be admitted to the cylinder, and the speed
    of the engine will be increased to the requisite extent.</P>

    <P>97. <EM>Q.</EM>--The piston must be made to fit the cylinder
    accurately so as to prevent the passage of steam?</P>

    <P><EM>A.</EM>--The piston is accurately fitted to the cylinder, and
    made to move in it steam tight by a packing of hemp driven tightly into
    a groove or recess round the edge of the piston, and which is squeezed
    down by an iron ring held by screws. The piston divides the cylinder
    into two compartments, between which there is no communication by which
    steam or any other elastic fluid can pass. A casing set beside the
    cylinder contains the valves, by means of which the steam which impels
    the piston is admitted and withdrawn, as the piston commences its
    motion in each direction. The upper steam box B, is divided into three
    compartments by two valves. Above the upper steam valve V, is a
    compartment communicating with the steam pipe B. Below the lower valve
    E is another compartment communicating with a pipe called the eduction
    pipe, which leads downwards from the cylinder to the condenser, in
    which vessel the steam is condensed by a jet of cold water. By the
    valve V, a communication may be opened or closed between the boiler and
    the top of the cylinder, so as to permit or prevent a supply of steam
    from the one to pass to the other. By the valve E a communication may
    be open or closed between the top of the cylinder and the condenser, so
    that the steam in the top compartment of the cylinder may either be
    permitted to escape into the condenser, or may be confined to the
    cylinder. The continuation of the steam pipe leads to the lower steam
    box B&#39;, which, like the upper, is divided into three compartments
    by two valves V&#39; and E&#39;, and the action of the lower valves is
    in all respects the same as that of the upper.</P>

    <P>98. <EM>Q.</EM>--Are all these valves connected together so that
    they act simultaneously?</P>

    <P><EM>A.</EM>--The four valves V, E, V&#39;, E&#39; are connected by
    rods to a single handle H, which handle is moved alternately up and
    down by means of pins or tappets, placed on the rod which works the air
    pump. When the handle H is pressed down, the levers in connexion with
    it open the upper exhausting valve E, and the lower steam valve V&#39;,
    and close the upper steam valve V and the lower exhausting valve
    E&#39;. On the other hand, when the handle H is pressed up it opens the
    upper steam valve V and the lower exhausting valve E&#39;, and at the
    same time closes the upper exhausting valve E, and the lower steam
    valve V&#39;.</P>

    <P>99. <EM>Q.</EM>--Where is the condenser situated?</P>

    <P><EM>A.</EM>--The condenser K is immerged in a cistern of cold water.
    At its side there is a tube I, for the admission of water to condense
    the steam, and which is governed by a cock, by opening which to any
    required extent, a jet of cold water may be made to play in the
    condenser. From the bottom of the condenser a short pipe leads to the
    air pump J, and in this pipe there is a flap valve, called the foot
    valve, opening towards the air pump. The air pump is a pump set in the
    same cistern of cold water that holds the condenser, and it is fitted
    with a piston or bucket worked by the rod L, attached to the great
    beam, and fitted with a valve opening upwards in the manner of a common
    sucking pump. The upper part of the air pump communicates with a small
    cistern S, called the hot well, through a valve opening outwards and
    called the delivery valve. A pump M, called the hot water pump, lifts
    hot water out of the hot well to feed the boiler, and another pump N
    lifts cold water from a well or other source of supply, to maintain the
    supply of water to the cold water cistern, in which the condenser and
    air pump are placed.</P>

    <P>100. Q.--Will you explain now the manner in which the engine
    acts?</P>

    <P>A.--The piston being supposed to be at the top of the cylinder, the
    handle H will be raised by the lower pin or tappet on the air pump rod,
    and the valves V and E&#39; will be opened, and at the same time the
    other pair of valves V&#39; and E will be closed. Steam will therefore
    be admitted above the piston and the steam or air which had previously
    filled the cylinder below the piston will be drawn off to the
    condenser. It will there encounter the jet of cold water, which is kept
    constantly playing there by keeping the cock I sufficiently open. It
    will thus be immediately condensed or reduced to water, and the
    cylinder below the piston will have a vacuum in it. The steam therefore
    admitted from the steam pipe through the open valve V to the top of the
    cylinder, not being resisted by pressure below, will press the piston
    to the bottom of the cylinder. As it approaches that position, the
    handle H will be struck down by the upper pin or tappet on the air pump
    rod, and the valves V and E&#39;, previously open, will be closed,
    while the valves V&#39; and E, previously closed, will be opened. The
    steam which has just pressed down the piston, and which now fills the
    cylinder above the piston, will then flow off, through the open valve
    E, to the condenser, where it will be immediately condensed by the jet
    of cold water; and steam from the boiler, admitted through the open
    valve V&#39;, will fill the cylinder below the piston, and press the
    piston upwards. When the piston has reached the top of the cylinder,
    the lower pin on the air pump rod will have struck the handle upwards,
    and will thereby have closed the valves V&#39; and E, and opened the
    valves V and E&#39;. The piston will then be in the same situation as
    in the commencement, and will again descend, and so will continue to be
    driven up and down by the steam.</P>

    <P>101. Q.--But what becomes of the cold water which is let into the
    condenser to condense the steam?</P>

    <P>A.--It is pumped out by the air pump in the shape of hot water, its
    temperature having been raised considerably by the admixture of the
    steam in it. When the air pump piston ascends it leaves behind it a
    vacuum; and the foot valve being relieved from all pressure, the weight
    of the water in the condenser forces it open, and the warm water flows
    from the condenser into the lower part of the air pump, from which its
    return to the condenser is prevented by the intervening valve. When the
    air pump piston descends, its pressure on the liquid under it will
    force open the valve in it, through which the hot water will ascend;
    and when the bucket descends to the bottom of the pump barrel, the warm
    water which was below it will all have passed above it, and cannot
    return. When the bucket next ascends, the water above it, not being
    able to return through the bucket valve, will be forced into the hot
    well through the delivery valve S. The hot water pump M, pumps a small
    quantity of this hot water into the boiler, to compensate for the
    abstraction of the water that has passed off in the form of steam. The
    residue of the hot water runs to waste.</P>

    <P>102. <EM>Q.</EM>--By what expedient is the piston rod enabled to
    pass through the cylinder cover without leaking steam out of the
    cylinder or air into it?</P>

    <P><EM>A.</EM>--The hole in the cylinder lid, through which the piston
    rod passes, is furnished with a recess called a stuffing box, into
    which a stuffing or packing of plaited hemp is forced, which, pressing
    on the one side against the interior of the stuffing box, and on the
    other side against the piston rod, which is smooth and polished,
    prevents any leakage in this situation. The packing of this stuffing
    box is forced down by a ring of metal tightened by screws. This ring,
    which accurately fits the piston rod, has a projecting flange, through
    which bolts pass for tightening the ring down upon the packing; and a
    similar expedient is employed in nearly every case in which packing is
    employed.</P>

    <P>103. <EM>Q.</EM>--In what way is the piston rod connected to the
    great beam?</P>

    <P><EM>A.</EM>--The piston rod is connected to the great beam by means
    of two links, one at each side of the beam shown at <EM>f g</EM>, (fig.
    21.) These links are usually made of the same length as the crank, and
    their purpose is to enable the end of the great beam to move in the arc
    of a circle while the piston rod maintains the vertical position. The
    point of junction, therefore, of the links and the piston rod is of the
    form of a knuckle or bend at some parts of the stroke.</P>

    <P>104. <EM>Q.</EM>--But what compels the top of the piston rod to
    maintain the vertical position?</P>

    <P><EM>A.</EM>--Some engines have guide rods set on each side of the
    piston rod, and eyes on the top of the piston rod engage these guide
    rods, and maintain the piston rod in a vertical position in every part
    of the stroke. More commonly, however, the desired end is attained by
    means of a contrivance called the parallel motion.</P>

    <P>105. <EM>Q.</EM>--What is the parallel motion?</P>

    <P><EM>A.</EM>--The parallel motion is an arrangement of jointed rods,
    so connected together that the divergence from the vertical line at any
    point in the arc described by the beam is corrected by an equal and
    opposite divergence due to the arc performed by the jointed rods during
    the stroke; and as these opposite deviations mutually correct one
    another, the result is that the piston rod moves in a vertical
    direction.</P>

    <P>106. <EM>Q.</EM>--Will you explain the action more in detail?</P>

    <P><EM>A.</EM>--The pin, fig 21, which passes through the end of the
    beam at <EM>f</EM> has a link <EM>f g</EM> hung on each side of the
    beam, and a short cross bar, called a cross head, extends from the
    bottom of one of these links to the bottom of the other, which cross
    head is perforated with a hole in the middle for the reception of the
    piston rod. There are similar links <EM>b d</EM> at the point of the
    main beam, where the air pump rod is attached. There are two rods <EM>d
    g</EM> connecting the links <EM>b d</EM> with the links <EM>f g</EM>,
    and these rods, as they always continue parallel to the main beam
    throughout the stroke, are called <EM>parallel bars</EM>. Attached to
    the end of these two rods at <EM>d</EM> are two other rods <EM>c
    d</EM>, of which the ends at <EM>c</EM> are attached to stationary
    pins, while the ends at <EM>d</EM> follow the motion of the lower ends
    of the links <EM>b d</EM>. These rods are called the <EM>radius
    bars</EM>. Now it is obvious that the arc described by the point
    <EM>d</EM>, with <EM>c</EM> as a centre, is opposite to the arc
    described by the point <EM>g</EM> with <EM>d</EM> as a centre. The rod
    <EM>d g</EM> is, therefore, drawn back horizontally by the arc
    described at <EM>d</EM> to an extent equal to the versed sine of the
    arc described at <EM>g</EM>, or, in other words, the line described by
    the point <EM>g</EM> becomes a straight line instead of a curve.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig21.png" WIDTH="600" HEIGHT="339" ALT=
    "Fig. 21"></P>

    <P>107. <EM>Q.</EM>--Does the air pump rod move vertically as well as
    the piston rod?</P>

    <P><EM>A.</EM>--It does. The air pump rod is suspended from a cross
    head, passing from the centre of one of the links <EM>b d</EM> to the
    centre of the other link, on the opposite side of the beam. Now, as the
    distance from the central axis of the great beam to the point
    <EM>b</EM> is equal to the length of the rod <EM>c d</EM>, it will
    follow that the upper end of the link will follow one arc, and the
    lower end an equal and opposite arc. A point in the centre of the link,
    therefore, where these opposite motions meet, will follow no arc at
    all, but will move up and down vertically in a straight line.</P>

    <P>108. <EM>Q.</EM>--The use of the crank is to obtain a circular
    motion from a reciprocating motion?</P>

    <P><EM>A.</EM>--That is the object of it, and it accomplishes its
    object in a very perfect manner, as it gradually arrests the velocity
    of the piston towards the end of the stroke, and thus obviates what
    would otherwise be an injurious shock upon the machine. When the crank
    approaches the lowest part of its throw, and at the same time the
    piston is approaching the top of the cylinder, the motion of the crank
    becomes nearly horizontal, or, in other words, the piston is only
    advanced through a very short distance, for any given distance measured
    on the circle described by the crank pin. Since, then, the velocity of
    rotation of the crank is nearly uniform, it will follow that the piston
    will move very slowly as it approaches the end of the stroke; and the
    piston is brought to a state of rest by this gradually retarded motion,
    both at the top and the bottom of the stroke.</P>

    <P>109. <EM>Q.</EM>--What causes the crank to revolve at a uniform
    velocity?</P>

    <P><EM>A.</EM>--The momentum of the machinery moved by the piston, but
    more especially of the fly wheel, which by its operation redresses the
    unequal pressures communicated by the crank, and compels the crank
    shaft to revolve at a nearly uniform velocity. Everyone knows that a
    heavy wheel if put into rapid rotation cannot be immediately stopped.
    At the beginning and end of the stroke when the crank is vertical, no
    force of torsion can be exerted on the crank shaft by the crank, but
    this force is at its maximum when the crank is horizontal. From the
    vertical point, where this force is nothing, to the horizontal point,
    where it is at its maximum, the force of torsion exerted on the crank
    shaft is constantly varying; and the fly wheel by its momentum
    redresses these irregularities, and carries the crank through that
    &quot;dead point,&quot; as it is termed, where the piston cannot impart
    any rotative force.</P>

    <P>110. <EM>Q.</EM>--Are the configuration and structure of the steam
    engine, as it left the hand of Watt, materially different from those of
    modern engines?</P>

    <P><EM>A.</EM>--There is not much difference. In modern rotative land
    engines, the valves for admitting the steam to the cylinder or
    condenser, instead of being clack or pot-lid valves moved by tappets on
    the air pump rod, are usually sluice or sliding valves, moved by an
    eccentric wheel on the crank shaft. Sometimes the beam is discarded
    altogether, and malleable iron is more largely used in the construction
    of engines instead of the cast iron, which formerly so largely
    prevailed. But upon the whole the steam engine of the present day is
    substantially the engine of Watt; and he who perfectly understands the
    operation of Watt&#39;s engine, will have no difficulty in
    understanding the operation of any of the numerous varieties of engines
    since introduced.</P>

    <H4 CLASS="subhead"><A NAME="b03"></A>THE MARINE ENGINE.</H4>

    <P>111. <EM>Q.</EM>--Will you describe the principal features of the
    kind of steam engine employed for the propulsion of vessels?</P>

    <P><EM>A.</EM>--Marine engines are of two kinds,--paddle engines and
    screw engines. In the one case the propelling instrument is paddle
    wheels kept in rotation at each side of the ship: in the other case,
    the propelling instrument is a screw, consisting of two or more twisted
    vanes, revolving beneath the water at the stern. Of each class of
    engines there are many distinct varieties.</P>

    <P>112. <EM>Q.</EM>--What are the principal varieties of the paddle
    engine?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig2223.png" WIDTH="600" HEIGHT="504"
    ALT="Fig. 22 Fig. 23"></P>

    <P><EM>A.</EM>--There is the side lever engine (fig. 26), and the
    oscillating engine (fig. 27), besides numerous other forms of engine
    which are less known or employed, such as the trunk (fig. 22), double
    cylinder (fig. 23), annular, Gorgon (fig. 24), steeple (fig. 25), and
    many others. The side lever engine, however, and the oscillating
    engine, are the only kinds of paddle engines which have been received
    with wide or general favor.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig24.png" WIDTH="467" HEIGHT="550" ALT=
    "Fig. 24"></P>

    <P>113. <EM>Q.</EM>--Will you explain the main distinctive features of
    the side lever engine?</P>

    <P><EM>A.</EM>--In all paddle vessels, whatever be their subordinate
    characteristics, a great shaft of wrought iron, s, turned round by the
    engine, has to be carried from side to side of the vessel, on which
    shaft are fixed the paddle wheels. The paddle wheels may either be
    formed with fixed float boards for engaging the water, like the boards
    of a common undershot water wheel, or they may be formed with
    <EM>feathering</EM> float boards as they are termed, which is float
    boards movable on a centre, and so governed by appropriate mechanism
    that they enter and leave the water in a nearly vertical position. The
    common fixed or radial floats, however, are the kind most widely
    employed, and they are attached to the arms of two or more rings of
    malleable iron which are fixed by appropriate centres on the paddle
    shaft. It is usual in steam vessels to employ two engines, the cranks
    of which are set at right angles with one another. When the paddle
    wheels are turned by the engines, the float boards engaging the water
    cause a forward thrust to be imparted to the shaft, which propels
    forward the vessel on the same principle that a boat is propelled by
    the action of oars.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig25.png" ALIGN="right" WIDTH="331"
    HEIGHT="550" ALT="Fig. 25"></P>

    <P>114. <EM>Q.</EM>--These remarks apply to all paddle vessels?</P>

    <P><EM>A.</EM>--They do. With respect to the side lever engine, it may
    be described to be such a modification of the land beam engine already
    described, as will enable it to be got below the deck of a vessel. With
    this view, instead of a single beam being placed overhead, two beams
    are used, one of which is set on each side of the engine as low down as
    possible. The cross head which engages the piston rod is made somewhat
    longer than the diameter of the cylinder, and two great links or rods
    proceed one from each end of the cross head to one of the side levers
    or beams. A similar cross bar at the other end of the beams serves to
    connect them together and to the connecting rod which, proceeding from
    thence upwards, engages the crank, and thereby turns round the paddle
    wheels.</P>

    <P>115. <EM>Q.</EM>--Will you further illustrate this general
    description by an example?</P>

    <P><EM>Q.</EM>--Fig. 26 is a side elevation of a side lever engine; x x
    represent the beams or keelsons to which the engines are attached, and
    on which the boilers rest. The engines are tied down by strong bolts
    passing through the bottom of the vessel, but the boiler keeps its
    position by its weight alone. The condenser and air pump are worked off
    the side levers by means of side rods and a cross head. A strong
    gudgeon, called the <EM>main centre</EM>, passes through the condenser
    at K, the projecting ends of which serve to support the side levers or
    beams. L is the piston rod, which, by means of the cross head and side
    rods, is connected to the side levers or beams, one of which is shown
    at H H. The line M represents the connecting rod, to which motion is
    imparted by the beams, through the medium of the cross tail extending
    between the beams, and which by means of the crank turns the paddle
    shaft S. The eccentric which works the slide valve is placed upon the
    paddle shaft. It consists of a disc of metal encircled by a hoop, to
    which a rod is attached, and the disc is perforated with a hole for the
    shaft, not in the centre, but near one edge. When, therefore, the shaft
    revolves, carrying the eccentric with it, the rod attached to the
    encircling hoop receives a reciprocating motion, just as it would do if
    attached to a crank in the shaft.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig26.png" WIDTH="600" HEIGHT="526" ALT=
    "Fig. 26"></P>

    <P>116. <EM>Q.</EM>--Will you describe the mode of starting the
    engine?</P>

    <P><EM>A.</EM>--I may first mention that when the engine is at rest,
    the connection between the eccentric and the slide valve is broken, by
    lifting the end of the eccentric rod out of a notch which engages a pin
    on the valve shaft, and the valve is at such times free to be moved by
    hand by a bar of iron, applied to a proper part of the valve gear for
    that purpose. This being so, the engineer, when he wishes to start the
    engine, first opens a small valve called the <EM>blow through
    valve</EM>, which permits steam from the boiler to enter the engine
    both above and below the piston, and also to fill the condenser and air
    pump. This steam expels the air from the interior of the engine, and
    also any water which may have accumulated there; and when this has been
    done, the blow through valve is shut, and a vacuum very soon forms
    within the engine, by the condensation of the steam. If now the slide
    valve be moved by hand, the steam from the boiler will be admitted on
    one side of the piston, while there is a vacuum on the other side, and
    the piston will, therefore, be moved in the desired direction. When the
    piston reaches the end of the stroke, the valve has to be moved in the
    reverse direction, when the piston will return, and after being moved
    thus by hand, once or twice, the connection of the valve with the
    eccentric is to be restored by allowing the notch on the end of the
    eccentric rod to engage the pin on the valve lever, when the valve will
    be thereafter moved by the engine in the proper manner. It will, of
    course, be necessary, when the engine begins to move, to open the
    injection cock a little, to enable water to enter for the condensation
    of the steam. In the most recent marine engines, a somewhat different
    mechanism from this is used for giving motion to the valves, but that
    mechanism will be afterwards described.</P>

    <P>117. <EM>Q.</EM>--Are all marine engines condensing engines?</P>

    <P><EM>A.</EM>--Nearly all of them are so; but recently a number of
    gunboats have been constructed, with high pressure engines. In general,
    however, marine engines are low pressure or condensing engines.</P>

    <P>118. <EM>Q.</EM>--Will you now describe the chief features of the
    oscillating paddle marine engine?</P>

    <P><EM>A.</EM>--In the oscillating paddle marine engine, the
    arrangement of the paddle shaft and paddle wheels is the same as in the
    case already described, but the whole of the side levers, side rods,
    cross head, cross tail, and connecting rod are discarded. The cylinder
    is set immediately under the crank; the top of the piston rod is
    connected immediately to the crank pin; and, to enable the piston rod
    to accommodate itself to the movement of the crank, the cylinder is so
    constructed as to be susceptible of vibrating or oscillating upon two
    external axes or trunnions. These trunnions are generally placed about
    half way up on the sides of the cylinder; and through one of them steam
    is received from the boiler, while through the other the steam escapes
    to the condenser. The air pump is usually worked by means of a crank in
    the shaft, which crank moves the air pump bucket up and down as the
    shaft revolves.</P>

    <P>119. <EM>Q.</EM>--Will you give an example of a paddle oscillating
    engine?</P>

    <P><EM>A.</EM>--I will take as an example the oscillating engines
    constructed by Messrs. Ravenhill &amp; Salked, for the Holyhead
    Packets. Fig. 27 is a longitudinal section of this vessel, showing an
    engine and boiler; and fig. 28 is a transverse section of one of the
    engines, showing also one of the wheels. There are two cylinders in
    this vessel, and one air pump, which lies in an inclined position, and
    is worked by a crank in the shaft which stretches between the
    cylinders, and which is called the <EM>intermediate shaft</EM>. A A, is
    one of the cylinders, B B the piston rod, and C C the crank. D is the
    crank in the intermediate shaft, which works the air pump E. There are
    double eccentrics fixed on the shaft, whereby the movement of the slide
    valves is regulated. The purpose of the double eccentrics is to enable
    an improved arrangement of valve gear to be employed, which is
    denominated the <EM>link motion</EM>, and which will be described
    hereafter. I I are the steam pipes leading to the steam trunnions K K,
    on which, and on the eduction trunnions connected with the pipe M, the
    cylinders oscillate.</P>

    <P>120. <EM>Q.</EM>--By what species of mechanism are the positions of
    the paddle floats of feathering wheels governed?</P>

    <P><EM>A.</EM>--The floats are supported by spurs projecting from the
    rim of the wheel, and they may be moved upon the points of the spurs,
    to which they are attached by pins, by means of short levers proceeding
    from the backs of the floats, and connected to rods which proceed
    towards the centre of the wheel. The centre, however, to which these
    rods proceed is not concentric with the wheel, and the rods, therefore,
    are moved in and out as the wheel revolves, and impart a corresponding
    motion to the floats. In some feathering wheels the proper motion is
    given to the rods by means of an eccentric on the ship&#39;s side. The
    action of paddle wheels, whether radial or feathering, will be more
    fully described in the chapter on Steam Navigation.</P>

    <H4 CLASS="subhead"><A NAME="b04"></A>SCREW ENGINES.</H4>

    <P>121. <EM>Q.</EM>--What are the principal varieties of screw
    engines?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig27.png" WIDTH="572" HEIGHT="550" ALT=
    "Fig. 27"></P>

    <P><EM>A.</EM>--The engines employed for the propulsion of screw
    vessels are divided into two great classes,--geared engines and direct
    acting engines; and each of these classes again has many varieties. In
    screw vessels, the shaft on which the screw is set requires to revolve
    at a much greater velocity than is required in the case of the paddle
    shaft of a paddle vessel; and in geared engines this necessary velocity
    of rotation is obtained by the intervention of toothed wheels,--the
    engines themselves moving with the usual velocity of paddle engines;
    whereas in direct acting engines the required velocity of rotation is
    obtained by accelerating the speed of the engines, and which are
    connected immediately to the screw shaft.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig28.png" WIDTH="398" HEIGHT="550" ALT=
    "Fig. 28"></P>

    <P>122. <EM>Q.</EM>--Will you describe some of the principal varieties
    of geared engines?</P>

    <P><EM>A.</EM>--A good many of the geared engines for screw vessels are
    made in the same manner as land engines, with a beam overhead, which by
    means of a connecting rod extending downwards, gives motion to the
    crank shaft, on which are set the cog wheels which give motion to
    pinions on the screw shaft,--the teeth of the wheels being generally of
    wood and the teeth of the pinions of iron. There are usually several
    wheels on the crank shaft and several pinions on the screw shaft; but
    the teeth of each do not run in the same line, but are set a little in
    advance of one another, so as to divide the thickness of the tooth into
    as many parts as there are independent wheels or pinions. By this
    arrangement the wheels work more smoothly than they would otherwise
    do.</P>

    <P>123. <EM>Q.</EM>--What other forms are there of geared screw
    engines?</P>

    <P><EM>A.</EM>--In some cases the cylinders lie on their sides in the
    manner of the cylinders of a locomotive engine. In other cases vertical
    trunk engines are employed; and in other cases vertical oscillating
    engines.</P>

    <P>124. <EM>Q.</EM>--Will you give an example of a geared vertical
    oscillating engine?</P>

    <P><EM>A.</EM>--The engines of a geared oscillating engine are similar
    to the paddle wheel engines (figs. 27 and 28), but the engines are
    placed lengthways of the ship, and instead of a paddle wheel on the
    main shaft, there is a geared wheel which connects with a pinion on the
    screw shaft. The engines of the Great Britain are made off the same
    patterns as the paddle engines constructed by Messrs. John Penn &amp;
    Son, for H.M.S. Sphinx. The diameter of each cylinder is 82-1/2 inches,
    the length of travel or stroke of the piston is 6 feet, and the nominal
    power is 500 horses. The Great Britain is of 3,500 tons burden, and her
    displacement at 16 feet draught of water is 2,970 tons. The diameter of
    the screw is 15-1/2 feet, length of screw in the line of the shaft, 3
    feet 2 inches, and the pitch of the screw, 19 feet.</P>

    <P>125. <EM>Q.</EM>--What do you mean by the pitch of the screw?</P>

    <P><EM>A.</EM>--A screw propeller may be supposed to be a short piece
    cut off a screw of large diameter like a spiral stair, and the pitch of
    a spiral stair is the vertical height from any given step to the step
    immediately overhead.</P>

    <P>126. <EM>Q.</EM>--What is the usual number of arms?</P>

    <P><EM>A.</EM>--Generally a screw has two arms, but sometimes it has
    three or more. The Great Britain had three arms or twisted blades
    resembling the vanes of a windmill. The multiple of the gearing in the
    Great Britain is 3 to 1, and there are 17-1/2 square feet of heating
    surface in the boiler for each nominal horse power. The crank shaft
    being put into motion by the engine, carries round with it the great
    cog wheel, or aggregation of cog wheels, affixed to its extremity; and
    these wheels acting on suitable pinions on the screw shaft, cause the
    screw to make three revolutions for every revolution made by the
    engine.</P>

    <P>127. <EM>Q.</EM>--What are the principal varieties of direct acting
    screw engines?</P>

    <P><EM>A.</EM>--In some cases four engines have been employed instead
    of two, and the cylinders have been laid on their sides on each side of
    the screw shaft. This multiplication of engines, however, introduces
    needless complication, and is now but little used. In other cases two
    inverted cylinders are set above the screw shaft on appropriate
    framing; and connecting rods attached to the ends of the piston rods
    turn round cranks in the screw shaft.</P>

    <P>128. <EM>Q.</EM>--What is the kind of direct acting screw engine
    employed by Messrs. Penn.</P>

    <P><EM>A.</EM>--It is a horizontal trunk engine. In this engine a round
    pipe called a trunk penetrates the piston, to which it is fixed, being
    in fact cast in one piece with it; and the trunk also penetrates the
    top and bottom of the cylinder, through which it moves, and is made
    tight therein by means of stuffing boxes. The connecting rod is
    attached at one end to a pin fixed in the middle of the trunk, while
    the other end engages the crank in the usual manner. The air pump is
    set within the condenser, and is wrought by a rod which is fixed to the
    piston and derives its motion therefrom. The air pump is of that
    species which is called double-acting. The piston or bucket is formed
    without valves in it, but an inlet and outlet valve is fixed to each
    end of the pump, through the one of which the water is drawn into the
    pump barrel, and through the other of which it is expelled into the hot
    well.</P>

    <H4 CLASS="subhead"><A NAME="b05"></A>THE LOCOMOTIVE ENGINE.</H4>

    <P>129. <EM>Q.</EM>--Will you describe the more important features of
    the locomotive engine?</P>

    <P><EM>A.</EM>--The locomotive employed to draw carriages upon
    railways, consists of a cylindrical boiler filled with brass tubes,
    through which the hot air passes on its progress from the furnace to
    the chimney, and attached to the boiler are two horizontal cylinders
    fitted with pistons, valves, connecting rods, and other necessary
    apparatus to enable the power exerted by the pistons to turn round the
    cranked axle to which the driving wheels are attached. There are,
    therefore, two independent engines entering into the composition of a
    locomotive, the cranks of which are set at right angles with one
    another, so that when one crank is at its dead point, the other crank
    is in a position to act with its maximum efficacy. The driving wheels,
    which are fixed on the crank shaft and turn round with it, propel the
    locomotive forward on the rails by the mere adhesion of friction, and
    this is found sufficient not merely to move the locomotive, but to draw
    a long train of carriages behind it.</P>

    <P>130. <EM>Q.</EM>--Are locomotive engines condensing or high pressure
    engines.</P>

    <P><EM>A.</EM>--They are invariably high pressure engines, and it would
    be impossible or at least highly inconvenient, to carry the water
    necessary for the purpose of condensation. The steam, therefore, after
    it has urged the piston to the end of the stroke, escapes into the
    atmosphere. In locomotive engines the waste steam is always discharged
    into the chimney through a vertical pipe, and by its rapid passage it
    greatly increases the intensity of the draught in the chimney, whereby
    a smaller fire grate suffices for the combustion of the fuel, and the
    evaporative power of the boiler is much increased.</P>

    <P>131. <EM>Q.</EM>--Can you give an example of a good locomotive
    engine of the usual form?</P>

    <P><EM>A.</EM>--To do this I will take the example of one of
    Hawthorn&#39;s locomotive engines with six wheels represented in fig.
    29; not one of the most modern construction now in use, nor yet one of
    the most antiquated. M is the cylinder, R the connecting rod, C C the
    eccentrics by which the slide valve is moved; J J is the steam pipe by
    which the steam is conducted from the steam dome of the boiler to the
    cylinder. Near the smoke stack end of this pipe is a valve K or
    regulator moved by a handle <EM>p</EM> at the front of the boiler, and
    of which the purpose is to regulate the admission of the steam to the
    cylinder; <EM>f</EM> is a safety valve kept closed by springs; N is the
    eduction pipe, or, as it is commonly termed in locomotives, the
    <EM>blast pipe</EM>, by which the steam, escaping from the cylinder
    after the stroke has been performed, is projected up the chimney H. The
    water in the boiler of course covers the tubes and also the top of the
    furnace or fire box. It will be understood that there are two engines
    in each locomotive, though, from the figure being given in section,
    only one engine can be shown. The cylinders of this engine are each 14
    inches diameter; the length of the stroke of the piston is 21 inches.
    There are two sets of driving wheels, 5 feet diameter, with outside
    connections.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig29.png" WIDTH="700" HEIGHT="402" ALT=
    "Fig. 29"></P>

    <P>132. <EM>Q.</EM>--What is the tender of a locomotive?</P>

    <P><EM>A.</EM>--It is a carriage attached to the locomotive, of which
    the purpose is to contain coke for feeding the furnace, and water for
    replenishing the boiler.</P>

    <P>133. <EM>Q.</EM>--Can you give examples of modern locomotives?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig30.png" WIDTH="700" HEIGHT="418" ALT=
    "Fig. 30"></P>

    <P><EM>A.</EM>--The most recent locomotives resemble in their material
    features the locomotive represented in fig. 29. I can, however, give
    examples of some of the most powerful engines of recent construction.
    Fig. 30 represents Gooch&#39;s express engine, adapted for the wide
    gauge of the Great Western Railway; and fig. 31 represents
    Crampton&#39;s express engine, adapted for the ordinary or narrow gauge
    railways. The cylinders of Gooch&#39;s engine are each 18 inches
    diameter, and 24 inches stroke; the driving wheels are 8 feet in
    diameter; the fire grate contains 21 square feet of area; and the
    heating surface of the fire box is 153 square feet. There are in all
    305 tubes in the boiler, each of 2 inches diameter, giving a heating
    surface in the tubes of 1799 square feet. The total heating surface,
    therefore, is 1952 square feet. Mr. Gooch states that an engine of this
    class will evaporate from 300 to 360 cubic feet of water in the hour,
    and will convey a load of 236 tons at a speed of 40 miles an hour, or a
    load of 181 tons at a speed of 60 miles an hour. The weight of this
    engine empty is 31 tons; of the tender 8-1/2 tons; and the total weight
    of the engine when loaded is 50 tons. In one of Crampton&#39;s
    locomotives, the Liverpool, with one set more of carrying wheels than
    the fig., the cylinders are of 24 inches diameter and 18 inches stroke;
    the driving wheels are 8 feet in diameter; the fire grate contains
    21-1/2 square feet of area; and the heating surface of the fire box is
    154 square feet. There are in all 300 tubes in the boiler of 2-3/16
    inches external diameter, giving a surface in the tubes of 2136 square
    feet, and a total heating surface of 2290 square feet. The weight of
    this engine is stated to be 35 tons when ready to proceed on a journey.
    Both engines were displayed at the Great Exhibition in 1851, as
    examples of the most powerful locomotive engines then made. The weight
    of such engines is very injurious to the railway; bending, crushing,
    and disturbing the rails, and trying very severely the whole of the
    railway works. No doubt the weight may be distributed upon a greater
    number of wheels, but if the weight resting on the driving wheels be
    much reduced, they will not have sufficient bite upon the rails to
    propel the train without slipping. This, however, is only one of the
    evils which the demand for high rates of speed has produced. The width
    of the railway, or, as it is termed, the <EM>gauge</EM> of the rails,
    being in most of the railways in this kingdom limited to 4 feet 8-1/2
    inches, a corresponding limitation is imposed on the diameter of the
    boiler; which in its turn restricts the number of the tubes which can
    be employed. As, however, the attainment of a high rate of speed
    requires much power, and consequently much heating surface in the
    boiler, and as the number of tubes cannot be increased without reducing
    their diameter, it has become necessary, in the case of powerful
    engines, to employ tubes of a small diameter, and of a great length, to
    obtain the necessary quantity of heating surface; and such tubes
    require a very strong draught in the chimney to make them effective.
    With a draught of the usual intensity the whole of the heat will be
    absorbed in the portion of the tube nearest the fire box, leaving that
    portion nearest the smoke box nothing to do but to transmit the smoke;
    and with long tubes of small diameter, therefore, a very strong draught
    is indispensable. To obtain such a draught in locomotives, it is
    necessary to contract the mouth of the blast pipe, whereby the waste
    steam will be projected into the chimney with greater force; but this
    contraction involves an increase of the pressure on the eduction side
    of the piston, and consequently causes a diminution in the power of the
    engine. Locomotives with small and long tubes, therefore, will require
    more coke to do the same work than locomotives in which larger and
    shorter tubes may be employed.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig31.png" WIDTH="700" HEIGHT="400" ALT=
    "Fig. 31"></P>

    <H2 CLASS="chapter"><A NAME="ch02"></A>CHAPTER II.</H2>

    <H3>HEAT, COMBUSTION, AND STEAM.</H3>

    <H4 CLASS="subhead"><A NAME="d01"></A>HEAT.</H4>

    <P>134. <EM>Q.</EM>--What is meant by latent heat?</P>

    <P><EM>A.</EM>--By latent heat is meant the heat existing in bodies
    which is not discoverable by the touch or by the thermometer, but which
    manifests its existence by producing a change of state. Heat is
    absorbed in the liquefaction of ice, and in the vaporization of water,
    yet the temperature does not rise during either process, and the heat
    absorbed is therefore said to become latent. The term is somewhat
    objectionable, as the effect proper to the absorption of heat has in
    each case been made visible; and it would be as reasonable to call hot
    water latent steam. Latent heat, in the present acceptation of the
    term, means sensible liquefaction or vaporization; but to produce these
    changes heat is as necessary as to produce the expansion of mercury in
    a thermometer tube, which is taken as the measure of temperature; and
    it is hard to see on what ground heat can be said to be latent when its
    presence is made manifest by changes which only heat can effect. It is
    the <EM>temperature</EM> only that is latent, and latent temperature
    means sensible vaporization or liquefaction.</P>

    <P>135. <EM>Q.</EM>--But when you talk of the latent heat of steam,
    what do you mean to express?</P>

    <P><EM>A.</EM>--I mean to express the heat consumed in accomplishing
    the vaporization compared with that necessary for producing the
    temperature. The latent heat of steam is usually reckoned at about 1000
    degrees, by which it is meant that there is as much heat in any given
    weight of steam as would raise its constituent water 1000 degrees if
    the expansion of the water could be prevented, or as would raise 1000
    times that quantity of water one degree. The boiling point of water,
    being 212 degrees, is 180 degrees above the freezing point of
    water--the freezing point being 32 degrees; so that it requires 1180
    times as much heat to raise 1 lb. of water into steam, as to raise 1180
    lbs. of water one degree; or it requires about as much heat to raise a
    pound of boiling water into steam, as would raise 5-1/2 lbs. of water
    from the freezing to the boiling point; 5-1/2 multiplied by 180 being
    990 or 1000 nearly.</P>

    <P>136. <EM>Q.</EM>--When it is stated that the latent heat of steam is
    1000 degrees, it is only meant that this is a rough approximation to
    the truth?</P>

    <P><EM>A.</EM>--Precisely so. The latent heat, in point of fact, is not
    uniform at all temperatures, neither is the total amount of heat the
    same at all temperatures. M. Regnault has shown, by a very elaborate
    series of experiments on steam, which he has lately concluded, that the
    total heat in steam increases somewhat with the pressure, and that the
    latent heat diminishes somewhat with the pressure. This will be made
    obvious by the following numbers:</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "Pressure; Temperature; Total Heat; Latent heat">
      <TR>
        <TD>
          <P>Pressure.</P>
        </TD>

        <TD>
          <P>Temperature.</P>
        </TD>

        <TD>
          <P>Total heat.</P>
        </TD>

        <TD>
          <P>Latent heat.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>15 lbs.</P>
        </TD>

        <TD>
          <P>213.1&deg;</P>
        </TD>

        <TD>
          <P>1178.9&deg;</P>
        </TD>

        <TD>
          <P>965.8&deg;</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>50</P>
        </TD>

        <TD>
          <P>281.0</P>
        </TD>

        <TD>
          <P>1199.6</P>
        </TD>

        <TD>
          <P>918.6</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>100</P>
        </TD>

        <TD>
          <P>327.8</P>
        </TD>

        <TD>
          <P>1213.9</P>
        </TD>

        <TD>
          <P>886.1</P>
        </TD>
      </TR>
    </TABLE>
    <BR>
    <BR>


    <P>If, then, steam of 100 lbs. be expanded down to steam of 15 lbs., it
    will have 35 degrees of heat over that which is required for the
    maintenance of the vaporous state, or, in other words, it will be
    surcharged with heat.</P>

    <P>137. <EM>Q.</EM>--What do you understand by specific heat?</P>

    <P><EM>A.</EM>--By specific heat, I understand the relative quantities
    of heat in bodies at the same temperature, just as by specific gravity
    I understand the relative quantities of matter in bodies of the same
    bulk. Equal weights of quicksilver and water at the same temperature do
    not contain the same quantities of heat, any more than equal bulks of
    those liquids contain the same quantity of matter. The absolute
    quantity of heat in any body is not known; but the relative heat of
    bodies at the same temperature, or in other words their specific heats,
    have been ascertained and arranged in tables,-- the specific heat of
    water being taken as unity.</P>

    <P>138. <EM>Q.</EM>--In what way does the specific heat of a body
    enable the quantity of heat in it to be determined?</P>

    <P><EM>A.</EM>--If any body has only half the specific heat of water,
    then a pound of that body will, at any given temperature, have only
    half the heat in it that is in a pound of water at the same
    temperature. The specific heat of air is .2669, that of water being 1;
    or it is 3.75 times less than that of water. An amount of heat,
    therefore, which would raise a pound of water 1 degree would raise a
    pound of air 3.75 degrees.</P>

    <H4 CLASS="subhead"><A NAME="d02"></A>COMBUSTION.</H4>

    <P>139. <EM>Q.</EM>--What is the nature of combustion?</P>

    <P><EM>A.</EM>--Combustion is nothing more than an energetic chemical
    combination, or, in other words, it is the mutual neutralization of
    opposing electricities. When coal is brought to a high temperature it
    acquires a strong affinity for oxygen, and combination with oxygen will
    produce more than sufficient heat to maintain the original temperature;
    so that part of the heat is rendered applicable to other purposes.</P>

    <P>140. <EM>Q.</EM>--Does air consist of oxygen?</P>

    <P><EM>A.</EM>--Air consists of oxygen and nitrogen mixed together in
    the proportion of 3.29 lbs. of nitrogen to 1 lb. of oxygen. Every pound
    of coal requires about 2.66 lbs. of oxygen for its saturation, and
    therefore for every pound of coal burned, 8.75 pounds of nitrogen must
    pass through the fire, supposing all the oxygen to enter into
    combination. In practice, however, this perfection of combination does
    not exist; from one-third to one-half of the oxygen will pass through
    the fire without entering into combination at all; so that from 16 to
    18 lbs. of air are required for every pound of coal burned. 18 lbs. of
    air are about 240 cubic feet, which may be taken as the quantity of air
    required for the combustion of a pound of coal in practice.</P>

    <P>141. <EM>Q.</EM>--What are the constituents of coal?</P>

    <P><EM>A.</EM>--The chief constituent of coal is carbon or pure
    charcoal, which is associated in various proportions with volatile and
    earthy matters. English coal contains 80 to 90 per cent. of carbon, and
    from 8 to 18 per cent. of volatile and earthy matters, but sometimes
    more than this. The volatile matters are hydrogen, nitrogen, oxygen,
    and sulphur.</P>

    <P>142. <EM>Q.</EM>--What is the difference between anthracite and
    bituminous coal?</P>

    <P><EM>A.</EM>--Anthracite consists almost entirely of carbon, having
    91 per cent. of carbon, with about 7 per cent. of volatile matter and 2
    per cent. of ashes. Newcastle coal contains about 83 per cent. of
    carbon, 14 per cent. of volatile matter, and 3 per cent. of ashes.</P>

    <P>143. <EM>Q.</EM>--Will you recapitulate the steps by which you
    determine the quantity of air required for the combustion of coal?</P>

    <P><EM>A.</EM>--Looking to the quantity of oxygen required to unite
    chemically with the various constituents of the coal, we find for
    example that in 100 lbs. of anthracite coal, consisting of 91.44 lbs.
    of carbon, and 3.46 lbs. of hydrogen, we shall for the 91.44 lbs. of
    carbon require 243.84 lbs. of oxygen--since to saturate a pound of
    carbon by the formation of carbonic acid, requires 2-2/3 lbs. of
    oxygen. To saturate a pound of hydrogen in the formation of water,
    requires 8 lbs. of oxygen; hence 3.46 Fibs. of hydrogen will take 27.68
    lbs. of oxygen for its saturation. If then we add 243.84 lbs. to 27.68
    lbs. we have 271.52 lbs. of oxygen required for the combustion of 100
    lbs. of coal. A given weight of air contains nearly 23.32 per cent of
    oxygen; hence to obtain 271.52 lbs. of oxygen, we must have about four
    times that quantity of atmospheric air, or more accurately, 1164 lbs.
    of air for the combustion of 100 lbs. of coal. A cubic foot of air at
    ordinary temperature weighs about .075 lbs.; so that 100 lbs. of coal
    require 15,524 cubic feet of air, or 1 lb. of coal requires about 155
    cubic feet of air, supposing every atom of the oxygen to enter into
    combination. If, then, from one-third to one-half of the air passes
    unconsumed through the fire, an allowance of 240 cubic feet of air for
    each pound of coal will be a small enough allowance to answer the
    requirements of practice, and in some cases as much as 300 cubic feet
    will be required,--the difference depending mainly on the peculiar
    configuration of the furnace.</P>

    <P>144. <EM>Q.</EM>--Can you state the evaporative efficacy of a pound
    of coal?</P>

    <P><EM>A.</EM>--The evaporative efficacy of a pound of carbon has been
    found experimentally to be equivalent to that necessary to raise 14,000
    lbs. of water through 1 degree, or 14 lbs. of water through 1000
    degrees, supposing the whole heat generated to be absorbed by the
    water. Now, if the water be raised into steam from a temperature of
    60&deg;, then 1118.9&deg; of heat will have to be imparted to it to
    convert it into steam of 15 lbs. pressure per square inch. 14,000 /
    1118.9 = 12.512 Lbs. will be the number of pounds of water, therefore,
    which a pound of carbon can raise into steam of 15 lbs. pressure from a
    temperature of 60&deg;. This, however, is a considerably larger result
    than can be expected in practice.</P>

    <P>145. <EM>Q.</EM>--Then what is the result that may be expected in
    practice?</P>

    <P><EM>A.</EM>--The evaporative powers of different coals appear to be
    nearly proportional to the quantity of carbon in them; and bituminous
    coal is, therefore, less efficacious than coal consisting chiefly of
    pure carbon. A pound of the best Welsh or anthracite coal is capable of
    raising from 9-1/2 to 10 lbs. of water from 212&deg; into steam,
    whereas a pound of the best Newcastle is not capable of raising more
    than about 8-1/2 lbs. of water from 212&deg; into steam; and inferior
    coals will not raise more than 6-1/2 lbs. of water into steam. In
    America it has been found that 1 lb. of the best coal is equal to 2-1/2
    lbs. of pine wood, or, in some cases to 3 lbs.; and a pound of pine
    wood will not usually evaporate more than about 2 1/2 lbs. of water,
    though, by careful management, it may be made to evaporate 4 1/2 lbs.
    Turf will generate rather more steam than wood. Coke is equal or
    somewhat superior to the best coal in evaporative effect.</P>

    <P>146. <EM>Q.</EM>--How much water will a pound of coal raise into
    steam in ordinary boilers?</P>

    <P><EM>A.</EM>--From 6 to 8 lbs. of water in the generality of land
    boilers of medium quality, the difference depending on the kind of
    boiler, the kind of coal, and other circumstances. Mr. Watt reckoned
    his boilers as capable of evaporating 10.08 cubic feet of water with a
    bushel or 84 lbs. of Newcastle coal, which is equivalent to 7 1/2 lbs.
    of water evaporated by 1 lb. of coal, and this may be taken as the
    performance of common land boilers at the present time. In some of the
    Cornish boilers, however, a pound of coal raises 11.8 lbs. of boiling
    water into steam, or a cwt. of coal evaporates about 21 cubic feet of
    water from 212&deg;.</P>

    <P>147. <EM>Q.</EM>--What method of firing ordinary furnaces is the
    best?</P>

    <P><EM>A.</EM>--The coals should be broken up into small pieces, and
    sprinkled thinly and evenly over the fire a little at a time. The
    thickness of the stratum of coal upon the grate should depend upon the
    intensity of the draught: in ordinary land or marine boilers it should
    be thin, whereas in locomotive boilers it requires to be much thicker.
    If the stratum of coal be thick while the draught is sluggish, the
    carbonic acid resulting from combustion combines with an additional
    atom of carbon in passing through the fire, and is converted into
    carbonic oxide, which may be defined to be invisible smoke, as it
    carries off a portion of the fuel: if, on the contrary, the stratum of
    coal be thin while the draught is very rapid, an injurious
    refrigeration is occasioned by the excess of air passing through the
    furnace. The fire should always be spread of uniform thickness over the
    bars of the grate, and should be without any holes or uncovered places,
    which greatly diminish the effect of the fuel by the refrigeratory
    action of the stream of cold air which enters thereby. A wood fire
    requires to be about 6 inches thicker than a coal one, and a turf fire
    requires to be 3 or 4 inches thicker than a wood one, so that the
    furnace bars must be placed lower where wood or turf is burned, to
    enable the surface of the fire to be at the same distance from the
    bottom of the boiler.</P>

    <P>148. <EM>Q.</EM>--Is a slow or a rapid combustion the most
    beneficial?</P>

    <P><EM>A.</EM>--A slow combustion is found by experiment to give the
    best results as regards economy of fuel, and theory tells us that the
    largest advantage will necessarily be obtained where adequate time has
    been afforded for a complete combination of the constituent atoms of
    the combustible, and the supporter of combustion. In many of the cases,
    however, which occur in practice, a slow combustion is not attainable;
    but the tendencies of slow combustion are both to save the fuel, and to
    burn the smoke.</P>

    <P>149. <EM>Q.</EM>--Is not the combustion in the furnaces of the
    Cornish boilers very slow?</P>

    <P>A.--Yes, very slow; and there is in consequence very little smoke
    evolved. The coal used in Cornwall is Welsh coal, which evolves but
    little smoke, and is therefore more favorable for the success of a
    smokeless furnace; but in the manufacturing districts, where the coal
    is more bituminous, it is found that smoke may be almost wholly
    prevented by careful firing and by the use of a large capacity of
    furnace.</P>

    <P>150. <EM>Q.</EM>--Do you consider slow combustion to be an advisable
    thing to practise in steam vessels?</P>

    <P><EM>A.</EM>--No, I do not. When the combustion is slow, the heat in
    the furnaces and flues is less intense, and a larger amount of heating
    surface consequently becomes necessary to absorb the heat. In
    locomotives, where the heat of the furnace is very intense, there will
    be the same economy of fuel with an allowance of 5 or 6 square feet of
    surface to evaporate a cubic foot of water as in common marine boilers
    with 10 or 12.</P>

    <P>151. <EM>Q.</EM>--What is the method of consuming smoke pursued in
    the manufacturing districts?</P>

    <P><EM>A.</EM>--In Manchester, where some stringent regulations for the
    prevention of smoke have for some time been in force, it is found that
    the readiest way of burning the smoke is to have a very large
    proportion of furnace room, whereby slow combustion may be carried on.
    In some cases, too, a favourable result is arrived at by raising a
    ridge of coal across the furnace lying against the bridge, and of the
    same height: this ridge speedily becomes a mass of incandescent coke,
    which promotes the combustion of the smoke passing over it.</P>

    <P>152. <EM>Q.</EM>--Is the method of admitting a stream of air into
    the flues to burn the smoke regarded favorably?</P>

    <P><EM>A.</EM>--No; it is found to be productive of injury to the
    boiler by the violent alternations of temperature it occasions, as at
    some times cold air impinges on the iron of the boiler, and at other
    times flame,--just as there happens to be smoke or no smoke emitted by
    the furnace. Boilers, therefore, operating upon this principle,
    speedily become leaky, and are much worn by oxidation, so that, if the
    pressure is considerable, they are liable to explode. It is very
    difficult to apportion the quantity of air admitted, to the varying
    wants of the fire; and as air may at some times be rushing in when
    there is no smoke to consume, a loss of heat, and an increased
    consumption of fuel may be the result of the arrangement; and, indeed,
    such is the result in practice, though a carefully performed experiment
    usually demonstrates a saving in fuel of 10 or 12 per cent.</P>

    <P>153. <EM>Q.</EM>--What other plans have been contrived for obviating
    the nuisance of smoke?</P>

    <P><EM>A.</EM>--They are too various for enumeration, but most of them
    either operate upon the principle of admitting air into the flues to
    accomplish the combustion of the uninflammable parts of the smoke, or
    seek to attain the same object by passing the smoke over or through the
    fire or other incandescent material. Some of the plans, indeed, profess
    to burn the inflammable gases as they are evolved from the coal,
    without permitting the admixture of any of the uninflammable products
    of combustion which enter into the composition of smoke; but this
    object has been very imperfectly fulfilled in any of the contrivances
    yet brought under the notice of the public, and in some cases these
    contrivances have been found to create weightier evils than they
    professed to relieve.</P>

    <P>154. <EM>Q.</EM>--You refer, I suppose, to Mr. Charles Wye
    Williams&#39; Argand furnace?</P>

    <P><EM>A.</EM>--I chiefly refer to it, though I also comprehend all
    other schemes in which there is a continuous admission of air into the
    flues, with an intermittent generation of smoke.</P>

    <P>155. <EM>Q.</EM>--This is not so in Prideaux&#39;s furnace?</P>

    <P><EM>A.</EM>--No; in that furnace the air is admitted only during a
    certain interval, or for so long, in fact, as there is smoke to be
    consumed.</P>

    <P>156. <EM>Q.</EM>--Will you explain the chief peculiarities of that
    furnace?</P>

    <P><EM>A.</EM>--The whole peculiarity is in the furnace door. The front
    of the door consists of metal Venetians, which are opened when the top
    lever is lifted up, and shut when that lever descends to its lowest
    position. When the furnace door is opened to replenish the fire with
    coals, the top lever is raised up, and with it the piston of the small
    cylinder attached to the side of the furnace. The Venetians are thereby
    opened, and a stream of air enters the furnace, which, being heated in
    its passage among the numerous heated plates attached to the back of
    the furnace door, is in a favorable condition for effecting the
    combustion of the inflammable parts of the smoke. The piston in the
    small cylinder gradually subsides and closes the Venetians; and the
    rate of the subsidence of the piston may obviously be regulated by a
    cock, or, as in this case, a small screw valve, so that the Venetians
    shall just close when there is no more smoke to be consumed;--the air
    or other fluid within the cylinder being forced out by the piston in
    its descent.</P>

    <P>157. <EM>Q.</EM>--Had Mr. Watt any method of consuming smoke?</P>

    <P><EM>A.</EM>--He tried various methods, but eventually fixed upon the
    method of coking the coal on a dead plate at the furnace door, before
    pushing it into the fire. That method is perfectly effectual where the
    combustion is so slow that the requisite time for coking is allowed,
    and it is much preferable to any of the methods of admitting air at the
    bridge or elsewhere, to accomplish the combustion of the inflammable
    parts of the smoke.</P>

    <P>158. <EM>Q.</EM>--What are the details of Mr. Watt&#39;s arrangement
    as now employed?</P>

    <P><EM>A.</EM>--The fire bars and the dead plate are both set at a
    considerable inclination, to facilitate the advance of the fuel into
    the furnace. In Boulton and Watt&#39;s 30 horse power land boiler, the
    dead plate and the furnace bars are both about 4 feet long, and they
    are set at the angle of 30 degrees with the horizon.</P>

    <P>159. <EM>Q.</EM>--Is the use of the dead plate universally adopted
    in Boulton and Watt&#39;s land boilers?</P>

    <P><EM>A.</EM>--It is generally adopted, but in some cases Boulton and
    Watt have substituted the plan of a revolving grate for consuming the
    smoke, and the dead plate then becomes both superfluous and
    inapplicable. In this contrivance the fire is replenished with coals by
    a self-acting mechanism.</P>

    <P>160. <EM>Q.</EM>--Will you explain the arrangement of the revolving
    grate?</P>

    <P><EM>A.</EM>--The fire grate is made like a round table capable of
    turning horizontally upon a centre; a shower of coal is precipitated
    upon the grate through a slit in the boiler near the furnace mouth, and
    the smoke evolved from the coal dropped at the front part of the fire
    is consumed by passing over the incandescent fuel at the back part,
    from which all the smoke must have been expelled in the revolution of
    the grate before it can have reached that position.</P>

    <P>161. <EM>Q.</EM>--Is a furnace with a revolving grate applicable to
    a steam vessel?</P>

    <P><EM>A.</EM>--I see nothing to prevent its application. But the
    arrangement of the boiler would perhaps require to be changed, and it
    might be preferable to combine its use with the employment of vertical
    tubes, for the transmission of the smoke. The introduction of any
    effectual automatic contrivance for feeding the fire in steam vessels,
    would bring about an important economy, at the same time that it would
    give the assurance of the work being better done. It is very difficult
    to fire furnaces by hand effectually at sea, especially in rough
    weather and in tropical climates; whereas machinery would be unaffected
    by any such disturbing causes, and would perform with little expense
    the work of many men.</P>

    <P>162. <EM>Q.</EM>--The introduction of some mechanical method of
    feeding the fire with coals would enable a double tier of furnaces to
    be adopted in steam vessels without inconvenience?</P>

    <P><EM>A.</EM>--Yes, it would have at least that tendency; and as the
    space available for area of grate is limited in a steam vessel by the
    width of the vessel, it would be a great convenience if a double tier
    of furnaces could be employed without a diminished effect. It appears
    to me, however, that the objection would still remain of the steam
    raised by the lower furnace being cooled and deadened by the air
    entering the ash-pit of the upper fire, for it would strike upon the
    metal of the ash-pit bottom.</P>

    <P>163. <EM>Q.</EM>--Have any other plans been devised for feeding the
    fire by self-acting means besides that of a revolving grate?</P>

    <P><EM>A.</EM>--Yes, many plans, but none of them, perhaps, are free
    from an objectionable complication. In some arrangements the bars are
    made like screws, which being turned round slowly, gradually carry
    forward the coal; while in other arrangements the same object is sought
    to be attained by alternately lifting and depressing every second bar
    at the end nearest the mouth of the furnace. In Juckes&#39; furnace,
    the fire bars are arranged in the manner of rows of endless chains
    working over a roller at the mouth of the furnace, and another roller
    at the farther end of the furnace. These rollers are put into slow
    revolution, and the coal which is deposited at the mouth of the furnace
    is gradually carried forward by the motion of the chains, which act
    like an endless web. The clinkers and ashes left after the combustion
    of the coal, are precipitated into the ash-pit, where the chain turns
    down over the roller at the extremity of the furnace. In Messrs.
    Maudslays&#39; plan of a self-feeding furnace the fire bars are formed
    of round tubes, and are placed transversely across the furnace. The
    ends of the bars gear into endless screws running the whole length of
    the furnace, whereby motion is given to the bars, and the coal is thus
    carried gradually forward. It is very doubtful whether any of these
    contrivances satisfy all the conditions required in a plan for feeding
    furnaces of the ordinary form by self-acting means, but the problem of
    providing a suitable contrivance, does not seem difficult of
    accomplishment, and will no doubt be effected under adequate
    temptation.</P>

    <P>164. <EM>Q.</EM>--Have not many plans been already contrived which
    consume the smoke of furnaces very effectually?</P>

    <P><EM>A.</EM>--Yes, many plans; and besides those already mentioned
    there are Hall&#39;s, Coupland&#39;s, Godson&#39;s, Robinson&#39;s,
    Stevens&#39;s, Hazeldine&#39;s, Indie&#39;s, Bristow and Attwood&#39;s,
    and a great number of others. One plan, which promises well, consists
    in making the flame descend through the fire bars, and the fire bars
    are formed of tubes set on an incline and filled with water, which
    water will circulate with a rapidity proportionate to the intensity of
    the heat. After all, however, the best remedy for smoke appears to
    consist in removing from it those portions which form the smoke before
    the coal is brought into use. Many valuable products may be got from
    the coal by subjecting it to this treatment; and the residuum will be
    more valuable than before for the production of steam.</P>

    <H4 CLASS="subhead"><A NAME="d03"></A>STEAM.</H4>

    <P>165. <EM>Q.</EM>--Have experiments been made to determine the
    elasticity of steam at different temperatures?</P>

    <P><EM>A.</EM>--Yes; very careful experiments. The following rule
    expresses the results obtained by Mr. Southern:--To the given
    temperature in degrees of Fahrenheit add 51.3 degrees; from the
    logarithm of the sum, subtract the logarithm of 135.767, which is
    2.1327940; multiply the remainder by 5.13, and to the natural number
    answering to the sum, add the constant fraction .1, which will give the
    elastic force in inches of mercury. If the elastic force be known, and
    it is wanted to determine the corresponding temperature, the rule must
    be modified thus:--From the elastic force, in inches of mercury,
    subtract the decimal .1, divide the logarithm of the remainder by 5.13,
    and to the quotient add the logarithm 2.1327940; find the natural
    number answering to the sum, and subtract therefrom the constant 51.3;
    the remainder will be the temperature sought. The French Academy, and
    the Franklin Institute, have repeated Mr. Southern&#39;s experiments on
    a larger scale; the results obtained by them are not widely different,
    and are perhaps nearer the truth, but Mr. Southern&#39;s results are
    generally adopted by engineers, as sufficiently accurate for practical
    purposes.</P>

    <P>166. <EM>Q.</EM>--Have not some superior experiments upon this
    subject been lately made in France?</P>

    <P><EM>A.</EM>--Yes, the experiments of M. Regnault upon this subject
    have been very elaborate and very carefully conducted, and the results
    are probably more accurate than have been heretofore obtained.
    Nevertheless, it is questionable how far it is advisable to disturb the
    rules of Watt and Southern, with which the practice of engineers is
    very much identified, for the sake of emendations which are not of such
    magnitude as to influence materially the practical result. M. Regnault
    has shown that the total amount of heat, existing in a given weight of
    steam, increases slightly with the pressure, so that the sum of the
    latent and sensible heats do not form a constant quantity. Thus, in
    steam of the atmospheric pressure, or with 14.7 Lbs. upon the square
    inch, the sensible heat of the steam is 212 degrees, the latent heat
    966.6 degrees, and the sum of the latent and sensible heats 1178.6
    degrees; whereas in steam of 90 pounds upon the square inch the
    sensible heat is 320.2 degrees, the latent heat 891.4 degrees, and the
    sum of the latent and sensible heats 1211.0 degrees. There is,
    therefore, 33 degrees less of heat in any given weight of water, raised
    into steam of the atmospheric pressure, than if raised into steam of 90
    Lbs. <A NAME="fnr1"></A> <A HREF="#fn1" CLASS="fnsuper">1</A>
    pressure.</P>

    <P>167. <EM>Q.</EM>--What expansion does water undergo in its
    conversion into steam?</P>

    <P><EM>A.</EM>--A cubic inch of water makes about a cubic foot of steam
    of the atmospheric pressure.</P>

    <P>168. <EM>Q.</EM>--And how much at a higher pressure?</P>

    <P><EM>A.</EM>--That depends upon what the pressure is. But the
    proportion is easily ascertained, for the pressure and the bulk of a
    given quantity of steam, as of air or any other elastic fluid, are
    always inversely proportional to one another. Thus if a cubic inch of
    water makes a cubic foot of steam, with the pressure of one atmosphere,
    it will make half a cubic foot with the pressure of two atmospheres, a
    third of a cubic foot with the pressure of three atmospheres, and so on
    in all other proportions. High pressure steam indeed is just low
    pressure steam forced into a less space, and the pressure will always
    be great in the proportion in which the space is contracted.</P>

    <P>169. <EM>Q.</EM>--If this be so, the quantity of heat in a given
    weight of steam must be nearly the same, whether the steam is high or
    low pressure?</P>

    <P><EM>A.</EM>--Yes; the heat in steam is nearly a constant quantity,
    at all pressures, but not so precisely. Steam to which an additional
    quantity of heat has been imparted after leaving the boiler, or as it
    is called &quot;surcharged steam,&quot; comes under a different law,
    for the elasticity of such steam may be increased without any addition
    being made to its weight; but surcharged steam is not at present
    employed for working engines, and it may therefore be considered in
    practice that a pound of steam contains very nearly the same quantity
    of heat at all pressures.</P>

    <P>170. <EM>Q.</EM>--Does not the quantity of heat in any body vary
    with the temperature?</P>

    <P><EM>A.</EM>--Other circumstances remaining the same the quantity of
    heat in a body increases with the temperatures.</P>

    <P>171. <EM>Q.</EM>--And is not high pressure steam hotter than low
    pressure steam?</P>

    <P><EM>A.</EM>--Yes, the temperature of steam rises with the
    pressure.</P>

    <P>172. <EM>Q.</EM>--How then comes it, that there is the same quantity
    of heat in the same weight of high and low pressure steam, when the
    high pressure steam has the highest temperature?</P>

    <P><EM>A.</EM>--Because although the temperature or sensible heat rises
    with the pressure, the latent heat becomes less in about the same
    proportion. And as has been already explained, the latent and sensible
    heats taken together make up nearly the same amount at all
    temperatures; but the amount is somewhat greater at the higher
    temperatures. As a damp sponge becomes wet when subjected to pressure,
    so warm vapor becomes hot when forced into less bulk, but in neither
    case does the quantity of moisture or the quantity of heat sustain any
    alteration. Common air becomes so hot by compression that tinder may be
    inflamed by it, as is seen in the instrument for producing
    instantaneous light by suddenly forcing air into a syringe.</P>

    <P>173. <EM>Q.</EM>--What law is followed by surcharged steam on the
    application of heat?</P>

    <P><EM>A.</EM>--The same as that followed by air, in which the
    increments in volume are very nearly in the same proportion as the
    increments in temperature; and the increment in volume for each degree
    of increased temperature is 1/490th part of the volume at 32&deg;. A
    volume of air which, at the temperature of 32&deg;, occupies 100 cubic
    feet, will at 212&deg; fill a space of 136.73 cubic feet. The volume
    which air or steam--out of contact with water--of a given temperature
    acquires by being heated to a higher temperature, the pressure
    remaining the same, may be found by the following rule:--To each of the
    temperatures before and after expansion, add the constant number 458:
    divide the greater sum by the less, and multiply the quotient by the
    volume at the lower temperature; the product will give the expanded
    volume.</P>

    <P>174. <EM>Q.</EM>--If the relative volumes of steam and water are
    known, is it possible to tell the quantity of water which should be
    supplied to a boiler, when the quantity of steam expended is
    specified?</P>

    <P><EM>A.</EM>--Yes; at the atmospheric pressure, about a cubic inch of
    water has to be supplied to the boiler for every cubic foot of steam
    abstracted; at other pressures, the relative bulk of water and steam
    may be determined as follows:--To the temperature of steam in degrees
    of Fahrenheit, add the constant number 458, multiply the sum by 37.3,
    and divide the product by the elastic force of the steam in pounds per
    square inch; the quotient will give the volume required.</P>

    <P>175. <EM>Q.</EM>--Will this rule give the proper dimensions of the
    pump for feeding the boiler with water?</P>

    <P><EM>A.</EM>--No; it is
    necessary in practice that the feed pump should be able to supply the
    boiler with a much larger quantity of water than what is indicated by
    these proportions, from the risk of leaks, priming, or other
    disarrangements, and the feed pump is usually made capable of raising
    3-1/2 times the water evaporated by the boiler. About 1/240th of the
    capacity of the cylinder answers very well for the capacity of the feed
    pump in the case of low pressure engines, supposing the cylinder to be
    double acting, and the pump single acting; but it is better to exceed
    this size.</P>

    <P>176. <EM>Q.</EM>--Is this rule for the size of the feed pump
    applicable to the case of high pressure engines?</P>

    <P><EM>A.</EM>--Clearly not; for since a cylinder full of high pressure
    steam, contains more water than the same cylinder full of low pressure
    steam, the size of the feed must vary in the same proportion as the
    density of the steam. In all pumps a good deal of the effect is lost
    from the imperfect action of the valves; and in engines travelling at a
    high rate of speed, in particular, a large part of the water is apt to
    return, through the suction valve of the pump, especially if much lift
    be permitted to that valve. In steam vessels moreover, where the boiler
    is fed with salt water, and where a certain quantity of supersalted
    water has to be blown out of the boiler from time to time, to prevent
    the water from reaching too high a degree of concentration, the feed
    pump requires to be of additional size to supply the extra quantity of
    water thus rendered necessary. When the feed water is boiling or very
    hot, as in some engines is the case, the feed pump will not draw from a
    depth, and will altogether act less efficiently, so that an extra size
    of pump has to be provided in consequence. These and other
    considerations which might be mentioned, show the propriety of making
    the feed pump very much larger than theory requires. The proper
    proportions of pumps, however, forms part of a subsequent chapter.</P>

    <P CLASS="footnote"><A NAME="fn1"></A> <A HREF="#fnr1">[1]</A> A table
    containing the results arrived at by M. Regnault is given in the
    Key.</P>

    <H2 CLASS="chapter"><A NAME="ch03"></A>CHAPTER III.</H2>

    <H3>EXPANSION OF STEAM AND ACTION OF THE VALVES.</H3>

    <P>177. <EM>Q.</EM>--What is meant by working engines expansively?</P>

    <P><EM>A.</EM>--Adjusting the valves, so that the steam is shut off
    from the cylinder before the end of the stroke, whereby the residue of
    the stroke is left to be completed by the expanding steam.</P>

    <P>178. <EM>Q.</EM>--And what is the benefit of that practice?</P>

    <P><EM>A.</EM>--It accomplishes an important saving of steam, or, what
    is the same thing, of fuel; but it diminishes the power of the engine,
    while increasing the power of the steam. A larger engine will be
    required to do the same work, but the work will be done with a smaller
    consumption of fuel. If, for example, the steam be shut off when only
    half the stroke is completed, there will only be half the quantity of
    steam used. But there will be more than half the power exerted; for
    although the pressure of the steam decreases after the supply entering
    from the boiler is shut off, yet it imparts, during its expansion,
    <EM>some</EM> power, and that power, it is clear, is obtained without
    any expenditure of steam or fuel whatever.</P>

    <P>179. <EM>Q.</EM>--What will be the pressure of the steam, under such
    circumstances, at the end of the stroke?</P>

    <P><EM>A.</EM>--If the steam be shut off at half stroke, the pressure
    of the steam, reckoning the total pressure both below and above the
    atmosphere, will just be one-half of what it was at the beginning of
    the stroke. It is a well known law of pneumatics, that the pressure of
    elastic fluids varies inversely as the spaces into which they are
    expanded or compressed. For example, if a cubic foot of air of the
    atmospheric density be compressed into the compass of half a cubic
    foot, its elasticity will be increased from 15 lbs. on the square inch
    to 30 lbs. on the square inch; whereas, if its volume be enlarged to
    two cubic feet, its elasticity will be reduced to 7-1/2 lbs. on the
    square inch, being just half its original pressure. The same law holds
    in all other proportions, and with all other gases and vapors, provided
    their temperature remains unchanged; and if the steam valve of an
    engine be closed, when the piston has descended through one-fourth of
    the stroke, the steam within the cylinder will, at the end of the
    stroke, just exert one-fourth of its initial pressure.</P>

    <P>180. <EM>Q.</EM>--Then by computing the varying pressure at a number
    of stages, the average or mean pressure throughout the stroke may be
    approximately determined?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig32.png" WIDTH="355" HEIGHT="550" ALT=
    "Fig. 32. Diagram showing law of expansion of steam in a cylinder."></P>

    <P><EM>A.</EM>--Precisely so. Thus in the accompanying figure, (fig.
    32), let E be a cylinder, J the piston, <EM>a</EM> the steam pipe,
    <EM>c</EM> the upper port, <EM>f</EM> the lower port, <EM>d</EM> the
    steam pipe, prolonged to <EM>e</EM> the equilibrium valve, <EM>g</EM>
    the eduction valve, M the steam jacket, N the cylinder cover, O
    stuffing box, <EM>n</EM> piston rod, P cylinder bottom; let the
    cylinder be supposed to be divided in the direction of its length into
    any number of equal parts, say twenty, and let the diameter of the
    cylinder represent the pressure of the steam, which, for the sake of
    simplicity, we may take at 10 lbs., so that we may divide the cylinder,
    in the direction of its diameter, into ten equal parts. If now the
    piston be supposed to descend through five of the divisions, and the
    steam valve then be shut, the pressure at each subsequent position of
    the piston will be represented by a series, computed according to the
    laws of pneumatics, and which, if the initial pressure be represented
    by 1, will give a pressure of .5 at the middle of the stroke, and .25
    at the end of it.</P>

    <P>If this series be set off on the horizontal lines, it will mark out
    a hyperbolic curve--the area of the part exterior to which represents
    the total efficacy of the stroke, and the interior area, therefore,
    represents the diminution in the power of a stroke, when the steam is
    cut off at one-fourth of the descent. If the squares above the point,
    where the steam is cut off, be counted, they will be found to amount to
    50; and if those beneath that point be counted or estimated, they will
    be found to amount to about 69. These squares are representative of the
    power exerted; so that while an amount of power represented by 50 has
    been obtained by the expenditure of a quarter of a cylinder full of
    steam, we get an amount of power represented by 69, without any
    expenditure of steam at all, merely by permitting the steam first used
    to expand into four times its original volume.</P>

    <P>181. <EM>Q.</EM>--Then by working an engine expansively, the power
    of the steam is increased, but the power of the engine is
    diminished?</P>

    <P><EM>A.</EM>--Yes. The efficacy of a given quantity of steam is more
    than doubled by expanding the steam four times, while the efficacy of
    each stroke is made nearly one-half less. And, therefore, to carry out
    the expansive principle in practice, the cylinder requires to be larger
    than usual, or the piston faster than usual, in the proportion in which
    the expansion is carried out. Every one who is acquainted with simple
    arithmetic, can compute the terminal pressure of steam in a cylinder,
    when he knows the initial pressure and the point at which the steam is
    cut off; and he can also find, by the same process, any pressure
    intermediate between the first and the last. By setting down these
    pressures in a table, and taking their mean, he can determine the
    effect, with tolerable accuracy, of any particular measure of
    expansion. It is necessary to remark, that it is the total pressure of
    the steam that he must take; not the pressure above the atmosphere, but
    the pressure above a perfect vacuum.</P>

    <P>182. <EM>Q.</EM>--Can you give any rule for ascertaining at one
    operation the amount of benefit derivable from expansion?</P>

    <P><EM>A.</EM>--Divide the length of stroke through which the steam
    expands, by the length of stroke performed with full pressure, which
    last call 1; the hyperbolic logarithm of the quotient is the increase
    of efficiency due to expansion. According to this rule it will be
    found, that if a given quantity of steam, the power of which working at
    full pressure is represented by 1, be admitted into a cylinder of such
    a size that its ingress is concluded when one-half the stroke has been
    performed, its efficacy will be raised by expansion to 1.69; if the
    admission of the steam be stopped at one-third of the stroke, the
    efficacy will be 2.10; at one-fourth, 2.39; at one-fifth, 2.61; at
    one-sixth, 2.79; at one-seventh, 2.95; at one-eighth, 3.08. The
    expansion, however, cannot be carried beneficially so far as
    one-eighth, unless the pressure of the steam in the boiler be very
    considerable, on account of the inconvenient size of cylinder or speed
    of piston which would require to be adopted, the friction of the
    engine, and the resistance of vapor in the condenser, which all become
    relatively greater with a smaller urging force.</P>

    <P>183. <EM>Q.</EM>--Is this amount of benefit actually realized in
    practice?</P>

    <P><EM>A.</EM>--Only in some cases. It appears to be indispensable to
    the realization of any large amount of benefit by expansion, that the
    cylinder should be enclosed in a steam jacket, or should in some other
    way be effectually protected from refrigeration. In some engines not so
    protected, it has been found experimentally that less benefit was
    obtained from the fuel by working expansively than by working without
    expansion--the whole benefit due to expansion being more than
    counteracted by the increased refrigeration due to the larger surface
    of the cylinder required to develop the power. In locomotive engines,
    with outside cylinders, this condition of the advantageous use of
    expansion has been made very conspicuous, as has also been the case in
    screw steamers with four cylinders, and in which the refrigerating
    surface of the cylinders was consequently large.</P>

    <P>184. <EM>Q.</EM>--The steam is admitted to and from the cylinder by
    means of a slide or sluice valve?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig33.png" ALIGN="right" WIDTH="120"
    HEIGHT="346" ALT="Fig. 33"></P>

    <P><EM>A.</EM>--Yes; and of the slide valve there are many varieties;
    but the kinds most in use are the D valve,--so called from its
    resemblance to a half cylinder or D in its cross section--and the three
    ported valve, shown in fig. 33, which consists of a brass or iron box
    set over the two ports or openings into the cylinder, and a central
    port which conducts away the steam to the atmosphere or condenser; but
    the length of the box is so adjusted that it can only cover one of the
    cylinder ports and the central or eduction port at the same time. The
    effect, therefore, of moving the valve up and down, as is done by the
    eccentric, is to establish a connection alternately between each
    cylinder port and the central passage whereby the steam escapes; and
    while the steam is escaping from beneath the piston, the position of
    the valve is such, that a free communication exists between the space
    above the piston and the steam in the boiler. The piston is thus urged
    alternately up and down--the valve so changing its position before the
    piston arrives at the end of the stroke, that the pressure is by that
    time thrown on the reverse side of the piston, so as to urge it into
    motion in the opposite direction.</P>

    <P>185. <EM>Q.</EM>--Is the motion of the valve, then, the reverse of
    that of the piston?</P>

    <P><EM>A.</EM>--No. The valve does not move down when the piston moves
    down, nor does it move down when the piston moves up; but it moves from
    its mid position, to the extremity of its throw, and back again to its
    mid position, while the piston makes an upward or downward movement, so
    that the motion is as it were at right angles to the motion of the
    piston; or it is the same motion that the piston of another engine, the
    crank of which is set at right angles with that of the first engine,
    would acquire.</P>

    <P>186. <EM>Q.</EM>--Then in a steam vessel the valve of one engine may
    be worked from the piston of the other?</P>

    <P><EM>A.</EM>--Yes, it may; or it may be worked from its own
    connecting rod; and in the case of locomotive engines, this has
    sometimes been done.</P>

    <P>187. <EM>Q.</EM>--What is meant by the lead of the valve?</P>

    <P><EM>A.</EM>--The amount of opening which the valve presents for the
    admission of the steam, when the piston is just beginning its stroke.
    It is found expedient that the valve should have opened a little to
    admit steam on the reverse side of the piston before the stroke
    terminates; and the amount of this opening, which is given by turning
    the eccentric more or less round upon the shaft, is what is termed the
    lead.</P>

    <P>188. <EM>Q.</EM>--And what is meant by the lap of the valve?</P>

    <P><EM>A.</EM>--It is an elongation of the valve face to a certain
    extent over the port, whereby the port is closed sooner than would
    otherwise be the case. This extension is chiefly effected at that part
    of the valve where the steam is admitted, or upon the <EM>steam
    side</EM> of the valve, as the technical phrase is; and the intent of
    the extension is to close the steam passage before the end of the
    stroke, whereby the engine is made to operate to a certain extent
    expansively. In some cases, however, there is also a certain amount of
    lap given to the escape or eduction side, to prevent the eduction from
    being performed too soon when the lead is great; but in all cases there
    is far less lap on the eduction than on the steam side, very often
    there is none, and sometimes less than none, so that the valve is
    incapable of covering both the ports at once.</P>

    <P>189. <EM>Q.</EM>--What is the usual proportional length of stroke of
    the valve?</P>

    <P><EM>A.</EM>--The common stroke of the valve in rotative engines is
    twice the breadth or depth of the port, and the length of the valve
    face will then be just the breadth of the port when there is lap on
    neither the steam nor eduction side. Whatever lap is given, therefore,
    makes the valve face just so much longer. In some engines, however, the
    stroke of the valve is a good deal more than twice the breadth of the
    port; and it is to the stroke of the valve that the amount of lap
    should properly be referred.</P>

    <P>190. <EM>Q.</EM>--Can you tell what amount of lap will accomplish
    any given amount of expansion?</P>

    <P><EM>A.</EM>--Yes, when the stroke of the valve is known. From the
    length of the stroke of the piston subtract that part of the stroke
    which is intended to be accomplished before the steam is cut off;
    divide the remainder by the length of the stroke of the piston, and
    extract the square root of the quotient, which multiply by half the
    stroke of the valve, and from the product take half the lead; the
    remainder will be the lap required.</P>

    <P>191. <EM>Q.</EM>--Can you state how we may discover at what point of
    the stroke the eduction passage will be closed?</P>

    <P><EM>A.</EM>--To find how much before the end of the stroke the
    eduction passage will be closed:--to the lap on the steam side add the
    lead, and divide the sum by half the stroke of the valve; find the arc
    whose sine is equal to the quotient, and add 90&deg; to it.; divide the
    lap on the eduction side by half the stroke of the valve, and find the
    arc whose cosine is equal to the quotient; subtract this arc from the
    one last obtained, and find the cosine of the remainder; subtract this
    cosine from 2, and multiply the remainder by half the stroke of the
    piston; the product is the distance of the piston from the end of the
    stroke when the eduction passage is closed.</P>

    <P>192. <EM>Q.</EM>--Can you explain how we may determine the distance
    of the piston from the end of the stroke, before the steam urging it
    onward is allowed to escape?</P>

    <P><EM>A.</EM>--To find how far the piston is from the end of its
    stroke when the steam that is propelling it by expansion is allowed to
    escape to the atmosphere or condenser--to the lap on the steam side add
    the lead; divide the sum by half the stroke of the valve, and find the
    arc whose sine is equal to the quotient; find the arc whose sine is
    equal to the lap on the eduction side, divided by half the stroke of
    the valve; add these two arcs together and subtract 90&deg;; find the
    cosine of the residue, subtract it from 1, and multiply the remainder
    by half the stroke of the piston; the product is the distance of the
    piston from the end of its stroke when the steam that is propelling it
    is allowed to escape into the atmosphere or condenser. In using these
    rules, all the dimensions are to be taken in inches, and the answers
    will be found in inches also.</P>

    <P>193. <EM>Q.</EM>--Is it a benefit or a detriment to open the
    eduction passage before the end of the stroke?</P>

    <P><EM>A.</EM>--In engines working at a high rate of speed, such as
    locomotive engines, it is very important to open the exhaust passage
    for the escape of the steam before the end of the stroke, as an
    injurious amount of back pressure is thus prevented. In the earlier
    locomotives a great loss of effect was produced from inattention to
    this condition; and when lap was applied to the valves to enable the
    steam to be worked expansively, it was found that a still greater
    benefit was collaterally obtained by the earlier escape of the steam
    from the eduction passages, and which was incidental to the application
    of lap to the valves. The average consumption of coke per mile was
    reduced by Mr. Woods from 40 lbs. per mile to 15 lbs. per mile, chiefly
    by giving a free outlet to the escaping steam.</P>

    <P>194. <EM>Q.</EM>--To what extent can expansion be carried
    beneficially by means of lap upon the valve?</P>

    <P><EM>A.</EM>--To about one-third of the stroke; that is, the valve
    may be made with so much lap, that the steam will be cut off when two
    thirds of the stroke have been performed, leaving the residue to be
    accomplished by the agency of the expanding steam; but if more lap be
    put on than answers to this amount of expansion, a very distorted
    action of the valve will be produced, which may impair the efficiency
    of the engine. If a further amount of expansion than this is wanted, it
    may be accomplished by wire drawing the steam, or by so contracting the
    steam passage that the pressure within the cylinder must decline when
    the speed of the piston is accelerated, as it is about the middle of
    the stroke.</P>

    <P>195. <EM>Q.</EM>--Will you explain how this result ensues?</P>

    <P><EM>A.</EM>--If the valve be so made as to shut off the steam by the
    time two thirds of the stroke have been performed, and the steam be at
    the same time throttled in the steam pipe, the full pressure of the
    steam within the cylinder cannot be maintained except near the
    beginning of the stroke where the piston travels slowly; for, as the
    speed of the piston increases, the pressure necessarily subsides, until
    the piston approaches the other end of the cylinder, where the pressure
    would rise again but that the operation of the lap on the valve by this
    time has had the effect of closing the communication between the
    cylinder and steam pipe, so as to prevent more steam from entering. By
    throttling the steam, therefore, in the manner here indicated, the
    amount of expansion due to the lap may be doubled, so that an engine
    with lap enough upon the valve to cut off the steam at two-thirds of
    the stroke, may, by the aid of wire drawing, be virtually rendered
    capable of cutting off the steam at one-third of the stroke.</P>

    <P>196. <EM>Q.</EM>--Is this the usual way of cutting off the
    steam?</P>

    <P><EM>A.</EM>--No; the usual way of cutting off the steam is by means
    of a separate valve, termed an expansion valve; but such a device
    appears to be hardly necessary in ordinary engines. In the Cornish
    engines, where the steam is cut off in some cases at one-twelfth of the
    stroke, a separate valve for the admission of steam, other than that
    which permits its escape, is of course indispensable; but in common
    rotative engines, which may realize expansive efficacy by throttling, a
    separate expansion valve does not appear to be required.</P>

    <P>197. <EM>Q.</EM>--That is, where much expansion is required, an
    expansion valve is a proper appendage, but where not much is required,
    a separate expansion valve may be dispensed with?</P>

    <P><EM>A.</EM>--Precisely so. The wire drawing of the steam causes a
    loss of part of its power, and the result will not be quite so
    advantageous by throttling as by cutting off. But for moderate amounts
    of expansion it will suffice, provided there be lap upon the slide
    valve.</P>

    <P>198. <EM>Q.</EM>--Will you explain the structure or configuration of
    expansion apparatus of the usual construction?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig34.png" ALIGN="left" WIDTH="291"
    HEIGHT="400" ALT="Fig. 34"></P>

    <P><EM>A.</EM>--The structure of expansion apparatus is very various;
    but all the kinds operate either on the principle of giving such a
    motion to the slide valve as will enable it to cut off the steam, at
    the desired point, or on the principle of shutting off the steam by a
    separate valve in the steam pipe or valve casing. The first class of
    apparatus has not been found so manageable, and is not in extensive
    use, except in that form known as the link motion. Of the second class,
    the most simple probably is the application of a cam giving motion to
    the throttle valve, or to a valve of the same construction, which
    either accurately fits the steam pipe, or which comes round to a face,
    which, however, it is restrained from touching by a suitable
    construction of the cam. A kind of expansion valve, often employed in
    marine engines of low speed, is the kind used in the Cornish engines,
    and known as the equilibrium valve. This valve is represented in fig.
    34. It consists substantially of an annulus or bulging cylinder of
    brass, with a steam-tight face both at its upper and lower edges, at
    which points it fits accurately upon a stationary seat. This annulus
    may be raised or lowered without being resisted by the pressure of the
    steam, and in rotative engines it is usually worked by a cam on the
    shaft. The expansion cam is put on the shaft in two pieces, which are
    fastened to each other by means of four bolts passing through lugs, and
    is fixed to the shaft by keys. A roller at one end of a bell-crank
    lever, which is connected with the expansion valve, presses against the
    cam, so that the motion of the lever will work the valve. The roller is
    kept against the cam by a weight on a lever attached to the same shaft,
    but a spring is necessary for high speeds. If the cam were concentric
    with the shaft, the lever which presses upon it would remain
    stationary, and also the expansion valve; but by the projection of the
    cam, the end of the lever receives a reciprocating motion, which is
    communicated to the valve.</P>

    <P>199. <EM>Q.</EM>--The cam then works the valve?</P>

    <P><EM>A.</EM>--Yes. The position of the projection of the cam
    determines the point in relation to the stroke at which the valve is
    opened, and its circumferential length determines the length of the
    time during which the valve continues open. The time at which the valve
    should begin to open is the same under all circumstances, but the
    duration of its opening varies with the amount of expansion desired. In
    order to obtain this variable extent of expansion, there are several
    projections made upon the cam, each of which gives a different degree,
    or <EM>grade</EM> as it is usually called, of expansion. These grades
    all begin at the same point on the cam, but are of different lengths,
    so that they begin to move the lever at the same time, but differ in
    the time of returning it to its original position.</P>

    <P>200. <EM>Q.</EM>--How is the degree of expansion changed?</P>

    <P><EM>A.</EM>--The change of expansion is effected by moving the
    roller on to the desired grade; which is done by slipping the lever
    carrying the roller endways on the shaft or pin sustaining it.</P>

    <P>201. <EM>Q.</EM>--Are such cams applicable in all cases?</P>

    <P><EM>A.</EM>--In engines moving at a high rate of speed the roller
    will be thrown back from the cam by its momentum, unless it be kept
    against it by means of springs. In some cases I have employed a spring
    formed of a great number of discs of India rubber to keep the roller
    against the cam, but a few brass discs require to be interposed to
    prevent the India rubber discs from being worn in the central hole.</P>

    <P>202. <EM>Q.</EM>--May not the percussion incident to the action of a
    cam at a high speed, when the roller is not kept up to the face by
    springs, be obviated by giving a suitable configuration to the cam
    itself?</P>

    <P><EM>A.</EM>--It may at all events be reduced. The outline of the cam
    should be a parabola, so that the valve may be set in motion precisely
    as a falling body would be; but it will, nevertheless, be necessary
    that the roller on which the cam presses should be forced upward by a
    spring rather than by a counterweight, as there will thus be less
    inertia or momentum in the mass that has to be moved.</P>

    <P>203. <EM>Q.</EM>--An additional slide valve is sometimes used for
    cutting off the steam?</P>

    <P><EM>A.</EM>--Yes, very frequently; and the slide valve is sometimes
    on the side or back of the valve casing, and sometimes on the back of
    the main or distributing valve, and moving with it.</P>

    <P>204. <EM>Q.</EM>--Are cams used in locomotive engines?</P>

    <P><EM>A.</EM>--In locomotive engines the use of cams is inadmissible,
    and other expedients are employed, of which those contrived by
    Stephenson and by Cabrey operate on the principle of accomplishing the
    requisite variations of expansion by altering the throw of the slide
    valve.</P>

    <P>205. <EM>Q.</EM>--What is Stephenson&#39;s arrangement?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig35.png" WIDTH="700" HEIGHT="327" ALT=
    "Fig. 35"></P>

    <P><EM>A.</EM>--Stephenson connects the ends of the forward and
    backward eccentric rods by a link with a curved slot in which a pin
    upon the end of the valve rod works. By moving this link so as to bring
    the forward eccentric rod in the same line with the valve rod, the
    valve receives the motion due to that eccentric; whereas if the
    backward eccentric rod is brought in a line with the valve rod, the
    valve gets the motion proper for reversing, and if the link be so
    placed that the valve rod is midway between the two eccentric rods, the
    valve will remain nearly stationary. This arrangement, which is now
    employed extensively, is what is termed &quot;the link motion.&quot; It
    is represented in the annexed figure, fig. 35, where <EM>e</EM> is the
    valve rod, which is attached by a pin to an open curved link
    susceptible of being moved up and down by the bell-crank lever
    <EM>f&#39;&#39;</EM> <EM>f&#39;&#39;</EM>, supported on the centre
    <EM>g</EM>, and acting on the links <EM>f</EM>, while the valve rod
    <EM>e</EM> remains in the same horizontal plane; <EM>d d&#39;</EM> are
    the eccentric rods, and the link is represented in its lowest position.
    The dotted lines <EM>h&#39; h&#39;&#39;</EM> show the position of the
    eccentric rods when the link is in its highest position, and <EM>l
    l&#39;</EM> when in mid position.</P>

    <P>206. <EM>Q.</EM>--What is Cabrey&#39;s arrangement?</P>

    <P><EM>A.</EM>--Mr. Cabrey makes his eccentric rod terminate in a pin
    which works into a straight slotted lever, furnished with jaws similar
    to the jaws on the eccentric rods of locomotives. By raising the pin of
    the eccentric rod in this slot, the travel of the valve will be varied,
    and expansive action will be the result.</P>

    <P>207. <EM>Q.</EM>--What other forms of apparatus are there for
    working steam expansively?</P>

    <P><EM>A.</EM>--They are too numerous for description here, but a few
    of them may be enumerated. Fenton seeks to accomplish the desired
    object by introducing a spiral feather on the crank axle, by moving the
    eccentric laterally against which the eccentric is partially turned
    round so as to cut off the steam at a different part of the stroke.
    Dodds seeks to attain the same end by corresponding mechanical
    arrangements. Farcot, Edwards, and Lavagrian cut off the steam by the
    application of a supplementary valve at the back of the ordinary valve,
    which supplementary valve is moved by tappets fixed to the valve
    casing. Bodmer, in 1841, and Meyer, in 1842, employed two slides or
    blocks fitted over apertures in the ordinary slide valve, and which
    blocks were approximated or set apart by a right and left handed screw
    passing through both. <A NAME="fnr2"></A> <A HREF="#fn2" CLASS=
    "fnsuper">1</A> Hawthorn, in 1843, employed as an expansion valve a
    species of frame lying on the ordinary cylinder face upon the outside
    of the valve, and working up against the steam side of the valve at
    each end so as to cut off the steam. In the same year Gonzenbach
    patented an arrangement which consists of an additional slide valve and
    valve casing placed on the back of the ordinary slide valve casing, and
    through this supplementary valve the steam must first pass. This
    supplementary valve is worked by a double ended lever, slotted at one
    end for the reception of a pin on the valve link, the position of which
    in the slot determines the throw of the supplementary valve, and the
    consequent degree of expansion.</P>

    <P>208. <EM>Q.</EM>--What is the arrangement of expansion valve used in
    the most approved modern engines?</P>

    <P><EM>A.</EM>--In modern engines, either marine or locomotive, it is
    found that if they are fitted with the link motion, as they nearly all
    are, a very good expansive action can be obtained by giving a suitable
    adjustment to it, without employing an expansion valve at all. Diagrams
    taken from engines worked in this manner show a very excellent result,
    and most of the modern engines trust for their expansive working to the
    link motion and the throttle valve.</P>

    <P CLASS="footnote"><A NAME="fn2"></A> <A HREF="#fnr2">[1]</A> In 1838
    I patented an arrangement of expansion valve, consisting of two movable
    plates set upon the ordinary slide valve, and which might be drawn
    together or asunder by means of a right and left handed screw passing
    through both plates. The valve spindle was hollow, and a prolongation
    of the screw passed up through it, and was armed on the top with a
    small wheel, by means of which the plates might be adjusted while the
    engine was at work. In 1839 I fitted an expansion valve in a steam
    vessel, consisting of two plates, connected by a rod, and moved by
    tappets up against the steam edges of the valve. In another steam
    vessel I fitted the same species of valve, but the motion was not
    derived from tappets, but from a moving part of the engine, though at
    the moderate speed at which these engines worked I found tappets to
    operate well and make little noise. In 1837 I employed, as an expansion
    valve, a rectangular throttle valve, accurately fitting a bored out
    seat, in which it might be made to revolve, though it did not revolve
    in working. This valve was moved by a pin in a pinion, making two
    revolutions for every revolution of the engine, and the configuration
    of the seat determined the amount of the expansion. In 1855 I have
    again used expansion valves of this construction in engines making one
    hundred revolutions per minute, and with perfectly satisfactory
    results.-- J.B.</P>

    <H2 CLASS="chapter"><A NAME="ch04"></A>CHAPTER IV.</H2>

    <H3>MODES OF ESTIMATING THE POWER AND PERFORMANCE OF ENGINES AND
    BOILERS.</H3>

    <H4 CLASS="subhead"><A NAME="f01"></A>HORSES POWER.</H4>

    <P>209. <EM>Q.</EM>--What do you understand by a horse power?</P>

    <P><EM>A.</EM>--An amount of mechanical force that will raise 33,000
    lbs. one foot high in a minute. This standard was adopted by Mr. Watt,
    as the average force exerted by the strongest London horses; the object
    of his investigation being to enable him to determine the relation
    between the power of a certain size of engine and the power of a horse,
    so that when it was desired to supersede the use of horses by the
    erection of an engine, he might, from the number of horses employed,
    determine the size of engine that would be suitable for the work.</P>

    <P>210. <EM>Q.</EM>--Then when we talk of an engine of 200 horse power,
    it is meant that the impelling efficacy is equal to that of 200 horses,
    each lifting 33,000 lbs. one foot high in a minute?</P>

    <P><EM>A.</EM>--No, not now; such was the case in Watt&#39;s engines,
    but the capacity of cylinder answerable to a horse power has been
    increased by most engineers since his time, and the pressure on the
    piston has been increased also, so that what is now called a 200 horse
    power engine exerts, almost in every case, a greater power than was
    exerted in Watt&#39;s time, and a horse power, in the popular sense of
    the term, has become a mere conventional unit for expressing a certain
    size of engine, without reference to the power exerted.</P>

    <P>211. <EM>Q.</EM>--Then, each nominal horse power of a modern engine
    may raise much more than 33,000 lbs. one foot high in a minute?</P>

    <P><EM>A.</EM>--Yes; some raise 52,000 lbs., others 60,000 lbs., and
    others 66,000 lbs., one foot high in a minute by each nominal horse
    power. Some engines indeed work as high as five times above the nominal
    power, and therefore no comparison can be made between the performances
    of different engines, unless the power actually exerted be first
    discovered.</P>

    <P>212. <EM>Q.</EM>--How is the power actually exerted by engines
    ascertained?</P>

    <P><EM>A.</EM>--By means of an instrument called the indicator, which
    is a miniature cylinder and piston attached to the cylinder cover of
    the main engine, and which indicates, by the pressure exerted on a
    spring, the amount of pressure or vacuum existing within the cylinder.
    From this pressure, expressed in pounds per square inch, deduct a pound
    and a half of pressure for friction, the loss of power in working the
    air pump, &amp;c.; multiply the area of the piston in square inches by
    this residual pressure, and by the motion of the piston, in feet per
    minute, and divide by 33,000; the quotient is the actual number of
    horses power of the engine. The same result is attained by squaring the
    diameter of the cylinder, multiplying by the pressure per square inch,
    as shown by the indicator, less a pound and a half, and by the motion
    of the piston, in feet per minute, and dividing by 42,017.</P>

    <P>213. <EM>Q.</EM> How is the nominal power of an engine
    ascertained?</P>

    <P><EM>A.</EM>--Since the nominal power is a mere conventional
    expression, it is clear that it must be determined by a merely
    conventional process. The nominal power of ordinary condensing engines
    may be ascertained by the following rule: multiply the square of the
    diameter of the cylinder in inches, by the velocity of the piston in
    feet per minute, and divide the product by 6,000; the quotient is the
    number of nominal horses power. In using this rule, however, it is
    necessary to adopt the speed of piston prescribed by Mr. Watt, which
    varies with the length of the stroke. The speed of piston with a 2 feet
    stroke is, according to his system, 160 per minute; with a 2 ft. 6 in.
    stroke, 170; 3 ft., 180; 3 ft. 6 in., 189; 4 ft., 200; 5 ft., 215; 6
    ft., 228; 7 ft., 245; 8 ft., 256 ft.</P>

    <P>214. <EM>Q.</EM>--Does not the speed of the piston increase with the
    length of the stroke?</P>

    <P><EM>A.</EM>--It does: the speed of the piston varies nearly as the
    cube root of the length of the stroke.</P>

    <P>215. <EM>Q.</EM>--And may not therefore some multiple of the cube
    root of the length of the stroke be substituted for the velocity of the
    piston in determining the nominal power?</P>

    <P><EM>A.</EM>--The substitution is quite practicable, and will
    accomplish some simplification, as the speed of piston proper for the
    different lengths of stroke cannot always be remembered. The rule for
    the nominal power of condensing engines when thus arranged, will be as
    follows: multiply the square of the diameter of the cylinder in inches
    by the cube root of the stroke in feet, and divide the product by 47;
    the quotient is the number of nominal horses power of the engine,
    supposing it to be of the ordinary condensing description. This rule
    assumes the existence of a uniform effective pressure upon the piston
    of 7 lbs. per square inch; Mr. Watt estimated the effective pressure
    upon the piston of his 4 horse power engines at 6-8 lbs. per square
    inch, and the pressure increased slightly with the power, and became
    6.94 lbs. per square inch in engines of 100 horse power; but it appears
    to be more convenient to take a uniform pressure of 7 lbs. for all
    powers. Small engines, indeed, are somewhat less effective in
    proportion than large ones, but the difference can be made up by
    slightly increasing the pressure in the boiler; and small boilers will
    bear such an increase without inconvenience.</P>

    <P>216. <EM>Q.</EM>--How do you ascertain the power of high pressure
    engines?</P>

    <P><EM>A.</EM>--The actual power is readily ascertained by the
    indicator, by the same process by which the actual power of low
    pressure engines is ascertained. The friction of a locomotive engine
    when unloaded is found by experiment to be about 1 lb. per square inch
    on the surface of the pistons, and the additional friction caused by
    any additional resistance is estimated at about .14 of that resistance;
    but it will be a sufficiently near approximation to the power consumed
    by friction in high pressure engines, if we make a deduction of a pound
    and a half from the pressure on that account, as in the case of low
    pressure engines. High pressure engines, it is true, have no air pump
    to work; but the deduction of a pound and a half of pressure is
    relatively a much smaller one where the pressure is high, than where it
    does not much exceed the pressure of the atmosphere. The rule,
    therefore, for the actual horse power of a high pressure engine will
    stand thus: square the diameter of the cylinder in inches, multiply by
    the pressure of the steam in the cylinder per square inch less 1-1/2
    lb., and by the speed of the piston in feet per minute, and divide by
    42,017; the quotient is the actual horse power.</P>

    <P>217. <EM>Q.</EM>--But how do you ascertain the nominal horse power
    of high pressure engines?</P>

    <P><EM>A.</EM>--The nominal horse power of a high pressure engine has
    never been defined; but it should obviously hold the same relation to
    the actual power as that which obtains in the case of condensing
    engines, so that an engine of a given nominal power may be capable of
    performing the same work, whether high pressure or condensing. This
    relation is maintained in the following rule, which expresses the
    nominal horse power of high pressure engines: multiply the square of
    the diameter of the cylinder in inches by the cube root of the length
    of stroke in feet, and divide the product by 15.6. This rule gives the
    nominal power of a high pressure engine three times greater than that
    of a low pressure engine of the same dimensions; the average effective
    pressure being taken at 21 lbs. per square inch instead of 7 lbs., and
    the speed of the piston in feet per minute being in both rules 128
    times the cube root of the length of stroke. <A NAME="fnr3"></A> <A
    HREF="#fn3" CLASS="fnsuper">1</A></P>

    <P>218. <EM>Q.</EM>--Is 128 times the cube root of the stroke in feet
    per minute the ordinary speed of all engines?</P>

    <P><EM>A.</EM>--Locomotive engines travel at a quicker speed--an
    innovation brought about not by any process of scientific deduction,
    but by the accidents and exigencies of railway transit. Most other
    engines, however, travel at about the speed of 128 times the cube root
    of the stroke in feet; but some marine condensing engines of recent
    construction travel at as high a rate as 700 feet per minute. To
    mitigate the shock of the air pump valves in cases in which a high
    speed has been desirable, as in the case of marine engines employed to
    drive the screw propeller without intermediate gearing, India rubber
    discs, resting on a perforated metal plate, are now generally adopted;
    but the India rubber should be very thick, and the guards employed to
    keep the discs down should be of the same diameter as the discs
    themselves.</P>

    <P>219. <EM>Q.</EM>--Can you suggest any eligible method of enabling
    condensing engines to work satisfactorily at a high rate of speed?</P>

    <P><EM>A.</EM>--The most feasible way of enabling condensing engines to
    work satisfactorily at a high speed, appears to lie in the application
    of balance weights to the engine, so as to balance the momentum of its
    moving parts, and the engine must also be made very strong and rigid.
    It appears to be advisable to perform the condensation partly in the
    air pump, instead of altogether in the condenser, as a better vacuum
    and a superior action of the air pump valves will thus be obtained.
    Engines constructed upon this plan may be driven at four times the
    speed of common engines, whereby an engine of large power may be
    purchased for a very moderate price, and be capable of being put into a
    very small compass; while the motion, from being more equable, will be
    better adapted for most purposes for which a rotary motion is required.
    Even for pumping mines and blowing iron furnaces, engines of this kind
    appear likely to come into use, for they are more suitable than other
    engines for driving the centrifugal pump, which in many cases appears
    likely to supersede other kinds of pumps for lifting water; and they
    are also conveniently applicable to the driving of fans, which, when so
    arranged that the air condensed by one fan is employed to feed another,
    and so on through a series of 4 or 5, have succeeded in forcing air
    into a furnace with a pressure of 2-1/2 lbs. on the square inch, and
    with a far steadier flow than can be obtained by a blast engine with
    any conceivable kind of compensating apparatus. They are equally
    applicable if blast cylinders be employed.</P>

    <P>220. <EM>Q.</EM>--Then, if by this modification of the engine you
    enable it to work at four times the speed, you also enable it to exert
    four times the power?</P>

    <P><EM>A.</EM>--Yes; always supposing it to be fully supplied with
    steam. The nominal power of this new species of engine can readily be
    ascertained by taking into account the speed of the piston, and this is
    taken into account by the Admiralty rule for power.</P>

    <P>221. <EM>Q.</EM>--What is the Admiralty rule for determining the
    power of an engine?</P>

    <P><EM>A.</EM>--Square the diameter of the cylinder in inches, which
    multiply by the speed of the piston in feet per minute, and divide by
    6,000; the quotient is the power of the engine by the Admiralty rule.
    <A NAME="fnr4"></A> <A HREF="#fn4" CLASS="fnsuper">2</A></P>

    <P>222. <EM>Q.</EM>--The high speed engine does not require so heavy a
    fly wheel as common engines?</P>

    <P><EM>A.</EM>--No; the fly wheel will be lighter, both by virtue of
    its greater velocity of rotation, and because the impulse communicated
    by the piston is less in amount and more frequently repeated, so as to
    approach more nearly to the condition of a uniform pressure.</P>

    <P>223. <EM>Q.</EM>--Can nominal be transformed into actual horse
    power?</P>

    <P><EM>A.</EM>--No; that is not possible in the case of common
    condensing engines. The actual power exerted by an engine cannot be
    deduced from its nominal power, neither can the nominal power be
    deduced from the power actually exerted, or from anything else than the
    dimensions of the cylinder. The actual horse power being a dynamical
    unit, and the nominal horse power a measure of capacity of the
    cylinder, are obviously incomparable things.</P>

    <P>224. <EM>Q.</EM>--That is, the <EM>nominal</EM> power is a
    commercial unit by which engines are bought and sold, and the
    <EM>actual</EM> power a scientific unit by which the quality of their
    performance is determined?</P>

    <P><EM>A.</EM>--Yes; the nominal power is as much a commercial measure
    as a yard or a bushel, and is not a thing to be ascertained by any
    process of science, but to be fixed by authority in the same manner as
    other measures. The actual power, on the contrary, is a mechanical
    force or dynamical effort capable of raising a given weight through a
    given distance in a given time, and of which the amount is
    ascertainable by scientific investigation.</P>

    <P>225. <EM>Q.</EM>--Is there any other measure of an actual horse
    power than 33,000 lbs. raised one foot high in the minute?</P>

    <P><EM>A.</EM>--There cannot be any <EM>different</EM> measure, but
    there are several equivalent measures. Thus the evaporation of a cubic
    foot of water in the hour, or the expenditure of 33 cubic feet of low
    pressure steam per minute, is reckoned equivalent to an actual horse
    power, or 528 cubic feet of water raised one foot high in the minute
    involves the same result.</P>

    <P CLASS="footnote"><A NAME="fn3"></A> <A HREF="#fnr3">[1]</A> Tables
    of the horse power of both high and low pressure engines are given in
    the Key.</P>

    <P CLASS="footnote"><A NAME="fn4"></A> <A HREF="#fnr4">[2]</A>
    Example.--What is the power of an engine of 42 inches diameter, 3-1/2
    feet stroke, and making 85 strokes per minute? The speed of the piston
    will be 7 (the length of a double stroke) x 85 = 595 feet per minute.
    Now 42 x 42 = 1,764 x 595 = 1,049,580 &divide; 6,000 = 175 horses
    power.</P>

    <H4 CLASS="subhead"><A NAME="f02"></A>DUTY OF ENGINES AND BOILERS.</H4>

    <P>226. <EM>Q.</EM>--What is meant by the duty of a engine?</P>

    <P><EM>A.</EM>--The work done in relation to the fuel consumed.</P>

    <P>227. <EM>Q.</EM>--And how is the duty ascertained?</P>

    <P><EM>A.</EM>--In ordinary mill or marine engines it can only be
    ascertained by the indicator, as the load upon such engines is
    variable, and cannot readily be determined; but in the case of engines
    pumping water, where the load is constant, the number of strokes
    performed by the engine will represent the work done, and the amount of
    work done by a given quantity of coal represents the duty. In Cornwall
    the duty of an engine is expressed by the number of millions of pounds
    raised one foot high by a bushel, or 94 lbs. of Welsh coal. A bushel of
    Newcastle coal will only weigh 84 Lbs.; and in comparing the duty of a
    Cornish engine with the performance of an engine in some locality where
    a different kind of coal is used, it is necessary to pay regard to such
    variations.</P>

    <P>228. <EM>Q.</EM>--Can you tell the duty of an engine when you know
    its consumption of coal per horse power per hour?</P>

    <P><EM>A.</EM>--Yes, if the power given be the actual, and not the
    nominal, power. Divide 166.32 by the number of pounds of coal consumed
    per actual horse power per hour; the quotient is the duty in millions
    of pounds. If you already have the duty in millions of pounds, and wish
    to know the equivalent consumption in pounds per actual horse power per
    hour, divide 166.32 by the duty in millions of pounds; the quotient is
    the consumption per actual horse power per hour. The duty of a
    locomotive engine is expressed by the weight of coke it consumes in
    transporting a ton through the distance of one mile upon a railway; but
    this is a very imperfect method of representing the duty, as the
    tractive efficacy of a pound of coke becomes less as the speed of the
    locomotive becomes greater; and the law of variation is not accurately
    known.</P>

    <P>229. <EM>Q.</EM>--What amount of power is generated in good engines
    of the ordinary kind by a given weight of coal?</P>

    <P><EM>A.</EM>--The duty of different kinds of engines varies very
    much, and there are also great differences in the performance of
    different engines of the same class. In ordinary rotative condensing
    engines of good construction, 10 lbs. of coal per nominal horse power
    per hour is a common consumption; but such engines exert nearly twice
    their nominal power, so that the consumption per actual horse power per
    hour may be taken at from 5 to 6 lbs. Engines working very expansively,
    however, attain an economy much superior to this. The average duty of
    the pumping engines in Cornwall is about 60,000,000 lbs. raised 1 ft.
    high by a bushel of Welsh coals, which weighs 94 lbs. This is
    equivalent to a consumption of 3.1 lbs. of coal per actual horse power
    per hour; but some engines reach a duty of above 100,000,000, or 1.74
    lbs. of coal per actual horse power per hour. Locomotives consume from
    8 to 10 lbs. of coke in evaporating a cubic foot of water, and the
    evaporation of a cubic foot of water per hour may be set down as
    representing an actual horse power in locomotives as well as in
    condensing engines, if expansion be not employed. When the locomotive
    is worked expansively, however, there is of course a less consumption
    of water and fuel per horse power, or per ton per mile, than when the
    full pressure is used throughout the stroke; and most locomotives now
    operate with as much expansion as can be conveniently given by the
    slide valves.</P>

    <P>230. <EM>Q.</EM>--But is not the evaporative power of locomotives
    affected materially by the proportions of the boiler?</P>

    <P><EM>A.</EM>--Yes, but this may be said of all boilers; but in
    locomotive boilers, perhaps, the effect of any misproportion becomes
    more speedily manifest. A high temperature of the fire box is found to
    be conducive to economy of fuel; and this condition, in its turn,
    involves a small area of grate bars. The heating surface of locomotive
    boilers should be about 80 square feet for each square foot of grate
    bars, and upon each foot of grate bars about 1 cwt. of coke should be
    burnt in the hour.</P>

    <P>231. <EM>Q.</EM>--Probably the heat is more rapidly absorbed when
    the temperature of the furnace is high?</P>

    <P><EM>A.</EM>--That seems to be the explanation. The rapidity with
    which a hot body imparts heat to a colder, varies as the square of the
    difference of temperature; so that if the temperature of the furnace be
    very high, the larger part of the heat passes into the water at the
    furnace, thereby leaving little to be transmitted by the tubes. If, on
    the contrary, the temperature of the furnace be low, a large part of
    the heat will pass into the tubes, and more tube surface will be
    required to absorb it. About 16 cubic feet of water should be
    evaporated by a locomotive boiler for each, square foot of fire grate,
    which, with the proportion of heating surface already mentioned, leaves
    5 square feet of heating surface to evaporate a cubic foot of water in
    the hour. This is only about half the amount of surface usual in land
    and marine boilers per cubic foot evaporated, and its small amount is
    due altogether to the high temperature of the furnace, which, by the
    rapidity of transmission it causes, is tantamount to an additional
    amount of heating surface.</P>

    <P>232. <EM>Q.</EM>--You have stated that the steam and vacuum gauges
    are generally glass tubes, up which mercury is forced by the steam or
    sucked by the vacuum?</P>
    <P><EM>A.</EM>--Vacuum gauges are very often of this
    construction, but steam gauges more frequently consist of a small iron
    tube, bent like the letter U, and into which mercury is poured. The one
    end of this tube communicates with the boiler, and the other end with
    the atmosphere; and when the pressure of the steam rises in the boiler,
    the mercury is forced down in the leg communicating with the boiler and
    rises in the other leg, and the difference of level in the legs denotes
    the pressure of the steam. In this gauge a rise of the mercury one inch
    in the one leg involves a difference of the level between the two legs
    of two inches, and an inch of rise is, therefore, equivalent to two
    inches of mercury, or a pound of pressure. A small float of wood is
    placed in the open leg to show the rise or fall of the mercury, and
    this leg is surmounted by a brass scale, graduated in inches, to the
    marks of which the float points.</P>

    <P>233. <EM>Q.</EM>--What other kinds of steam and vacuum gauges are
    there?</P>

    <P><EM>A.</EM>--There are many other kinds; but probably Bourdon&#39;s
    gauges are now in more extended use than, any other, and their
    operation has been found to be satisfactory in practice. The principle
    of their action may be explained to be, that a thin elliptical metal
    tube, if bent into a ring, will seek to coil or uncoil itself if
    subjected to external or internal pressure, and to an extent
    proportional to the pressure applied. The end of the tube is sharpened
    into an index, and moves to an extent corresponding to the pressure
    applied to the tube; but in the more recent forms of this apparatus, a
    dial and a hand, like those of a clock, are employed, and the hand is
    moved round by a toothed sector connected to the tube, and which sector
    acts on a pinion attached to the hand. Mr. Shank, of Paisley, has
    lately introduced a form of steam gauge like a thermometer, with a
    flattened bulb; and the pressure of the steam, by compressing the bulb,
    causes the mercury to rise to a point proportional to the pressure
    applied.</P>

    <H4 CLASS="subhead"><A NAME="f03"></A>THE INDICATOR.</H4>

    <P>234. <EM>Q.</EM>--You have already stated that the actual power of
    an engine is ascertained by an instrument called the indicator, which
    consists of a small cylinder with a piston moving against a spring, and
    compressing it to an extent answerable to the pressure of the steam.
    Will you explain further the structure and mode of using that
    instrument?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig36.png" ALIGN="left" WIDTH="222"
    HEIGHT="550" ALT="Fig. 36"></P>

    <P><EM>A.</EM>--The structure of the common form of indicator will be
    most readily apprehended by a reference to fig. 36, which is a
    McNaught&#39;s indicator. Upon a movable barrel A, a piece of paper is
    wound, the ends of which are secured by the slight brass clamps shown
    in the drawing. The barrel is supported by the bracket <EM>b</EM>,
    proceeding from the body of the indicator, and at the bottom of the
    barrel a watch spring is coiled with one end attached to the barrel and
    the other end to the bracket, so that when the barrel is drawn round by
    a string wound upon its lower end like a roller blind, the spring
    returns the barrel to its original position, when the string is
    relaxed. The string is attached to some suitable part of the engine,
    and at every stroke the string is drawn out, turning round the barrel,
    and the barrel is returned again by the spring on the return
    stroke.</P>

    <P>235. <EM>Q</EM>--But in what way can these reciprocations of the
    barrel determine the power of the engine?</P>

    <P><EM>A.</EM>--They do not determine it of themselves, but are only
    part of the operation. In the inside of the cylinder <EM>c</EM> there
    is a small piston moving steam tight in a cylinder of which <EM>d</EM>
    is the piston rod, and <EM>e</EM> a spiral spring of steel, which the
    piston, when forced upwards by the steam or sucked downwards by the
    vacuum, either compresses or extends; <EM>f</EM> is a cock attached to
    the cylinder of the indicator, and which is screwed into the cylinder
    cover. It is obvious that, so soon as this cock is opened, the piston
    will be forced up when the space above the piston of the engine is
    opened to the boiler, and sucked down when that space is opened to the
    condenser--in each case to an extent proportionate to the pressure of
    the steam or the perfection of the vacuum, the top of the piston
    <EM>c</EM> being open to the atmosphere. A pencil, <EM>p</EM>, with a
    knife hinge, is inserted into the piston rod, at <EM>e</EM>, and the
    point of the pencil bears upon the surface of the paper wound upon the
    drum A. If the drum A did not revolve, this pencil would merely trace
    on the paper a vertical line; but as the drum A moves round and back
    again every stroke of the engine, and as the pencil moves up and down
    again every stroke of the engine, the combined movements trace upon the
    paper a species of rectangle, which is called an indicator diagram; and
    the nature of this diagram determines the nature of the engine&#39;s
    performance.</P>

    <P>236. <EM>Q.</EM>--How does it do this?</P>

    <P><EM>A.</EM>--It is clear that if the pencil was moved up
    instantaneously to the top of its stroke, and was also moved down
    instantaneously to the bottom of its stroke, and if it remained without
    fluctuation while at the top and bottom, the figure described by the
    pencil would be a perfect rectangle, of which the vertical height would
    represent the total pressure of the steam and vacuum, and therefore the
    total pressure urging the piston of the engine. But in practice the
    pencil will neither rise nor fall instantaneously, nor will it remain
    at a uniform height throughout the stroke. If the steam be worked
    expansively the pressure will begin to fall so soon as the steam is cut
    off; and at the end of the stroke, when the steam comes to be
    discharged, the subsidence of pressure will not be instantaneous, but
    will occupy an appreciable time. It is clear, therefore, that in no
    engine can the diagram described by an indicator be a complete
    rectangle; but the more nearly it approaches to a rectangle, the larger
    will be the power produced at every stroke with any given pressure, and
    the area of the space included within the diagram will in every case
    accurately represent the power exerted by the engine during that
    stroke.</P>

    <P>237. <EM>Q.</EM>--And how is this area ascertained?</P>

    <P><EM>A.</EM>--It may be ascertained in various ways; but the usual
    mode is to take the vertical height of the diagram at a number of
    equidistant points on a base line, and then to take the mean of these
    several heights as representative of the mean pressure actually urging
    the piston. Now if you have the pressure on the piston per square inch,
    and if you know the number of square inches in its area, and the
    velocity with which it moves in feet per minute, you have obviously the
    dynamical effort of the engine, or, in other words, its actual
    power.</P>

    <P>238. <EM>Q.</EM>--How is the base line you have referred to
    obtained?</P>

    <P><EM>A.</EM>--In proceeding to take an indicator diagram, the first
    thing to be done is to allow the barrel to make two or three
    reciprocations with the pencil resting against it, before opening the
    cock attached to the cylinder. There will thus be traced a horizontal
    line, which is called the <EM>atmospheric line</EM>, and in condensing
    engines, a part of the diagram will be above and a part of it below
    this line; whereas, in high pressure engines the whole of the diagram
    will be above this line. Upon this line the vertical ordinates may be
    set off at equal distances, or upon any base line parallel to it; but
    the usual course is to erect the ordinates on the atmospheric line.</P>

    <P>239. <EM>Q.</EM>--Will you give an example of an indicator
    diagram?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig37.png" WIDTH="700" HEIGHT="277" ALT=
    "Fig. 37"></P>

    <P><EM>A.</EM>--Fig. 37 is an indicator diagram taken from a low
    pressure engine, and the waving line <EM>a b c</EM>, forming a sort of
    irregular parallelogram, is that which is described by the pencil. The
    atmospheric line is represented by the line o o. The scale at the side
    shows the pressure of the steam, which in this engine rose to about 9
    lbs. per square inch, and the vacuum fell to 11 lbs. The steam begins
    to be cut off when, about one-fourth of the stroke has been performed,
    and the pressure consequently falls.</P>

    <P>240. <EM>Q.</EM>--Is this species of indicator which you have just
    described applicable to locomotive engines?</P>

    <P><EM>A.</EM>--It is no doubt applicable under suitable conditions;
    but another species of indicator has been applied by Mr. Gooch to
    locomotive engines, which presents several features of superiority for
    such a purpose.</P>

    <P>This indicator has its cylinder placed horizontally; and its piston
    compresses two elliptical springs; a slide valve is substituted for a
    cock, to open or close the communication with the engine. The top of
    the piston rod of this indicator is connected to the short arm of a
    smaller lever, to the longer arm of which the pencil is attached, and
    the pencil has thus a considerably larger amount of motion than the
    piston; but it moves in the arc of a circle instead of in a straight
    line. The pencil marks on a web of paper, which is unwound from one
    drum and wound on to another, so that a succession of diagrams are
    taken without the necessity of any intermediate manipulation.</P>

    <P>241. <EM>Q.</EM>--These diagrams being taken with a pencil moving in
    an arc, will be of a distorted form?</P>

    <P><EM>A.</EM>--They will not be of the usual form, but they may be
    easily translated into the usual form. It is undoubtedly preferable
    that the indicator should act immediately in the production of the
    final form of diagram.</P>

    <H4 CLASS="subhead"><A NAME="f04"></A>DYNAMOMETER, GAUGES, AND
    CATARACT.</H4>

    <P>242. <EM>Q.</EM>--What other gauges or instruments are there for
    telling the state, or regulating the power of an engine?</P>

    <P><EM>A.</EM>--There is the counter for telling the number of strokes
    the engine makes, and the dynamometer for ascertaining the tractive
    power of steam vessels or locomotives; then there are the gauge cocks,
    and glass tubes, or floats, for telling the height of water in the
    boiler; and in pumping engines there is the cataract for regulating the
    speed of the engine.</P>

    <P>243. <EM>Q.</EM>--Will you describe the mechanism of the
    counter?</P>

    <P><EM>A.</EM>--The counter consists of a train of wheel work, so
    contrived that by every stroke of the engine an index hand is moved
    forward a certain space, whereby the number of strokes made by the
    engine in any given time is accurately recorded. In most cases the
    motion is communicated by means of a detent,--attached to some
    reciprocating part of the engine,--to a ratchet wheel which gives
    motion to the other wheels in its slow revolution; but it is preferable
    to derive the motion from some revolving part of the engine by means of
    an endless screw, as where the ratchet is used the detent will
    sometimes fail to carry it round the proper distance. In the counter
    contrived by Mr. Adie, an endless screw works into the rim of two small
    wheels situated on the same axis, but one wheel having a tooth more
    than the other, whereby a differential motion is obtained; and the
    difference in the velocity of the two wheels, or their motion upon one
    another, expresses the number of strokes performed. The endless screw
    is attached to some revolving part of the engine, whereby a rotatory
    motion is imparted to it; and the wheels into which the screws work
    hang down from it like a pendulum, and are kept stationary by the
    action of gravity.</P>

    <P>244. <EM>Q.</EM>--What is the nature of the dynamometer?</P>

    <P><EM>A.</EM>--The dynamometer employed for ascertaining the traction
    upon railways consists of two flat springs joined together at the ends
    by links, and the amount of separation of the springs at the centre
    indicates, by means of a suitable hand and dial, the force of traction.
    A cylinder of oil, with a small hole through its piston, is sometimes
    added to this instrument to prevent sudden fluctuations. In screw
    vessels the forward thrust of the screw is measured by a dynamometer
    constructed on the principle of a weighing machine, in which a small
    spring pressure at the index will balance a very great pressure where
    the thrust is employed; and in each case the variations of pressure are
    recorded by a pencil on a sheet of paper, carried forward by suitable
    mechanism, whereby the mean thrust is easily ascertained. The tractive
    force of paddle wheel steamers is ascertained by a dynamometer fixed on
    shore, to which the floating vessel is attached by a rope. Sometimes
    the power of an engine is ascertained by a friction break dynamometer
    applied to the shaft.</P>

    <P>345. <EM>Q.</EM>--What will determine the amount of thrust shown by
    the dynamometer?</P>

    <P><EM>A.</EM>--In locomotives and in paddle steamers it will be
    determined by the force turning the wheels, and by the smallness of the
    diameter of the wheels; for with small wheels the thrust will be
    greater than with large wheels. In screw vessels the thrust will be
    determined by the force turning round the screw, and by the smallness
    of the screw&#39;s pitch; for with any given force of torsion a fine
    pitch of screw will give a greater thrust than a coarse pitch of screw,
    just as is the case when a screw works in a solid nut.</P>

    <P>246. <EM>Q.</EM>--Will you explain the use of the glass gauges
    affixed to the boiler?</P>

    <P><EM>A.</EM>--The glass gauges are tubes affixed to the fronts of
    boilers, by the aid of which the height of the water within the boilers
    is readily ascertainable, for the water will stand at the same height
    in the tube as in the boiler, with which there is a communication
    maintained both at the top and bottom of the tube by suitable
    stopcocks. The cocks connecting the glass tube with the boiler should
    always be so constructed that the tube may be blown through with the
    steam, to clear it of any internal concretion that may impair its
    transparency; and the construction of the sockets in which the tube is
    inserted should be such, that, even when there is steam in the boiler,
    a broken tube may be replaced with facility.</P>

    <P>247. <EM>Q.</EM>--What then are the gauge cocks?</P>

    <P><EM>A.</EM>--The gauge cocks are cocks penetrating the boiler at
    different heights, and which, when opened, tell whether it is water or
    steam that exists at the level at which they are respectively inserted.
    It is unsafe to trust to the glass gauges altogether as a means of
    ascertaining the water level, as sometimes they become choked, and it
    is necessary, therefore, to have gauge cocks in addition; but if the
    boiler be short of steam, and a partial vacuum be produced within it,
    the glass gauges become of essential service, as the gauge cocks will
    not operate in such a case, for though opened, instead of steam and
    water escaping from them, the air will rush into the boiler. It is
    expedient to carry a pipe from the lower end of the glass tube downward
    into the water of the boiler, and a pipe from the upper end upward into
    the steam in the boiler, so as to prevent the water from boiling down
    through the tube, as it might otherwise do, and prevent the level of
    the water from being ascertainable. The average level of water in the
    boiler should be above the centre of the tube; and the lowest of the
    gauge cocks should always run water, and the highest should always blow
    steam.</P>

    <P>248. <EM>Q.</EM>--Is not a float sometimes employed to indicate the
    level of the water in the boiler?</P>

    <P><EM>A.</EM>--A float for telling the height of water in the boiler
    is employed only in the case of land boilers, and its action is like
    that of a buoy floating on the surface, which, by means of a light rod
    passing vertically through the boiler, shows at what height the water
    stands. The float is usually formed of stone or iron, and is so
    counterbalanced as to make its operation the same as if it were a buoy
    of timber; and it is generally put in connection with the feed valve,
    so that in proportion as the float rises, the supply of feed water is
    diminished. The feed water in land boilers is admitted from a small
    open cistern, situated at the top of an upright or stand pipe set upon
    the boiler, and in which there is a column of water sufficiently high
    to balance the pressure of the steam.</P>

    <P>249. <EM>Q.</EM>--What is the cataract which is employed to regulate
    the speed of pumping engines?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig38.png" WIDTH="658" HEIGHT="550" ALT=
    "Fig. 38"></P>

    <P><EM>A.</EM>--The cataract consists of a small pump-plunger
    <EM>b</EM> and barrel, set in a cistern of water, the barrel being
    furnished on the one side with a valve, <EM>c</EM>, opening inwards,
    through which the water obtains admission to the pump chamber from the
    cistern, and on the other by a plug, <EM>d</EM>, through which, if the
    plunger be forced down, the water must pass out of the pump chamber.
    The engine in the upward stroke of the piston, which is accomplished by
    the preponderance of weight at the pump end of the beam, raises up the
    plunger of the cataract by means of a small rod,--the water entering
    readily through the valve already referred to; and when the engine
    reaches the top of the stroke, it liberates the rod by which the
    plunger has been drawn up, and the plunger then descends by gravity,
    forcing out the water through the cock, the orifice of which has
    previously been adjusted, and the plunger in its descent opens the
    injection valve, which causes the engine to make a stroke.</P>

    <P>250. <EM>Q.</EM>--Suppose the cock of the cataract be shut?</P>

    <P><EM>A.</EM>--If the cock of the cataract be shut, it is clear that
    the plunger cannot descend at all, and as in that case the injection
    valve cannot be opened, the engine must stand still; but if the cock be
    slightly opened, the plunger will descend slowly, the injection valve
    will slowly open, and the engine will make a gradual stroke as it
    obtains the water necessary for condensation. The extent to which the
    cock is open, therefore, will regulate the speed with which the engine
    works; so that, by the use of the cataract, the speed of the engine may
    be varied to suit the variations in the quantity of water requiring to
    be lifted from the mine. In some cases an air cylinder, and in other
    cases an oil cylinder, is employed instead of the apparatus just
    described; but the principle on which the whole of these contrivances
    operate is identical, and the only difference is in the detail.</P>

    <P>251. <EM>Q.</EM>--You have now shown that the performance of an
    engine is determinable by the indicator; but how do you determine the
    power of the boiler?</P>

    <P><EM>A.</EM>--By the quantity of water it evaporates. There is,
    however, no very convenient instrument for determining the quantity of
    water supplied to a boiler, and the consequence is that this element is
    seldom ascertained.</P>

    <H2 CLASS="chapter"><A NAME="ch05"></A>CHAPTER V.</H2>

    <H3>PROPORTIONS OF BOILERS.</H3>

    <H4 CLASS="subhead"><A NAME="g01"></A>HEATING AND FIRE GRATE
    SURFACE.</H4>

    <P>252. <EM>Q.</EM>--What are the considerations which must chiefly be
    attended to in settling the proportions of boilers?</P>

    <P><EM>A.</EM>--In the first place there must be sufficient grate
    surface to enable the quantity of coal requisite for the production of
    the steam to be conveniently burnt, taking into account the intensity
    of the draught; and in the next place there must be a sufficient flue
    surface readily to absorb the heat thus produced, so that there may be
    no needless waste of heat by the chimney. The flues, moreover, must
    have such an area, and the chimney must be of such dimensions, as will
    enable a suitable draught through the fire to be maintained; and
    finally the boiler must be made capable of containing such supplies of
    water and steam as will obviate inconvenient fluctuations in the water
    level, and abate the risk of water being carried over into the engine
    with the steam. With all these conditions the boiler must be as light
    and compact as possible, and must be so contrived as to be capable of
    being cleaned and repaired with facility.</P>

    <P>253. <EM>Q.</EM>--Supposing, then, that you had to proportion a
    boiler, which should be capable of supplying steam sufficient to propel
    a steam vessel or railway train at a given speed, or to perform any
    other given work, how would you proceed?</P>

    <P><EM>A.</EM>--I would first ascertain the resistance which had to be
    overcome, and the velocity with which it was necessary to overcome it.
    I should then be in a position to know what pressure and volume of
    steam were required to overcome the resistance at the prescribed rate
    of motion; and, finally, I should allow a sufficient heating and fire
    grate surface in the boiler according to the kind of boiler it was, to
    furnish the requisite quantity of steam, or, in other words, to
    evaporate the requisite quantity of water.</P>

    <P>254. <EM>Q.</EM>--will you state the amount of heating surface and
    grate surface necessary to evaporate a given quantity of water?</P>

    <P><EM>A.</EM>--The number of square feet of heating or flue surface,
    required to evaporate a cubic foot of water per hour, is about 70
    square feet in Cornish boilers, 8 to 11 square feet in land and marine
    boilers, and 5 or 6 square feet in locomotive boilers. The number of
    square feet of heating surface per square foot of fire grate, is from
    13 to 15 square feet in wagon boilers; about 40 square feet in Cornish
    boilers; and from 50 to 90 square feet in locomotive boilers. About 80
    square feet in locomotives is a very good proportion.</P>

    <P>255. <EM>Q.</EM>--What is the heating surface of boilers per horse
    power?</P>

    <P><EM>A.</EM>--About 9 square feet of flue and furnace surface per
    horse power is the usual proportion in wagon boilers, reckoning the
    total surface as effective surface, if the boilers be of a considerable
    size; but in the case of small boilers the proportion is larger. The
    total heating surface of a two horse power wagon boiler is, according
    to Boulton and Watt&#39;s proportions, 30 square feet, or 15 ft. per
    horse power; whereas, in the case of a 45 horse power boiler the total
    heating surface is 438 square feet, or 9.6 ft. per horse power. In
    marine boilers nearly the same proportions obtain. The original boilers
    of the Great Western steamer, by Messrs. Maudslay, were proportioned
    with about 10 square feet of flue and furnace surface per horse power,
    reckoning the total amount as effective; but in the boilers of the
    Retribution, by the same makers, but of larger size, a somewhat smaller
    proportion of heating surface was adopted. Boulton and Watt have found
    that in their marine flue boilers, 9 square feet of flue and furnace
    surface are requisite to boil off a cubic foot of water per hour, which
    is the proportion of heating surface that is allowed in their land
    boilers per horse power; but inasmuch as in most modern engines, and
    especially in marine engines, the nominal considerably exceeds the
    actual power, they allow 11 or 12 square feet of heating surface per
    nominal horse power in their marine boilers, and they reckon as
    effective heating surface the tops of the flues, and the whole of the
    sides of the flues, but hot the bottoms. For their land engines they
    still retain Mr. Watt&#39;s standard of power, which makes the actual
    and the nominal power identical; and an actual horse power is the
    equivalent of a cubic foot of water raised into steam every hour.</P>

    <P>256. <EM>Q.</EM>--What is the proper proportion of fire grate per
    horse power?</P>

    <P><EM>A.</EM>--Boulton and Watt allow 0.64 of a square foot area of
    grate bars per nominal horse power in their marine boilers, and a good
    effect arises from this proportion; but sometimes so large an area of
    fire grate cannot be conveniently got, and the proportion of half a
    square foot per horse power, which is the proportion adopted in the
    original boiler of the Great Western, seems to answer very well in
    engines working with a moderate pressure, and with some expansion; and
    this proportion is now very widely adopted. With this allowance, there
    will be 22 to 24 square feet of heating surface per square foot of fire
    grate; and if the consumption of fuel be taken at 6 lbs. per nominal
    horse power per hour, there will be about 12 lbs. of coal consumed per
    hour on each square foot of grate. The furnaces should not be more than
    6 ft. long, as, if much longer than this, it will be impossible to work
    them properly for any considerable length of time, as they will become
    choked with clinker at the back ends.</P>

    <P>257. <EM>Q.</EM>--What quantity of fuel is usually consumed per hour
    on each square foot of fire grate?</P>

    <P><EM>A.</EM>--The quantity of fuel burned on each square foot of fire
    grate per hour, varies very much in different boilers; in wagon boilers
    it is from 10 to 13 lbs.; in Cornish boilers from 3-1/2 to 4 lbs.; and
    in locomotive boilers from 80 to 150 lbs.; but about 1 cwt. per hour is
    a good proportion in locomotives, as has been already explained.</P>

    <H4 CLASS="subhead"><A NAME="g02"></A>CALORIMETER AND VENT.</H4>

    <P>258. <EM>Q.</EM>--In what manner are the proper sectional area and
    the proper capacity of the flue of a boiler determined?</P>

    <P><EM>A.</EM>--The proper collective area for the escape of the smoke
    and flame over the furnace bridges in marine boilers is 19 square
    inches per nominal horse power, according to Boulton and Watt&#39;s
    practice, and for the sectional area of the flue they allow 18 square
    inches per horse power. The sectional area of the flue in square inches
    is what is termed the <EM>calorimeter</EM> of the boiler, and the
    calorimeter divided by the length of the flue in feet is what is termed
    the <EM>vent</EM>. In marine flue boilers of good construction the vent
    varies between the limits of 20 and 25, according to the size of the
    boiler and other circumstances--the largest boilers having generally
    the largest vents; and the calorimeter divided by the vent will give
    the length of the flue in feet. The flues of all flue boilers diminish
    in their calorimeter as they approach the chimney, as the smoke
    contracts in its volume in proportion as it parts with its heat.</P>

    <P>259. <EM>Q.</EM>--Is the method of determining the dimensions of a
    boiler flue, by a reference to its vent and calorimeter, the method
    generally pursued?</P>

    <P><EM>A.</EM>--It is Boulton and Watt&#39;s method; but some very
    satisfactory boilers have been made by allowing a proportion of 0.6 of
    a square foot of fire grate per nominal horse power, and making the
    sectional area of the flue at the largest part 1/7th of the area of
    fire grate, and at the smallest part, where it enters the chimney,
    1/11th of the area of the fire grate. These proportions are retained
    whether the boiler is flue or tubular, and from 14 to 16 square feet of
    tube surface is allowed per nominal horse power.</P>

    <P>260. <EM>Q.</EM>--Are the proportions of vent and calorimeter, taken
    by Boulton and Watt for marine flue boilers, applicable also to wagon
    and tubular boilers?</P>

    <P><EM>A.</EM>--No. In wagon and tubular boilers very different
    proportions prevail, yet the proportions of every kind of boiler are
    determinable on the same general principle. In wagon boilers the
    proportion of the perimeter of the flue which is effective as heating
    surface, is to the total perimeter as 1 to 3, or, in some cases as 1 to
    2.5; and with any given area of flue, therefore, the length of the flue
    must be from 3 to 2.5 times greater than would be necessary if the
    total surface were effective, else the requisite quantity of heating
    surface will not be obtained. If, then, the vent be the calorimeter,
    divided by the length, and the length be made 3 or 2.5 times greater,
    the vent must become 3 or 2.5 times less; and in wagon boilers
    accordingly, the vent varies from 8 to 11 instead of from 21 to 25, as
    in the case of marine flue boilers. In tubular marine boilers the
    calorimeter is usually made only about half the amount allowed by
    Boulton and Watt for marine flue boilers, or, in other words, the
    collective sectional area of the tubes, for the transmission of the
    smoke, is from 8 to 9 square inches per nominal horse power. It is
    better, however, to make the sectional area larger than this, and to
    work the boiler with the damper sufficiently closed to prevent the
    smoke and flame from rushing exclusively through a few of the
    tubes.</P>

    <P>261. <EM>Q.</EM>--What are the ordinary dimensions of the flue in
    wagon boilers?</P>

    <P><EM>A.</EM>--In Boulton and Watt&#39;s 45 horse wagon boiler the
    area of flue is 18 square inches per horse power, but the area per
    horse power increases very rapidly as the size of the boiler becomes
    less, and amounts to about 80 square inches per horse power in a boiler
    of 2 horse power. Some such increase is obviously inevitable, if a
    similar form of flue be retained in the larger and smaller powers, and
    at the same time the elongation of the flue in the same proportion as
    the increase of any other dimension is prevented; but in the smaller
    class of wagon boilers the consideration of facility of cleaning the
    flues is also operative in inducing a large proportion of sectional
    area. Boulton and Watt&#39;s 2 horse power wagon boiler has 30 square
    feet of surface, and the flue is 18 inches high above the level of the
    boiler bottom, by 9 inches wide; while their 12 horse wagon boiler has
    118 square feet of heating surface, and the dimensions of the flue
    similarly measured are 36 inches by 13 inches. The width of the smaller
    flue, if similarly proportioned to the larger one, would be 6-1/2
    inches, instead of 9 inches, and, by assuming this dimension, we should
    have the same proportion of sectional area per square foot of heating
    surface in both boilers. The length of flue in the 2 horse boiler is
    19.5 ft., and in the 12 horse boiler 39 ft., so that the length and
    height of the flue are increased in the same proportion.</P>

    <P>262. <EM>Q.</EM>--Will you give an example of the proportions of a
    flue, in the case of a marine boiler?</P>

    <P><EM>A.</EM>--The Nile steamer, with engines of 110 horse power by
    Boulton and Watt, is supplied with steam by two boilers, which are,
    therefore, of 55 horses power each. The height of the flue winding
    within the boiler is 60 inches, and its mean width 16-1/2 inches,
    making a sectional area or calorimeter of 990 square inches, or 18
    square inches per horse power of the boiler. The length of the flue is
    39 ft., making the vent 25, which is the vent proper for large boilers.
    In the Dee and Solway steamers, by Scott and Sinclair, the calorimeter
    is only 9.72 square inches per horse power; in the Eagle, by Caird,
    11.9; in the Thames and Medway, by Maudslay, 11.34, and in a great
    number of other cases it does not rise above 12 square inches per horse
    power; but the engines of most of these vessels are intended to operate
    to a certain extent expansively, and the boilers are less powerful in
    evaporating efficacy on that account.</P>

    <P>263. <EM>Q.</EM>--Then the chief difference in the proportions
    established by Boulton and Watt, and those followed by the other
    manufacturers you have mentioned is, that Boulton and Watt set a more
    powerful boiler to do the same work?</P>

    <P><EM>A.</EM>--That is the main difference. The proportion which one
    part of the boiler bears to another part is very similar in the cases
    cited, but the proportion of boiler relatively to the size of the
    engine varies very materially. Thus the calorimeter <EM>of each
    boiler</EM> of the Dee and Solway is 1296 square inches; of the Eagle,
    1548 square inches; and of the Thames and Medway, 1134 square inches;
    and the length of flue is 57, 60, and 52 ft. in the boilers
    respectively, which makes the respective vents 22-1/2, 25, and 21.
    Taking then the boiler of the Eagle for comparison with the boiler of
    the Nile, as it has the same vent, it will be seen that the proportions
    of the two are almost identical, for 990 is to 1548 as 39 is to 60,
    nearly; but Messrs. Boulton and Watt would not have set a boiler like
    that of the Eagle to do so much work.</P>

    <P>264. <EM>Q.</EM>--Then the evaporating power of the boiler varies as
    the sectional area of the flue?</P>

    <P><EM>A.</EM>--The evaporating power varies as the square root of the
    area of the flue, if the length of the flue remain the same; but it
    varies as the area simply, if the length of the flue be increased in
    the same proportion as its other dimensions. The evaporating power of a
    boiler is referable to the amount of its heating surface, and the
    amount of heating surface in any flue or tube is proportional to the
    product of the length of the tube and the square root of its sectional
    area, multiplied by a certain quantity that is constant for each
    particular form. But in similar tubes the length is proportional to the
    square root of the sectional area; therefore, in similar tubes, the
    amount of heating surface is proportional to the sectional area. On
    this area also depends the quantity of hot air passing through the
    flue, supposing the intensity of the draught to remain unaffected, and
    the quantity of hot air or smoke passing through the flue should vary
    in the same ratio as the quantity of surface.</P>

    <P>265. <EM>Q.</EM>--A boiler, therefore, to exert four times the
    power, should have four times the extent of heating surface, and four
    times the sectional area of flue for the transmission of the smoke?</P>

    <P><EM>A.</EM>--Yes; and if the same form of flue is to be retained, it
    should be of twice the diameter and twice the length; or twice the
    height and width if rectangular, and twice the length. As then the
    diameter or square root of the area increases in the same ratio as the
    length, the square root of the area divided by the length ought to be a
    constant quantity in each type of boiler, in order that the same
    proportions of flue may be retained; and in wagon boilers without an
    internal flue, the height in inches of the flue encircling the boiler
    divided by the length of the flue in feet will be 1 very nearly.
    Instead of the square root of the area, the effective perimeter, or
    outline of that part of the cross section of the flue which is
    effective in generating steam, may be taken; and the effective
    perimeter divided by the length ought to be a constant quantity in
    similar forms of flues and with the same velocity of draught, whatever
    the size of the flue may be.</P>

    <P>266. <EM>Q.</EM>--Will this proportion alter if the form of the flue
    be changed?</P>

    <P><EM>A.</EM>--It is clear, that with any given area of flue, to
    increase the perimeter by adopting a different shape is tantamount to a
    diminution of the length of the flue; and, if the perimeter be
    diminished, the length of the flue must at the same time be increased,
    else it will be impossible to obtain the necessary amount of heating
    surface. In Boulton and Watt&#39;s wagon boilers, the sectional area of
    the flue in square inches per square foot of heating surface is 5.4 in
    the two horse boiler; in the three horse it is 4.74; in the four horse,
    4.35; six horse, 3.75; eight horse, 4.33; ten horse, 3.96; twelve
    horse, 3.63; eighteen horse, 3.17; thirty horse, 2.52; and in the
    forty-five horse boiler, 2.05 square inches. Taking the amount of
    heating surface in the 45 horse boiler at 9 square feet per horse
    power, we obtain 18 square inches of sectional area of flue per horse
    power, which is also Boulton and Watt&#39;s proportion of sectional
    area for marine boilers with internal flues.</P>

    <P>267. <EM>Q.</EM>--If to increase the perimeter of a flue is
    virtually to diminish the length, then a tubular boiler where the
    perimeter is in effect greatly extended ought to have but a short
    length of tube?</P>

    <P><EM>A.</EM>--The flue of the Nile steamer if reduced to the
    cylindrical form would be 35-1/2 inches in diameter to have the same
    area; but it would then require to be made 47-3/4 feet long, to have
    the same amount of heating surface, excluding the bottom as
    non-effective. Supposing that with these proportions the heat is
    sufficiently extracted from the smoke, then every tube of a tubular
    boiler in which the same draught existed ought to have very nearly the
    same proportions.</P>

    <P>268. <EM>Q.</EM>--But what are the best proportions of the parts of
    tubular boilers relatively with one another?</P>

    <P><EM>A.</EM>--The proper relative proportions of the parts of tubular
    boilers may easily be ascertained by a reference to the settled
    proportions of flue boilers; for the same general principles are
    operative in both cases. In the Nile steamer each boiler of 55 horse
    power has about 497 square feet of flue surface or 9 square feet per
    horse power, reckoning the total surface as effective. The area of the
    flue, which is rectangular is 990 square inches, therefore the area is
    equal to that of a tube 35-1/2 inches in diameter; and such a tube, to
    have a heating surface of 497 square feet, must be 53.4 feet or 640.8
    inches in length. The length, therefore, of the tube, will be about 18
    times its diameter, and with the same velocity of draught these
    proportions must obtain, whatever the absolute dimensions of the tube
    may be. With a calorimeter, therefore, of 18 square inches per horse
    power, the length of a tube 3 inches diameter must not exceed 4 feet 6
    inches, since the heat will be sufficiently extracted from the smoke in
    this length, if the smoke only travels at the velocity due to a
    calorimeter of 18 square inches per horse power.</P>

    <P>269. <EM>Q.</EM>--Is this, then, the maximum length of flue which
    can be used in tubular boilers with advantage?</P>

    <P><EM>A.</EM>--By no means. The tubes of tubular boilers are almost
    always more than 4 feet 6 inches long, but then the calorimeter is
    almost always less than 18 square inches per horse power--generally
    about two thirds of this. Indeed, tubular boilers with a large
    calorimeter are not found to be so satisfactory as where the
    calorimeter is small, partly from the propensity of the smoke in such
    cases to pass through a few of the tubes instead of the whole of them,
    and partly from the deposit of soot which takes place when the draught
    is sluggish. It is a very confusing practice, however, to speak of
    nominal horse power in connection with boilers, since that is a
    quantity quite indeterminate.</P>

    <H4 CLASS="subhead"><A NAME="g03"></A>EVAPORATIVE POWER OF
    BOILERS.</H4>

    <P>270. <EM>Q.</EM>--The main thing after all in boilers is their
    evaporative powers?</P>

    <P><EM>A.</EM>--The proportions of tubular boilers, as of all boilers,
    should obviously have reference to the evaporation required, whereas
    the demand upon the boiler for steam is very often reckoned contingent
    upon the nominal horse power of the engine; and as the nominal power of
    an engine is a conventional quantity by no means in uniform proportion
    to the actual quantity of steam consumed, perplexing complications as
    to the proper proportions of boilers have in consequence sprung up, to
    which most of the failures in that department of engineering may be
    imputed. It is highly expedient, therefore, in planning boilers for any
    particular engine, to consider exclusively the actual power required to
    be produced, and to apportion the capabilities of the boiler
    accordingly.</P>

    <P>271. <EM>Q.</EM>--In other words you would recommend the inquiry to
    be restricted to the mode of evaporating a given number of cubic feet
    of water in the hour, instead of embracing the problem how an engine of
    a given nominal power was to be supplied with steam?</P>

    <P><EM>A.</EM>--I would first, as I have already stated, consider the
    actual power required to be produced, and then fix the amount of
    expansion to be adopted. If the engine had to work up to three times
    its nominal power, as is now common in marine engines, I should either
    increase correspondingly the quantity of evaporating surface in the
    boiler, or adopt such an amount of expansion as would increase
    threefold the efficacy of the steam, or combine in a modified manner
    both of these arrangements. Reckoning the evaporation of a cubic foot
    of water in the hour as equivalent to an actual horse power, and
    allowing a square yard or 9 square feet as the proper proportion of
    flue surface to evaporate a cubic foot of water in the hour, it is
    clear that I must either give 27 square feet of heating surface in the
    boiler to have a trebled power without expansion, or I must cut off the
    steam at one seventh of the stroke to obtain a three-fold power without
    increasing the quantity of heating surface. By cutting off the steam,
    however, at one third of the stroke, a heating surface of 13-1/2 square
    feet will give a threefold power, and it will usually be the most
    judicious course to carry the expansion as far as possible, and then to
    add the proportion of heating surface necessary to make good the
    deficiency still found to exist.</P>

    <P>272. <EM>Q.</EM>--But is it certain that a cubic foot of water
    evaporated in the hour is equivalent to an actual horse power?</P>

    <P><EM>A.</EM>--An actual horse power as fixed by Watt is 33,000 lbs.
    raised one foot high in the minute; and in Watt&#39;s 40 horse power
    engine, with a 31-1/2 inch cylinder, 7 feet stroke, and making 17-1/2
    strokes a minute, the effective pressure is 6.92 lbs. on the square
    inch clear of all deductions. Now, as a horse power is 33,000 lbs.
    raised one foot high, and as there are 6.92 lbs, on the square inch, it
    is clear that 33,000 divided by 6.92, on 4768 square inches with 6.92
    lbs. on each if lifted 1 foot or 12 inches high, will also be equal to
    a horse power. But 4768 square inches multiplied by 12 inches in height
    is 57224.4 cubic inches, or 33.1 cubic feet, and this is the quantity
    of steam which must be expended per minute to produce an actual horse
    power.</P>

    <P>273. <EM>Q.</EM>--But are 33 cubic feet of steam expended per minute
    equivalent to a cubic foot of water expended in the hour?</P>

    <P><EM>A.</EM>.--Not precisely, but nearly so. A cubic foot of water
    produces 1669 cubic feet of steam of the atmospheric density of 15 lbs.
    per square inch, whereas a consumption of 33 cubic feet of steam in the
    minute is 1980 cubic feet in the hour. In Watt&#39;s engines about one
    tenth was reckoned as loss in filling the waste spaces at the top and
    bottom of the cylinder, making 1872 cubic feet as the quantity consumed
    per hour without this waste; and in modern engines the waste at the
    ends of the cylinder is inconsiderable.</P>

    <P>274. <EM>Q.</EM>--What power was generated by a cubic foot of water
    in the case of the Albion Mill engines when working without
    expansion?</P>

    <P><EM>A.</EM>--In the Albion Mill engines when working without
    expansion, it was found that 1 lb. of water in the shape of steam
    raised 28,489 lbs. 1 foot high. A cubic foot of water, therefore, or
    62-1/2 lbs., if consumed in the hour, would raise 1780562.5 lbs. one
    foot high in the hour, or would raise 29,676 lbs. one foot high in a
    minute; and if to this we add one tenth for waste at the ends of the
    cylinder, a waste which hardly exists in modern engines, we have 32,643
    lbs. raised one foot high in the minute, or a horse power very nearly.
    In some cases the approximation appears still nearer. Thus, in a 40
    horse engine working without expansion, Watt found that .674 feet of
    water were evaporated from the boiler per minute, which is just a cubic
    foot per horse power per hour; but it is not certain in this case that
    the nominal and actual power were precisely identical. It will be quite
    safe, however, to reckon an actual horse power as producible by the
    evaporation of a cubic foot of water in the hour in the case of engines
    working without expansion; and for boiling off this quantity in flue or
    wagon boilers, about 8 lbs. of coal will be required and 9 square feet
    of flue surface.</P>

    <H4 CLASS="subhead"><A NAME="g04"></A>MODERN MARINE AND LOCOMOTIVE
    BOILERS.</H4>

    <P>275. <EM>Q.</EM>--These proportions appear chiefly to refer to old
    boilers. I wish you to state what are the proportions of modern flue
    and tubular marine boilers.</P>

    <P><EM>A.</EM>--In modern marine boilers the area of fire grate is less
    than in Mr. Watt&#39;s original boilers, where it was one square foot
    to nine square feet of heating surface. The heat in the furnace is
    consequently more intense, and a somewhat less amount of surface
    suffices to evaporate a cubic foot of water. In Boulton and Watt&#39;s
    modern flue boilers they allow for the evaporation of a cubic foot of
    water 8 square feet of heating surface, 70 square inches of fire grate,
    13 square inches sectional area of flues, 6 square inches sectional
    area of chimney, 14 square inches area over furnace bridges, ratio of
    area of flue to area of fire grate 1 to 5.4. To evaporate a cubic foot
    of water per hour in tubular boilers, the proportions are--heating
    surface 9 square feet, fire grate 70 square inches, sectional area of
    tubes 10 square inches, sectional area of back uptake 12 square inches,
    sectional area of front uptake 10 square inches, sectional area of
    chimney 7 square inches, ratio of diameter of tube to length of tube
    1/28th to 1/30th, cubical content of boiler exclusive of steam chest
    6.5 cubic feet, cubical content of steam chest 1.5 cubic feet.</P>

    <P>276. <EM>Q.</EM>--These proportions do not apply to locomotive
    boilers?</P>

    <P><EM>A.</EM>--Not at all. In locomotive boilers the draught is
    maintained by the projection of the waste steam which escapes from the
    cylinders up the chimney, and the draught is much more powerful and the
    combustion much more rapid than in cases in which the combustion is
    maintained by the natural draught of a chimney, except indeed the
    chimney be of very unusual temperature and height. The proportions
    proper for locomotive boilers will be seen by the dimensions of a few
    locomotives of approved construction, which have been found to give
    satisfactory results in practice, and which are recorded in the
    following Table:</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "Locomotives">
      <TR>
        <TD>
          <P>&nbsp;</P>
        </TD>

        <TD COLSPAN="4">
          <P>NAME OF ENGINE</P>
        </TD>
      </TR>

      <TR>
        <TD>
        </TD>

        <TD>
          <P>Great Britain.</P>
        </TD>

        <TD>
          <P>Pallas.</P>
        </TD>

        <TD>
          <P>Snake.</P>
        </TD>

        <TD>
          <P>Sphinx.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Diameter of cylinder</P>
        </TD>

        <TD>
          <P>18 in.</P>
        </TD>

        <TD>
          <P>15 in.</P>
        </TD>

        <TD>
          <P>14-1/4 in.</P>
        </TD>

        <TD>
          <P>18 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Length of stroke</P>
        </TD>

        <TD>
          <P>24 in.</P>
        </TD>

        <TD>
          <P>20 in.</P>
        </TD>

        <TD>
          <P>21 in.</P>
        </TD>

        <TD>
          <P>24 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Diameter of driving wheel</P>
        </TD>

        <TD>
          <P>8 ft.</P>
        </TD>

        <TD>
          <P>6 ft.</P>
        </TD>

        <TD>
          <P>6-1/2 ft.</P>
        </TD>

        <TD>
          <P>5 ft.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Inside diameter of fire box</P>
        </TD>

        <TD>
          <P>53 in.</P>
        </TD>

        <TD>
          <P>55 in.</P>
        </TD>

        <TD>
          <P>41-1/3 in.</P>
        </TD>

        <TD>
          <P>44 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Inside width of fire box</P>
        </TD>

        <TD>
          <P>63 in.</P>
        </TD>

        <TD>
          <P>42 in.</P>
        </TD>

        <TD>
          <P>43-1/4 in.</P>
        </TD>

        <TD>
          <P>39-1/2 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Height of fire box above bars</P>
        </TD>

        <TD>
          <P>63 in.</P>
        </TD>

        <TD>
          <P>52 in.</P>
        </TD>

        <TD>
          <P>48-1/3 in.</P>
        </TD>

        <TD>
          <P>55-1/2 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Number of fire bars</P>
        </TD>

        <TD>
          <P>29</P>
        </TD>

        <TD>
          <P>.....</P>
        </TD>

        <TD>
          <P>32</P>
        </TD>

        <TD>
          <P>16</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Thickness of fire bars</P>
        </TD>

        <TD>
          <P>3/4 in.</P>
        </TD>

        <TD>
          <P>1-3/4 in.</P>
        </TD>

        <TD>
          <P>5/8 in.</P>
        </TD>

        <TD>
          <P>1 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Number of Tubes</P>
        </TD>

        <TD>
          <P>305</P>
        </TD>

        <TD>
          <P>134</P>
        </TD>

        <TD>
          <P>181</P>
        </TD>

        <TD>
          <P>142</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Outside diameter of tubes</P>
        </TD>

        <TD>
          <P>2 in.</P>
        </TD>

        <TD>
          <P>2 in.</P>
        </TD>

        <TD>
          <P>1-7/8 in.</P>
        </TD>

        <TD>
          <P>2-1/8 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Length of tubes</P>
        </TD>

        <TD>
          <P>11 ft 3 in</P>
        </TD>

        <TD>
          <P>10 ft 6 in</P>
        </TD>

        <TD>
          <P>10 ft 3-1/2 in.</P>
        </TD>

        <TD>
          <P>14 ft 3-1/4 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Space between tubes</P>
        </TD>

        <TD>
          <P>1/2 in.</P>
        </TD>

        <TD>
          <P>3/4 in.</P>
        </TD>

        <TD>
          <P>1/2 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Inside diameter of ferules</P>
        </TD>

        <TD>
          <P>1-9/16 in.</P>
        </TD>

        <TD>
          <P>1-1/2 in.</P>
        </TD>

        <TD>
          <P>1-5/16 in.</P>
        </TD>

        <TD>
          <P>1-5/8 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Diameter of chimney</P>
        </TD>

        <TD>
          <P>17 in.</P>
        </TD>

        <TD>
          <P>15 in.</P>
        </TD>

        <TD>
          <P>13 in.</P>
        </TD>

        <TD>
          <P>15-1/2 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Diameter of blast orifice</P>
        </TD>

        <TD>
          <P>5-1/2 in.</P>
        </TD>

        <TD>
          <P>4-5/8 in.</P>
        </TD>

        <TD>
          <P>4-1/2 in.</P>
        </TD>

        <TD>
          <P>4-3/4 in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area of grate</P>
        </TD>

        <TD>
          <P>21 sq. ft.</P>
        </TD>

        <TD>
          <P>16.04 sq. ft.</P>
        </TD>

        <TD>
          <P>12.4 sq. ft.</P>
        </TD>

        <TD>
          <P>10.56 sq. ft</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area of air space of grate</P>
        </TD>

        <TD>
          <P>11.4 sq. ft.</P>
        </TD>

        <TD>
          <P>4.08 sq. ft.</P>
        </TD>

        <TD>
          <P>5.54 sq. ft.</P>
        </TD>

        <TD>
          <P>5 sq. ft.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area of tubes</P>
        </TD>

        <TD>
          <P>5.46 sq. ft.</P>
        </TD>

        <TD>
          <P>2.40 sq. ft.</P>
        </TD>

        <TD>
          <P>2.8 sq. ft.</P>
        </TD>

        <TD>
          <P>2.92 sq. ft.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area though ferules</P>
        </TD>

        <TD>
          <P>4 sq. ft.</P>
        </TD>

        <TD>
          <P>1.64 sq. ft.</P>
        </TD>

        <TD>
          <P>2 sq. ft.</P>
        </TD>

        <TD>
          <P>2.04 sq. ft.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area of chimney</P>
        </TD>

        <TD>
          <P>1.77 sq. ft.</P>
        </TD>

        <TD>
          <P>1.23 sq. ft.</P>
        </TD>

        <TD>
          <P>921 sq. ft.</P>
        </TD>

        <TD>
          <P>1.31 sq. ft.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Area of blast orifice</P>
        </TD>

        <TD>
          <P>23.76 sq.in.</P>
        </TD>

        <TD>
          <P>16.8 sq.in.</P>
        </TD>

        <TD>
          <P>14.18 sq. in.</P>
        </TD>

        <TD>
          <P>17.7 sq. in.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Heating surface of tubes</P>
        </TD>

        <TD>
          <P>1627 sq.ft.</P>
        </TD>

        <TD>
          <P>668.7 sq. ft.</P>
        </TD>

        <TD>
          <P>823 sq. ft.</P>
        </TD>

        <TD>
          <P>864 sq. ft.</P>
        </TD>
      </TR>
    </TABLE>

    <H4 CLASS="subhead"><A NAME="g05"></A>THE BLAST IN LOCOMOTIVES.</H4>

    <P>277. <EM>Q.</EM>--What is the amount of draught produced in
    locomotive boilers in comparison with that existing in other
    boilers?</P>

    <P><EM>A.</EM>--A good chimney of a land engine will produce a degree
    of exhaustion equal to from 1-1/2 to 2-1/2 inches of water. In
    locomotive boilers the exhaustion is in some cases equal to 12 or 13
    inches of water, but from 3 to 6 inches is a more common
    proportion.</P>

    <P>278. <EM>Q.</EM>--And what force of blast is necessary to produce
    this exhaustion?</P>

    <P><EM>A.</EM>--The amount varies in different engines, depending on
    the sectional area of the tubes and other circumstances. But on the
    average, it may be asserted that such a pressure of blast as will
    support an inch of mercury, will maintain sufficient exhaustion in the
    smoke box to support an inch of water; and this ratio holds whether the
    exhaustion is little or great. To produce an exhaustion in the smoke
    box, therefore, of 6 inches of water, the waste steam would require to
    be of sufficient pressure to support a column of 6 inches of mercury,
    which is equivalent to a pressure of 3 lbs. on the square inch.</P>

    <P>279. <EM>Q.</EM>--How is the force of the blast determined?</P>

    <P><EM>A.</EM>--By the amount of contraction given to the mouth of the
    blast pipe, which is a pipe which conducts the waste steam from the
    cylinders and debouches at the foot of the chimney. If a strong blast
    be required, the mouth of this pipe requires to be correspondingly
    contracted, but such contraction throws a back pressure on the piston,
    and it is desirable to obtain the necessary draught with as little
    contraction of the blast pipe as possible. The blast pipe is generally
    a breeches pipe of which the legs join just before reaching the
    chimney; but it is better to join the two cylinders below, and to let a
    single pipe ascend to within 12 or 18 inches of the foot of the
    chimney. If made with too short a piece of pipe above the joining, the
    steam will be projected against each side of the chimney alternately,
    and the draught will be damaged and the chimney worn. The blast pipe
    should not be regularly tapered, but should be large in the body and
    gathered in at the mouth.</P>

    <P>280. <EM>Q.</EM>--Is a large and high chimney conducive to strength
    of draught in locomotives?</P>

    <P><EM>A.</EM>--It has not been found to be so. A chimney of three or
    four times its own diameter in height appears to answer fully as well
    as a longer one; and it was found that when in an engine with 17 inch
    cylinders a chimney of 15-1/4 inches was substituted for a chimney of
    17-1/2 inches, a superior performance was the result. The chimney of a
    locomotive should have half the area of the tubes at the ferules, which
    is the most contracted part, and the blast orifice should have 1/10th
    of the area of the chimney. The sectional area of the tubes through the
    ferules should be as large as possible. Tubes without ferules it is
    found pass one fourth more air, and tubes with ferules only at the
    smoke box end pass one tenth more air than when there are ferules at
    both ends.</P>

    <P>281. <EM>Q.</EM>--Is the exhaustion produced by the blast as great
    in the fire box as in the smoke box?</P>

    <P><EM>A.</EM>--Experiments have been made to determine this, and in
    few cases has it been found to be more than about half as great as
    ordinary speeds; but much depends on the amount of contraction in the
    tubes. In an experiment made with an engine having 147 tubes of 1-3/4
    inches external diameter, and 13 feet 10 inches long, and with a fire
    grate having an area of 9-1/2 square feet, the exhaustion at all speeds
    was found to be three times greater in the smoke box than in the fire
    box. The exhaustion in the smoke box was generally equivalent to 12
    inches of water, while in the fire box it was equivalent to only 4
    inches of water; showing that 4 inches were required to draw the air
    through the grate and 8 inches through the tubes.</P>

    <P>282. <EM>Q.</EM>--What will be the increase of evaporation in a
    locomotive from a given increase of exhaustion?</P>

    <P><EM>A.</EM>--The rate of evaporation in a locomotive or any other
    boiler will vary as the quantity of air passing through the fire, and
    the quantity of air passing through the fire will vary nearly as the
    square root of the exhaustion. With four times the exhaustion,
    therefore, there will be about twice the evaporation, and experiment
    shows that this theoretical law holds with tolerable accuracy in
    practice.</P>

    <P>283. <EM>Q.</EM>--But the same exhaustion will not be produced by a
    given strength of blast in all engines?</P>

    <P><EM>A.</EM>--No; engines with contracted fire grates and an
    inadequate sectional area of tubes, will require a stronger blast than
    engines of better proportions; but in any given engine the relations
    between the blast exhaustion and evaporation, hold which have been
    already defined.</P>

    <P>284. <EM>Q.</EM>--Is the intensity of the draught under easy
    regulation?</P>

    <P><EM>A.</EM>--The intensity of the draught may easily be diminished
    by partially closing the damper in the chimney, and it may be increased
    by contracting the orifice of the blast. A variable blast pipe, the
    orifice of which may be enlarged or contracted at pleasure, has been
    much used. There are various devices for this purpose, but the best
    appears to be that adopted in Stephenson&#39;s engine, where a conical
    nozzle is moved up or down within the blast pipe, which is made
    somewhat larger in diameter than the base of the cone, but with a ring
    projecting internally, against which the base of the cone abuts when
    the nozzle is pushed up. When the nozzle stands at the top of the pipe
    the whole of the steam has to pass through it, and the intensity of the
    blast is increased by the increased velocity thus given to the steam;
    whereas when the nozzle is moved downward the steam escapes through the
    annular opening left between the nozzle and the pipe, as well as
    through the nozzle itself, and the intensity of the blast is diminished
    by the enlargement of the opening for the escape of the steam thus made
    available.</P>

    <P>285.<EM>Q.</EM>--What is the best diameter for the tubes of
    locomotive boilers?</P>

    <P><EM>A.</EM>--Bury&#39;s locomotive with 14 inch cylinders contains
    92 tubes of 2-1/8th inches external diameter, and 10 feet 6 inches
    long; whereas Stephenson&#39;s locomotive with 15 inch cylinders
    contains 150 tubes of 1-5/8ths external diameter, 13 feet 6 inches
    long. In Stephenson&#39;s boiler, in order that the part of the tubes
    next the chimney may be of any avail for the generation of steam, the
    draught has to be very intense, which in its turn involves a
    considerable expenditure of power; and it is questionable whether the
    increased expenditure of power upon the blast, in Stephenson&#39;s long
    tubed locomotives, is compensated by the increased generation of steam
    consequent upon the extension of the heating surface. When the tubes
    are small in diameter they are apt to become partially choked with
    pieces of coke; but an internal diameter of 1-5/8ths may be employed
    without inconvenience if the draught be of medium intensity.</P>

    <P>286. <EM>Q.</EM>--Will you illustrate the relation between the
    length and diameter of locomotive tubes by a comparison with the
    proportion of flues in flue boilers?</P>

    <P><EM>A.</EM>--In most locomotives the velocity of the draught is such
    that it would require very long tubes to extract the heat from the
    products of combustion, if the heat were transmitted through the metal
    of the tubes with only the same facility as through the iron of
    ordinary flue boilers. The Nile steamer, with engines of 110 nominal
    horses power each, and with two boilers having two independent flues in
    each, of such dimensions as to make each flue equivalent to 55 nominal
    horses power, works at 62 per cent. above the nominal power, so that
    the actual evaporative efficacy of each flue would be equivalent to 89
    actual horses power, supposing the engines to operate without
    expansion; but as the mean pressure in the cylinder is somewhat less
    than the initial pressure, the evaporative efficacy of each flue may be
    reckoned equivalent to 80 actual horses power. With this evaporative
    power there is a calorimeter of 990 square inches, or 12.3 square
    inches per actual horse power; whereas in Stephenson&#39;s locomotive
    with 150 tubes, if the evaporative power be taken at 200 cubic feet of
    water in the hour, which is a large supposition, the engine will be
    equal to 200 actual horses power. If the internal diameter of the tubes
    be taken at thirteen eighths of an inch, the calorimeter per actual
    horse power will only be 1.1136 square inches, or in other words the
    calorimeter in the locomotive boiler will be 11.11 times less than in
    the flue boiler for the same power, so that the draught in the
    locomotive must be 11.11 times stronger, and the ratio of the length of
    the tube to its diameter 11.11 times greater than in the flue boiler,
    supposing the heat to be transmitted with only the same facility. The
    flue of the Nile would require to be 35- 1/2 inches in diameter if made
    of the cylindrical form, and 47-3/4 feet long; the tubes of a
    locomotive if 1-3/8ths inch diameter would only require to be 22.19
    inches long with the same velocity of draught; but as the draught is
    11.11 times faster than in a flue boiler, the tubes ought to be 246.558
    inches, or about 20-1/2 feet long according to this proportion. In
    practice, however, they are one third less than this, which reduces the
    heating surface from 9 to 6 square feet per actual horse power, and
    this length even is found to be inconvenient. It is greatly preferable
    therefore to increase the calorimeter, and diminish the intensity of
    the draught.</P>

    <H4 CLASS="subhead"><A NAME="g06"></A>BOILER CHIMNEYS.</H4>

    <P>287. <EM>Q.</EM>--By what process do you ascertain the dimensions of
    the chimney of a land boiler?</P>

    <P><EM>A.</EM>--By a reference to the volume of air it is necessary in
    a given time to supply to the burning fuel, and to the velocity of
    motion produced by the rarefaction in the chimney; for the area of the
    chimney requires to be such, that with the velocity due to that
    rarefaction, the quantity of air requisite for the combustion of the
    fuel shall pass through the furnace in the specified time. Thus if 200
    cubic feet of air of the atmospheric density are required for the
    combustion of a pound of coal,--though 250 lbs. is nearer the quantity
    generally required,--and 10 lbs. of coal per horse power per hour are
    consumed by an engine, then 2000 cubic feet of air must be supplied to
    the furnace per horse power per hour, and the area of the chimney must
    be such as to deliver this quantity at the increased bulk due to the
    high temperature of the chimney when moving with the velocity the
    rarefaction within the chimney occasions, and which, in small chimneys,
    is usually such as to support a column of half an inch of water. The
    velocity with which a denser fluid flows into a rarer one is equal to
    the velocity a heavy body acquires in falling through a height equal to
    the difference of altitude of two columns of the heavier fluid of such
    heights as will produce the respective pressures; and, therefore, when
    the difference of pressure or amount of rarefaction in the chimney is
    known, it is easy to tell the velocity of motion which ought to be
    produced by it. In practice, however, these theoretical results are not
    to be trusted, until they have received such modifications as will make
    them representative of the practice of the most experienced
    constructors.</P>

    <P>288. <EM>Q.</EM>--What then is the rule followed by the most
    experienced constructors?</P>

    <P><EM>A.</EM>--Boulton and Watt&#39;s rule for the dimensions of the
    chimney of a land engine is as follows:--multiply the number of pounds
    of coal consumed under the boiler per hour by 12, and divide the
    product by the square root of the height of the chimney in feet; the
    quotient is the area of the chimney in square inches in the smallest
    part. A factory chimney suitable for a 20 horse boiler is commonly made
    about 20 in. square inside, and 80 ft. high; and these dimensions are
    those which answer to a consumption of 15 lbs. of coal per horse power
    per hour, which is a very common consumption in factory engines. If 15
    lbs. of coal be consumed per horse power per hour, the total
    consumption per hour in a 20 horse boiler will be 300 lbs., and 300
    multiplied by 12 = 3600, and divided by 9 (the square root of the
    height) = 400, which is the area of the chimney in square inches. It
    will not answer well to increase the height of a chimney of this area
    to more than 40 or 50 yards, without also increasing the area, nor will
    it be of utility to increase the area much without also increasing the
    height. The quantity of coal consumed per hour in pounds, multiplied by
    5, and divided by the square root of the height of the chimney, is the
    proper collective area of the openings between the bars of the grate
    for the admission of air to the fire.</P>

    <P>289. <EM>Q.</EM>--Is this rule applicable to the chimneys of steam
    vessels?</P>

    <P><EM>A.</EM>--In steam vessels Boulton and Watt have heretofore been
    in the habit of allowing 8-1/2 square inches of area of chimney per
    horse power, but they now allow 6 square inches to 7 square inches. In
    some steam vessels a steam blast like that of a locomotive, but of a
    smaller volume, is used in the chimney, and many of the evils of a
    boiler deficient in draught may be remedied by this expedient, but a
    steam blast in a low pressure engine occasions an obvious waste of
    steam; it also makes an unpleasant noise, and in steam vessels it
    frequently produces the inconvenience of carrying the smaller parts of
    the coal up the chimney, and scattering it over the deck among the
    passengers. It is advisable, therefore, to give a sufficient
    calorimeter in all low pressure boilers, and a sufficient height of
    chimney to enable the chimney to operate without a steam jet; but it is
    useful to know that a steam jet is a resource in the case of a
    defective boiler, or where the boiler has to be urged beyond its
    power.</P>

    <H4 CLASS="subhead"><A NAME="g07"></A>STEAM ROOM AND PRIMING.</H4>

    <P>290. <EM>Q.</EM>--What is the capacity of steam room allowed in
    boilers per horse power?</P>

    <P><EM>A.</EM>--The capacity of steam room allowed by Boulton and Watt
    in their land wagon boilers is 8-3/4 cubic feet per horse power in the
    two horse power boiler, and 5-3/4 cubic feet in the 20 horse power
    boiler; and in the larger class of boilers, such as those suitable for
    30 and 45 horse power engines, the capacity of the steam room does not
    fall below this amount, and, indeed, is nearer 6 than 5-3/4 cubic feet
    per horse power. The content of water is 18-1/2 cubic feet per horse
    power in the two horse power boiler, and 15 cubic feet per horse power
    in the 20 horse power boiler.</P>

    <P>291. <EM>Q.</EM>--Is this the proportion Boulton and Watt allow in
    their marine boilers?</P>

    <P><EM>A.</EM>--Boulton and Watt in their early steam vessels were in
    the habit of allowing for the capacity of the steam, space in marine
    boilers 16 times the content of the cylinder; but as there were two
    cylinders, this was equivalent to 8 times the content of both
    cylinders, which is the proportion commonly followed in land engines,
    and which agrees very nearly with the proportion of between 5 and 6
    cubic feet of steam room per horse power already referred to. Taking
    for example an engine with 23 inches diameter of cylinder and 4 feet
    stroke, which will be 18.4 horse power--the area of the cylinder will
    be 415.476 square inches, which, multiplied by 48, the number of inches
    in the stroke, will give 19942.848 for the capacity of the cylinder in
    cubic inches; 8 times this is 159542.784 cubic inches, or 92.3 cubic
    feet; 92.3 divided by 18.4 is rather more than 5 cubic feet per horse
    power.</P>

    <P>292. <EM>Q.</EM>--Is the production of the steam in the boiler
    uniform throughout the stroke of the engine?</P>

    <P><EM>A.</EM>--It varies with the slight variations in the pressure
    within the boiler throughout the stroke. Usually the larger part of the
    steam is produced during the first part of the stroke of the engine,
    for there is then the largest demand for steam, as the steam being
    commonly cut off somewhat before the end of the stroke, the pressure
    rises somewhat in the boiler during that period, and little steam is
    then produced. There is less necessity that the steam space should be
    large when the flow of steam from the boiler is very uniform, as it
    will be where there are two engines attached to the boiler at right
    angles with one another, or where the engines work at a great speed, as
    in the case of locomotive engines. A high steam chest too, by rendering
    boiling over into the steam pipes, or priming as it is called, more
    difficult, obviates the necessity for so large a steam space; as does
    also a perforated steam pipe stretching through the length of the
    boiler, so as not to take the steam from one place. The use of steam of
    a high pressure, worked expansively, has the same operation; so that in
    modern marine boilers, of the tubular construction, where the whole or
    most of these modifying circumstances exist, there is no necessity for
    so large a proportion of steam room as 5 or 6 cubic feet per nominal
    horse power, and about one, 1-1/2, or 2 cubic feet of steam room per
    cubic foot of water evaporated, more nearly represents the general
    practice.</P>

    <P>293. <EM>Q.</EM>--Is this the proportion of steam room adopted in
    locomotive boilers?</P>

    <P><EM>A.</EM>--No; in locomotive boilers the proportion of steam room
    per cubic foot of water evaporated is considerably less even than this.
    It does not usually exceed 1/5 of a cubic foot per cubic foot of water
    evaporated; and with clean water, with a steam dome a few feet high set
    on the barrel of the boiler, or with a perforated pipe stretching from
    end to end of the barrel, and with the steam room divided about equally
    between the barrel and the fire box, very little priming is found to
    occur even with this small proportion of total steam room. About 3/4
    the depth of the barrel is usually filled with water, and 1/4 with
    steam.</P>

    <P>294. <EM>Q.</EM>--What is priming?</P>

    <P><EM>A.</EM>--Priming is a violent agitation of the water within the
    boiler, in consequence of which a large quantity of water passes off
    with the steam in the shape of froth or spray. Such a result is
    injurious, both as regards the efficacy of the engine, and the safety
    of the engine and boiler; for the large volume of hot water carried by
    the steam into the condenser impairs the vacuum, and throws a great
    load upon the air pump, which diminishes the speed and available power
    of the engine; and the existence of water within the cylinder, unless
    there be safety valves upon the cylinder to permit its escape, will
    very probably cause some part of the machinery to break, by suddenly
    arresting the motion of the piston when it meets the surface of the
    water,--the slide valve being closed to the condenser before the
    termination of the stroke, in all engines with lap upon the valves, so
    that the water within the cylinder is prevented from escaping in that
    direction. At the same time the boiler is emptied of its water too
    rapidly for the feed pump to be able to maintain the supply, and the
    flues are in danger of being burnt from a deficiency of water above
    them.</P>

    <P>295. <EM>Q.</EM>--What are the causes of priming?</P>

    <P><EM>A.</EM>--The causes of priming are an insufficient amount of
    steam room, an inadequate area of water level, an insufficient width
    between the flues or tubes for the ascent of the steam and the descent
    of water to supply the vacuity the steam occasions, and the use of
    dirty water in the boiler. New boilers prime more than old boilers, and
    steamers entering rivers from the sea are more addicted to priming than
    if sea or river water had alone been used in the boilers--probably from
    the boiling point of salt water being higher than that of fresh,
    whereby the salt water acts like so much molten metal in raising the
    fresh water into steam. Opening the safety valve suddenly may make a
    boiler prime, and if the safety valve be situated near the mouth of the
    steam pipe, the spray or foam thus created may be mingled with the
    steam passing into the engine, and materially diminish its effective
    power; but if the safety valve be situated at a distance from the mouth
    of the steam pipe, the quantity of foam or spray passing into the
    engine may be diminished by opening the safety valve; and in
    locomotives, therefore, it is found beneficial to have a safety valve
    on the barrel of the boiler at a point remote from the steam chest, by
    partially opening which, any priming in that part of the boiler
    adjacent to the steam chest is checked, and a purer steam than before
    pusses to the engine.</P>

    <P>296. <EM>Q.</EM>--What is the proper remedy for priming?</P>

    <P><EM>A.</EM>--When a boiler primes, the engineer generally closes the
    throttle valve partially, turns off the injection water, and opens the
    furnace doors, whereby the generation of steam is checked, and a less
    violent ebullition in the boiler suffices. Where the priming arises
    from an insufficient amount of steam room, it may be mitigated by
    putting a higher pressure upon the boiler and working more expansively,
    or by the interposition of a perforated plate between the boiler and
    the steam chest, which breaks the ascending water and liberates the
    steam. In some cases, however, it may be necessary to set a second
    steam chest on the top of the existing one, and it will be preferable
    to establish a communication with this new chamber by means of a number
    of small holes, bored through the iron plate of the boiler, rather than
    by a single large orifice. Where priming arises from the existence of
    dirty water in the boiler, the evil may be remedied by the use of
    collecting vessels, or by blowing off largely from the surface; and
    where it arises from an insufficient area of water level, or an
    insufficient width between the flues for the free ascent of the steam
    and the descent of the superincumbent water, the evil may be abated by
    the addition of circulating pipes in some part of the boiler, which
    will allow the water to descend freely to the place from whence the
    steam rises, the width of the water spaces being virtually increased by
    restricting their function to the transmission of a current of steam
    and water to the surface. It is desirable to arrange the heating
    surface in such a way that the feed water entering the boiler at its
    lowest point is heated gradually as it ascends, until toward the
    superior part of the flues it is raised gradually into steam; but in
    all cases there will be currents in the boiler for which it is proper
    to provide. The steam pipe proceeding to the engine should obviously be
    attached to the highest point of the steam chest, in boilers of every
    construction.</P>

    <P>297. <EM>Q.</EM>--Having now stated the proportions proper to be
    adopted for evaporating any given quantity of water in steam boilers,
    will you proceed to show how you would proportion a boiler to do a
    given amount of work? say a locomotive boiler which will propel a train
    of 100 tons weight at a speed of 50 miles an hour.</P>

    <P><EM>A.</EM>--According to experiments on the resistance of railway
    trains at various rates of speed, made by Mr. Gooch, of the Great
    Western Railway, it appears that a train weighing, with locomotive,
    tender, and carriages, about 100 tons, experiences, at a speed of 50
    miles an hour, a resistance of about 3,000 lbs., or about 30 lbs. per
    ton; which resistance includes the resistance of the engine as well as
    that of the train. This, therefore, is the force which must be imparted
    at the circumference of the driving wheels, except that small part
    intercepted by the engine itself, and the force exerted by the pistons
    must be greater than that at the circumference of the driving wheel, in
    the proportion of their slower motion, or in the proportion of the
    circumference of the driving wheel to the length of a double stroke of
    the engine. If the diameter of the driving wheel be 5-1/2 feet, its
    circumference will be 17.278 feet, and if the length of the stroke be
    18 inches, the length of a double stroke will be 3 feet. The pressure
    on the pistons must therefore be greater than the traction at the
    circumference of the driving wheel, in the proportion of 17.278 to 3,
    or, in other words, the mean pressure on the pistons must be 17,278
    lbs.; and the area of cylinders, and pressure of steam, must be such as
    to produce conjointly this total pressure. It thus becomes easy to tell
    the volume and pressure of steam required, which steam in its turn
    represents its equivalent of water which is to be evaporated from the
    boiler, and the boiler must be so proportioned, by the rules already
    given, as to evaporate this water freely. In the case of a steam
    vessel, the mode of procedure is the same, and when the resistance and
    speed are known, it is easy to tell the equivalent value of steam.</P>

    <H4 CLASS="subhead"><A NAME="g08"></A>STRENGTH OF BOILERS.</H4>

    <P>298. <EM>Q.</EM>--What strain should the iron of boilers be
    subjected to in working?</P>

    <P><EM>A.</EM>--The iron of boilers, like the iron of machines or
    structures, is capable of withstanding a tensile strain of from 50,000
    to 60,000 lbs. upon every square inch of section; but it will only bear
    a third of this strain without permanent derangement of structure, and
    it does not appear expedient in any boiler to let the strain exceed
    4,000 lbs. upon the square inch of sectional area of metal, especially
    if it is liable to be weakened by corrosion.</P>

    <P>299.<EM>Q.</EM>--Have any experiments been made to determine the
    strength of boilers?</P>

    <P><EM>A.</EM>--The question of the strength of boilers was
    investigated very elaborately a few years ago by a committee of the
    Franklin Institute, in America, and it was found that the tenacity of
    boiler plate increased with the temperature up to 550&deg;, at which
    point the tenacity began to diminish. At 32&deg;, the cohesive force of
    a square inch of section was 56,000 lbs.; at 570&deg;, it was 66,500
    lbs.; at 720&deg;, 55,000 lbs.; at 1,050&deg;, 32,000 lbs.; at
    1,240&deg;, 22,000 lbs.; and at 1,317&deg;, 9,000 lbs. Copper follows a
    different law, and appears to be diminished in strength by every
    addition to the temperature. At 32&deg; the cohesion of copper was
    found to be 32,800 lbs. per square inch of section, which exceeds the
    cohesive force at any higher temperature, and the square of the
    diminution of strength seems to keep pace with the cube of the
    increased temperature. Strips of iron cut in the direction of the fibre
    were found to be about 6 per cent. stronger than when cut across the
    grain. Repeated piling and welding was found to increase the tenacity
    of the iron, but the result of welding together different kinds of iron
    was not found to be favorable. The accidental overheating of a boiler
    was found to reduce the ultimate or maximum strength of the plates from
    65,000 to 45,000 lbs. per square inch of section, and riveting the
    plates was found to occasion a diminution in their strength to the
    extent of one third. These results, however, are not precisely the same
    as those obtained by Mr. Fairbairn.</P>

    <P>300. <EM>Q.</EM>--What were the results obtained by him?</P>

    <P><EM>A.</EM>--He found that boiler plate bore a tensile strain of 23
    tons per square inch before rupture, which was reduced to 16 tons per
    square inch when joined together by a double row of rivets, and 13
    tons, or about 30,000, when joined together by a single row of rivets.
    A circular boiler, therefore, with the ends of its plates double
    riveted, will bear at the utmost about 36,000 lbs. per square inch of
    section, or about 12,000 lbs. per square inch of section without
    permanent derangement of structure.</P>

    <P>301. <EM>Q.</EM>--What pressure do cylindrical boilers sustain in
    practice?</P>

    <P><EM>A.</EM>--In some locomotive boilers, which are worked with a
    pressure of 80 lbs. upon the square inch, the thickness of the plates
    is only 5/16ths of an inch, while the barrel of the boiler is 39 inches
    in diameter. It will require a length of 3.2 inches of the boiler when
    the plates are 5/16ths thick to make up a sectional area of one square
    inch, and the separating force will be 39 times 3.2 multiplied by 80,
    which makes the separating force 9,984 lbs., sustained by two square
    inches of sectional area--one on each side; or the strain is 4,992 lbs.
    per square inch of sectional area, which is quite as great strain as is
    advisable. The accession of strength derived from the boiler ends is
    not here taken into account, but neither is the weakening effect
    counted that is caused by the rivet holes. Some locomotives of 4 feet
    diameter of barrel and of 3/8ths iron have been worked to as high a
    pressure as 200 lbs. on the inch; but such feats of daring are neither
    to be imitated nor commended.</P>

    <P>302.<EM>Q.</EM>--Can you give a rule for the proper thickness of
    cylindrical boilers?</P>

    <P><EM>A.</EM>--The thickness proper for cylindrical boilers of wrought
    iron, exposed to an internal pressure, may be found by the following
    rule:-- multiply 2.54 times the internal diameter of the cylinder in
    inches by the greatest pressure within the cylinder per circular inch,
    and divide by 17,800; the result is the thickness in inches. If we
    apply this rule to the example of the locomotive boiler just given, we
    have 39 x 2.54 &times; 62.832 (the pressure per circular inch
    corresponding to 80 lbs. per square inch) = 6224.1379, and this,
    divided by 17,800, gives 0.349 as the thickness in inches, instead of
    0.3125, or 5/16ths, the actual thickness. If we take the pressure per
    square inch instead of per circular inch, we obtain the following rule,
    which is somewhat simpler:--multiply the internal diameter of the
    cylinder in inches by the pressure in pounds per square inch, and
    divide the product by 8,900; the result is the thickness in inches.
    Both these rules give the strain about one fourth of the elastic force,
    or 4,450 lbs. per square inch of sectional area of the iron; but 3,000
    lbs. is enough when the flame impinges directly on the iron, as in some
    of the ordinary cylindrical boilers, and the rule may be adapted for
    that strain by taking 6,000 as a divisor instead of 8,900.</P>

    <P>303. <EM>Q.</EM>--In marine and wagon boilers, which are not of a
    cylindrical form, how do you procure the requisite strength?</P>

    <P><EM>A.</EM>--Where the sides of the boiler are flat, instead of
    being cylindrical, a sufficient number of stays must be introduced to
    withstand the pressure; and it is expedient not to let the strain upon
    these stays be more than 3,000 lbs. per square inch of section, as the
    strength of internal stays in boilers is generally soon diminished by
    corrosion. Indeed, a strain at all approaching that upon locomotive
    boilers would be very unsafe in the case of marine boilers, on account
    of the corrosion, both internal and external, to which marine boilers
    are subject. The stays should be small and numerous rather than large
    and few in number, as, when large stays are employed, it is difficult
    to keep them tight at the ends, and oxidation of the shell follows from
    leakage at the ends of the stays. All boilers should be proved, when
    new, to twice or three times the pressure they are intended to bear,
    and they should be proved occasionally by the hand pump when in use, to
    detect any weakness which corrosion may have occasioned.</P>

    <P>304. <EM>Q.</EM>--Will you describe the disposition of the stays in
    a marine boiler?</P>

    <P><EM>A.</EM>--If the pressure of steam be 20 lbs. on the square inch,
    which is a very common pressure in tubular boilers, there will be a
    pressure of 2,880 lbs. on every square foot of flat surface; so that if
    the strain upon the stays is not to exceed 3,000 lbs. on the square
    inch of section, there must be nearly a square inch of sectional area
    of stay for every square foot of flat surface on the top and bottom,
    sides, and ends of the boiler. This very much exceeds the proportion
    usually adopted; and in scarcely any instance are boilers stayed
    sufficiently to be safe when the shell is composed of flat surfaces.
    The furnaces should be stayed together with bolts of the best scrap
    iron, 1-1/4 inch in diameter, tapped through both plates of the water
    space with thin nuts in each furnace; and it is expedient to make the
    row of stays, running horizontally near the level of the bars,
    sufficiently low to come beneath the top of the bars, so as to be
    shielded from the action of the fire, with which view they should
    follow the inclination of the bars. The row of stays between the level
    of the bars and the top of the furnace should be as near the top of the
    furnace as will consist with the functions they have to perform, so as
    to be removed as far as possible from the action of the heat; and to
    support the furnace top, cross bars may either be adopted, to which the
    top is secured with bolts, as in the case of locomotives, or stays
    tapped into the furnace top, with a thin nut beneath, may be carried to
    the top of the boiler; but very little dependence can be put in such
    stays as stays for keeping down the top of the boiler; and the top of
    the boiler must, therefore, be stayed nearly as much as if the stays
    connecting it with the furnace crowns did not exist. The large rivets
    passing through thimbles, sometimes used as stays for water spaces or
    boiler shells, are objectionable; as, from the great amount of
    hammering such rivets have to receive to form the heads, the iron
    becomes crystalline, so that the heads are liable to come off, and,
    indeed, sometimes fly off in the act of being formed. If such a
    fracture occurs between the boilers after they are seated in their
    place, or in any position not accessible from the outside, it will in
    general be necessary to empty the faulty boiler, and repair the defect
    from the inside.</P>

    <P>305. <EM>Q.</EM>--What should be the pitch or numerical distribution
    of the stays?</P>

    <P><EM>A.</EM>--The stays, where the sides of the boiler are flat, and
    the pressure of the steam is from 20 to 30 lbs., should be pitched
    about a foot or 18 inches asunder; and in the wake of the tubes, where
    stays cannot be carried across to connect the boiler sides, angle iron
    ribs, like the ribs of a ship, should be riveted to the interior of the
    boiler, and stays of greater strength than the rest should pass across,
    above, and below the tubes, to which the angle irons would communicate
    the strain. The whole of the long stays within a boiler should be
    firmly riveted to the shell, as if built with and forming a part of it;
    as, by the common method of fixing them in by means of cutters, the
    decay or accidental detachment of a pin or cutter may endanger the
    safety of the boiler. Wherever a large perforation in the shell of any
    circular boiler occurs, a sufficient number of stays should be put
    across it to maintain the original strength; and where stays are
    intercepted by the root of the funnel, short stays in continuation of
    them should be placed inside.</P>

    <H4 CLASS="subhead"><A NAME="g09"></A>BOILER EXPLOSIONS.</H4>

    <P>306. <EM>Q.</EM>--What is the chief cause of boiler explosions?</P>

    <P><EM>A.</EM>--The chief cause of boiler explosions is, undoubtedly,
    too great a pressure of steam, or an insufficient strength of boiler;
    but many explosions have also arisen from the flues having been
    suffered to become red hot. If the safety valve of a boiler be
    accidentally jammed, or if the plates or stays be much worn by
    corrosion, while a high pressure of steam is nevertheless maintained,
    the boiler necessarily bursts; and if, from an insufficiency of water
    in the boiler, or from any other cause, the flues become highly heated,
    they may be forced down by the pressure of the steam, and a partial
    explosion may be the result. The worst explosion is where the shell of
    the boiler bursts; but the collapse of a furnace or flue is also very
    disastrous generally to the persons in the engine room; and sometimes
    the shell bursts and the flues collapse at the same time; for if the
    flues get red hot, and water be thrown upon them either by the feed
    pump or otherwise, the generation of steam may be too rapid for the
    safety valve to permit its escape with sufficient facility, and the
    shell of the boiler may, in consequence, be rent asunder. Sometimes the
    iron of the flues becomes highly heated in consequence of the improper
    configuration of the parts, which, by retaining the steam in contact
    with the metal, prevents the access of the water: the bottoms of large
    flues, upon which the flame beats down, are very liable to injury from
    this cause; and the iron of flues thus acted upon may be so softened
    that the flues will collapse upward with the pressure of the steam. The
    flues of boilers may also become red hot in some parts from the
    attachment of scale, which, from its imperfect conducting power, will
    cause the iron to be unduly heated; and if the scale be accidentally
    detached, a partial explosion may occur in consequence.</P>

    <P>307. <EM>Q.</EM>--Does the contact of water with heated metal
    occasion an instantaneous generation of steam?</P>

    <P><EM>A.</EM>--It is found that a sudden disengagement of steam does
    not immediately follow the contact of water with the hot metal, for
    water thrown upon red hot iron is not immediately converted into steam,
    but assumes the spheroidal form and rolls about in globules over the
    surface. These globules, however high the temperature of the metal may
    be on which they are placed, never rise above the temperature of
    205&deg;, and give off but very little steam; but if the temperature of
    the metal be lowered, the water ceases to retain the spheroidal form,
    and comes into intimate contact with the metal, whereby a rapid
    disengagement of steam takes place. If water be poured into a very hot
    copper flask, the flask may be corked up, as there will be scarce any
    steam produced so long as the high temperature is maintained; but so
    soon as the temperature is suffered to fall below 350&deg; or 400&deg;,
    the spheroidal condition being no longer maintainable, steam is
    generated with rapidity, and the cork will be projected from the mouth
    of the flask with great force.</P>

    <P>308. <EM>Q.</EM>--What precautions can be taken to prevent boiler
    explosions?</P>

    <P><EM>A.</EM>--One useful precaution against the explosion of boilers
    from too great an internal pressure, consists in the application of a
    steam gauge to each boiler, which will make the existence of any undue
    pressure in any of the boilers immediately visible; and every boiler
    should have a safety valve of its own, the passage leading to which
    should have no connection with the passage leading to any of the stop
    valves used to cut off the connection between the boilers; so that the
    action of the safety valve may be made independent of the action of the
    stop valve. In some cases stop valves have jammed, or have been carried
    from their seats into the mouth of the pipe communicating between them,
    and the action of the safety valves should be rendered independent of
    all such accidents. Safety valves, themselves, sometimes stick fast
    from corrosion, from the spindles becoming bent, from a distortion of
    the boiler top with a high pressure, in consequence of which the
    spindles become jammed in the guides, and from various other causes
    which it would be tedious to enumerate; but the inaction of the safety
    valves is at once indicated by the steam gauge, and when discovered,
    the blow through valves of the engine and blow off cocks of the boiler
    should at once be opened, and the fires raked out. A cone in the ball
    of the waste steam pipe to send back the water carried upward by the
    steam, should never be inserted; as in some cases this cone has become
    loose, and closed up the mouth of the waste steam pipe, whereby the
    safety valves being rendered inoperative, the boiler was in danger of
    bursting.</P>

    <P>309. <EM>Q.</EM>--May not danger arise from excessive priming?</P>

    <P><EM>A.</EM>--If the water be carried out of the boiler so rapidly by
    priming that the level of the water cannot be maintained, and the flues
    or furnaces are in danger of becoming red hot, the best plan is to open
    every furnace door and throw in a few buckets full of water upon the
    fire, taking care to stand sufficiently to the one side to avoid being
    scalded by the rush of steam from the furnace. There is no time to
    begin drawing the fires in such an emergency, and by this treatment the
    fires, though not altogether extinguished, will be rendered incapable
    of doing harm. If the flues be already red hot, on no account must cold
    water be suffered to enter the boiler, but the heat should be
    maintained in the furnaces, and the blow off cocks be opened, or the
    mud hole doors loosened, so as to let all the water escape; but at the
    same time the pressure must be kept quite low in the boiler, so that
    there will be no danger of the hot flues collapsing with the pressure
    of the steam.</P>

    <P>310. <EM>Q.</EM>--Are plugs of fusible metal useful in preventing
    explosions?</P>

    <P><EM>A.</EM>--Plugs of fusible metal were at one time in much repute
    as a precaution against explosion, the metal being so compounded that
    it melted with the heat of high pressure steam; but the device, though
    ingenious, has not been found of any utility in practice. The basis of
    fusible metal is mercury, and it is found that the compound is not
    homogeneous, and that the mercury is forced by the pressure of the
    steam out of the interstices of the metal combined with it, leaving a
    porous metal which is not easily fusible, and which is, therefore,
    unable to perform its intended function. In locomotives, however, and
    also in some other boilers, a lead rivet is inserted with advantage in
    the crown of the fire box, which is melted out if the water becomes too
    low, and thus gives notice of the danger.</P>

    <P>311. <EM>Q.</EM>--May not explosion occur in marine boilers from the
    accumulation of salt on the flues?</P>

    <P><EM>A.</EM>--Yes, in marine boilers this is a constant source of
    danger, which is only to be met by attention on the part of the
    engineer. If the water in the boiler be suffered to become too salt, an
    incrustation of salt will take place on the furnaces, which may cause
    them to become red hot, and they may then be collapsed even by their
    own weight aided by a moderate pressure of steam. The expedients which
    should be adopted for preventing such an accumulation of salt from
    taking place within the boiler as will be injurious to it, properly
    fall under the head of the management of steam boilers, and will be
    explained in a subsequent chapter.</P>

    <H2 CLASS="chapter"><A NAME="ch06"></A>CHAPTER VI.</H2>

    <H3>PROPORTIONS OF ENGINES.</H3>

    <H4 CLASS="subhead"><A NAME="h01"></A>STEAM PASSAGES.</H4>

    <P>312. <EM>Q.</EM>--What size of orifice is commonly allowed for the
    escape of the steam through the safety valve in low pressure
    engines?</P>

    <P><EM>A.</EM>--About 0.8 of a circular inch per horse power, or a
    circular inch per 1-1/4 horse power. The following rule, however, will
    give the dimensions suitable for all kinds of engines, whether high or
    low pressure:--multiply the square of the diameter of the cylinder in
    inches by the speed of the piston in feet per minute, and divide the
    product by 375 times the pressure on the boiler per square inch; the
    quotient is the proper area of the safety valve in square inches. This
    rule of course supposes that the evaporating surface has been properly
    proportioned to the engine power.</P>

    <P>313. <EM>Q.</EM>--Is this rule applicable to locomotives?</P>

    <P><EM>A.</EM>--It is applicable to high pressure engines of every
    kind. The dimensions of safety valves, however, in practice are very
    variable, being in some cases greater, and in some cases less, than
    what the rule gives, the consideration being apparently as often what
    proportions will best prevent the valve from sticking in its seat, as
    what proportions will enable the steam to escape freely. In Bury&#39;s
    locomotives, the safety valve was generally 2-1/2 inches diameter for
    all sizes of boiler, and the valve was kept down by a lever formed in
    the proportion of 5 to 1, fitted at one end with a Salter&#39;s
    balance. As the area of the valve was 5 square inches, the number of
    pounds shown on the spring balance denoted the number of pounds
    pressure on each square inch of the boiler.</P>

    <P>314. <EM>Q.</EM>--Is there only one safety valve in a locomotive
    boiler?</P>

    <P><EM>A.</EM>--There are always two.</P>

    <P>315. <EM>Q.</EM>--And are they always pressed down by a spring
    balance, and never by weights?</P>

    <P><EM>A.</EM>--They are never pressed down by weights; in fact,
    weights would not answer on a locomotive at all, as they would jump up
    and down with the jerks or jolts of the train, and cause much of the
    steam to escape. In land and marine boilers, however, the safety valve
    is always kept down by weights; but in steam vessels a good deal of
    steam is lost in stormy weather by the opening of the valve, owing to
    the inertia of the weights when the ship sinks suddenly in the deep
    recess between the waves.</P>

    <P>316. <EM>Q.</EM>--What other sizes of safety valves are used in
    locomotives?</P>

    <P><EM>A.</EM>--Some are as large as 4 inches diameter, giving 12
    square inches of area; and others are as small as 1-3/16 inch diameter,
    giving 1 square inch of area.</P>

    <P>317. <EM>Q.</EM>--And are these valves all pressed down by a
    Salter&#39;s spring balance?</P>

    <P><EM>A.</EM>--In the great majority of cases they are so, and the
    lever by which they are pressed down is generally graduated in the
    proportion of the area of the valve to unity; that is, in the case of a
    valve of 12 inches area, the long end of the lever to which the spring
    balance is attached is 12 times the length of the short end, so that
    the weight or pressure on the balance shows the pressure per square
    inch on the boiler. In some cases, however, a spiral spring, and in
    other cases a pile of elliptical springs, is placed directly upon the
    top of the valve, and it appears desirable that one of the valves at
    least should be loaded in this manner. It is difficult when the lever
    is divided in such a proportion as 12 to 1, to get sufficient lift of
    the valve without a large increase of pressure on the spring; and it
    appears expedient, therefore, to employ a shorter lever, which involves
    either a reduction in the area of the valve, or an increased strength
    in the spring.</P>

    <P>318. <EM>Q.</EM>--What are the proper dimensions of the steam
    passages?</P>

    <P><EM>A.</EM>--In slow working engines the common size of the cylinder
    passages is one twenty-fifth of the area of the cylinder, or one fifth
    of the diameter of the cylinder, which is the same thing. This
    proportion corresponds very nearly with one square inch per horse power
    when the length of the cylinder is about equal to its diameter; and one
    square inch of area per horse power for the cylinder ports and eduction
    passages answers very well in the case of engines working at the
    ordinary speed of 220 feet per minute. The area of the steam pipe is
    usually made less than the area of the eduction pipe, especially when
    the engine is worked expansively, and with a considerable pressure of
    steam. In the case of ordinary condensing engines, however, working
    with the usual pressure of from 4 to 8 lbs. above the atmosphere, the
    area of the steam pipe is not less than a circular inch per horse
    power. In such engines the diameter of the steam pipe may be found by
    the following rule: divide the number of nominal horse power by 0.8 and
    extract the square root of the quotient, which will be the internal
    diameter of the steam pipe.</P>

    <P>319. <EM>Q.</EM>--Will you explain by what process of computation
    these proportions are arrived at?</P>

    <P><EM>A.</EM>--The size of the steam pipe is so regulated that there
    will be no material disparity of pressure between the cylinder and
    boiler; and in fixing the size of the eduction passage the same object
    is kept in view. When the diameter of the cylinder and the velocity
    with which the piston travels are known, it is easy to tell what the
    velocity of the steam in the steam pipe will be; for if the area of the
    cylinder be 25 times greater than that of the steam pipe, the steam in
    the steam pipe must travel 25 times faster than the piston, and the
    difference of pressure requisite to produce this velocity of the steam
    can easily be ascertained, by finding what height a column of steam
    must be to give that velocity, and what the weight or pressure is of
    such a column. In practice, however, this proportion is always exceeded
    from the condensation of steam in the pipe.</P>

    <P>320. <EM>Q.</EM>--If the relation you have mentioned subsist between
    the area of the steam passages and the velocity of the piston, then the
    passages must be larger when the piston travels very rapidly?</P>

    <P><EM>A.</EM>--And they are so made. The area of the ports of
    locomotive engines is usually so proportioned as to be from 1/10th to
    1/8th the area of the cylinder--in some cases even as much as 1/6th;
    and in all high speed engines the ports should be very large, and the
    valve should have a good deal of travel so as to open the port very
    quickly. The area of port which it appears advisable to give to modern
    engines of every description, is expressed by the following
    rule:--multiply the area of the cylinder in square inches by the speed
    of the piston in feet per minute, and divide the product by 4,000; the
    quotient is the area of each cylinder port in square inches. This rule
    gives rather more than a square inch of port per nominal horse power to
    condensing engines working at the ordinary speed; but the excess is but
    small, and is upon the right side. For engines travelling very fast it
    gives a good deal more area than the common proportion, which is too
    small in nearly every case. In locomotive engines the eduction pipe
    passes into the chimney and the force of the issuing steam has the
    effect of maintaining a rapid draught through the furnace as before
    explained. The orifice of the waste steam pipe, or the blast pipe as it
    is termed, is much contracted in some engines with the view of
    producing a fiercer draught, and an area of 1/22d of the cylinder is a
    common proportion; but this is as much contraction as should be
    allowed, and is greater than is advisable.</P>

    <P>321. <EM>Q.</EM>--In engines moving at a high rate of speed, you
    have stated that it is important to give the valve lead, or in other
    words to allow the steam to escape before the end of the stroke?</P>

    <P><EM>A.</EM>--Yes, this is very important, else the piston will have
    to force out the steam from the cylinder, and will be much resisted.
    Near the end of the stroke the piston begins to travel slowly, and if
    the steam be then permitted to escape, very little of the effective
    stroke is lost, and time is afforded to the steam, before the motion of
    the piston is again accelerated, to make its escape by the port. In
    some locomotives, from inattention to this adjustment, and from a
    contracted area of tube section, which involved a strong blast, about
    half the power of the engine has been lost; but in more recent engines,
    by using enlarged ports and by giving sufficient lead, this loss has
    been greatly diminished.</P>

    <P>322. <EM>Q.</EM>--What do you call sufficient lead?</P>

    <P><EM>A.</EM>--In fast going engines I would call it sufficient lead,
    when the eduction port was nearly open at the end of the stroke.</P>

    <P>323. <EM>Q.</EM>--Can you give any example of the benefit of
    increasing the lead?</P>

    <P><EM>A.</EM>--The early locomotives were made with very little lead,
    and the proportions were in fact very much the same as those previously
    existing in land engines. About 1832, the benefits of lap upon the
    valve, which had been employed by Boulton and Watt more than twenty
    years before, were beginning to be pretty generally apprehended; and,
    in the following year, this expedient of economy was applied to the
    steamer Manchester, in the Clyde, and to some other vessels, with very
    marked success. Shortly after this time, lap began to be applied to the
    valves of locomotives, and it was found that not only was there a
    benefit from the operation of expansion, but that there was a still
    greater benefit from the superior facility of escape given to the
    steam, inasmuch as the application of lap involved the necessity of
    turning the eccentric round upon the shaft, which caused the eduction
    to take place before the end of the stroke. In 1840, one of the engines
    of the Liverpool and Manchester Railway was altered so as to have 1
    inch lap on the valve, and 1 inch opening on the eduction side at the
    end of the stroke, the valve having a total travel of 4-1/4 inches. The
    consumption of fuel per mile fell from 36.3 lbs. to 28.6 lbs, or about
    25 per cent., and a softer blast sufficed. By using larger exhaust
    passages, larger tubes, and closer fire bars, the consumption was
    subsequently brought down to 15 lbs. per mile.</P>

    <H4 CLASS="subhead"><A NAME="h02"></A>AIR PUMP, CONDENSER, AND HOT AND
    COLD WATER PUMPS.</H4>

    <P>324. <EM>Q.</EM>--Will you state the proper dimensions of the air
    pump and condenser in laud and marine engines?</P>

    <P><EM>A</EM>--Mr. Watt made the air pump of his engine half the
    diameter of the cylinder and half the stroke, or one eighth of the
    capacity, and the condenser was usually made about the same size as the
    air pump; but as the pressure of the steam has been increased in all
    modern engines, it is better to make the air pump a little larger than
    this proportion. 0.6 of the diameter of the cylinder and half the
    stroke answers very well, and the condenser may be made as large as it
    can be got with convenience, though the same size as the air pump will
    suffice.</P>

    <P>325. <EM>Q.</EM>--Are air pumps now sometimes made double
    acting?</P>

    <P><EM>A.</EM>--Most of the recent direct acting marine engines for
    driving the screw are fitted with a double acting air pump, and when
    the air pump is double acting, it need only be about half the size that
    is necessary when it is single acting. It is single acting in nearly
    every case, except the case of direct acting screw engines of recent
    construction.</P>

    <P>326. <EM>Q.</EM>--What is the difference between a single and a
    double acting air pump?</P>

    <P><EM>A.</EM>--The single acting air pump expels the air and water
    from the condenser only in the upward stroke of the pump, whereas a
    double acting air pump expels the air and water both in the upward and
    downward stroke. It has, therefore, to be provided with inlet and
    outlet valves at both ends, whereas the single acting pump has only to
    be provided with an inlet or foot valve, as it is termed, at the
    bottom, and with an outlet or delivery valve, as it is termed, at the
    top. The single acting air pump requires to be provided with a valve or
    valves in the piston or bucket of the pump, to enable the air and water
    lying below the bucket when it begins to descend, and which have
    entered from the condenser during the upward stroke, to pass through
    the bucket into the space above it during the downward stroke, from
    whence they are expelled into the atmosphere on the upward stroke
    succeeding. But in the double acting air pump no valve is required in
    the piston or bucket of the pump, and all that is necessary is an inlet
    and outlet valve at each end.</P>

    <P>337. <EM>Q</EM>--What are the dimensions of the foot and discharge
    valves of the air pump?</P>

    <P><EM>A.</EM>--The area through the foot and discharge valves is
    usually made equal to one fourth of the area of the air pump, and the
    diameter of the waste water pipe is made one fourth of the diameter of
    the cylinder, which gives an area somewhat less than that of the foot
    and discharge valve passages. But this proportion only applies in slow
    engines. In fast engines, with the air pump bucket moving as fast as
    the piston, the area through the foot and discharge valves should be
    equal to the area of the pump itself, and the waste water pipe should
    be of about the same dimensions.</P>

    <P>328. <EM>Q.</EM>--You have stated that double acting air pumps need
    only be of half the size of single acting ones. Does that relation hold
    at all speeds?</P>

    <P><EM>A.</EM>--It holds at all speeds if the velocity of the pump
    buckets are in each case the same; but it does not hold if the engine
    with the single acting pump works slowly, and the engine with the
    double acting pump moves rapidly, as in the case of direct acting screw
    engines. All pumps moving at a high rate of speed lose part of their
    efficiency, and such pumps should therefore be of extra size.</P>

    <P>329. <EM>Q.</EM>--How do you estimate the quantity of water
    requisite for condensation?</P>

    <P><EM>A.</EM>--Mr. Watt found that the most beneficial temperature of
    the hot well of his engines was 100 degrees. If, therefore, the
    temperature of the steam be 212&deg;, and the latent heat 1,000&deg;,
    then 1,212&deg; may be taken to represent the heat contained in the
    steam, or 1,112&deg; if we deduct the temperature of the hot well. If
    the temperature of the injection water be 50&deg;, then 50 degrees of
    cold are available for the abstraction of heat; and as the total
    quantity of heat to be abstracted is that requisite to raise the
    quantity of water in the steam 1,112 degrees, or 1,112 times that
    quantity one degree, it would raise one fiftieth of this, or 22.24
    times the quantity of water in the steam, 50 degrees. A cubic inch of
    water therefore raised into steam will require 22.24 cubic inches of
    water at 50 degrees for its condensation, and will form therewith 23.24
    cubic inches of hot water at 100 degrees. Mr. Watt&#39;s practice was
    to allow about a wine pint (28.9 cubic inches) of injection water, for
    every cubic inch of water evaporated from the boiler.</P>

    <P>330. <EM>Q.</EM>--Is not a good vacuum in an engine conducive to
    increased power?</P>

    <P><EM>A.</EM>--It is.</P>

    <P>331. <EM>Q.</EM>--And is not the vacuum good in the proportion in
    which the temperature is low, supposing there to be no air leaks?</P>

    <P><EM>A.</EM>--Yes.</P>

    <P>332. <EM>Q.</EM>--Then how could Mr. Watt find a temperature of
    100&deg; in the water drawn from the condenser, to be more beneficial
    than a temperature of 70&deg; or 80&deg;, supposing there to be an
    abundant supply of cold water?</P>

    <P>333. <EM>A.</EM>--Because the superior vacuum due to a temperature
    of 70&deg; or 80&deg; involves the admission of so much cold water into
    the condenser, which has afterward to be pumped out in opposition to
    the pressure of the atmosphere, that the gain in the vacuum does not
    equal the loss of power occasioned by the additional load upon the
    pump, and there is therefore a clear loss by the reduction of the
    temperature below 100&deg;, if such reduction be caused by the
    admission of an additional quantity of water. If the reduction of
    temperature, however, be caused by the use of colder water, there is a
    gain produced by it, though the gain will within certain limits be
    greater if advantage be taken of the lowness of the temperature to
    diminish the quantity of injection.</P>

    <P>334.<EM>Q.</EM>--How do you determine the proper area of the
    injection orifice?</P>

    <P><EM>A.</EM>--The area of the injection orifice proper for any engine
    can easily be told when the quantity of water requisite to condense the
    steam is known, and the pressure is specified under which the water
    enters the condenser. The vacuum in the condenser may be taken at 26
    inches of mercury, which is equivalent to a column of water 29.4 ft.
    high, and the square root of 29.4 multiplied by 8.021 is 43.15, which
    is the velocity in feet per second that a heavy body would acquire in
    falling 29.4 ft., or with which the water would enter the condenser.
    Now, if a cubic foot of water evaporated per hour be equivalent to an
    actual horse power, and 28.9 cubic inches of water be requisite for the
    condensation of a cubic inch of water in the form of steam, 28.9 cubic
    feet of condensing water per horse power per hour, or 13.905 cubic
    inches per second, will be necessary for the engine, and the size of
    the injection orifice must be such that this quantity of water flowing
    with the velocity of 43.15 ft. per second, or 517.8 inches per second,
    will gain admission to the condenser. Dividing, therefore, 13.905, the
    number of cubic inches to be injected, by 517.8, the velocity of influx
    in inches per second, we get 0.02685 for the area of the orifice in
    square inches; but inasmuch as it has been found by experiment that the
    actual discharge of water through a hole in a thin plate is only six
    tenths of the theoretical discharge on account of the contracted vein,
    the area of the orifice must be increased in the proportion of such
    diminution of effect, or be made 0.04475, or 1/22d of a square inch per
    horse power. This, it will be remarked, is the theoretical area
    required per actual horse power; but as the friction and contractions
    in the pipe further reduce the discharge, the area is made 1/15th of a
    square inch per actual horse power, or rather per cubic foot of water
    evaporated from the boiler.</P>

    <P>335. <EM>Q.</EM>--Cannot the condensation of the steam be
    accomplished by any other means than by the admission of cold water
    into the condenser?</P>

    <P><EM>A.</EM>--It may be accomplished by the method of external cold,
    as it is called, which consists in the application of a large number of
    thin metallic surfaces to the condenser, on the one side of which the
    steam circulates, while on the other side there is a constant current
    of cold water, and the steam is condensed by coming into contact with
    the cold surfaces, without mingling with the water used for the purpose
    of refrigeration. The first kind of condenser employed by Mr. Watt was
    constructed after this fashion, but he found it in practice to be
    inconvenient from its size, and to become furred up or incrusted when
    the water was bad, whereby the conducting power of the metal was
    impaired. He therefore reverted to the use of the jet of cold water, as
    being upon the whole preferable. The jet entered the condenser instead
    of the cylinder as was the previous practice, and this method is now
    the one in common use. Some few years ago, a good number of steam
    vessels were fitted with Hall&#39;s condensers, which operated on the
    principle of external cold, and which consisted of a faggot of small
    copper tubes surrounded by water; but the use of those condensers has
    not been persisted in, and most of the vessels fitted with them have
    returned to the ordinary plan.</P>

    <P>336. <EM>Q.</EM>--You stated that the capacity of the feed pump was
    1/240th of the capacity of the cylinder in the case of condensing
    engines,--the engine being double acting and the pump single
    acting,--and that in high pressure engines the capacity of the pump
    should be greater in proportion to the pressure of the steam. Can you
    give any rule that will express the proper capacity for the feed pump
    at all pressures?</P>

    <P><EM>A.</EM>--That will not be difficult. In low pressure engines the
    pressure in the boiler may be taken at 5 lbs. above the atmospheric
    pressure, or 20 lbs. altogether; and as high pressure steam is merely
    low pressure steam compressed into a smaller compass, the size of the
    feed pump in relation to the size of the cylinder must obviously vary
    in the direct proportion of the pressure; and if it be 1/240th of the
    capacity of the cylinder when the total pressure of the steam is 20
    lbs., it must be 1/120th of the capacity of the cylinder when the
    pressure is 40 lbs. per square inch, or 25 lbs. per square inch above
    the atmospheric pressure. This law of variation is expressed by the
    following rule:--multiply the capacity of the cylinder in cubic inches
    by the total pressure of the steam in lbs. per square inch, or the
    pressure per square inch on the safety valve plus 15, and divide the
    product by 4,800; the quotient is the capacity of the feed pump in
    cubic inches, when the feed pump is single acting and the engine double
    acting. If the feed pump be double acting, or the engine single acting,
    the capacity of the pump must just be one half of what is given by this
    rule.</P>

    <P>337. <EM>Q.</EM>--But should not some addition be made to the size
    of pump thus obtained if the pump works at a high rate of speed?</P>

    <P><EM>A.</EM>--No; this rule makes allowance for defective action. All
    pumps lift much less water than is due to the size of their barrels and
    the number of their strokes. Moderately good pumps lose 50 per cent. of
    their theoretical effect, and bad pumps 80 per cent.</P>

    <P>338. <EM>Q.</EM>--To what is this loss of effect to be chiefly
    ascribed?</P>

    <P><EM>A.</EM>--Mainly to the inertia of the water, which, if the pump
    piston be drawn up very rapidly, cannot follow it with sufficient
    rapidity; so that there may be a vacant space between the piston and
    the water; and at the return stroke the momentum of the water in the
    pipe expends itself in giving a reverse motion to the column of water
    approaching the pump. Messrs. Kirchweger and Prusman, of Hanover, have
    investigated this subject by applying a revolving cock at the end of a
    pipe leading from an elevated cistern containing water, and the water
    escaped at every revolution of the cock in the same manner as if a pump
    were drawing it. With a column of water of 17 feet, they found that at
    80 revolutions of the cock per minute, the water delivered per minute
    by the cock was 9.45 gallons; but with 140 revolutions of the cock per
    minute, the water delivered per minute by the cock was only 5.42
    gallons. They subsequently applied an air vessel to the pipe beside the
    cock, when the discharge rose to 12.9 gallons per minute with 80
    revolutions, and 18.28 gallons with 140 revolutions. Air vessels should
    therefore be applied to the suction side of fast moving pumps, and this
    is now done with good results.</P>

    <P>339. <EM>Q.</EM>--What are the usual dimensions of the cold water
    pump of land engines?</P>

    <P><EM>A.</EM>--If to condense a cubic inch of water raised into steam
    28.9 cubic inches of condensing water are required, then the cold water
    pump ought to be 28.9 times larger than the feed pump, supposing that
    its losses were equally great. The feed pump, however, is made
    sufficiently large to compensate for leaks in the boiler and loss of
    steam through the safety valve, so that it will be sufficient if the
    cold water pump be 24 times larger than the feed pump. This ratio is
    preserved by the following rule:--multiply the capacity of the cylinder
    in cubic inches by the total pressure of the steam per square inch, or
    the pressure on the safety valve plus 15, and divide the product by
    200. The quotient is the proper capacity of the cold water pump in
    cubic inches when the engine is double acting, and the pump single
    acting.</P>

    <H4 CLASS="subhead"><A NAME="h03"></A>FLY WHEEL.</H4>

    <P>340. <EM>Q.</EM>--By what considerations do you determine the
    dimensions of the fly wheel of an engine?</P>

    <P><EM>A.</EM>--By a reference to the power generated, each half stroke
    of the engine, and the number of half strokes that are necessary to
    give to the fly wheel its standard velocity, supposing the whole power
    devoted to that object. In practice the power resident in the fly
    varies from 2-1/2 to 6 times that generated each half stroke; and if
    the weight of the wheel be equal to the pressure on the piston, its
    velocity must be such as it would acquire by falling through a height
    equal to from 2-1/2 to 6 times the stroke, according to the purpose for
    which the engine is intended. If a very equable motion is required, a
    heavier or swifter fly wheel must be employed.</P>

    <P>341. <EM>Q.</EM>--What is Boulton and Watt&#39;s rule for fly
    wheels?</P>

    <P><EM>A.</EM>--Their rule is one which under any given circumstances
    fixes the sectional area of the fly wheel rim, and it is as
    follows:--multiply 44,000 times the square of the diameter of the
    cylinder in inches by the length of the stroke in feet, and divide this
    product by the product of the square of the number of revolutions of
    the fly wheel per minute, multiplied by the cube of its diameter in
    feet. The quotient is the area of section of the fly wheel rim in
    square inches.</P>

    <H4 CLASS="subhead"><A NAME="h04"></A>STRENGTHS OF LAND ENGINES.</H4>

    <P>342. <EM>Q.</EM>--Can you give a rule for telling the proper
    thickness of the cylinders of steam engines?</P>

    <P><EM>A.</EM>--In low pressure engines the thickness of metal of the
    cylinder, in engines of a medium size, should be about 1/40th of the
    diameter of the cylinder, which, with a pressure of steam of 20 lbs.
    above the atmosphere, will occasion a strain of only 400 Lbs. per
    square inch of section of the metal; the thickness of the metal of the
    trunnion bearings of oscillating engines should be 1/32d of the
    diameter of the cylinder, and the breadth of the bearing should be
    about half its diameter. In high pressure engines the thickness of the
    cylinder should be about 1/16th its diameter, which, with a pressure of
    steam of 80 lbs. upon the square inch, will occasion a strain of 640
    lbs. upon the square inch of section of the metal; and the thickness of
    the metal of the trunnion bearings of high pressure oscillating engines
    should be 1/13th of the diameter of the cylinder. The strength,
    however, is not the sole consideration in proportioning cylinders, for
    they must be made of a certain thickness, however small the pressure is
    within them, that they may not be too fragile, and will stand boring.
    While, also, an engine of 40 inches diameter would be about one inch
    thick, the thickness would not be quite two inches in an 80 inch
    cylinder. In fact there will be a small constant added to the thickness
    for all diameters, which will be relatively larger the smaller the
    cylinders become. In the cylinders of Penn&#39;s 12 horse power
    engines, the diameter of cylinder being 21-1/2 inches, the thickness of
    the metal is 9/16ths: in Penn&#39;s 40 inch cylinders, the thickness is
    1 inch, and in the engines of the Ripon, Pottinger, and Indus, by
    Messrs. Miller, Ravenhill and Co., with cylinders 76 inches diameter,
    the thickness of the metal is 1-11/16. These are all oscillating
    engines.</P>

    <P>343. <EM>Q.</EM>--What is the proportion of the piston rod?</P>

    <P><EM>A.</EM>--The diameter of the piston rod is usually made 1/10th
    of the diameter of the cylinder, or the sectional area of the piston
    rod is 1/100th of the area of the cylinder. This proportion, however,
    is not applicable to locomotive, or even fast moving marine engines. In
    locomotive engines the piston rod is made 1/7th of the diameter of the
    cylinder, and it is obvious that where the pressure on the piston is
    great, the piston rod must be larger than when the pressure on the
    piston is small.</P>

    <P>344. <EM>Q.</EM>--What are the proper dimensions of the main links
    of a land beam engine?</P>

    <P><EM>A.</EM>--The sectional area of the main links in land beam
    engines is 1/113th of the area of the cylinder, and the length of the
    main links is usually half the length of the stroke.</P>

    <P>345. <EM>Q.</EM>--What are the dimensions of the connecting rod of a
    land engine?</P>

    <P><EM>A.</EM>--In land engines the connecting rod is usually of cast
    iron with a cruciform section: the breadth across the arms of the cross
    is about 1/20th of the length of the rod, the sectional area at the
    centre 1/28th of the area of the cylinder, and at the ends 1/35th of
    the area of the cylinder: the length of the rod is usually 3-1/2 times
    the length of the stroke. It is preferable, however, to make the
    connecting rod of malleable iron, and then the dimensions will be those
    proper for marine engines.</P>

    <P>346. <EM>Q.</EM>--What was Mr. Watt&#39;s rule for the connecting
    rod?</P>

    <P><EM>A.</EM>--Some of his connecting rods were of iron and some of
    wood. To determine the thickness when of wood, multiply the square of
    the diameter of the cylinder in inches by the length of the stroke in
    feet, and divide the product by 24. Extract the fourth root of the
    quotient, which is the thickness in inches. For iron the rule is the
    same, only the divisor was 57.6 instead of 24.</P>

    <P>347. <EM>Q.</EM>--What are the dimensions of the end studs of a land
    engine beam?</P>

    <P><EM>A.</EM>--In low pressure engines the diameter of the end studs
    of the engine beam are usually made 1/9th of the diameter of the
    cylinder when of cast iron, and 1/10th when of wrought iron, which
    gives a load with low steam of about 500 lbs. per circular inch of
    transverse section; but a larger size is preferable, as with large
    bearings the brasses do not wear so rapidly and the straps are not so
    likely to be burst by the bearings becoming oval. These sizes, as also
    those which immediately follow, suppose the pressure on the piston to
    be 18 lbs. per circular inch.</P>

    <P>348. <EM>Q.</EM>--How is the strength of a cast iron gudgeon
    computed?</P>

    <P><EM>A.</EM>--To find the proper size of a cast iron gudgeon adapted
    to sustain any given weight:--multiply the weight in lbs. by the
    intended length of bearing expressed in terms of the diameter; divide
    the product by 500, and extract the square root of the quotient, which
    is the diameter in inches.</P>

    <P>349. <EM>Q.</EM>--What was Mr. Watt&#39;s rule for the strength of
    gudgeons?</P>

    <P><EM>A.</EM>--Supposing the gudgeon to be square, then, to ascertain
    the thickness, multiply the weight resting on the gudgeon by the
    distance between the trunnions, and divide the product by 333. Extract
    the cube root of the quotient, which is the thickness in inches.</P>

    <P>350. <EM>Q.</EM>--How do you find the proper strength for the cast
    iron beam of a land engine?</P>

    <P><EM>A.</EM>--If the force acting at the end of an engine beam be
    taken at 18 lbs. per circular inch of the piston, then the force acting
    at the middle will be 36 lbs. per circular inch of the piston, and the
    proper strength of the beam at the centre will be found by the
    following rule:--divide the weight in lbs. acting at the centre by 250,
    and multiply the quotient by the distance between the extreme centres.
    To find the depth, the breadth being given:--divide this product by the
    breadth in inches, and extract the square root of the quotient, which
    is the depth. The depth of a land engine beam at the ends is usually
    made one third of the depth at the centre (the depth at the centre
    being equal to the diameter of the cylinder in the case of low pressure
    engines), while the length is made equal to three times the length of
    the stroke, and the mean thickness 1/108th of the length--the width of
    the edge bead being about three times the thickness of the web. In many
    modern engines the force acting at the end of the beam is more than 18
    lbs. per circular inch of the piston, but the above rules are still
    applicable by taking an imaginary cylinder with an area larger in the
    proportion of the larger pressure.</P>

    <P>351. <EM>Q.</EM>--What was Mr. Watt&#39;s rule for the main beams of
    his engines?</P>

    <P><EM>A.</EM>--Some of those beams were of wood and some of cast iron.
    The wood beams were so proportioned that the thickness was 1/58th of
    the circumference, and the depth 1/375. The side of the beam, supposing
    it square, was found by multiplying the diameter of the cylinder by the
    length of the stroke, and extracting the cube root of the quotient,
    which will be the depth or thickness of the beam. This rule allows a
    beam 16 feet long to bend 1/8th of an inch, and a beam 32 feet long to
    bend 1/4 of an inch. For cast iron beams the square of the diameter of
    the cylinder, multiplied by the length between the centres, is equal to
    the square of the depth, multiplied by the thickness.</P>

    <P>352. <EM>Q.</EM>--What law does the strength of beams and shafts
    follow?</P>

    <P><EM>A.</EM>--In the case of beams subjected to a breaking force, the
    strength with any given cohesion of the material will be proportional
    to the breadth, multiplied by the square of the depth; and in the case
    of revolving shafts exposed to a twisting strain, the strength with any
    given cohesive power of the material will be as the cube of the
    diameter.</P>

    <P>353. <EM>Q.</EM>--How is the strength of a cast iron shaft to resist
    torsion determined?</P>

    <P><EM>A.</EM>--Experiments upon the force requisite to twist off cast
    iron necks show that if the cube of the diameter of neck in inches be
    multiplied by 880, the product will be the force of torsion which will
    twist them off when acting at 6 inches radius; on this fact the
    following rule is founded: To find the diameter of a cast iron fly
    wheel shaft:--multiply the square of the diameter of the cylinder in
    inches, by the length of the crank in inches, and extract the cube root
    of the product, which multiply by 0.3025, and the result will be the
    proper diameter of the shaft in inches at the smallest part, when of
    cast iron.</P>

    <P>354. <EM>Q.</EM>--What was Mr. Watt&#39;s rule for the necks of his
    crank shafts?</P>

    <P><EM>A.</EM>--Taking the pressure on the piston at 12 lbs. pressure
    on the square inch, and supposing this force to be applied at one foot
    radius, divide the total pressure of the piston reduced to 1 foot of
    radius by 31.4, and extract the cube root of the quotient, which is the
    diameter of the shaft: or extract the cube root of 13.7 times the
    number of cubic feet of steam required to make one revolution, which is
    also the diameter of the shaft.</P>

    <P>355. <EM>Q.</EM>--Can you give any rule for the strength of the
    teeth of wheels?</P>

    <P><EM>A.</EM>--To find the proper dimensions for the teeth of a cast
    iron wheel:--multiply the diameter of the pitch circle in feet by the
    number of revolutions to be made per minute, and reserve the product
    for a divisor; multiply the number of <EM>actual</EM> horses power to
    be transmitted by 240, and divide the product by the above divisor,
    which will give the strength. If the pitch be given to find the
    breadth, divide the above strength by the square of the pitch in
    inches; or if the breadth be given, then to find the pitch divide the
    strength by the breadth in inches, and extract the square root of the
    quotient, which is the proper pitch in inches. The length of the teeth
    is usually about 5/8ths of the pitch. Pinions to work satisfactorily
    should not have less than 30 or 40 teeth, and where the speed exceeds
    220 feet in the minute, the teeth of the larger wheel should be of
    wood, made a little thicker, to keep the strength unimpaired.</P>

    <P>356. <EM>Q.</EM>--What was Mr. Watt&#39;s rule for the pitch of
    wheels?</P>

    <P><EM>A.</EM>--Multiply five times the diameter of the larger wheel by
    the diameter of the smaller, and extract the fourth root of the
    product, which is the pitch.</P>

    <H4 CLASS="subhead"><A NAME="h05"></A>STRENGTH OF MARINE AND LOCOMOTIVE
    ENGINES.</H4>

    <P>357. <EM>Q.</EM>--Cannot you give some rules of strength which will
    be applicable whatever pressure may be employed?</P>

    <P><EM>A.</EM>--In the rules already given, the effective pressure may
    be reckoned at from 18 to 20 lbs. upon every square inch of the piston,
    as is usual in land engines; and if the pressure upon every square inch
    of the piston be made twice greater, the dimensions must just be those
    proper for an engine of twice the area of piston. It will not be
    difficult, however, to introduce the pressure into the rules as an
    element of the computation, whereby the result will be applicable both
    to high and low pressure engines.</P>

    <P>358. <EM>Q.</EM>--Will you apply this mode of computation to a
    marine engine, and first find the diameter of the piston rod?</P>

    <P><EM>A.</EM>--The diameter of the piston rod may be found by
    multiplying the diameter of the cylinder in inches, by the square root
    of the pressure on the piston in lbs. per square inch, and dividing by
    50, which makes the strain 1/7th of the elastic force.</P>

    <P>359. <EM>Q.</EM>--What will be the rule for the connecting rod,
    supposing it to be of malleable iron?</P>

    <P><EM>A.</EM>--The diameter of the connecting rod at the ends, may be
    found by multiplying 0.019 times the square root of the pressure on the
    piston in lbs. per square inch by the diameter of the cylinder in
    inches; and the diameter of the connecting rod in the middle may be
    found by the following rule:--to 0.0035 times the length of the
    connecting rod in inches, add 1, and multiply the sum by 0.019 times
    the square root of the pressure on the piston in lbs. per square inch,
    multiplied by the diameter of the cylinder in inches. The strain is
    equal to 1/6th of the elastic force.</P>

    <P>360. <EM>Q.</EM>--How will you find the diameter of the cylinder
    side rods of a marine engine?</P>

    <P><EM>A.</EM>--The diameter of the cylinder side rods at the ends may
    be found by multiplying 0.0129 times the square root of the pressure on
    the piston in lbs. per square inch by the diameter of the cylinder; and
    the diameter of the cylinder side rods at the middle is found by the
    following rule:--to 0.0035 times the length of the rod in inches, add
    1, and multiply the sum by 0.0129 times the square root of the pressure
    on the piston in lbs. per square inch, multiplied by the diameter of
    the cylinder in inches; the product is the diameter of each side rod at
    the centre in inches. The strain upon the side rods is by these rules
    equal to 1/6th of the elastic force.</P>

    <P>361. <EM>Q.</EM>--How do you determine the dimensions of the
    crank?</P>

    <P><EM>A.</EM>--To find the exterior diameter of the large eye of the
    crank when of malleable iron:--to 1.561 times the pressure of the steam
    upon the piston in lbs. per square inch, multiplied by the square of
    the length of the crank in inches, add 0.00494 times the square of the
    diameter of the cylinder in inches, multiplied by the square of the
    number of lbs. pressure per square inch on the piston; extract the
    square root of this quantity; divide the result by 75.59 times the
    square root of the length of the crank in inches, and multiply the
    quotient by the diameter of the cylinder in inches; square the product
    and extract the cube root of the square, to which add the diameter of
    the hole for the reception of the shaft, and the result will be the
    exterior diameter of the large eye of the crank when of malleable iron.
    The diameter of the small eye of the crank may be found by adding to
    the diameter of the crank pin 0.02521 times the square root of the
    pressure on the piston in lbs. per square inch, multiplied by the
    diameter of the cylinder in inches.</P>

    <P>362. <EM>Q.</EM>--What will be the thickness of the crank web?</P>

    <P><EM>A.</EM>--The thickness of the web of the crank, supposing it to
    be continued to the centre of the shaft, would at that point be
    represented by the following rule:--to 1.561 times the square of the
    length of the crank in inches, add 0.00494 times the square of the
    diameter of the cylinder in inches, multiplied by the pressure on the
    piston in lbs. per square inch; extract the square root of the sum,
    which multiply by the diameter of the cylinder squared in inches, and
    by the pressure on the piston in lbs. per square inch; divide the
    product by 9,000, and extract the cube root of the quotient, which will
    be the proper thickness of the web of the crank when of malleable iron,
    supposing the web to be continued to the centre of the shaft. The
    thickness of the web at the crank pin centre, supposing it to be
    continued thither, would be 0.022 times the square root of the pressure
    on the piston in lbs. per square inch, multiplied by the diameter of
    the cylinder. The breadth of the web of the crank at the shaft centre
    should be twice the thickness, and at the pin centre 1-1/2 times the
    thickness of the web; the length of the large eye of the crank would be
    equal to the diameter of the shaft, and of the small eye 0.0375 times
    the square root of the pressure on the piston in lbs. per square inch,
    multiplied by the diameter of the cylinder.</P>

    <P>363. <EM>Q.</EM>--Will you apply the same method of computation to
    find the dimensions of a malleable iron paddle shaft?</P>

    <P><EM>A.</EM>--The method of computation will be as follows:--to find
    the dimensions of a malleable iron paddle shaft, so that the strain
    shall not exceed 5/6ths of the elastic force, or 5/6ths of the force
    iron is capable of withstanding without permanent derangement of
    structure, which in tensile strains is taken at 17,800 lbs. per square
    inch: multiply the pressure in lbs. per square inch on the piston by
    the square of the diameter of the cylinder in inches, and the length of
    the crank in inches, and extract the cube root of the product, which,
    multiplied by 0.08264, will be the diameter of the paddle shaft journal
    in inches when of malleable iron, whatever the pressure of the steam
    may be. The length of the paddle shaft journal should be 1-1/4 times
    the diameter; and the diameter of the part where the crank is put on is
    often made equal to the diameter over the collars of the journal or
    bearing.</P>

    <P>364. <EM>Q.</EM>--How do you find the diameter of the crank pin?</P>

    <P><EM>A.</EM>--The diameter of the crank pin in inches may be found by
    multiplying 0.02836 times the square root of the pressure on the piston
    in lbs. per square inch, by the diameter of the cylinder in inches. The
    length of the pin is usually about 9/8th times its diameter, and the
    strain if all thrown upon the end of the pin will be equal to the
    elastic force; but in ordinary working, the strain will only be equal
    to 1/3d of the elastic force.</P>

    <P>365. <EM>Q.</EM>--What are the dimensions of the cross head?</P>

    <P><EM>A.</EM>--If the length of the cross head be taken at 1.4 times
    the diameter of the cylinder, the dimensions of the cross head will be
    as follows:--the exterior diameter of the eye in the cross head for the
    reception of the piston rod, will be equal to the diameter of the hole,
    plus 0.02827 times the cube root of the pressure on the piston in lbs.
    per square inch, multiplied by the diameter of the cylinder in inches;
    and the depth of the eye will be 0.0979 times the cube root of the
    pressure on the piston in lbs. per square inch, multiplied by the
    diameter of the cylinder in inches. The diameter of each cross head
    journal will be 0.01716 times the square root of the pressure on the
    piston in lbs. per square inch, multiplied by the diameter of the
    cylinder in inches--the length of the journal being 9/8ths its
    diameter. The thickness of the web at centre will be 0.0245 times the
    cube root of the pressure on the piston in lbs. per square inch,
    multiplied by the diameter of the cylinder in inches; and the depth of
    web at centre will be 0.09178 times the cube root of the pressure on
    the piston in lbs. per square inch, multiplied by the diameter of the
    cylinder in inches. The thickness of the web at journal will be 0.0122
    times the square root of the pressure on the piston in lbs. per square
    inch, multiplied by the diameter of the cylinder in inches; and the
    depth of the web at journal will be 0.0203 times the square root of the
    pressure upon the piston in lbs. per square inch, multiplied by the
    diameter of the cylinder in inches. In these rules for the cross head,
    the strain upon the web is 1/2.225 times the elastic force; the strain
    upon the journal in ordinary working is 1/2.33 times the elastic force;
    and if the outer ends of the journals are the only bearing points, the
    strain is 1/1.165 times the elastic force, which is very little in
    excess of the elastic force.</P>

    <P>366. <EM>Q.</EM>--How do you find the diameter of the main centre
    when proportioned according to this rule?</P>

    <P><EM>A.</EM>--The diameter of the main centre may be found by
    multiplying 0.0367 times the square root of the pressure upon the
    piston in lbs. per square inch, by the diameter of the cylinder in
    inches, which will give the diameter of the main centre journal in
    inches when of malleable iron, and the length of the main centre
    journal should be 1-1/2 times its diameter; the strain upon the main
    centre journal in ordinary working will be about 1/2 the elastic
    force.</P>

    <P>367. <EM>Q.</EM>--What are the proper dimensions of the gibs and
    cutters of an engine?</P>

    <P><EM>A.</EM>--The depth of gibs and cutters for attaching the piston
    rod to the cross head, is 0.0358 times the cube root of the pressure of
    the steam on the piston in lbs. per square inch, multiplied by the
    diameter of the cylinder; and the thickness of the gibs and cutters is
    0.007 times the cube root of the pressure on the piston in lbs. per
    square inch, multiplied by the diameter of its cylinder. The depth of
    the cutter through the piston is 0.017 times the square root of the
    pressure on the piston in lbs. per square inch, multiplied by the
    diameter of the cylinder in inches; and the thickness of the cutter
    through the piston is 0.007 times the square root of the pressure on
    the piston in lbs. per square inch, multiplied by the diameter of the
    cylinder.</P>

    <P>368. <EM>Q.</EM>--Are not some of the parts of an engine constructed
    according to these rules too weak, when compared with the other
    parts?</P>

    <P><EM>A.</EM>--It is obvious, from the varying proportions subsisting
    in the different parts of the engine between the strain and the elastic
    force, that in engines proportioned by these rules--which represent
    nevertheless the average practice of the best constructors--some of the
    parts must possess a considerable excess of strength over other parts,
    and it appears expedient that this disparity should be diminished,
    which may best be done by increasing the strength of the parts which
    are weakest; inasmuch as the frequent fracture of some of the parts
    shows that the dimensions at present adopted for those parts are
    scarcely sufficient, unless the iron of which they are made is of the
    best quality. At the same time it is quite certain, that engines
    proportioned by these rules will work satisfactorily where good
    materials are employed; but it is important to know in what parts good
    materials and larger dimensions are the most indispensable. In many of
    the parts, moreover, it is necessary that the dimensions should be
    proportioned to meet the wear and the tendency to heat, instead of
    being merely proportioned to obtain the necessary strength; and the
    crank pin is one of the parts which requires to be large in diameter,
    and as long as possible in the bearing, so as to distribute the
    pressure, and prevent the disposition to heat which would otherwise
    exist. The cross head journals also should be long and large; for as
    the tops of the side rods have little travel, the oil is less drawn
    into the bearings than if the travel was greater, and is being
    constantly pressed out by the punching strain. This strain should
    therefore be reduced as far as possible by its distribution over a
    large surface. In the rules which are contained in the answers to the
    ten preceding questions (358 to 367) the pressure on the piston in lbs.
    per square inch is taken as the sum of the pressure of steam in the
    boiler and of the vacuum; the latter being assumed to be 15 lbs. per
    square inch.</P>

    <H2 CLASS="chapter"><A NAME="ch07"></A>CHAPTER VII.</H2>

    <H3>CONSTRUCTIVE DETAILS OF BOILERS.</H3>

    <H4 CLASS="subhead"><A NAME="j01">LAND AND MARINE BOILERS.</A></H4>

    <P>369. <EM>Q.</EM>--Will you explain the course of procedure in the
    construction and setting of wagon boilers?</P>

    <P><EM>A.</EM>--Most boilers are made of plates three eighths of an
    inch thick, and the rivets are from three eighths to three fourths of
    an inch in diameter. In the bottom and sides of a wagon boiler the
    heads of the rivets, or the ends formed on the rivets before they are
    inserted, should be large and placed next the fire, or on the outside;
    whereas on the top of the boiler the heads should be on the inside. The
    rivets should be placed about two inches distant from centre to centre,
    and the centre of the row of rivets should be about one inch from the
    edge of the plate. The edges of the plates should be truly cut, both
    inside and outside, and after the parts of the boiler have been riveted
    together, the edges of the plates should be set up or caulked with a
    blunt chisel about a quarter of an inch thick in the point, and struck
    by a hammer of about three or four pounds weight, one man holding the
    caulking tool while another strikes.</P>

    <P>370. <EM>Q.</EM>--Is this the usual mode of caulking?</P>

    <P><EM>A.</EM>--No, it is not the usual mode; but it is the best mode,
    and is the mode adopted by Mr. Watt. The usual mode now is for one man
    to caulk the seams with a hammer in one hand and a caulking chisel in
    the other, and in some of the difficult corners of marine flue boilers
    it is not easy for two men to get in. A good deal of the caulking has
    also sometimes to be done with the left hand.</P>

    <P>371. <EM>Q.</EM>--Should the boiler be proved after caulking?</P>

    <P><EM>A.</EM>--The boiler should be filled with water and caulked
    afresh in any leaky part. When emptied again, all the joints should be
    painted with a solution of sal ammoniac in urine, and so soon as the
    seams are well rusted they should be dried with a gentle fire, and then
    be painted over with a thin putty formed of whiting and linseed oil,
    the heat being continued until the putty becomes so hard that it cannot
    be readily scratched with the nail, and care must be taken neither to
    burn the putty nor to discontinue the fire until it has become quite
    dry.</P>

    <P>372. <EM>Q.</EM>--How should the brickwork setting of a wagon boiler
    be built?</P>

    <P><EM>A.</EM>--In building the brickwork for the setting of the
    boiler, the part upon which the heat acts with most intensity is to be
    built with clay instead of mortar, but mortar is to be used on the
    outside of the work. Old bars of flat iron may be laid under the boiler
    chime to prevent that part of the boiler from being burned out, and
    bars of iron should also run through the brickwork to prevent it from
    splitting. The top of the boiler is to be covered with brickwork laid
    in the best lime, and if the lime be not of the hydraulic kind, it
    should be mixed with Dutch terrass, to make it impenetrable to water.
    The top of the boiler should be well plastered with this lime, which
    will greatly conduce to the tightness of the seams. Openings into the
    flues must be left in convenient situations to enable the flues to be
    swept out when required, and these openings may be closed with cast
    iron doors jointed with clay or mortar, which may be easily removed
    when required. Adjacent to the chimney a slit must be left in the top
    of the flue with a groove in the brickwork to enable the sliding door
    or damper to be fixed in that situation, which by being lowered into
    the flue will obstruct the passage of the smoke and moderate the
    draught, whereby the chimney will be prevented from drawing the flame
    into it before the heat has acted sufficiently upon the boiler.</P>

    <P>373. <EM>Q.</EM>--Are marine constructed in the same way as land
    boilers?</P>

    <P><EM>A.</EM>--There is very little difference in the two cases: the
    whole of the shells of marine boilers, however, should be double
    riveted with rivets 11/16ths of an inch in diameter, and 2-3/8th inches
    from centre to centre, the weakening effect of double riveting being
    much less than that of single riveting. The furnaces above the line of
    bars should be of the best Lowmoor, Bowling, or Staffordshire scrap
    plates, and the portion of each furnace above the bars should consist
    only of three plates, one for the top and one for each side, the lower
    seam of the side plates being situated beneath the level of the bars,
    so as not to be exposed to the heat of the furnace. The tube plates of
    tubular boilers should be of the best Lowmoor, or Bowling iron, seven
    eighths to one inch thick: the shells should be of the best
    Staffordshire, or Thornycroft S crown iron, 7/16ths of an inch
    thick.</P>

    <P>374. <EM>Q.</EM>--Of what kind of iron should the angle iron or
    corner iron be composed?</P>

    <P><EM>A.</EM>--Angle iron should not be used in the construction of
    boilers, as in the manufacture it becomes reedy, and is apt to split up
    in the direction of its length: it is much the safer practice to bend
    the plates at the corners of the boiler; but this must be carefully
    done, without introducing any more sharp bends than can be avoided, and
    plates which require to be bent much should be of Lowmoor iron. It will
    usually be found expedient to introduce a ring of angle iron around the
    furnace mouths, though it is discarded in the other parts of the
    boiler; but it should be used as sparingly as possible, and any that is
    used should be of the best quality.</P>

    <P>375. <EM>Q.</EM>--Is it not important to have the holes in the
    plates opposite to one another?</P>

    <P><EM>A.</EM>--The whole of the plates of a boiler should have the
    holes for the rivets punched, and the edges cut straight, by means of
    self-acting machinery, in which a travelling table carries forward the
    plate with an equal progression every stroke of the punch or shears;
    and machinery of this kind is now extensively employed. The practice of
    forcing the parts of boilers together with violence, by means of
    screw-jacks, and drifts through the holes, should not be permitted; as
    a great strain may thus be thrown upon the rivets, even when there is
    no steam in the boiler. All rivets should be of the best Lowmoor iron.
    The work should be caulked both within and without wherever it is
    accessible, but in the more confined situations within the flues the
    caulking will in many cases have to be done with the hand or chipping
    hammer, instead of the heavy hammer previously prescribed.</P>

    <P>376. <EM>Q.</EM>--How is the setting of marine boilers with internal
    furnaces effected?</P>

    <P><EM>A.</EM>--In the setting of marine boilers care must be taken
    that no copper bolts or nails project above the wooden platform upon
    which they rest, and also that no projecting copper bolts in the sides
    of the ship touch the boiler, as the galvanic action in such a case
    would probably soon wear the points of contact into holes. The platform
    may consist of three inch planking laid across the keelsons nailed with
    iron, nails, the heads of which are well punched down, and caulked and
    puttied like a deck. The surface may then be painted over with thin
    putty, and fore and aft boards of half the thickness may then be laid
    down and nailed securely with iron nails, having the heads well punched
    down. This platform must then be covered thinly and evenly with mastic
    cement and the boiler be set down upon it, and the cement must be
    caulked beneath the boiler by means of wooden caulking tools, so as
    completely to fill every vacuity. Coomings of wood sloped on the top
    must next be set round the boiler, and the space between the coomings
    and the boiler must be caulked full of cement, and be smoothed off on
    the top to the slope of the coomings, so as to throw off any water that
    might be disposed to enter between the coomings and the boiler.</P>

    <P>377. <EM>Q.</EM>--How is the cement used for setting marine boilers
    compounded?</P>

    <P><EM>A.</EM>--Mastic cement proper for the setting of boilers is sold
    in many places ready made. Hamelin&#39;s mastic is compounded as
    follows:--to any given weight of sand or pulverized earthenware add two
    thirds such given weight of powdered Bath, Portland, or other similar
    stone, and to every 560 lbs. weight of the mixture add 40 lbs. weight
    of litharge, 2 lbs. of powdered glass or flint, 1 lb. of minium, and 2
    lbs. of gray oxide of lead; pass the mixture through a sieve, and keep
    it in a powder for use. When wanted for use, a sufficient quantity of
    the powder is mixed with some vegetable oil upon a board or in a trough
    in the manner of mortar, in the proportion of 605 lbs. of the powder to
    5 gallons of linseed, walnut, or pink oil, and the mixture is stirred
    and trodden upon until it assumes the appearance of moistened sand,
    when it is ready for use. The cement should be used on the same day as
    the oil is added, else it will be set into a solid mass.</P>

    <P>378. <EM>Q.</EM>--What is the best length of the furnaces of marine
    boilers?</P>

    <P><EM>A.</EM>--It has already been stated that furnace bars should not
    much exceed six feet in length, as it is difficult to manage long
    furnaces; but it is a frequent practice to make the furnaces long and
    narrow, the consequence of which is, that it is impossible to fire them
    effectually at the after end, especially upon long voyages and in
    stormy weather, and air escapes into the flues at the after end of the
    bars, whereby the efficacy of the boiler is diminished. Where the bars
    are very long it will generally be found that an increased supply of
    steam and a diminished consumption of coal will be the consequence of
    shortening them, and the bars should always lie with a considerable
    inclination to facilitate the distribution of the fuel over the after
    part of the furnace. When there are two lengths of bars in the furnace,
    it is expedient to make the central cross bar for bearing up the ends
    double, and to leave a space between the ends of the bars so that the
    ashes may fall through between them. The space thus left enables the
    bars to expand without injury on the application of heat, whereas
    without some such provision the bars are very liable to get burned out
    by bending up in the centre, or at the ends, as they must do if the
    elongation of the bars on the application of heat be prevented; and
    this must be the effect of permitting the spaces at the ends of the
    bars to be filled up with ashes. At each end of each bed of bars it is
    expedient to leave a space which the ashes cannot fill up so as to
    cause the bars to jam; and care must be taken that the heels of the
    bars do not come against any of the furnace bearers, whereby the room
    left at the end of the bars to permit the expansion would be rendered
    of no avail.</P>

    <P>379. <EM>Q.</EM>--Have you any remarks to offer respecting the
    construction and arrangement of the furnace bridges and dampers of
    marine boilers?</P>

    <P><EM>A.</EM>--The furnace bridges of marine boilers are walls or
    partitions built up at the ends of the furnaces to narrow the opening
    for the escape of heat into the flues. They are either made of fire
    brick or of plate iron containing water: in the case of water bridges,
    the top part of the bridge should be made with a large amount of slant
    so as to enable the steam to escape freely, but notwithstanding this
    precaution the plates of water bridges are apt to crack at the bend, so
    that fire brick bridges appear on the whole to be preferable. In
    shallow furnaces the bridges often come too near the furnace top to
    enable a man to pass over them; and it will save expense if in such
    bridges the upper portion is constructed of two or three fire blocks,
    which may be lifted off where a person requires to enter the flues to
    sweep or repair them, whereby the perpetual demolition and
    reconstruction of the upper part of the bridge will be prevented.</P>

    <P>380. <EM>Q.</EM>--What is the benefit of bridges?</P>

    <P><EM>A.</EM>--Bridges are found in practice to have a very sensible
    operation in increasing the production of steam, and in some boilers in
    which the brick bridges have been accidentally knocked down by the
    firemen, a very considerable diminution in the supply of steam has been
    experienced. Their chief operation seems to lie in concentrating the
    heat within the furnace to a higher temperature, whereby the heat is
    more rapidly transmitted from the furnace to the water, and less heat
    has consequently to be absorbed by the flues. In this way the bridges
    render the heating surface of a boiler more effective, or enable a
    smaller amount of heating surface to suffice.</P>

    <P>381. <EM>Q.</EM>--Are the bridges behind the furnaces the only
    bridges used in steam boilers?</P>

    <P><EM>A.</EM>--It is not an uncommon practice to place a hanging
    bridge, consisting of a plate of iron descending a certain distance
    into the flue, at that part of the flue where it enters the chimney,
    whereby the stratum of hot air which occupies the highest part of the
    flue is kept in protracted contact with the boiler, and the cooler air
    occupying the lower part of the flue is that which alone escapes. The
    practice of introducing a hanging bridge is a beneficial one in the
    case of some boilers, but is not applicable universally, as boilers
    with a small calorimeter cannot be further contracted in the flue
    without a diminution in their evaporating power. In tubular boilers a
    hanging bridge is not applicable, but in some cases a perforated plate
    is placed against the ends of the tubes, which by suitable connections
    is made to operate as a sliding damper which partially or totally
    closes up the end of every tube, and at other times a damper
    constructed in the manner of a venetian blind is employed in the same
    situation. These varieties of damper, however, have only yet been used
    in locomotive boilers, though applicable to tubular boilers of every
    description.</P>

    <P>382. <EM>Q.</EM>--Is it a benefit to keep the flues or tubes
    appertaining to each furnace distinct?</P>

    <P><EM>A.</EM>--In a flue boiler this cannot be done, but in a tubular
    boiler it is an advantage that there should be a division between the
    tubes pertaining to each furnace, so that the smoke of each furnace may
    be kept apart from the smoke of the furnace adjoining it until the
    smoke of both enters the chimney, as by this arrangement a furnace only
    will be rendered inoperative in cleaning the fires instead of a boiler,
    and the tubes belonging to one furnace may be swept if necessary at sea
    without interfering injuriously with the action of the rest. In a steam
    vessel it is necessary at intervals to empty out one or more furnaces
    every watch to get rid of the clinkers which would otherwise accumulate
    in them; and it is advisable that the connection between the furnaces
    should be such that this operation, when being performed on one
    furnace, shall injure the action of the rest as little as possible.</P>

    <P>383. <EM>Q.</EM>--Can any constructive precautions be taken to
    prevent the furnaces and tube plates of the boiler from being burned by
    the intensity of the heat?</P>

    <P><EM>A.</EM>--The sides of the internal furnaces or flues in all
    boilers should be so constructed that the steam may readily escape from
    their surfaces, with which view it is expedient to make the bottom of
    the flue somewhat wider than the top, or slightly conical in the cross
    section; and the upper plates should always be overlapped by the plates
    beneath, so that the steam cannot be retained in the overlap, but will
    escape as soon as it is generated. If the sides of the furnace be made
    high and perfectly vertical, they will speedily be buckled and cracked
    by the heat, as a film of steam in such a case will remain in contact
    with the iron which will prevent the access of the water, and the iron
    of the boiler will be injured by the high temperature it must in that
    case acquire. To moderate the intensity of the heat acting upon the
    furnace sides, it is expedient to bring the outside fire bars into
    close contact with the sides of the furnace, so as to prevent the
    entrance of air through the fire in that situation, by which the
    intensity of the heat would be increased. The tube plate nearest the
    furnace in tubular boilers should also be so inclined as to facilitate
    the escape of the steam; and the short bent plate or flange of the tube
    plate, connecting the tube plate with the top of the furnace, should be
    made with a gradual bend, as, if the bend be sudden, the iron will be
    apt to crack or burn away from the concretion of salt. Where the
    furnace mouths are contracted by bending in the sides and top of the
    furnace, as is the general practice, the bends should be gradual, as
    salt is apt to accumulate in the pockets made by a sudden bend, and the
    plates will then burn into holes.</P>

    <P>384. <EM>Q.</EM>--In what manner is the tubing of boilers
    performed?</P>

    <P><EM>A.</EM>--The tubes of marine boilers are generally iron tubes,
    three inches in diameter, and between six and seven feet long; but
    sometimes brass tubes of similar dimensions are employed. When brass
    tubes are employed, the use of ferules driven into the ends of the
    tubes is sometimes employed to keep them tight; but when the tubes are
    of malleable iron, of the thickness of Russell&#39;s boiler tubes, they
    may be made tight merely by firmly driving them into the tube plates,
    and the same may be done with thick brass tubes. The holes in the tube
    plate next the front of the boiler are just sensibly larger in diameter
    than the holes in the other tube plate, and the holes upon the outer
    surfaces of both tube plates are very slightly countersunk. The whole
    of the tubes are driven through both tube plates from the front of the
    boiler,--the precaution, however, being taken to drive them in gently
    at first with a light hand hammer, until the whole of the tubes have
    been inserted to an equal depth, and then they may be driven up by
    degrees with a heavy hammer, whereby any distortion of the holes from
    unequal driving will be prevented. Finally, the ends of the tubes
    should be riveted up so as to fill the countersink; the tubes should be
    left a little longer than the distance between the outer surfaces of
    the tube plates, so that the countersink at the ends may be filled by
    staving up the end of the tube rather than by riveting it over; and the
    staving will be best accomplished by means of a mandril with a collar
    upon it, which is driven into the tube so that the collar rests upon
    the end of the tube to be riveted; or a tool like a blunt chisel with a
    recess in its point may be used, as is the more usual practice.</P>

    <P>385. <EM>Q.</EM>--Should not stays be introduced in substitution of
    some of the tubes?</P>

    <P><EM>A.</EM>--It appears expedient in all cases that some of the
    tubes should be screwed at the ends, so as to serve as stays if the
    riveting at the tube ends happens to be burned away, and also to act as
    abutments to the riveted tube--or else to introduce very strong rods of
    about the same diameter as a tube, in substitution of some of the
    tubes; and these stays should have nuts at each end both within and
    without the tube plates, which nuts should be screwed up, with white
    lead interposed, before the tubes are inserted. If the tubes are long,
    their expansion when the boiler is being blown off will be apt to start
    them at the ends, unless very securely fixed; and it is difficult to
    prevent brass tubes of large diameter and proportionate length from
    being started at the ends, even when secured by ferules; but the brass
    tubes commonly employed are so small as to be susceptible of sufficient
    compression endways by the adhesion due to the ferules to compensate
    for the expansion, whereby they are prevented from starting at the
    ends. In some, of the early marine boilers fitted with brass tubes, a
    galvanic action at the ends of the tubes was found to take place, and
    the iron of the tube plates was wasted away in consequence, with
    rapidity; but further experience proved the injury to be attributable
    chiefly to imperfect fitting, whereby a leakage was caused that induced
    oxidation, and when, the tubes were well fitted any injurious action at
    the ends of the tubes was found to cease.</P>

    <P>386. <EM>Q.</EM>--What is the best mode of constructing the chimney
    and the parts in connection therewith?</P>

    <P><EM>A.</EM>--In sea-going steamers the funnel plates are usually
    about nine feet long and 3/16ths thick; and where different flues or
    boilers have their debouch in the same chimney, it is expedient to run
    division plates up the chimney for a considerable distance, to keep the
    draughts distinct. The dampers should not be in the chimney but at the
    end of the boiler flue, so that they may be available for use if the
    funnel by accident be carried away. The waste steam pipe should be of
    the same height as the funnel, so as to carry the waste steam clear of
    it, for if the waste steam strikes the funnel it will wear the iron
    into holes; and the waste steam pipes should be made at the bottom with
    a faucet joint, to prevent the working of the funnel, when the vessel
    rolls, from breaking the pipe at the neck. There should be two hoops
    round the funnel, for the attachment of the funnel shrouds, instead of
    one, so that the funnel may not be carried overboard if one hoop
    breaks, or if the funnel breaks at the upper hoop from the corrosive
    action of the waste steam, as sometimes happens. The deck over the
    steam chest should be formed of an iron plate supported by angle iron
    beams, and there should be a high angle iron cooming round the hole in
    the deck through which the chimney ascends, to prevent any water upon
    the deck from leaking down upon the boiler. Around the lower part of
    the funnel there should be a sheet iron casing to prevent any
    inconvenient dispersion of heat in that situation, and another short
    piece of casing, of a somewhat larger diameter, and riveted to the
    chimney, should descend over the first casing, so as to prevent the
    rain or spray which may beat against the chimney from being poured down
    within the casing upon the top of the boiler. The pipe for conducting
    away the waste water from the top of the safety valve should lead
    overboard, and not into the bilge of the ship, as inconvenience arises
    from the steam occasionally passing through it, if it has its
    termination in the engine room.</P>

    <P>387. <EM>Q.</EM>--Are not the chimneys of some vessels made so that
    they may be lowered when required?</P>

    <P><EM>A.</EM>--The chimneys of small river vessels which have to pass
    under bridges are generally formed with a hinge, so that they may be
    lowered backward when passing under a bridge; and the chimneys of some
    screw vessels are made so as to shut up like a spyglass when the fires
    are put out and the vessel is navigated under sails. In smaller
    vessels, however, two lengths of chimney suffice; and in that case
    there is a standing piece on deck, which, however, does not project
    above the bulwarks.</P>

    <P>388. <EM>Q.</EM>--Will you explain any further details in the
    construction of marine boilers which occur to you as important?</P>

    <P><EM>A.</EM>--The man-hole and mud-hole doors, unless put on from the
    outside, like a cylinder cover, with a great number of bolts, should be
    put on from the inside with cross bars on the outside, and the bolts
    should be strong, and have coarse threads and square nuts, so that the
    threads may not be overrun, nor the nuts become round, by the unskilful
    manipulations of the firemen, by whom these doors are removed or
    replaced. It is very expedient that sufficient space should be left
    between the furnace and the tubes in all tubular boilers to permit a
    boy to go in to clear away any scale that may have formed, and to hold
    on the rivets in the event of repair being wanted; and it is also
    expedient that a vertical row of tubes should be left out opposite to
    each water space to allow the ascent of the steam and descent of the
    water, as it has been found that the removal of the tubes in that
    position, even in a boiler with deficient heating surface, has
    increased the production of steam, and diminished the consumption of
    fuel. The tubes should all be kept in the same vertical line, so as to
    permit the introduction of an instrument to scrape them; but they may
    be zig-zagged in the horizontal line, whereby a greater strength of
    metal will be obtained around the holes in the tube plates, and the
    tubes should not be placed too close together, else their heating
    efficacy will be impaired.</P>

    <H4 CLASS="subhead"><A NAME="j02"></A>INCRUSTATION AND CORROSION OF
    BOILERS.</H4>

    <P>389. <EM>Q.</EM>--What is the cause of the formation of scale in
    marine boilers?</P>

    <P><EM>A.</EM>--Scale is formed in all boilers which contain earthy or
    saline matters, just in the way in which a scaly deposit, or rock, as
    it is sometimes termed, is formed in a tea kettle. In sea water the
    chief ingredient is common salt, which exists in solution: the water
    admitted to the boiler is taken away in the shape of steam, and the
    saline matter which is not vaporizable accumulates in process of time
    in the boiler, until its amount is so great that the water is
    saturated, or unable to hold any more in solution; the salt is then
    precipitated and forms a deposit which hardens by heat. The formation
    of scale, therefore, is similar to the process of making salt from sea
    water by evaporation, the boiler being, in fact, a large salt pan.</P>

    <P>390. <EM>Q.</EM>--But is the scale soluble in fresh water like the
    salt in a salt pan?</P>

    <P><EM>A.</EM>--No, it is not; or if soluble at all, is only so to a
    very limited extent. The several ingredients in sea water begin to be
    precipitated from solution at different degrees of concentration; and
    the sulphate and carbonate of lime, which begin to be precipitated when
    a certain state of concentration is reached, enter largely into the
    composition of scale, and give it its insoluble character. Pieces of
    waste or other similar objects left within a marine boiler appear, when
    taken out, as if they had been petrified; and the scale deposited upon
    the flues of a marine boiler resembles layers of stone.</P>

    <P>391. <EM>Q/</EM>--Is much inconvenience experienced in marine
    boilers from these incrustations upon the flues?</P>

    <P><EM>A.</EM>--Incrustation in boilers at one time caused much more
    perplexity than it does at present, as it was supposed that in some
    seas it was impossible to prevent the boilers of a steamer from
    becoming salted up; but it has now been satisfactorily ascertained that
    there is very little difference in the saltness of different seas, and
    that however salt the water may be, the boiler will be preserved from
    any injurious amount of incrustation by blowing off, as it is called,
    very frequently, or by permitting a considerable portion of the
    supersalted water to escape at short intervals into the sea. If blowing
    off be sufficiently practised, the scale upon the flues will never be
    much thicker than a sheet of writing paper, and <EM>no excuse</EM>
    should be accepted from engineers for permitting a boiler to be damaged
    by the accumulation of calcareous deposit.</P>

    <P>392. <EM>Q.</EM>--What is the temperature at which sea water boils
    in a steam boiler?</P>

    <P><EM>A.</EM>--Sea water contains about 1/33rd its weight of salt, and
    in the open air it boils at the temperature of 213.2&deg;; if the
    proportion of salt be increased to 2/33rds of the weight of the water,
    the boiling point will rise to 214.4&deg;; with 3/33rds of salt the
    boiling point will be 215.5&deg;; 4/33rds, 216.7&deg;; 5/33rds,
    217.9&deg;; 6/33rds, 219&deg;; 7/33rds, 220.2&deg;; 8/33rds,
    221.4&deg;; 9/33rds, 222.5&deg;; 10/33rds, 223.7&deg;; 11/33rds,
    224.9&deg;; and 12/33rds, which is the point of saturation, 226&deg;.
    In a steam boiler the boiling points of water containing these
    proportions of salt must be higher, as the elevation of temperature due
    to the pressure of the steam has to be added to that due to the
    saltness of the water; the temperature of steam at the atmospheric
    pressure being 212&deg;, its temperature, at a pressure of 15 lbs. per
    square inch above the atmosphere, will be 250&deg;, and adding to this
    4.7&deg; as the increased temperature due to the saltness of the water
    when it contains 4/33rds of salt, we have 254.7&deg; as the temperature
    of the water in the boiler, when it contains 4/33rds of salt and the
    pressure of the steam is 15 lbs. on the square inch.</P>

    <P>393. <EM>Q.</EM>--What degree of concentration of the salt water may
    be safely permitted in a boiler?</P>

    <P><EM>A.</EM>--It is found by experience that when the concentration
    of the salt water in a boiler is prevented from exceeding that point at
    which it contains 2/33rds its weight of salt, no injurious incrustation
    will take place, and as sea water contains only 1/33rd of its weight of
    salt, it is clear that it must be reduced by evaporation to one half of
    its bulk before it can contain 2/33rds of salt; or, in other words, a
    boiler must blow out into the sea one half of the water it receives as
    feed, in order to prevent the water from rising above 2/33rds of
    concentration, or 8 ounces of salt to the gallon.</P>

    <P>394. <EM>Q.</EM>--How do you determine 8 ounces to the gallon to be
    equivalent to twice the density of salt water, or &quot;two salt
    waters&quot; as it is sometimes called?</P>

    <P><EM>A.</EM>--The density of the water of different seas varies
    somewhat. A gallon of fresh water weighs 10 lbs.; a gallon of salt
    water from the Baltic weighs 10.15 lbs.; a gallon of salt water from
    the Irish Channel weighs 10.28 lbs.; and a gallon of salt water from
    the Mediterranean 10.29 lbs. If we take an average saltness represented
    by a weight of 10.25 lbs., then a gallon of water concentrated to twice
    this saltness will weigh 10.5 lbs., or the salt in it will weigh .5 lbs
    or 8 oz., which is the proportion of 8 oz. to the gallon. However, the
    proportion of 2/33rds gives a greater proportion than 8 oz. to the
    gallon, for 2/33 = 1/16 nearly, and 1/16 of 10 lbs. = 10 oz. By keeping
    the density of the water in a marine boiler at the proportion of 8 or
    10 oz. to the gallon, no inconvenient amount of scale will be deposited
    on the flues or tubes. The bulk of water, it may be remarked, is not
    increased by putting salt in it up to the point of saturation, but only
    its density is increased.</P>

    <P>395. <EM>Q.</EM>--Is there not a great loss of heat by blowing off
    so large a proportion of the heated water from the boiler?</P>

    <P><EM>A.</EM>--The loss is not very great. Boilers are sometimes
    worked at a saltness of 4/33rds, and taking this saltness and supposing
    the latent heat of steam to be at 1000&deg; at the temperature of
    212&deg;, and reckoning the sum of the latent and sensible heats as
    forming a constant quantity, the latent heat of steam at the
    temperature of 250&deg; will be 962&deg;, and the total heat of the
    steam will be 1212&deg; in the case of fresh water; but as the feed
    water is sent into the boiler at the temperature of 100&deg;, the
    accession of heat it receives from the fuel will be 1112&deg; in the
    case of fresh water, or 1112&deg; increased by 3.98&deg; in the case of
    water containing 4/33ds of salt-- the 3.98&deg; being the 4.7&deg;
    increase of temperature due to the presence of 4/33rds of salt,
    multiplied by 0.847 the specific heat of steam. This makes the total
    accession of heat received by the steam in the boiler equal to
    1115.98&deg;, or say 1116&deg;, which multiplied by 3, as 3 parts of
    the water are raised into steam, gives us 3348&deg; for the heat in the
    steam, while the accession of heat received in the boiler by the 1 part
    of residual brine will be 154.7&deg;, multiplied by 0.85, the specific
    heat of the brine, or 130.495&deg;; and 3348&deg; divided by
    130.495&deg; is about 1/26th. It appears, therefore, that by blowing
    off the boiler to such an extent that the saltness shall not rise above
    what answers to 4/33rds of salt, about 1/25th of the heat is blown into
    the sea; this is but a small proportion, and as there will be a greater
    waste of heat, if from the existence of scale upon the flues the heat
    can be only imperfectly transmitted to the water, there cannot be even
    an economy of fuel in niggard blowing off, while it involves the
    introduction of other evils. The proportion of 4/33rds of saltness,
    however, or 16 oz. to the gallon, is larger than is advisable,
    especially as it is difficult to keep the saltness at a perfectly
    uniform point, and the working point should, therefore, be 2/33rds as
    before prescribed.</P>

    <P>396. <EM>Q.</EM>--Have no means been devised for turning to account
    the heat contained in the brine which is expelled from the boiler?</P>

    <P><EM>A.</EM>--To save a part of the heat lost by the operation of
    blowing off, the hot brine is sometimes passed through a number of
    small tubes surrounded by the feed water; but there is no very great
    gain from the use of such apparatus, and the tubes are apt to become
    choked up, whereby the safety of the boiler may be endangered by the
    injurious concentration of its contents. Pumps, worked by the engine
    for the extraction of the brine, are generally used in connection with
    the small tubes for the extraction of the heat from the supersalted
    water; and if the tubes become choked the pumps will cease to eject the
    water, while the engineer may consider them to be all the while in
    operation.</P>

    <P>397.<EM>Q.</EM>--What is the usual mode of blowing off the
    supersalted water from the boiler?</P>

    <P><EM>A.</EM>--The general mode of blowing off the boiler is to allow
    the water to rise gradually for an hour or two above the lowest Working
    level, and then to open the cock communicating with the sea, and keep
    it open until the surface of the water within the boiler has fallen
    several inches; but in some cases a cock of smaller size is allowed to
    run water continuously, and in other cases brine pumps are used as
    already mentioned. In every case in which the supersalted water is
    discharged from the boiler in a continuous stream, a hydrometer or salt
    gauge of some convenient construction should be applied to the boiler,
    so that the density of the water may at all times be visible, and
    immediate notice be given of any interruption of the operation. Various
    contrivances have been devised for this purpose, the most of which
    operate on the principle of a hydrometer; but perhaps a more
    satisfactory principle would be that of a differential steam gauge,
    which would indicate the difference of pressure between the steam in
    the boiler and the steam of a small quantity of fresh water enclosed in
    a suitable vessel, and immerged in the water of the boiler.</P>

    <P>398. <EM>Q.</EM>--What is the advantage of blowing off from the
    surface of the water in the boiler?</P>

    <P><EM>A.</EM>--Blowing off from a point near the surface of the water
    is more beneficial than blowing off from the bottom of the boiler.
    Solid particles of any kind, it is well known, if introduced into
    boiling water, will lower the boiling point in a slight degree, and the
    steam will chiefly be generated on the surface of the particles, and
    indeed will have the appearance of coming out of them; if the particles
    be small the steam generated beneath and around them will balloon them
    to the surface of the water, where the steam will be liberated and the
    particles will descend; and the impalpable particles in a marine
    boiler, which by their subsidence upon the flues concrete into scale,
    are carried in the first instance to the surface of the water, so that
    if they be caught there and ejected from the boiler, the formation of
    scale will be prevented.</P>

    <P>399. <EM>Q.</EM>--Are there any plans in operation for taking
    advantage of this property of particles rising to the surface?</P>

    <P><EM>A.</EM>--Advantage is taken of this property in Lamb&#39;s Scale
    Preventer, which is substantially a contrivance for blowing off from
    the surface of the water that in practice is found to be very
    effectual; but a float in connection with a valve at the mouth of the
    discharging pipe is there introduced, so as to regulate the quantity of
    water blown out by the height of the water level, or by the extent of
    opening given to the feed cock. The operation, however, of the
    contrivance would be much the same if the float were dispensed with;
    but the float acts advantageously in hindering the water from rising
    too high in the boiler, should too much feed be admitted, and thereby
    obviates the risk of the water running over into the cylinder. In some
    boilers sheet iron vessels, called sediment collectors, are employed,
    which collect into them the impalpable matter, which in Lamb&#39;s
    apparatus is ejected from the boiler at once. One of these vessels, of
    about the size and shape of a loaf of sugar, is put into each boiler
    with the apex of the cone turned downwards into a pipe leading
    overboard, for conducting the sediment away from the boiler. The base
    of the cone stands some distance above the water line, and in its sides
    conical slits are cut, so as to establish a free communication between
    the water within the conical vessel and the water outside it. The
    particles of stony matter which are ballooned to the surface by the
    steam in every other part of the boiler, subside within the cone,
    where, no steam being generated, the water is consequently tranquil;
    and the deposit is discharged overboard by means of a pipe
    communicating with the sea. By blowing off from the surface of the
    water, the requisite cleansing action is obtained with less waste of
    heat; and where the water is muddy, the foam upon the surface of the
    water is ejected from the boiler--thereby removing one of the chief
    causes of priming.</P>

    <P>400. <EM>Q.</EM>--What is the cause of the rapid corrosion of marine
    boilers?</P>

    <P><EM>A.</EM>--Marine boilers are corroded externally in the region of
    the steam chest by the dripping of water from the deck; the bottom of
    the boiler is corroded by the action of the bilge water, and the ash
    pits by the practice of quenching the ashes with, salt water. These
    sources of injury, however, admit of easy remedy; the top of the boiler
    may be preserved from external corrosion by covering it with felt upon
    which is laid sheet lead soldered at every joint so as to be
    impenetrable to water; the ash pits may be shielded by guard plates
    which are plates fitting into the ash pits and attached to the boiler
    by a few bolts, so that when worn they may be removed and new ones
    substituted, whereby any wear upon the boiler in that part will be
    prevented; and there will be very little wear upon the bottom of a
    boiler if it be imbedded in mastic cement laid upon a suitable
    platform.</P>

    <P>401. <EM>Q.</EM>--Are not marine boilers subject to internal
    corrosion?</P>

    <P><EM>A.</EM>--Yes; the greatest part of the corrosion of a boiler
    takes place in the inside of the steam chest, and the origin of this
    corrosion is one of the obscurest subjects in the whole range of
    engineering. It cannot be from the chemical action of the salt water
    upon the iron, for the flues and other parts of the boiler beneath the
    water suffer very little from corrosion, and in steam vessels provided
    with Hall&#39;s condensers, which supply the boiler with fresh water,
    not much increased durability of the boiler has been experienced.
    Nevertheless, marine boilers seldom last more than for 5 or 6 years,
    whereas land boilers made of the same quality of iron often last 18 or
    20 years, and it does not appear probable that land boilers would last
    a very much shorter time if salt water were used in them. The thin film
    of scale spread over the parts of a marine boiler situated beneath the
    water, effectually protect them from corrosion; and when the other
    parts are completely worn out the flues generally remain so perfect,
    that the hammer marks upon them are as conspicuous as at their first
    formation. The operation of the steam in corroding the interior of the
    boiler is most capricious--the parts which are most rapidly worn away
    in one boiler being untouched in another; and in some cases one side of
    a steam chest will be very much wasted away while the opposite side
    remains uninjured. Sometimes the iron exfoliates in the shape of a
    black oxide which comes away in flakes like the leaves of a book, while
    in other cases the iron appears as if eaten away by a strong acid which
    had a solvent action upon it. The application of felt to the outside of
    a boiler, has in several cases been found to accelerate sensibly its
    internal corrosion; boilers in which there is a large accumulation of
    scale appear to be more corroded than where there is no such deposit;
    and where the funnel passes through the steam chest the iron of the
    steam chest is invariably much more corroded than where the funnel does
    not pass through it.</P>

    <P>402. <EM>Q.</EM>--Can you suggest no reason for the rapid internal
    corrosion of marine boilers?</P>

    <P><EM>A.</EM>--The facts which I have enumerated appear to indicate
    that the internal corrosion of marine boilers is attributable chiefly
    to the existence of surcharged steam within them, which is steam to
    which an additional quantity of heat has been communicated subsequently
    to its generation, so that its temperature is greater than is due to
    its elastic force; and on this hypothesis the observed facts relative
    to corrosion become to some extent explicable. Felt, applied to the
    outside of a boiler, may accelerate its internal corrosion by keeping
    the steam in a surcharged state, when by the dispersion of a part of
    the heat it would cease to be in that state; boilers in which there is
    a large accumulation of scale must have worked with the water very
    salt, which necessarily produces surcharged steam; for the temperature
    of steam cannot be less than that of the water from which it is
    generated, and inasmuch as the boiling point of water, under any given
    pressure, rises with the saltness of the water, the temperature of the
    steam must rise with the saltness of the water, the pressure remaining
    the same; or, in other words, the steam must have a higher temperature
    than is due to its elastic force, or be in the state of surcharged
    steam. The circumstance of the chimney flue passing through the steam
    will manifestly surcharge the steam with heat, so that all the
    circumstances which are found to accelerate corrosion, are it appears
    such as would also induce the formation of surcharged steam.</P>

    <P>403. <EM>Q.</EM>--Is it the natural effect of surcharged steam to
    waste away iron?</P>

    <P><EM>A.</EM>--It is the natural effect of surcharged steam to oxidate
    the iron with which it is in contact, as is illustrated by the familiar
    process for making hydrogen gas by sending steam through a red hot tube
    filled with pieces of iron; and although the action of the surcharged
    steam in a boiler is necessarily very much weaker than where the iron
    is red hot, it manifestly must have <EM>some</EM> oxidizing effect, and
    the amount of corrosion produced may be very material where the action
    is perpetual. Boilers with a large extent of heating surface, or with
    descending flues circulating through the cooler water in the bottom of
    the boiler before ascending the chimney, will be less corroded
    internally than boilers in which a large quantity of the heat passes
    away in the smoke; and the corrosion of the boiler will be diminished
    if the interior of any flue passing through the steam be coated with
    fire brick, so as to present the transmission of the heat in that
    situation. The best practice, however, appears to consist in the
    transmission of the smoke through a suitable passage on the outside of
    the boiler, so as to supersede the necessity of carrying any flue
    through the steam at all; or a column of water may be carried round the
    chimney, into which as much of the feed water may be introduced as the
    heat of the chimney is capable of raising to the boiling point, as
    under this limitation the presence of feed water around the chimney in
    the steam chest will fail to condense the steam.</P>

    <P>404. <EM>Q.</EM>--In steam vessels there are usually several
    boilers?</P>

    <P><EM>A.</EM>--Yes, in steam vessels of considerable power and
    size.</P>

    <P>405. <EM>Q.</EM>--Are these boilers generally so constructed, that
    any one of them may be thrown out of use?</P>

    <P><EM>A.</EM>--Marine boilers are now generally supplied with stop
    valves, whereby one boiler may be thrown out of use without impairing
    the efficacy of the remainder. These stop valves are usually spindle
    valves of large size, and they are for the most part set in a pipe
    which runs across the steam chests, connecting the several boilers
    together. The spindles of these valves should project through stuffing
    boxes in the covers of the valve chests, and they should be balanced by
    a weighted lever, and kept in continual action by the steam. If the
    valves be lifted up, and be suffered to remain up, as is the usual
    practice, they will become fixed by corrosion in that position, and it
    will be impossible after some time to shut them on an emergency. These
    valves should always be easily accessible from the engine room; and it
    ought not to be necessary for the coal boxes to be empty to gain access
    to them.</P>

    <P>406. <EM>Q.</EM>--Should each boiler have at least one safety valve
    for itself?</P>

    <P><EM>A.</EM>--Yes; it would be quite unsafe without this provision,
    as the stop valve might possibly jam. Sometimes valves jam from a
    distortion in the shape of the boiler when a considerable pressure is
    put upon it.</P>

    <P>407. <EM>Q.</EM>--How is the admission of the water into the boiler
    regulated?</P>

    <P><EM>A.</EM>--The admission of feed water into the boiler is
    regulated by hand by the engineer by means of cocks, and sometimes by
    spindle valves raised and lowered by a screw. Cocks appear to be the
    preferable expedient, as they are less liable to accident or
    derangement than screw valves, and in modern steam vessels they are
    generally employed.</P>

    <P>408. <EM>Q.</EM>--At what point of the boiler is the feed
    introduced?</P>

    <P><EM>A.</EM>--The feed water is usually conducted from the feed cock
    to a point near the bottom of the boiler by means of an internal pipe,
    the object of this arrangement being to prevent the rising steam from
    being condensed by the entering water. By being introduced near the
    bottom of the boiler, the water comes into contact in the first place
    with the bottoms of the furnaces and flues, and extracts heat from them
    which could not be extracted by water of a higher temperature, whereby
    a saving of fuel is accomplished. In some cases the feed water is
    introduced into a casing around the chimney, from whence it descends
    into the boiler. This plan appears to be an expedient one when the
    boiler is short of heating surface, and more than a usual quantity of
    heat ascends the chimney; but in well proportioned boilers a water
    casing round the chimney is superfluous. When a water casing is used
    the boiler is generally fed by a head of water, the feed water being
    forced up into a small tank, from whence it descends into the boiler by
    the force of gravity, while the surplus runs to waste, as in the
    feeding apparatus of land engines.</P>

    <P>409. <EM>Q.</EM>--Suppose that the engineer should shut off the feed
    water from the boilers while the engine was working, what would be the
    result?</P>

    <P><EM>A.</EM>--The result would be to burst the feed pipes, except for
    a safety valve placed on the feed pipe between the engine and the
    boilers, which safety valve opens when any undue pressure comes upon
    the pipes, and allows the water to escape. There is, however, generally
    a cock on the suction side of the feed pump, which regulates the
    quantity of water drawn into the pump. But there must be cocks on the
    boilers also to determine into which boiler the water shall be chiefly
    discharged, and these cocks are sometimes all shut accidentally at the
    same time.</P>

    <P>410. <EM>Q.</EM>--Is there no expedient in use in steam vessels for
    enabling the position of the water level in the boiler to determine the
    quantity of feed water admitted?</P>

    <P><EM>A.</EM>--In some steam vessels floats have been introduced to
    regulate the feed, but their action cannot be depended on in agitated
    water, if applied after the common fashion. Floats would probably
    answer if placed in a cylinder which communicates with the water in the
    boiler by means of small holes; and a disc of metal might be attached
    to the end of a rod extending beneath the water level, so as to resist
    irregular movements from the motion of the ship at sea, which would
    otherwise impair the action of the apparatus.</P>

    <P>411. <EM>Q.</EM>--How is the proper level of the water in the boiler
    of a steam vessel maintained when, the engine is stopped for some time,
    and the boiler is blowing off steam?</P>

    <P><EM>A.</EM>--By means of a separate pump worked sometimes by hand,
    but usually by a small separate engine called the Donkey engine. This
    pump, by the aid of suitable cocks, will pump from the sea into the
    boiler; from the sea upon deck either to wash decks or to extinguish
    fire; and from the bilge overboard, through a suitable orifice in the
    side of the ship.</P>

    <H4 CLASS="subhead"><A NAME="j03"></A>LOCOMOTIVE BOILERS.</H4>

    <P>412. <EM>Q.</EM>--Will you recapitulate the general features of
    locomotive boilers?</P>

    <P><EM>A.</EM>--Locomotive boilers consist of three portions (see fig.
    29): the barrel E, E, containing the tubes, the fire box B, and the
    smoke box F; of which the barrel smoke box, and external fire box are
    always of iron, but the internal fire box is generally made of copper,
    though sometimes also it is made of iron. The tubes are sometimes of
    iron, but generally of brass fixed in by ferules. The whole of the iron
    plates of a locomotive boiler Which are subjected to the pressure of
    steam, should be Lowmoor or Bowling plates of the best quality; and the
    copper should be coarse grained, rather than rich or soft, and be
    perfectly free from irregularities of structure and lamination.</P>

    <P>413. <EM>Q.</EM>--What are the usual dimensions of the barrel?</P>

    <P><EM>A.</EM>--The thickness of the plates composing the barrel of the
    boiler varies generally from 5/16ths to 3/8ths of an inch, and the
    plates should run in the direction of the circumference, so that the
    fibres of the iron may be in the direction of the strain. The diameter
    of the barrel commonly varies from 3 ft. to 3 ft. 6 inches; the
    diameter of the rivets should be from 11/16ths to 3/4ths of an inch,
    and the pitch of the rivets or distance between their centres should be
    from 17/8th to 2 inches.</P>

    <P>414. <EM>Q.</EM>--How are the fire boxes of a locomotive
    constructed?</P>

    <P><EM>A.</EM>--The space between the external and internal fire boxes
    forms a water space, which must be stayed every 4-1/2 or 5 inches by
    means of copper or iron stay bolts, screwed through the outer fire box
    into the metal of the inner fire box, and securely riveted within it:
    iron stay bolts are as durable as copper, and their superior tenacity
    gives them an advantage. Sometimes tubes are employed as stays. The
    internal and external fire boxes are joined together at the bottom by a
    N-shaped iron, and round the fire door they are connected by means of a
    copper ring 1-1/4 in. thick, and 2 in. broad,--the inner fire box being
    dished sufficiently outward at that point, and the outer fire box
    sufficiently inward, to enable a circle of rivets 3/4 of an inch in
    diameter passing through the copper ring and the two thicknesses of
    iron, to make a water-tight joint. The thickness of the plates
    composing the external fire box is in general 3/8ths of an inch if the
    fire box is circular, and from 3/8ths to 1/2 inch if the fire box is
    square; and the thickness of the internal fire box is in most cases
    7/16ths if copper, and from 3/8ths to 7/16ths of an inch if of iron.
    Circular internal fire boxes, if made of iron, should be welded rather
    than riveted, as the rivet heads are liable to be burnt away by the
    action of the fire; and when the fire boxes are square each side should
    consist of a single plate, turned over at the edges with a radius of 3
    inches, for the introduction of the rivets.</P>

    <P>415. <EM>Q.</EM>--Is there any provision for stiffening the crown of
    the furnace in a locomotive?</P>

    <P><EM>A.</EM>--The roof of the internal fire box, whether flat as in
    Stephenson&#39;s engines, or dome shaped as in Bury&#39;s, requires to
    be stiffened with cross stay bars, but the bars require to be stronger
    and more numerous when applied to a flat surface. The ends of these
    stay bars rest above the vertical sides of the fire box; and to the
    stay bars thus extending across the crown, the crown is attached at
    intervals by means of stay bolts. There are projecting bosses upon the
    stay bars encircling the bolts at every point where a bolt goes
    through, but in the other parts they are kept clear of the fire box
    crown so as to permit the access of water to the metal; and, with the
    view of facilitating the ascent of the steam, the bottom of each stay
    bar should be sharpened away in those parts where it does not touch the
    boiler.</P>

    <P>416. <EM>Q.</EM>--Is any inconvenience experienced from the intense
    heat in a locomotive furnace?</P>

    <P><EM>A.</EM>--The fire bars in locomotives have always been a source
    of trouble, as from the intensity of the heat in the furnace they
    become so hot as to throw off a scale, and to bend under the weight of
    the fuel. The best alleviation of these evils lies in making the bars
    deep and thin: 4 or 5 inches deep by five eighths of an inch thick on
    the upper side, and three eighths of an inch on the under side, are
    found in practice to be good dimensions. In some locomotives a frame
    carrying a number of fire bars is made so that it may be dropped
    suddenly by loosening a catch; but it is found that any such mechanism
    can rarely be long kept in working order, as the molten clinker by
    running down between the frame and the boiler will generally glue the
    frame into its place. It is therefore found preferable to fix the
    frame, and to lift up the bars by the dart used by the stoker, when any
    cause requires the fire to be withdrawn. The furnace bars of
    locomotives are always made of malleable iron, and indeed for every
    species of boiler malleable iron bars are to be preferred to bars of
    cast iron, as they are more durable, and may if thin be set closer
    together, whereby the small coal or coke is saved that would otherwise
    fall into the ash pit. The ash box of locomotives is made of plate
    iron, a quarter thick: it should not be less than 10 in. deep, and its
    bottom should be about 9 in. above the level of the rails. The chimney
    of a locomotive is made of plate iron one eighth of an inch thick: it
    is usually of the same diameter as the cylinder, but is better smaller,
    and must not stand more than 14 ft. high above the level of the
    rails.</P>

    <P>417. <EM>Q.</EM>--Are locomotive boilers provided with a steam
    chest?</P>

    <P><EM>A.</EM>--The upper portion of the external fire box is usually
    formed into a steam chest, which is sometimes dome shaped, sometimes
    semicircular, and sometimes of a pyramidical form, and from this steam
    chest the steam is conducted away by an internal pipe to the cylinders;
    but in other cases an independent steam chest is set upon the barrel of
    the boiler, consisting of a plate iron cylinder, 20 inches in diameter,
    2 feet high, and three eighths of an inch thick, with a dome shaped
    top, and with the seam welded and the edge turned over to form a flange
    of attachment to the boiler. The pyramidical dome, of the form employed
    in Stephenson&#39;s locomotives, presents a considerable extent of flat
    surface to the pressure of the steam, and this flat surface requires to
    be very strongly stayed with angle irons and tension rods; whereas the
    semiglobular dome of the kind employed in Bury&#39;s engines requires
    no staying whatever. Latterly, however, these domes over the fire box
    have been either much reduced in size or abandoned altogether.</P>

    <P>418. <EM>Q.</EM>--Is any beneficial use made of the surplus steam of
    a locomotive?</P>

    <P><EM>A.</EM>--To save the steam which is formed when the engine is
    stationary, a pipe is usually fitted to the boiler, which on a cock
    being turned conducts the steam into the water in the tender, whereby
    the feed water is heated, and less fuel is subsequently required. This
    method of disposing of the surplus steam may be adopted when the
    locomotive is descending inclines, or on any occasion where more steam
    is produced than the engine can consume.</P>

    <P>419.<EM>Q.</EM>--What means are provided to facilitate the
    inspection and cleaning of locomotive boilers?</P>

    <P><EM>A.</EM>--The man hole, or entrance into the boiler, consists of
    a circular or oval aperture of about 15 in. diameter, placed in
    Bury&#39;s locomotive at the apex of the dome, and in Stephenson&#39;s
    upon the front of the boiler, a few inches below the level of the
    rounded part; and the cover of the man hole in Bury&#39;s engine
    contains the safety valve seats. In whatever situation this man hole is
    placed, the surfaces of the ring encircling the hole, and of the
    internal part of the door or cover, should be accurately fitted
    together by scraping or grinding, so that they need only the
    interposition of a little red lead to make them quite tight when
    screwed together. Lead or canvas joints, if of any considerable
    thickness, will not long withstand the action of high pressure steam;
    and the whole of the joints about a locomotive should be such that they
    require nothing more than a little paint or putty, or a ring of wire
    gauze smeared with white or red lead to make them perfectly tight.
    There must be a mud hole opposite the edge of each water space, if the
    fire box be square, to enable the boiler to be easily cleaned out, and
    these holes are most conveniently closed by screwed plugs made slightly
    taper. A cock for emptying the boiler is usually fixed at the bottom of
    the fire box, and it should be so placed as to be accessible when the
    engine is at work, in order that the engine driver may blow off some
    water if necessary; but it must not be in such a position as to send
    the water blown off among the machinery, as it might carry sand or grit
    into the bearings, to their manifest injury.</P>

    <P>420. <EM>Q.</EM>--Will you state the dimensions of the tube plate,
    and the means of securing the tubes in it?</P>

    <P><EM>A.</EM>--The tube plates are generally made from five eighths to
    three fourths of an inch thick, but seven eighths of an inch thick
    appears to be preferable, as when the plate is thick the holes will not
    be so liable to change their figure during the process of feruling the
    tubes: the distance between the tubes should never be made less than
    three fourths of an inch, and the holes should be slightly tapered so
    as to enable the tubes to hold the tube plates together. The tubes are
    secured in the tube plates by means of taper ferules driven into the
    ends of the tubes. The ferules are for the most part made of steel at
    the fire box end, and of wrought iron at the smoke box end, though
    ferules of malleable cast iron have in some cases been used with
    advantage: malleable cast iron ferules are almost as easily expanded
    when hammered cold upon a mandrel, as the common wrought iron ones are
    at a working heat. Spring steel, rolled with a feather edge, to
    facilitate its conversion into ferules, is supplied by some of the
    steel- makers of Sheffield, and it appears expedient to make use of
    steel thus prepared when steel ferules are employed. In cases where
    ferules are not employed, it may be advisable to set out the tube
    behind the tube plate by means of an expanding mandrel. There are
    various forms of this instrument. One form is that known as
    Prosser&#39;s expanding mandrel, in which there are six or eight
    segments, which are forced out by means of a hexagonal or octagonal
    wedge, which is forced forward by a screw. When the wedge is withdrawn,
    the segments collapse sufficiently to enable them to enter the tube,
    and there is an annular protuberance on the exterior circle of the
    segments, which protuberance, when the mandrel is put into the tube,
    just comes behind the inner edge of the tube plate. When the wedge is
    tightened up by the screw, the protuberance on the exterior of the
    segments composing the mandrel causes a corresponding bulge to take
    place in the tube, at the back of the tube plate, and the tube is
    thereby brought into more intimate contact with the tube plate than
    would otherwise be the case. There is a steel ring indented into the
    segments of Prosser&#39;s mandrel, to contract the segments when the
    central wedge is withdrawn. A more convenient form of the instrument,
    however, is obtained by placing the segments in a circular box, with
    one end projecting; and supporting each segment in the box by a tenon,
    which fits into a mortise in the cylindrical box. To expand the
    segments, a round tapered piece of steel, like a drift, is forced into
    a central hole, round which the segments are arranged. A piece of steel
    tube, also slit up to enable a central drift to expand it, answers very
    well; but the thickness of that part of the tube in which there
    requires to be spring enough to let the mandrel expand, requires to be
    sufficiently reduced to prevent the pieces from cracking when the
    central drift is driven in by a hammer. The drift is better when made
    with a globular head, so that it may be struck back by the hammer, as
    well as be driven in. An expanding mandrel, with a central drift, is
    more rapid in its operation than when the expansion is produced by
    means of a screw.</P>

    <P>421. <EM>Q.</EM>--Will you explain the means that are adopted to
    regulate the admission of steam to the cylinders?</P>

    <P><EM>A.</EM>--In locomotives, the admission of the steam from the
    boiler to the cylinders is regulated by a valve called the regulator,
    which is generally placed immediately above the internal fire box, and
    is connected with two copper pipes;--one conducting steam from the
    highest point of the dome down to it, and the other conducting the
    steam that has passed through it along the boiler to the upper part of
    the smoke box. Regulators may be divided into two sorts, viz., those
    with, sliding valves and steam ports, and those with conical valves and
    seats, of which the latter kind are the best. The former kind have for
    the most part consisted of a circular valve and face, with radial
    apertures, the valve resembling the outstretched wings of a butterfly,
    and being made to revolve on its central pivot by connecting links
    between its outer edges, or by its central spindle. In some of
    Stephenson&#39;s engines the regulator consists of a slide valve
    covering a port on the top of the valve chests. A rod passes from this
    valve through the smoke box below the boiler, and by means of a lever
    parallel to the starting lever, is brought up to the engineer&#39;s
    reach. Cocks were at first used as regulators, but were given up, as
    they were found liable to stick fast. A gridiron slide valve has been
    used by Stephenson, which consists of a perforated square moving upon a
    face with an equal number of holes. This plan of a valve gives, with a
    small movement, a large area of opening. In Bury&#39;s engines a sort
    of conical plug is used, which is withdrawn by turning the handle in
    front of the fire box: a spiral grove of a very large pitch is made in
    the valve spindle, in which fits a pin fixed to the boiler, and by
    turning the spindle an end motion is given to it, which either shuts or
    opens the steam passage according to the direction in which it is
    turned. The best regulator would probably be a valve of the equilibrium
    description, such as is used in the Cornish engine: there would be no
    friction in such a regulator, and it could be opened or shut with a
    small amount of force. Such valves, indeed, are now sometimes employed
    for regulators in locomotives.</P>

    <H2 CLASS="chapter"><A NAME="ch08"></A>CHAPTER VIII.</H2>

    <H3>CONSTRUCTIVE DETAILS OF ENGINES.</H3>

    <H4 CLASS="subhead"><A NAME="k01"></A>PUMPING ENGINES.</H4>

    <P>422. <EM>Q.</EM>--Will you explain the course of procedure in the
    erection of a pumping engine, such as Boulton and Watt introduced into
    Cornwall?</P>

    <P><EM>A.</EM>--The best instructions on this subject are those of Mr.
    Watt himself, which are as follows:--Having fixed on the proper
    situation of the pump in the pit, from its centre measure out the
    distance to the centre of the cylinder, from which set off all the
    other dimensions of the house, including the thickness of the walls,
    and dig out the whole of the included ground to the depth of the bottom
    of the cellar, so that the bottom of the cylinder may stand on a level
    with the natural ground of the place, or lower, if convenient, for the
    less the height of the house above the ground, the firmer it will be.
    The foundations of the walls must be laid at least two feet lower than
    the bottom of the cellar, unless the foundation be firm rock; and care
    must be taken to leave a small drain into the pit quite through the
    lowest part of the foundation of the lever wall, to let off any water
    that may be spilt in the engine house, or may naturally come into the
    cellar. If the foundation at that depth does not prove good, you must
    either go down to a better if in your reach, or make it good by a
    platform of wood or piles, or both.</P>

    <P>423. <EM>Q.</EM>--These directions refer to the foundations?</P>

    <P><EM>A.</EM>.--Yes; but I will now proceed to the other parts. Within
    the house, low walls must be built to carry the cylinder beams, so as
    to leave sufficient room to come at the holding down bolts, and the
    ends of these beams must also be lodged in the wall The lever wall must
    be built in the firmest manner, and run solid, course by course, with
    thin lime mortar, care being taken that the lime has not been long
    slaked. If the house be built of stone, let the stones be large and
    long, and let many headers be laid through the wall: it should also be
    a rule, that every stone be laid on the broadest bed it has, and never
    set on its edge. A course or two above the lintel of the door that
    leads to the condenser, build into the wall two parallel flat thin bars
    of iron equally distant from each other, and from the outside and
    inside of the wall, and reaching the whole breadth of the lever wall.
    About a foot higher in the wall, lay at every four feet of the breadth
    of the front, other bars of the same kind at right angles to the former
    course, and reaching quite through the thickness of the wall; and at
    each front corner lay a long bar in the middle of the side walls, and
    reaching quite through the front wall; if these bars are 10 feet or 12
    feet long it will be sufficient. When the house is built up nearly to
    the bottom of the opening under the great beam another double course of
    bars is to be built in, as has been directed. At the level of the upper
    cylinder beams, holes must be left in the walls for their ends, with
    room to move them laterally, so that the cylinder may be got in; and
    smaller holes must be left quite through the walls for the introduction
    of iron bars, which being firmly fastened to the cylinder beams at one
    end, and screwed at the other or outer end, will serve, by their going
    through both the front and back walls, to bind the house more firmly
    together. The spring beams or iron bars fastened to them must reach
    quite through the back wall, and be keyed or screwed up tight; and they
    must be firmly fastened to the lever wall on each side, either by iron
    bars, firm pieces of wood, or long strong stones, reaching far back
    into the wall. They must also be bedded solidly, and the residue of the
    opening must be built up in the firmest manner.</P>

    <P>424. <EM>Q.</EM>--If there be a deficiency of water for the purpose
    of condensation, what course should be pursued?</P>

    <P><EM>A.</EM>--If there be no water in the neighborhood that can be
    employed for the purpose of condensation, it will be necessary to make
    a pond, dug in the earth, for the reception of the water delivered by
    the air pump, to the end that it may be cooled and used again for the
    engine. The pond may be three or four feet deep, and lined with turf,
    puddled, or otherwise made water tight. Throwing up the water into the
    air in the form of a jet to cool it, has been found detrimental; as the
    water is then charged with air which vitiates the vacuum.</P>

    <P>425. <EM>Q.</EM>--How is the piston of a pumping engine packed?</P>

    <P><EM>A.</EM>--To pack the piston, take sixty common-sized white or
    untarred rope-yarns, and with them plait a gasket or flat rope as close
    and firm as possible, tapering for eighteen inches at each end, and
    long enough to go round the piston, and overlapped for that length;
    coil this rope the thin way as hard as possible, and beat it with a
    sledge hammer until its breadth answers the place; put it in and beat
    it down with a wooden drift and a hand mallet, pour some melted tallow
    all around, then pack in a layer of white oakum half an inch thick, so
    that the whole packing may have the depth of five to six inches,
    depending on the size of the engine; finally, screw down the junk ring.
    The packing should be beat solid, but not too hard, otherwise it will
    create so great a friction as to prevent the easy going of the engine.
    Abundance of tallow should be allowed, especially at first; the
    quantity required will be less as the cylinder grows smooth. In some of
    the more modern pumping engines, the piston is provided with metallic
    packing, consisting for the most part of a single ring with a tongue
    piece to break the joint, and packed behind with hemp. The upper edge
    of the metallic ring is sharpened away from the inside so as to permit
    more conveniently the application of hemp packing behind it; and the
    junk ring is made much the same as if no metallic packing were
    employed.</P>

    <P>426. <EM>Q.</EM>--Will you explain the mode of putting the engine
    into operation?</P>

    <P><EM>A.</EM>--To set the engine going, the steam must be raised until
    the pressure in the steam pipe is at least equal to three pounds on the
    square inch; and when the cylinder jacket is fully warmed, and steam
    issues freely from the jacket cock, open all the valves or regulators;
    the steam will then forcibly blow out the air or water contained in the
    eduction pipe, and to get rid of the air in the cylinder, shut the
    steam valve after having blown through the engine for a few minutes.
    The cold water round the condenser will condense some of the steam
    contained in the eduction pipe, and its place will be supplied by some
    of the air from the cylinder. The steam valve must again be opened to
    blow out that air, and the operation is to be repeated until the air is
    all drawn out of the cylinder. When that is the case shut all the
    valves, and observe if the vacuum gauge shows a vacuum in the
    condenser; when there is a vacuum equivalent to three inches of
    mercury, open the injection a very little, and shut it again
    immediately; and if this produces any considerable vacuum, open the
    exhausting valve a very little way, and the injection at the same time.
    If the engine does not now commence its motion, it must be blown
    through again until it moves. If the engine be lightly loaded, or if
    there be no water in the pumps, the throttle valve must be kept nearly
    closed, and the top and exhaustion regulators must be opened only a
    very little way, else the engine will make its stroke with violence,
    and perhaps do mischief. If there is much unbalanced weight on the pump
    end, the plug which opens the steam valve must be so regulated, that
    the valve will only be opened very slightly; and if after a few strokes
    it is found that the engine goes out too slowly, the valve may be then
    so adjusted as to open wider. The engine should always be made to work
    full stroke, that is, until the catch pins be made to come within half
    an inch of the springs at each end, and the piston should stand high
    enough in the cylinder when the engine is at rest, to spill over into
    the perpendicular steam pipe any water which may be condensed above it;
    for if water remain upon the piston, it will increase the consumption
    of steam. When the engine is to be stopped, shut the injection valve
    and secure it, and adjust the tappets so as to prevent the exhausting
    valve from opening and to allow the steam valve to open and remain
    open, otherwise a partial vacuum may arise in the cylinder, and it may
    be filled with water from the injection or from leaks. A single acting
    engine, when it is in good order, ought to be capable of going as slow
    as one stroke in ten minutes, and as fast as ten strokes in one minute;
    and if it does not fulfil these conditions, there is some fault which
    should be ascertained and remedied.</P>

    <P>427. <EM>Q.</EM>--Your explanation has reference to the pumping
    engine as introduced into Cornwall by Watt: have any modifications been
    since made upon it?</P>

    <P><EM>A.</EM>--In the modern Cornish engines the steam is used very
    expansively, and a high pressure of steam is employed. In some cases a
    double cylinder engine is used, in which the steam, after having given
    motion to a small piston on the principle of a high pressure engine,
    passes into a larger cylinder, where it operates on the principle of a
    condensing engine; but there is no superior effect gained by the use of
    two cylinders, and there is greater complexity in the apparatus.
    Instead of the lever walls, cast iron columns are now frequently used
    for supporting the main beam in pumping engines, and the cylinder end
    of the main beam is generally made longer than the pump end in engines
    made in Cornwall, so as to enable the cylinder to have a long stroke,
    and the piston to move quickly, without communicating such a velocity
    to the pump buckets as will make them work with such a shock as to wear
    themselves out quickly. A high pressure of steam, too, can be employed
    where the stroke is long, without involving the necessity of making the
    working parts of such large dimensions as would otherwise be necessary;
    for the strength of the parts of a single acting engine will require to
    be much the same, whatever the length of the stroke may be.</P>

    <P>428. <EM>Q.</EM>--What kind of pump is mostly used in draining deep
    mines?</P>

    <P><EM>A.</EM>--The pump now universally preferred is the plunger pump,
    which admits of being packed or tightened while the engine is at work;
    but the lowest lift of a mine is generally supplied with a pump on the
    suction principle, both with the view of enabling the lowest pipe to
    follow the water with facility as the shaft is sunk deeper, and to
    obviate the inconvenience of the valves of the pump being rendered
    inaccessible by any flooding in the mine. The pump valves of deep mines
    are a perpetual source of expense and trouble, as from the pressure of
    water upon them it is difficult to prevent them from closing with
    violence; and many expedients have been contrived to mitigate the evil,
    of which the valve known as Harvey and West&#39;s valve has perhaps
    gained the widest acceptation.</P>

    <P>429. <EM>Q.</EM>--Will you describe Harvey and West&#39;s pump
    valve?</P>

    <P><EM>A.</EM>--This valve is a compromise between the equilibrium
    valve, of the kind employed for admitting the steam to and from the
    cylinder in single acting engines, and the common spindle valve
    formerly used for that purpose; and to comprehend its action, it is
    necessary that the action of the equilibrium valve, which has been
    already represented fig. 34, should first be understood. This valve
    consists substantially of a cylinder open at both ends, and capable of
    sliding upon a stationary piston fixed upon a rod the length of the
    cylinder, which proceeds from the centre of the orifice the valve is
    intended to close. It is clear, that when the cylinder is pressed down
    until its edge rests upon the bottom of the box containing it, the
    orifice of the pipe must be closed, as the steam can neither escape
    past the edge of the cylinder nor between the cylinder and the piston;
    and it is equally clear, that as the pressure upon the cylinder is
    equal all around it, and the whole of the downward pressure is
    maintained by the stationary piston, the cylinder can be raised or
    lowered without any further exertion of force than is necessary to
    overcome the friction of the piston and of the rod by which the
    cylinder is raised. Instead of the rubbing surface of a piston,
    however, a conical valve face between the cylinder and piston is
    employed, which is tight only when the cylinder is in its lowest
    position; and there is a similar face between, the edge of the cylinder
    and the bottom of the box in which it is placed. The moving part of the
    valve, too, instead of being a perfect cylinder, is bulged outward in
    the middle, so as to permit the steam to escape past the stationary
    piston when the cylindrical part of the valve is raised. It is clear,
    that if such a valve were applied to a pump, no pressure of water
    within the pump would suffice to open it, neither would any pressure of
    water above the valve cause it to shut with violence; and if an
    equilibrium valve, therefore, be used as a pump valve at all, it must
    be opened and shut by mechanical means. In Harvey and West&#39;s
    valves, however, the equilibrium principle is only partially adopted;
    the lower face is considerably larger in diameter than the upper face,
    and the difference constitutes an annulus of pressure, which will cause
    the valve to open or shut with the same force as a spindle valve of the
    area of the annulus. To deaden the shock still more effectually, the
    lower face of the valve is made to strike upon end wood driven into an
    annular recess in the pump bucket; and valves thus constructed work
    with very little noise or tremor; but it is found in practice, that the
    use of Harvey and West&#39;s valve, or any contrivance of a similar
    kind, adds materially to the load upon the pump, especially in low
    lifts where the addition of a load, to the valve makes a material
    addition to the total resistance which the engine has to overcome.
    Instead of end wood driven into a recess for the valve to strike upon,
    a mixture of tin and lead cast in a recess is now frequently used, and
    is found to be preferable to the wood.</P>

    <P>430. <EM>Q.</EM>--Is there any other kind of pump valve which is
    free from the shocks incidental to the working of common valves?</P>

    <P><EM>A.</EM>--In some cases canvass valves are used for pumps, with
    the effect of materially mitigating the shock; but they require
    frequent renewal, and are of inferior eligibility in their action to
    the slide valve, which might in many cases be applied to pumps without
    inconvenience.</P>

    <P>431. <EM>Q.</EM>--Could not a form of pump be devised capable of
    working without valves at all?</P>

    <P><EM>A.</EM>.--It appears probable, that by working a common
    reciprocating pump at a high speed, a continuous flow of water might be
    maintained through the pipes in such a way as to render the existence
    of any valves superfluous after once the action was begun, the momentum
    of the moving water acting in fact as valves. The centrifugal pump,
    however, threatens to supersede pumps of every other kind; and if the
    centrifugal pump be employed there will be no necessity for pump valves
    at all. There is less loss of effect by the centrifugal pump than by
    the common pump.</P>

    <P>432. <EM>Q.</EM>--What is the best form of the centrifugal pump?</P>

    <P><EM>A.</EM>--There are two forms in which the centrifugal pump may
    be applied to mines;--that in which the arms diverge from the bottom,
    like the letter V; and that in which revolving arms are set in a tight
    case near the bottom of the mine, and are turned by a shaft from the
    surface. Such pumps both draw and force; and either by arranging them
    in a succession of lifts in the shaft of the mine, or otherwise, the
    water may be drawn without inconvenience from any depth. The
    introduction of the centrifugal pump would obviously extinguish the
    single acting engine, as rotative engines working at a high speed would
    be the most appropriate form of engine where the centrifugal pump was
    employed.</P>

    <P>433. <EM>Q.</EM>--This would not be a heavy deprivation?</P>

    <P><EM>A.</EM>--The single acting engine is a remnant of engineering
    barbarism which must now be superseded by more compendious
    contrivances. The Cornish engines, though rudely manufactured, are very
    expensive in production, as a large engine does but little work;
    whereas by employing a smaller engine, moving with a high speed, the
    dimensions may be so far diminished that the most refined machinery may
    be obtained at less than the present cost.</P>

    <P>434. <EM>Q.</EM>--Are not the Cornish engines more economical in
    fuel than other engines?</P>

    <P><EM>A.</EM>--It is a mistake to suppose that there is any peculiar
    virtue in the existing form of Cornish engine to make it economical in
    fuel, or that a less lethargic engine would necessarily be less
    efficient. The large duty of the engines in Cornwall is traceable to
    the large employment of the principle of expansion, and to a few other
    causes which may be made of quite as decisive efficacy in smaller
    engines working with a quicker speed; and there is therefore no
    argument in the performance of the present engines against the proposed
    substitution.</P>

    <H4 CLASS="subhead"><A NAME="k02"></A>VARIOUS FORMS OF MARINE
    ENGINES.</H4>

    <P>435. <EM>Q.</EM>--What species of paddle engine do you consider to
    be the best?</P>

    <P><EM>A.</EM>--The oscillating engine.</P>

    <P>436. <EM>Q.</EM>--Will you explain the grounds of that
    preference?</P>

    <P><EM>A.</EM>--The engine occupies little space, consists of few
    parts, is easily accessible for repairs, and may be both light and
    strong at the same time. In the case of large engines the crank in the
    intermediate shaft is a disadvantage, as it is difficult to obtain such
    a forging quite sound. But by forging it in three cranked flat bars,
    which are then laid together and welded into a square shaft, a sound
    forging will be more probable, and the bars should be rounded a little
    on the sides which are welded to allow the scoriae to escape during
    that operation. It is important in so large a forging not to let the
    fire be too fierce, else the surface of the iron will be burnt before
    the heart is brought to a welding heat. In some cases in oscillating
    engines the air pump has been wrought by an eccentric, and that may at
    any time be done where doubt of obtaining a sound intermediate shaft is
    entertained; but the precaution must be taken to make the eccentric
    very wide so as to distribute the pressure over a large surface, else
    the eccentric will be apt to heat.</P>

    <P>437. <EM>Q.</EM>--Have not objections been brought against the
    oscillating engine?</P>

    <P><EM>A.</EM>--In common with every other improvement, the oscillating
    engine, at the time of its introduction, encountered much opposition.
    The cylinder, it was said, would become oval, the trunnion bearings
    would be liable to heat and the trunnion joints to leak, the strain
    upon the trunnions would be apt to bend in or bend out the sides of the
    cylinder; and the circumstance of the cylinder being fixed across its
    centre, while the shaft requires to accommodate itself to the working
    of the ship, might, it was thought, be the occasion of such a strain
    upon the trunnions as would either break them or bend the piston rod.
    It is a sufficient reply to these objections to say that they are all
    hypothetical, and that none of them in practice have been found to
    exist--to such an extent at least as to occasion any inconvenience; but
    it is not difficult to show that they are altogether unsubstantial,
    even without a recourse to the disproofs afforded by experience.</P>

    <P>438. <EM>Q.</EM>--Is there not a liability in the cylinder to become
    oval from the strain thrown on it by the piston?</P>

    <P><EM>A.</EM>--There is, no doubt, a tendency in oscillating engines
    for the cylinder and the stuffing box to become oval, but after a
    number of years&#39; wear it is found that the amount of ellipticity is
    less than that which is found to exist in the cylinders of side lever
    engines after a similar trial. The resistance opposed by friction to
    the oscillation of the cylinder is so small, that a man is capable of
    moving a large cylinder with one hand; whereas in the side lever
    engine, if the parallel motion be in the least untrue, which is, at
    some time or other, an almost inevitable condition, the piston is
    pushed with great force against the side of the cylinder, whereby a
    large amount of wear and friction is occasioned. The trunnion bearings,
    instead of being liable to heat like other journals, are kept down to
    the temperature of the steam by the flow of steam passing through them;
    and the trunnion packings are not liable to leak when the packings,
    before being introduced, are squeezed in a cylindrical mould.</P>

    <P>439. <EM>Q.</EM>--Might not the eduction trunnions be immersed in
    water?</P>

    <P><EM>A.</EM>--In some cases a hollow, or lantern brass, about one
    third or one fourth the length of the packing space, and supplied with
    steam or water by a pipe, is introduced in the middle of the packing,
    so that if there be any leakage through the trunnion, it will be a
    leakage of steam or water, which will not vitiate the vacuum; but in
    ordinary cases this device will not be necessary, and it is not
    commonly employed. It is clear that there can be no buckling of the
    sides of the cylinder by the strain upon the trunnions, if the cylinder
    be made strong enough, and in cylinders of the ordinary thickness such
    an action has never been experienced; nor is it the fact, that the
    intermediate shaft of steam vessels, to which part alone the motion is
    communicated by the engine, requires to adapt itself to the altering
    forms of the vessel, as the engine and intermediate shaft are rigidly
    connected, although the paddle shaft requires to be capable of such an
    adaptation. Even if this objection existed, however, it could easily be
    met by making the crank pin of the ball and socket fashion, which would
    permit the position of the intermediate shaft, relatively with that of
    the cylinder, to be slightly changed, without throwing an undue strain
    upon any of the working parts.</P>

    <P>440. <EM>Q.</EM>--Is the trunk engine inferior to the
    oscillating?</P>

    <P><EM>A.</EM>--A very elegant and efficient arrangement of trunk
    engine suitable for paddle vessels has latterly been employed by
    Messrs. Rennie, of which all the parts resemble those of Penn&#39;s
    oscillating engine except that the cylinders are stationary instead of
    being movable; and a round trunk or pipe set upon the piston, and
    moving steam tight through the cylinder cover, enables the connecting
    rod which is fixed to the piston to vibrate within it to the requisite
    extent. But the vice of all trunk engines is that they are necessarily
    more wasteful of steam, as the large mass of metal entering into the
    composition of the trunk, moving as it does alternately into the
    atmosphere and the steam, must cool and condense a part of the steam.
    The radiation of heat from the interior of the trunk will have the same
    operation, though in vertical trunk engines the loss from this cause
    might probably be reduced by filling the trunk with oil, so far as this
    could be done without the oil being spilt over the edge.</P>

    <P>441. <EM>Q.</EM>--What species of screw engine do you consider the
    best?</P>

    <P><EM>A.</EM>--I am inclined to give the preference to a variety of
    the horizontal steeple engine, such as was first used in H.M.S.
    Amphion. In this engine the cylinders lie on their sides, and they are
    placed near the side of the vessel with their mouths pointing to the
    keel. From each cylinder two long piston rods proceed across the vessel
    to a cross head working in guides; and from this cross head a
    connecting rod returns back to the centre of the vessel and gives
    motion to the crank. The piston rods are so placed in the piston that
    one of them passes above the crank shaft, and the other below the crank
    shaft. The cross head lies in the same horizontal plane as the centre
    of the cylinder, and a lug projects upwards from the cross head to
    engage one piston rod, and downwards from the cross head to engage the
    other piston rod. The air pump is double acting, and its piston or
    bucket has the same stroke as the piston of the engine. The air pump
    bucket derives its motion from an arm on the cross head, and a similar
    arm is usually employed in engines of this class to work the feed and
    bilge pumps.</P>

    <P>442. <EM>Q.</EM>--Is not inconvenience experienced in direct acting
    screw engines from the great velocity of their motion?</P>

    <P><EM>A.</EM>--Not if they are properly constructed; but they require
    to be much stronger, to be fitted with more care, and to have the
    bearing surfaces much larger than is necessary in engines moving
    slowly. The momentum of the reciprocating parts should also be balanced
    by a weight applied to the crank or crank shaft, as is done in
    locomotives. A very convenient arrangement for obtaining surface is to
    form the crank of each engine of two cast iron discs cast with heavy
    sides, the excess of weight upon the heavy sides being nearly equal to
    that of the piston and its connections. When the piston is travelling
    in one direction the weights are travelling in the opposite; and the
    momentum of the piston and its attachments, which is arrested at each
    reciprocation, is just balanced by the equal and opposite momentum of
    the weights. One advantage of the horizontal engine is, that a single
    engine may be employed, whereby greater simplicity of the machinery and
    greater economy of fuel will be obtained, since there will be less
    radiating surface in one cylinder than in two.</P>

    <H4 CLASS="subhead"><A NAME="k03"></A>CYLINDERS, PISTONS, AND
    VALVES,</H4>

    <P>443. <EM>Q.</EM>--Is it a beneficial practice to make cylinders with
    steam jackets?</P>

    <P><EM>A.</EM>--In Cornwall, where great attention is paid to economy
    of fuel, all the engines are made with steam jackets, and in some cases
    a flue winds spirally round the cylinder, for keeping the steam hot.
    Mr. Watt, in his early practice, discarded the steam jacket for a time,
    but resumed it again, as he found its discontinuance occasioned a
    perceptible waste of fuel; and in modern engines it has been found that
    where a jacket is used less coal is consumed than where the use of a
    jacket is rejected. The cause of this diminished effect is not of very
    easy perception, for the jacket exposes a larger radiating surface for
    the escape of the heat than the cylinder; nevertheless, the fact has
    been established beyond doubt by repeated trials, that engines provided
    with a jacket are more economical than engines without one. The
    exterior of the cylinder, or jacket, should be covered with several
    plies of felt, and then be cased in timber, which must be very narrow,
    the boards being first dried in a stove, and then bound round the
    cylinder with hoops, like the staves of a cask. In many of the Cornish
    engines the steam is let into casings formed in the cylinder cover and
    cylinder bottom, for the further economisation of the heat, and the
    cylinder stuffing box is made very deep, and a lantern or hollow brass
    is introduced into the centre of the packing, into which brass the
    steam gains admission by a pipe provided for the purpose; so that in
    the event of the packing becoming leaky, it will be steam that will be
    leaked into the cylinder instead of air, which, being incondensable,
    would impair the efficiency of the engine. A lantern brass, of a
    similar kind, is sometimes introduced into the stuffing boxes of
    oscillating engines, but its use there is to receive the lateral
    pressure of the piston rod, and thus take any strain off the
    packing.</P>

    <P>444. <EM>Q.</EM>--Will you explain the proper course to pursue in
    the production of cylinders?</P>

    <P><EM>A.</EM>--In all engines the valve casing, if made in a separate
    piece from the cylinder, should be attached by means of a metallic
    joint, as such a barbarism as a rust joint in such situations is no
    longer permissible. In the case of large engines with valve casings
    suitable for long slides, an expansion joint in the valve casing should
    invariably be inserted, otherwise the steam, by gaining admission to
    the valve casing before it can enter the cylinder, expands the casing
    while the cylinder remains unaltered in its dimensions, and the joints
    are damaged, and in some cases the cylinder is cracked by the great
    strain thus introduced. The chest of the blow-through valve is very
    commonly cast upon the valve casing; and in engines where the cylinders
    are stationary this is the most convenient practice. All engines, where
    the valve is not of such a construction as to leave the face when a
    pressure exceeding that of the steam is created in the cylinder by
    priming or otherwise, should be provided with an escape valve to let
    out the water, and such valve should be so constructed that the water
    cannot fly out with violence over the attendants; but it should be
    conducted away by a suitable pipe, to a place where its discharge can
    occasion no inconvenience. The stuffing boxes of all engines which
    cannot be stopped frequently to be repacked, should be made very deep;
    metallic packing in the stuffing box has been used in some engines,
    consisting in most instances of one or more rings, cut, sprung, and
    slipped upon the piston rod before the cross head is put on, and packed
    with hemp behind. This species of packing answers very well when the
    parallel motion is true, and the piston rod free from scratches, and it
    accomplishes a material saving of tallow. In some cases a piece of
    sheet brass, packed behind with hemp, has been introduced with good
    effect, a flange being turned over on the under edge of the brass to
    prevent it from slipping up or down with the motion of the rod. The
    sheet brass speedily puts an excellent polish upon the rod, and such a
    packing is more easily kept, and requires less tallow than where hemp
    alone is employed. In side lever marine engines the attachments of the
    cylinder to the diagonal stay are generally made of too small an area,
    and the flanges are made too thick. A very thick flange cast on any
    part of a cylinder endangers the soundness of the cylinder, by inducing
    an unequal contraction of the metal; and it is a preferable course to
    make the flange for the attachment or the framing thin, and the surface
    large--the bolts being turned bolts and nicely fitted. If from
    malformation in this part the framing works to an inconvenient extent,
    the best expedient appears to be the introduction of a number of steel
    tapered bolts, the holes having been previously bored out; and if the
    flanges be thick enough, square keys may also be introduced, half into
    one flange and half into the other, so as to receive the strain. If the
    jaw cracks or breaks away, however, it will be best to apply a
    malleable iron hoop around the cylinder to take the strain, and this
    will in all cases be the preferable expedient, where from any
    peculiarities of structure there is a difficulty in introducing bolts
    and keys of sufficient strength.</P>

    <P>445. <EM>Q.</EM>--Which is the most eligible species of piston?</P>

    <P><EM>A.</EM>--For large engines, pistons with a metallic packing,
    consisting of a single ring, with the ends morticed into one another,
    and a piece of metal let in flush over the joint and riveted to one end
    of the ring, appears to be the best species of piston; and if the
    cylinder be oscillating, it will be expedient to chamfer off the upper
    edge of the ring on the inner side, and to pack it at the back with
    hemp. If the cylinder be a stationary one, springs may be substituted
    for the hemp packing, but in any case it will be expedient to make the
    vertical joints of the ends of the ring run a little obliquely, so as
    to prevent the joint forming a ridge in the cylinder. For small pistons
    two rings may be employed, made somewhat eccentric internally to give a
    greater thickness of metal in the centre of the ring; these rings must
    be set one above the other in the cylinder, and the joints, which are
    oblique, must be set at right angles with one another, so as to obviate
    any disposition of the rings, in their expansion, to wear the cylinder
    oval. The rings must first be turned a little larger than the diameter
    of the cylinder, and a piece is then to be cut out, so that when the
    ends are brought together the ring will just enter within the cylinder.
    The ring, while retained in a state of compression, is then to be put
    in the lathe and turned very truly, and finally it is to be hammered on
    the inside with the small end of the hammer, to expand the metal, and
    thus increase the elasticity.</P>

    <P>446. <EM>Q.</EM>--The rings should be carefully fitted to one
    another laterally?</P>

    <P><EM>A.</EM>--The rings are to be fitted laterally to the piston, and
    to one another, by scraping--a steady pin being fixed upon the flange
    of the piston, and fitting into a corresponding hole in the lower ring,
    to keep the lower ring from turning round; and a similar pin being
    fixed into the top edge of the lower ring to prevent the upper ring
    from turning round; but the holes into which these pins fit must be
    made oblong, to enable the rings to press outward as the rubbing
    surfaces wear. In most cases it will be expedient to press the packing
    rings out with springs where they are not packed behind with hemp, and
    the springs should be made very strong, as the prevailing fault of
    springs is their weakness. Sometimes short bent springs, set round at
    regular intervals between the packing rings and body of the piston, are
    employed, the centre of each spring being secured by a steady pin or
    bolt screwed into the side of the piston; but it will not signify much
    what kind of springs is used, provided they have sufficient tension.
    When pistons are made of a single ring, or of a succession of single
    rings, the strength of each ring should be tested previously to its
    introduction into the piston, by means of a lever loaded by a heavy
    weight.</P>

    <P>447. <EM>Q.</EM>--What kind of piston is employed by Messrs.
    Penn?</P>

    <P><EM>A.</EM>--Messrs. Penn&#39;s piston for oscillating engines has a
    single packing ring, with a tongue piece, or mortice end, made in the
    manner already described. The ring is packed behind with hemp packing,
    and the piece of metal which covers the joint is a piece of thick sheet
    copper or brass, and is indented into the iron of the ring, so as to
    offer no obstruction to the application of the hemp. The ring is fitted
    to the piston only on the under edge; the top edge is rounded to a
    point from the inside, and the junk ring does not bear upon it, but the
    junk ring squeezes down the hemp packing between the packing ring and
    the body of the piston.</P>

    <P>448. <EM>Q.</EM>--How should the piston rod be secured to the
    piston?</P>

    <P><EM>A.</EM>--The piston rod, where it fits into the piston, should
    have a good deal of taper; for if the taper be too small the rod will
    be drawn through the hole, and the piston will be split asunder. Small
    grooves are sometimes turned out of the piston rod above and below the
    cutter hole, and hemp is introduced in order to make the piston eye
    tight. Most piston rods are fixed to the piston by means of a gib and
    cutter, but in some cases the upper portion of the rod within the eye
    is screwed, and it is fixed into the piston by means of an indented
    nut. This nut is in some cases hexagonal, and in other cases the
    exterior forms a portion of a cone which completely fills a
    corresponding recess in the piston; but nuts made in this way become
    rusted into their seat after some time, and cannot be started again
    without much difficulty. Messrs. Miller, Ravenhill &amp; Co. fix in
    their piston rods by means of an indented hexagonal nut, which may be
    started by means of an open box key. The thread of the screw is made
    flat upon the one side and much slanted on the other, whereby a greater
    strength is secured, without creating any disposition to split the nut.
    In side lever engines it is a judicious practice to add a nut to the
    top of the piston rod, in addition to the cutter for securing the
    piston rod to the cross head. In a good example of an engine thus
    provided, the piston rod is 7 in. in diameter, and the screw 5 in.; the
    part of the rod which fits into the cross head eye is 1 ft. 5-1/2 in.
    long, and tapers from 6-1/2 in. to 6- 13/16 in. diameter. This
    proportion of taper is a good one; if the taper be less, or if a
    portion of the piston rod within the cross head eye be left untapered,
    as is sometimes the case, it is very difficult to detach the parts from
    one another.</P>

    <P>449. <EM>Q.</EM>--Which is the most beneficial construction of slide
    valve?</P>

    <P><EM>A.</EM>--The best construction of slide valve appears to be that
    adopted by Messrs. Penn for their larger engines, and which consists of
    a three ported valve, to the back of which a ring is applied of an area
    equal to that of exhaustion port, and which, by bearing steam tight
    against the back of the casing, so that a vacuum may be maintained
    within the ring, puts the valve in equilibrium, so that it may be moved
    with an inconsiderable exercise of force. The back of the valve casing
    is put on like a door, and its internal surface is made very true by
    scraping. There is a hole through the valve so as to conduct away any
    steam which may enter within the ring by leakage, and the ring is kept
    tight against the back of the casing by means of a ring situated
    beneath the bearing ring, provided with four lugs, through which bolts
    pass tapped into bosses on the back of the valve; and, by unscrewing
    these bolts,--which may be done by means of a box key which passes
    through holes in the casing closed with screwed plugs,--the lower ring
    is raised upwards, carrying the bearing ring before it. The rings must
    obviously be fitted over a boss upon the back of the valve; and between
    the rings, which are of brass, a gasket ring is interposed to
    compensate by its compressibility for any irregularity of pressure, and
    each of the bolts is provided with a ratchet collar to prevent it from
    turning back, so that the engineer, in tightening these bolts, will
    have no difficulty in tightening them equally, if he counts the number
    of clicks made by the ratchet. Where this species of valve is used, it
    is indispensable that large escape valves be applied to the cylinder,
    as a valve on this construction is unable to leave the face. In
    locomotive engines, the valve universally employed is the common three
    ported valve.</P>

    <P>450. <EM>Q.</EM>--Might not an equilibrium valve be so constructed
    by the interposition of springs, as to enable it to leave the cylinder
    face when an internal force is applied?</P>

    <P><EM>A.</EM>--That can no doubt be done, and in some engines has been
    done. In the screw steamer Azof, the valve is of the equilibrium
    construction, but the plate which carries the packing on which the top
    ring rests, is an octagon, and fits into an octagonal recess on the
    back of the valve. Below each side of the octagon there is a bent flat
    spring, which lifts up the octagonal plate, and with it the packing
    ring against the back of the valve casing; and should water get into
    the cylinder, it escapes by lifting the valve, which is rendered
    possible by the compressibility of the springs. An equivalent
    arrangement is shown in figs. 39 and 40, where the ring is lifted by
    spiral springs.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig39.png" WIDTH="600" HEIGHT="391" ALT=
    "Fig. 39. EQUILIBRIUM GRIDIRON SLIDE VALVE. Longitudinal Section. Scale 3/4 inch = 1 foot.">
    </P>

    <P>451. <EM>Q.</EM>--What species of valve is that shown in figs. 39
    and 40?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig40.png" WIDTH="622" HEIGHT="550" ALT=
    "Fig. 40. EQUILIBRIUM GRIDIRON SLIDE VALVE. Back View with Ring removed. Scale 3/4 inch = 1 foot.">
    </P>

    <P><EM>A.</EM>--It is an equilibrium gridiron valve; so called because
    it lets the steam in and out by more than one port. A A are the
    ordinary steam passages to the top and bottom of the cylinder; B B is
    the ring which rubs against the back of the valve casing, and D is the
    eduction passage, S S S S shows the limits of the steam space, for the
    steam penetrates to the central chamber S S by the sides of the valve.
    When the valve is opened upon the steam side, the cylinder receives
    steam through both ports at that end of the cylinder, and both ports at
    the other end of the cylinder are at the same time open to the
    eduction. The benefit of this species of valve is, that it gives the
    same opening of the valve that is given in ordinary engines, with half
    the amount of travel; or if three ports were made instead of two, then
    it would give the same area of opening that is given in common engines
    with one third the amount of travel. For direct acting screw engines
    this species of valve is now extensively used.</P>

    <P>452. <EM>Q.</EM>--Will you describe the configuration and mode of
    attachment of the eccentric by which the valve is moved?</P>

    <P><EM>A.</EM>--In marine engines, whether paddle or screw, if moving
    at a slow rate of speed, the eccentric is generally loose upon the
    shaft, for the purpose of backing, and is furnished with a back balance
    and catches, so that it may stand either in the position for going
    ahead, or in that for going astern. The body of the eccentric is of
    cast iron, and it is put on the shaft in two pieces. The halves are put
    together with rebated joints to keep them from separating laterally,
    and they are prevented from sliding out by round steel pins, each
    ground into both halves; square keys would probably be preferable to
    round pins in this arrangement, as the pins tend to wedge the jaws of
    the eccentric asunder. In some cases the halves of the eccentric are
    bolted together by means of flanges, which is, perhaps, the preferable
    practice. The eccentric hoop in marine and land engines is generally of
    brass; it is expedient to cast an oil cup on the eccentric hoop, and,
    where practicable, a pan should be placed beneath the eccentric for the
    reception of the oil droppings. The notch of the eccentric rod for the
    reception of the pin of the valve shaft is usually steeled, to prevent
    inconvenient wear; for when the sides of the notch wear, the valve
    movement is not only disturbed, but it is very difficult to throw the
    eccentric rod out of gear. It is found to be preferable, however, to
    fit this notch with a brass bush, for the wear is then less rapid, and
    it is an easy thing to replace this bush with another when it becomes
    worn. The eccentric catches of the kind usually employed in marine
    engines, sometimes break off at the first bolt hole, and it is
    preferable to have a bolt in advance of the catch face, or to have a
    hoop encircling the shaft with the catches welded on it, the hoop
    itself being fixed by bolts or a key. This hoop may either be put on
    before the cranks in one piece or afterwards in two pieces.</P>

    <P>453. <EM>Q.</EM>--Are such eccentrics used in direct acting screw
    engines?</P>

    <P><EM>A.</EM>--No; direct acting screw engines are usually fitted with
    the link motion and two fixed eccentrics.</P>

    <H4 CLASS="subhead"><A NAME="k04"></A>AIR PUMP AND CONDENSER.</H4>

    <P>454. <EM>Q.</EM>--What are the details of the air pump?</P>

    <P><EM>A.</EM>--The air pump bucket and valves are all of brass in
    modern marine engines, and the chamber of the pump is lined with
    copper, or made wholly of brass, whereby a single boring suffices. When
    a copper lining is used, the pump is first bored out, and a bent sheet
    of copper is introduced, which is made accurately to fill the place, by
    hammering the copper on the inside. Air pump rods of Muntz&#39;s metal
    or copper are much used. Iron rods covered with brass are generally
    wasted away where the bottom cone fits into the bucket eye, and if the
    casing be at all porous, the water will insinuate itself between the
    casing and the rod and eat away the iron. If iron rods covered with
    brass be used, the brass casing should come some distance into the
    bucket eye; the cutter should be of brass, and a brass washer should
    cover the under side of the eye, so as to defend the end of the rod
    from the salt water. Rods of Muntz&#39;s metal are probably on the
    whole to be preferred. It is a good practice to put a nut on the top of
    the rod, to secure it more firmly in the cross head eye, where that
    plan can be conveniently adopted. The part of the rod which fits into
    the cross head eye should have more taper when made of copper or brass,
    than when made of iron; as, if the taper be small, the rod may get
    staved into the eye, whereby its detachment will be difficult.</P>

    <P>455. <EM>Q.</EM>--What species of packing is used in air pumps?</P>

    <P><EM>A.</EM>--Metallic packing has in some instances been employed in
    air pump buckets, but its success has not been such as to lead to its
    further adoption. The packing commonly employed is hemp. A deep solid
    block of metal, however, without any packing, is often employed with a
    satisfactory result; but this block should have circular grooves cut
    round its edge to hold water. Where ordinary packing is employed, the
    bucket should always be made with a junk ring, whereby the packing may
    be easily screwed down at any time with facility. In slow moving
    engines the bucket valve is generally of the spindle or pot-lid kind,
    but butterfly valves are sometimes used. The foot and delivery valves
    are for the most part of the flap or hanging kind. These valves all
    make a considerable noise in working, and are objectionable in many
    ways. Valves on Belidor&#39;s construction, which is in effect that of
    a throttle valve hung off the centre, were some years ago proposed for
    the delivery and foot valves; and it appears probable that their
    operation would be more satisfactory than that of the valves usually
    employed.</P>

    <P>456. <EM>Q.</EM>--Where is the delivery valve usually situated?</P>

    <P><EM>A.</EM>--Some delivery valve seats are bolted into the mouth of
    the air pump, whereby access to the pump bucket is rendered difficult:
    but more commonly the delivery valve is a flap valve exterior to the
    pump. If delivery valve seats be put in the mouth of the air pump at
    all, the best mode of fixing them appears to be that adopted by Messrs.
    Maudslay. The top of the pump barrel is made quite fair across, and
    upon this flat surface a plate containing the delivery valve is set,
    there being a small ledge all round to keep it steady. Between the
    bottom of the stuffing box of the pump cover and the eye of the valve
    seat a short pipe extends encircling the pump rod, its lower end
    checked into the eye of the valve seat, and its upper end widening out
    to form the bottom of the stuffing box of the pump cover. Upon the top
    of this pipe some screws press, which are accessible from the top of
    the stuffing box gland, and the packing also aids in keeping down the
    pipe, the function of which is to retain the valve seat in its place.
    When the pump bucket has to be examined the valve seat may be slung
    with the cover, so as to come up with the same purchase. For the bucket
    valves of such pumps Messrs. Maudslay employ two or more concentric
    ring valves with a small lift. These valves have given a good deal of
    trouble in some cases, in consequence of the frequent fracture of the
    bolts which guide and confine the rings; but this is only a fault of
    detail which is easily remedied, and the principle appears to be
    superior to that of any of the other metallic air pump valves at
    present in common use.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig41.png" ALIGN="left" WIDTH="252"
    HEIGHT="550" ALT=
    "Fig. 41. TRUNK AIR PUMP. Scale 3/4 inch to 1 foot."></P>

    <P>457. <EM>Q.</EM>--Are not air pump valves now very generally made of
    india rubber?</P>

    <P><EM>A.</EM>--They are almost invariably so made if the engines are
    travelling fast, as in the case of direct acting screw engines, and
    they are very often made of large discs or rings of india rubber, even
    when the engines travel slowly. A very usual and eligible arrangement
    for many purposes is that shown in fig. 41, where both foot and
    delivery valves are situated in the ends of the pump, and they, as well
    as the valve in the bucket are made of india rubber rings closing on a
    grating. The trunk in the air pump enables guide rods to be dispensed
    with.</P>

    <P>458. <EM>Q.</EM>--The air pump, when double acting, has of course
    inlet and outlet valves at each end?</P>

    <P><EM>A.</EM>--Yes; and the general arrangement of the valves of
    double acting air pumps, such as are usual in direct acting screw
    engines, is that represented in the figure of Penn&#39;s trunk engine
    already described in Chapter I. Each inlet and outlet valve consists of
    a number of india rubber discs set over a perforated brass plate, and
    each disc is bound down by a bolt in the middle, which bolt also
    secures a brass guard set above the disc to prevent it from rising too
    high. The usual configuration of those valves is that represented in
    figs. 42, 43, and 44; figs. 42 and 43 being a section and ground plan
    of the species of valve used by Messrs. Penn, and fig. 44 being a
    section of that used by Messrs. Maudslay. It is important in these
    valves to have the india rubber thick,--say about an inch thick for
    valves eight inches in diameter. It is also advisable to make the
    central bolts with a nut above and a nut below, and to form the bolt
    with a counter sunk neck, so that it will not fall down when the top
    nut is removed. The lower point of the bolt should be riveted over on
    the nut to prevent it from unscrewing, and the top end should have a
    split pin through the point for the same purpose. The hole through
    which the bolt passes should be tapped, though the bolt is not screwed
    into it, so that if a bolt breaks, a temporary stud may be screwed into
    the hole without the necessity of taking out the whole plate. The guard
    should be large, else the disc may stretch in the central hole until it
    comes over it; but the guard should not permit too much lift of the
    valve, else a good deal of the water and air will return into the pump
    at the return stroke before the valve shuts. Penn&#39;s guard is rather
    small, and Maudslay&#39;s permits too much lift.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig42.png" WIDTH="500" HEIGHT="300" ALT=
    "Fig. 42. PENN&#39;S DISK VALVE FOR AIR PUMP. Section."></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig43.png" WIDTH="444" HEIGHT="550" ALT=
    "Fig. 43. PENN&#39;S DISK VALVE FOR AIR PUMP. Ground Plan."></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig44.png" WIDTH="500" HEIGHT="319" ALT=
    "Fig. 44. MAUDSLAY&#39;S DISC VALVE FOR AIR PUMP. Section."></P>

    <P>459. <EM>Q.</EM>--What is the proper area through the valve
    gratings?</P>

    <P><EM>A.</EM>--The collective area should be at least equal to the
    area of the pump piston, and the lower edges of the perforations should
    be rounded off to afford more free ingress or egress to the water.</P>

    <P>460. <EM>Q.</EM>--Is there much strain thrown on the plates in which
    the valves are set?</P>

    <P><EM>A.</EM>--A good deal of strain; and in the earlier direct acting
    screw engines these plates were nearly in every case made too light.
    They should be made thick, have strong feathers upon them, and be very
    securely bolted down with split pins at the points of the bolts, to
    prevent them from unscrewing. The plate will be very apt to be broken
    should some of the bolts become loose. Of course all the bolts and
    split pins, as well as the plates and guards, must be of brass.</P>

    <P>461. <EM>Q.</EM>--How are the plates to be taken out should that
    become necessary?</P>

    <P><EM>A.</EM>--They are usually taken out through a door in the top of
    the hot well provided for that purpose, which door should be as large
    as the plates themselves; and it is a good precaution to cast upon this
    door--which will be of cast iron--six or eight stout projecting feet
    which will press upon the top of the outlet or delivery valve plate
    when the door is screwed down. The upper or delivery valve plate and
    the lower or foot valve plate should have similar feet. A large part of
    the strain will thus be transferred from the plates to the door, which
    can easily be made strong enough to sustain it. It is advisable that
    the plates should lie at an angle so that the shock of the water may
    not come upon the whole surface at once.</P>

    <P>462. <EM>Q.</EM>--Does the double acting air pump usual in direct
    acting screw engines, produce as good a vacuum as the single acting air
    pump usual in paddle engines?</P>

    <P><EM>A.</EM>--It will do so if properly constructed; but I do not
    know of any case of a double acting air pump, with india rubber valves,
    which has been properly constructed.</P>

    <P>463. <EM>Q.</EM>--What is the fault of such pumps?</P>

    <P><EM>A.</EM>--The pump frequently works by starts, as if at times it
    did not draw at all, and then again on a sudden gorged itself with
    water, so as to throw a great strain upon the working parts. The
    vacuum, moreover, is by no means so good as it should be, and it is a
    universal vice of direct acting screw engines that the vacuum is
    defective. I have been at some pains to investigate the causes of this
    imperfection; and in a sugar house engine fitted with pumps like those
    of a direct acting screw engine to maintain a vacuum in the pans, I
    found that a better vacuum was produced when the engine was going
    slowly than when it was going fast; which is quite the reverse of what
    was to have been expected, as the hot water which had to be removed by
    the condensation of the steam proceeding from the pan, was a constant
    quantity. In this engine, too, which was a high pressure one, the
    irregularities of the engine consequent upon the fitful catching of the
    water by the pump, was more conspicuous, as the working of this vacuum
    pump was the only work that the engine had to perform.</P>

    <P>464. <EM>Q.</EM>--And were you able to discover the cause of these
    irregularities?</P>

    <P><EM>A.</EM>--The main cause of them I found to be the largeness of
    the space left between the valve plates in this class of pumps, and out
    of which there is nothing to press the air or water which may be lying
    there. It consequently happens, that if there be the slightest leakage
    of air into the pump, this air is merely compressed, and not expelled,
    by the advance of the air pump piston. It expands again to its former
    bulk on the return of the pump piston, and prevents the water from
    entering until there is such an accumulation of pressure in the
    condenser as forces the water into the pump, when the air being
    expelled by the water, causes a good vacuum to be momentarily formed in
    the pump when it gorges itself by taking a sudden gulp of water. So
    soon, however, as the pressure falls in the condenser and some more air
    leaks into the pump, the former imperfect action recurs and is again
    redressed in the same violent manner.</P>

    <P>465. <EM>Q.</EM>--Is this irregular action of the pump the cause of
    the imperfect vacuum?</P>

    <P><EM>A.</EM>--It is one cause. Sometimes one end of the pump will
    alone draw and the other end will be inoperative, although it is
    equally open to the condenser, and this will chiefly take place at the
    stuffing box end, where a leakage of air is more likely to occur. I
    find, however, that even when both ends of the pump are acting equally
    and there is no leakage of air at all, the vacuum maintained by a
    double acting horizontal pump with india rubber valves, is not so good
    as that maintained by a single acting pump of the kind usual in old
    engines.</P>

    <P>466. <EM>Q.</EM>--Will you specify more precisely what were the
    results you obtained?</P>

    <P><EM>A.</EM>--When the vacuum pan was exhausted by the pumps without
    any boiling being carried on in the pan, but only a little cold water
    being let into it, and also into the pumps to enable them to act in
    their best manner, it was found that whereas with the old pump a vacuum
    of 114 on the sugar boiler&#39;s gauge could be readily obtained, equal
    to about 29-1/2 inches of mercury, the lowest that could possibly be
    got with the new horizontal pump was 122 degrees of the sugar
    boiler&#39;s gauge, or 29 inches of mercury, and to get that the engine
    must not go faster than 10 or 12 strokes per minute. The proper speed
    of the engine was 75 strokes per minute, but if allowed to go at that
    speed the vacuum fell to 130 of the sugar maker&#39;s gauge, or 28-1/2
    inches of mercury. When the steam was let into the worms of the pan so
    as to boil the water in it, the vacuum was 134 at 75 revolutions of the
    engine, and went down to 132 at 40 revolutions, but rose again to 135,
    equal to about 28-1/4 inches of mercury, at 20 revolutions.</P>

    <P>467. <EM>Q.</EM>--To what do you attribute the circumstance of a
    better vacuum being got at low speeds than at high speeds?</P>

    <P><EM>A.</EM>--It is difficult to assign the precise reason, but it
    appears to be a consequence of the largeness of the vacant space
    between the valve plates. When the piston of the air pump is drawn
    back, the air contained in this large collection of water will cause it
    to boil up like soda water; and when the piston of the pump is forced
    forward, this air, instead of being expelled, will be again driven into
    the water. There will consequently be a quantity of air in the pump
    which cannot be got rid of at all, and which will impair the vacuum as
    a matter of course.</P>

    <P>468. <EM>Q.</EM>--What expedient did you adopt to improve the vacuum
    in the engine to which you have referred?</P>

    <P><EM>A.</EM>--I put blocks of wood on the air pump piston, which at
    the end of its stroke projected between the valve plates and forced the
    water out. I also introduced a cock of water at each end of the pump
    between the valve plates, to insure the presence of water at each end
    of the pump to force the air out. With these ameliorations the pump
    worked steadily, and the vacuum obtained became as good as in the old
    pump. I had previously introduced an injection cock into each end of
    the air pump in steam vessels, from which I had obtained advantageous
    results; and in all horizontal air pumps I would recommend the piston
    and valve plates to be so constructed that the whole of the water will
    be expressed by the piston. I would also recommend an injection cock to
    be introduced at each end of the pump.</P>

    <H4 CLASS="subhead"><A NAME="k05"></A>PUMPS, COCKS, AND PIPES.</H4>

    <P>469. <EM>Q.</EM>--Will you explain the arrangement of the feed
    pump?</P>

    <P><EM>A.</EM>--In steam vessels, the feed pump plunger is generally of
    brass, and the barrel of the pump is sometimes of brass, but generally
    of cast iron. There should be a considerable clearance between the
    bottom of the plunger and the bottom of the barrel, as otherwise the
    bottom of the barrel may be knocked out, should coal dust or any other
    foreign substance gain admission, as it probably would do if the
    injection water were drawn at any time from the bilge of the vessel, as
    is usually done if the vessel springs a leak. The valves of the feed
    pump in marine engines are generally of the spindle kind, and are most
    conveniently arranged in a chest, which may be attached in any
    accessible position to the side of the hot well. There are two nozzles
    upon this chest, of which the lower one leads to the pump, and the
    upper one to the boiler. The pipe leading to the pump is a suction pipe
    when the plunger ascends, and a forcing pipe when the plunger descends.
    The plunger in ascending draws the water out of the hot well through
    the lowest of the valves, and in descending forces it through the
    centre valve into the space above it, which communicates with the feed
    pipe. Should the feed cock be shut so as to prevent any feed water from
    passing through it, the water will raise the topmost valve, which is
    loaded to a pressure considerably above the pressure of the steam, and
    escape into the hot well. This arrangement is neater and less expensive
    than that of having a separate loaded valve on the feed pipe with an
    overflow through the ship&#39;s side, as is the more usual
    practice.</P>

    <P>470. <EM>Q.</EM>--Will you describe what precautions are to be
    observed in the construction of the cocks used in engines?</P>

    <P><EM>A.</EM>--All the cocks about an engine should be provided with
    bottoms and stuffing boxes, and reliance should never be placed upon a
    single bolt passing through a bottom washer for keeping the plug in its
    place, in the case of any cock communicating with the boiler; for a
    great strain is thrown upon that bolt if the pressure of the steam be
    high, and if the plug be made with much taper; and should the bolt
    break, or the threads strip, the plug will fly out, and persons
    standing near may be scalded to death. In large cocks, it appears the
    preferable plan to cast the bottoms in; and the metal of which all the
    cocks about a marine engine are made, should be of the same quality as
    that used in the composition of the brasses, and should be without
    lead, or other deteriorating material. In some cases the bottoms of
    cocks are burnt in with hard solder, but this method cannot be depended
    upon, as the solder is softened and wasted away by the hot salt water,
    and in time the bottom leaks, or is forced out. The stuffing box of
    cocks should be made of adequate depth, and the gland should be secured
    by means of four strong copper bolts. The taper of blow-off cocks is an
    important element in their construction; as, if the taper be too great,
    the plugs will have a continual tendency to rise, which, if the packing
    be slack, will enable grit to get between the faces, while, if the
    taper be too little, the plug will be liable to jam, and a few times
    grinding will sink it so far through the shell that the waterways will
    no longer correspond. One eighth of an inch deviation from the
    perpendicular for every inch in height, is a common angle for the side
    of the cock, which corresponds with one quarter of an inch difference
    of diameter in an inch of height; but perhaps a somewhat greater taper
    than this, or one third of an inch difference in diameter for every
    inch of height, is a preferable proportion. The bottom of the plug must
    be always kept a small distance above the bottom of the shell, and an
    adequate surface must be left above and below the waterway to prevent
    leakage. Cocks formed according to these directions will be found to
    operate satisfactorily in practice, while they will occasion perpetual
    trouble if there be any malformation.</P>

    <P>471. <EM>Q.</EM>--What is the best arrangement and configuration of
    the blow- off cocks?</P>

    <P><EM>A.</EM>--The blow-off cocks of a boiler are generally placed
    some distance from the boiler; but it appears preferable that they
    should be placed quite close to it, as there are no means of shutting
    off the water from the pipe between the blow-off cock and the boiler,
    should fracture or leakage there arise. Every boiler must be furnished
    with a blow-off cock of its own, independently of the main blow-off
    cocks on the ship&#39;s sides, so that the boilers may be blown off
    separately, and may be shut off from one another. The preferable
    arrangement appears to be, to cast upon each blow-off cock a bend for
    attaching the cock to the bottom of the boiler, and the plug should
    stand about an inch in advance of the front of the boiler, so that it
    may be removed, or re-ground, with facility. The general arrangement of
    the blow-off pipes is to run a main blow-off pipe beneath the floor
    plates, across the ship, at the end of the engines, and into this pipe
    to lead a separate pipe, furnished with a cock, from each boiler. The
    main blow-off pipe, where it penetrates the ship&#39;s side, is
    furnished with a cock: and in modern steam vessels Kingston&#39;s
    valves are also used, which consist of a spindle or plate valve, fitted
    to the exterior of the ship, so that if the internal pipe or cock
    breaks, the external valve will still be operative. Some expedient of
    this kind is almost necessary, as the blow-off cocks require occasional
    regrinding, and the sea cocks cannot be re-ground without putting the
    vessel into dock, except by the use of Kingston&#39;s valves, or some
    equivalent expedient.</P>

    <P>472. Q.--What is the proper construction and situation of the
    injection cocks, and waste water valves?</P>

    <P>A.--The sea injection cocks are usually made in the same fashion as
    the sea blow-off cocks, and of about the same size, or rather larger.
    The injection water is generally admitted to the condenser by means of
    a slide valve, but a cock appears to be preferable, as it is more
    easily opened, and has not any disposition to shut of its own accord.
    In paddle vessels the sea injection pipes should be put through the
    ship&#39;s sides in advance of the paddles, so that the water drawn in
    may not be injuriously charged with air. The waste water pipe passing
    from the hot well through the vessel&#39;s side is provided with a stop
    valve, called the discharge valve, which is usually made of the spindle
    kind, so as to open when the water coming from the air pump presses
    against it. In some cases this valve is a sluice valve, but the hot
    well is then almost sure to be split, if the engine be set on without
    the valve having been opened. The opening of the waste water pipe
    should always be above the load water line, as it will otherwise be
    difficult to prevent leakage through the engine into the ship when the
    vessel is lying in harbor.</P>

    <P>473. Q.--What is the best arrangement of gauge cocks and glass
    gauges?</P>

    <P>A.--Gauge cocks are generally very inartificially made, and occasion
    needless annoyance. They are rarely made with bottoms, or with stuffing
    boxes, and are consequently, for the most part, adorned with
    stalactites of salt after a short period of service. The water
    discharged from them, too, from the want of a proper conduit,
    disfigures the front of the boiler, and adds to the corrosion in the
    ash pits. It would be preferable to combine the gauge cocks
    appertaining to each boiler into a single upright tube, connected
    suitably with the boiler, and the water flowing from them could be
    directed downward into a funnel tube communicating with the bilge. The
    cocks of the glass tubes, as well as of the gauge cocks, should be
    furnished with stuffing boxes and with bottoms, unless the water enters
    through the bottom of the plug, which in gauge cocks is sometimes the
    case. The glass gauge tubes should always be fitted with a cock at each
    neck communicating with the boiler, so that the water and steam may be
    shut off if the tube breaks; and the cocks should be so made as to
    admit of the tubes being blown through with steam to clear them, as in
    muddy water they will become so soiled that the water cannot be seen.
    The gauge cocks frequently have pipes running up within the boiler, to
    the end that a high water level may be made consistent with an easily
    accessible position of the gauge cocks themselves. With the glass
    tubes, however, this species of arrangement is not possible, and the
    glass tubes must always be placed in the position of the water
    level.</P>

    <P>474. Q.--What is the proper material of the pipes in steam
    vessels?</P>

    <P>A.--Most of the pipes of marine engines should be made of copper.
    The steam pipes may be of cast iron, if made very strong, but the waste
    water pipes should be of copper. Cast iron blow-off pipes have in some
    cases been employed, but they are liable to fracture, and are
    dangerous. The blow-off and feed pipes should be of copper, but the
    waste steam pipe may be of galvanized iron. Every pipe passing through
    the ship&#39;s side, and every pipe fixed at both ends, and liable to
    be heated and cooled, should be furnished with a faucet or expansive
    joint; and in the case of the cast iron pipes, the part of the pipe
    fitting into the faucet should be turned. In the distribution of the
    faucets of the pipes exposed to pressure, care must be taken that they
    be so placed that the parts of the pipe cannot be forced asunder, or
    turned round by the strain, as serious accidents have occurred from the
    neglect of this precaution.</P>

    <P>475. <EM>Q.</EM>--What is the best mode of making pipes tight where
    they penetrate the ship&#39;s side?</P>

    <P><EM>A.</EM>--In wooden vessels the pipes where they pierce the
    ship&#39;s side, should be made tight, as follows:--the hole being cut,
    a short piece of lead pipe, with a broad flange at one end, should be
    fitted into it, the place having been previously smeared with white
    lead, and the pipe should then be beaten on the inside, until it comes
    into close contact all around with the wood. A loose flange should next
    be slipped over the projecting end of the lead pipe, to which it should
    be soldered, and the flanges should both be nailed to the timber with
    scupper nails, white lead having been previously spread underneath.
    This method of procedure, it is clear, prevents the possibility of
    leakage down through the timbers; and all, therefore, that has to be
    guarded against after this precaution, is to prevent leakage into the
    ship. To accomplish this object, let the pipe which it is desired to
    attach be put through the leaden hause, and let the space between the
    pipe and the lead be packed with gasket and white lead, to which a
    little olive oil has been added. The pipe must have a flange upon it to
    close the hole in the ship&#39;s side; the packing must then be driven
    in from the outside, and be kept in by means of a gland secured with
    bolts passing through the ship&#39;s side. If the pipe is below the
    water line the gland must be of brass, but for the waste water pipe a
    cast iron gland will answer. This method of securing pipes penetrating
    the side, however, though the best for wooden vessels, will, it is
    clear, fail to apply to iron ones. In the case of iron vessels, it
    appears to be the best practice to attach a short iron nozzle,
    projecting inward from the skin, for the attachment of every pipe below
    the water line, as the copper or brass would waste the iron of the skin
    if the attachment were made in the usual way.</P>

    <H4 CLASS="subhead"><A NAME="k06"></A>DETAILS OF THE SCREW AND SCREW
    SHAFT.</H4>

    <P>476. <EM>Q.</EM>--What is the best method of fixing the screw upon
    the shaft?</P>

    <P><EM>A.</EM>--The best way is to cut two large grooves in the shaft
    coming up to a square end, and two corresponding grooves or key seats
    in the screw boss opposite the arms. Fit into the grooves on the shaft
    keys with heads, the length of which is equal to half the depth of the
    boss, and with the ends of the keys bearing against the ends of the
    grooves in the shaft. Then ship on the propeller, and drive other keys
    of an equal length from the other side of the boss, so that the points
    of the keys will nearly meet in the middle; next burr up the edge of
    the grooves upon the heads of the keys, to prevent them from working
    back; and finally tap a bolt into the side of the boss to penetrate the
    shaft. Propellers so fitted will never get slack.</P>

    <P>477. <EM>Q.</EM>--What is the best way of fitting in the screw pipe
    at the stern?</P>

    <P><EM>A.</EM>--It should have projecting rings, which should be
    turned; and cast iron pieces with holes in them, bored out to the sizes
    of these rings, should be secured to the stern frames, and the pipe be
    then shipped through all. Before this is done, however, the stern post
    must be bored out by a template to fit the pipe, and the pipe is to be
    secured at the end to the stern post either by a great external nut of
    cast iron, or by bolts passing through the stern post and through lugs
    on the pipe. The pipe should be bored throughout its entire length, and
    the shaft should be turned so as to afford a very long bearing which
    will prevent rapid wear.</P>

    <P>478. <EM>Q.</EM>--How is the hole formed in the deadwood of the ship
    in which the screw works?</P>

    <P><EM>A.</EM>--A great frame of malleable iron, the size of the hole,
    is first set up, and the plating of the ship is brought to the edge of
    this hole, and is riveted through the frame. It is important to secure
    this frame very firmly to the rest of the ship, with which view it is
    advisable to form a great palm, like the palm of a vice, on its inner
    superior corner, which, projecting into the ship, may be secured by
    breast-hook plates to the sides, whereby the strain which the screw
    causes will be distributed over the stern, instead of being
    concentrated on the rivets of the frame.</P>

    <P>479. <EM>Q.</EM>--Are there several lengths of screw shaft?</P>

    <P><EM>A.</EM>--There are.</P>

    <P>480. <EM>Q.</EM>--How then are these secured to one another?</P>

    <P><EM>A.</EM>--The best mode of securing the several lengths of shaft
    together is by forging the shafts with flanges at the ends, which are
    connected together by bolts, say six strong bolts in each, accurately
    fitted to the holes.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig44b.png" WIDTH="544" HEIGHT="550"
    ALT=
    "Fig 44. End of the Screw Shaft of Correo, showing the mode of receiving the Thrust. A, discs; B, tightening wedge.">
    </P>

    <P>481. <EM>Q.</EM>--How is the thrust of the shaft usually
    received?</P>

    <P><EM>A.</EM>--In some cases it is received on a number of metal discs
    set in a box containing oil; and should one of these discs stick fast
    from friction, the others will be free to revolve. This arrangement,
    which is represented in fig. 44, is used pretty extensively and answers
    the purpose perfectly. It is of course necessary that the box in which
    the discs A are set, shall be strong enough to withstand the thrust
    which the screw occasions. Another arrangement still more generally
    used, is that represented in figs. 55 and 56, p. 331. It is a good
    practice to make the thrust plummer block with a very long sole in the
    direction of the shaft, so as to obviate any risk of canting or
    springing forward when the strain is applied, as such a circumstance,
    if occurring even to a slight extent, would be very likely to cause the
    bearing to heat.</P>

    <P>482. <EM>Q.</EM>--Are there not arrangements existing in some
    vessels for enabling the screw to be lifted out of the water while the
    vessel is at sea?</P>

    <P><EM>A.</EM>--There are; but such arrangements are not usual in
    merchant vessels. In one form of apparatus the screw is set on a short
    shaft in the middle of a sliding frame, which can be raised or lowered
    in grooves like a window and the screw shaft within the ship can be
    protruded or withdrawn by appropriate mechanism, so as to engage or
    leave free this short shaft as may be required. When the screw has to
    be lifted, the screw shaft is drawn into the vessel, leaving the short
    shaft free to be raised up by the sliding frame, and the frame is
    raised by long screws turned round by a winch purchase on deck. A chain
    or rope, however, is better for the purpose of raising this frame, than
    long screws; but the frame should in such case be provided with pall
    catches like those of a windlass, which, if the rope should break, will
    prevent the screw from falling.</P>

    <H4 CLASS="subhead"><A NAME="k07"></A>DETAILS OF THE PADDLES AND PADDLE
    SHAFT.</H4>

    <P>483. <EM>Q.</EM>--What are the most important details of the
    construction of paddle wheels?</P>

    <P><EM>A.</EM>--The structure of the feathering wheel will be hereafter
    described in connection with an account of the oscillating engine; and
    it will be expedient now to restrict any account of the details to the
    common radial paddle, as applied to ocean steamers. The best plan of
    making the paddle centres is with square eyes, and each centre should
    be secured in its place by means of eight thick keys. The shaft should
    be burred up against the head of these keys with a chisel, so as to
    prevent the keys from coming back of their own accord. If the keys are
    wanted to be driven back, this burr must be cut off, and if made thick,
    and of the right taper, they may then be started without difficulty.
    The shaft must of course be forged with square projections on it, so as
    to be suitable for the application of centres with square eyes. Messrs.
    Maudslay &amp; Co. bore out their paddle centres, and turn a seat for
    them on the shaft, afterward fixing them on the shaft with a single
    key. This plan is objectionable for the two reasons, that it is
    insecure when new, and when old is irremovable. The general practice
    among the London engineers is to fix the paddle arms at the centre to a
    plate by means of bolts, a projection being placed upon the plates on
    each side of the arm, to prevent lateral motion; but this method is
    inferior in durability to that adopted in the Clyde, in which each arm
    is fitted into a socket by means of a cutter--a small hole being left
    opposite to the end of each arm, whereby the arm may be forced back by
    a drift.</P>

    <P>484. <EM>Q.</EM>--How are the arms attached to the outside
    rings?</P>

    <P><EM>A.</EM>--Some engineers join the paddle arms to the outer ring
    by means of bolts; but unless very carefully fitted, those bolts after
    a time become slack sideways, and a constant working of the parts of
    the wheel goes on in consequence. Sometimes the part of the other ring
    opposite the arm is formed into a mortise, and the arms are wedged
    tight in these holes by wedges driven in on each side; but the plan is
    an expensive one, and not satisfactory, as the wedges work loose even
    though riveted over at the point. The best mode of making a secure
    attachment of the arms to the ring, consists in making the arms with
    long T heads, and riveting the cross piece to the outer ring with a
    number of rivets, not of the largest size, which would weaken the outer
    ring too much. The best way of securing the inner rings to the arms is
    by means of lugs welded on the arms, and to which the rings are
    riveted.</P>

    <P>485. <EM>Q.</EM>--What are the scantlings of the paddle floats?</P>

    <P><EM>A.</EM>--The paddle floats are usually made either of elm or
    pine; if of the former, the common thickness for large sea-going
    vessels is about 2-1/2 inches; if of the latter, 3 inches. The floats
    should have plates on both sides, else the paddle arms will be very
    liable to cut into the wood, and the iron of the arms will be very
    rapidly wasted. When the floats have been fresh put on they must be
    screwed up several times before they come to a bearing. If this be not
    done, the bolts will be sure to get slack at sea, and all the floats on
    the weather side may be washed off. The bolts for holding on the paddle
    floats are made extra strong, on account of the corrosion to which they
    are subject; and the nuts should be made large, and should be square,
    so that they may be effectually tightened up, even though their corners
    be worn away by corrosion. It is a good plan to give the thread of the
    paddle bolts a nick with a chisel, after the nut has been screwed up,
    which will prevent the nut from turning back. Paddle floats, when
    consisting of more than one board, should be bolted together edgeways,
    by means of bolts running through their whole breadth. The floats
    should not be notched to allow of their projection beyond the outer
    ring, as, if the sides of the notch be in contact with the outer ring,
    the ring is soon eaten away in that part, and the projecting part of
    the float, being unsupported, is liable to be broken off.</P>

    <P>486. <EM>Q.</EM>--Do not the wheels jolt sideways when the vessel
    rolls?</P>

    <P><EM>A.</EM>--It is usual to put a steel plate at each end of the
    paddle shafts tightened with a key, to prevent end play when the vessel
    rolls, but the arrangement is precarious and insufficient. Messrs.
    Maudslay make their paddle shaft bearings with very large fillets in
    the corner, with the view of diminishing the evil; but it would be
    preferable to make the bearings of the crank shafts spheroidal; and,
    indeed, it would probably be an improvement if most of the bearings
    about the engine were to be made in the same fashion. The loose end of
    the crank pin should be made not spheroidal, but consisting of a
    portion of a sphere; and a brass bush might then be fitted into the
    crank eye, that would completely encase the ball of the pin, and yet
    permit the outer end of the paddle shaft to fall without straining the
    pin, the bush being at the same time susceptible of a slight end
    motion. The paddle shaft, where it passes through the vessel&#39;s
    side, is usually surrounded by a lead stuffing box, which will yield if
    the end of the shaft falls; this stuffing box prevents leakage into the
    ship from the paddle wheels: but it is expedient, as a further
    precaution, to have a small tank on the ship&#39;s side immediately
    beneath the stuffing box, with a pipe leading down to the bilge to
    catch and conduct away any water that may enter around the shaft.</P>

    <P>487. <EM>Q.</EM>--How is the outer bearing of the paddle wheels
    supplied with tallow?</P>

    <P><EM>A.</EM>--The bearing at the outer end of the paddle shaft is
    sometimes supplied with tallow, forced into a hole in the plummer block
    cover, as in the case of water wheels; but for vessels intended to
    perform long voyages, it is preferable to have a pipe leading down to
    the oil cup above the journal from the top of the paddle box, through
    which pipe oil may at any time be supplied.</P>

    <P>488. <EM>Q.</EM>--Will you explain the method of putting engines
    into a steam vessel?</P>

    <P><EM>A.</EM>--As an illustration of this operation it may be
    advisable to take the case of a side lever engine, and the method of
    proceeding is as follows:--First measure across from the inside of
    paddle bearers to the centre of the ship, to make sure that the central
    line, running in a fore and aft direction on the deck or beams, usually
    drawn by the carpenter, is really in the centre. Stretch a line across
    between the paddle bearers in the direction of the shaft; to this line,
    in the centre of the ship where the fore and aft mark has been made,
    apply a square with arms six or eight feet long, and bring a line
    stretched perpendicularly from the deck to the keelson, accurately to
    the edge of the square: the lower point of the line where it touches
    the keelson will be immediately beneath the marks made upon the deck.
    If this point does not come in the centre of the keelson, it will be
    better to shift it a little, so as to bring it to the centre, altering
    the mark upon the deck correspondingly, provided either paddle shaft
    will admit of this being done--one of the paddle brackets being packed
    behind with wood, to give it an additional projection from the side of
    the paddle bearer. Continue the line fore and aft upon the keelson as
    nearly as can be judged in the centre of the ship; stretch another line
    fore and aft through the mark upon the deck, and look it out of winding
    with the line upon the keelson. Fix upon any two points equally distant
    from the centre, in the line stretched transversely in the direction of
    the shaft; and from those points, as centres, and with any convenient
    radius, sweep across the fore and aft line to see that the two are at
    right angles; and, if not, shift the transverse line a little to make
    them so. From the transverse line next let fall a line upon each
    outside keelson, bringing the edge of the square to the line, the other
    edge resting on the keelson. A point will thus be got on each outside
    keelson, perpendicularly beneath the transverse line running in the
    direction of the shaft, and a line drawn between those two points will
    be directly below the shaft. To this line the line of the shaft marked
    on the sole plate has to be brought, care being taken, at the same
    time, that the right distance is preserved between the fore and aft
    line upon the sole plate, and the fore and aft line upon the central
    keelson.</P>

    <P>489. <EM>Q.</EM>--Of course the keelsons have first to be properly
    prepared?</P>

    <P><EM>A.</EM>--In a wooden vessel, before any part of the machinery is
    put in, the keelsons should be dubbed fair and straight, and be looked
    out of winding by means of two straight edges. The art of placing
    engines in a ship is more a piece of plain common sense than any other
    feat in engineering, and every man of intelligence may easily settle a
    method of procedure for himself. Plumb lines and spirit levels, it is
    obvious, cannot be employed on board a vessel, and the problem consists
    in so placing the sole plates, without these aids, that the paddle
    shaft will not stand awry across the vessel, nor be carried forward
    beyond its place by the framing shouldering up more than was expected.
    As a plumb line cannot be used, recourse must be had to a square; and
    it will signify nothing at what angle with the deck the keelsons run,
    so long as the line of the shaft across the keelsons is square down
    from the shaft centre. The sole plates being fixed, there is no
    difficulty in setting the other parts of the engine in their proper
    places upon them. The paddle wheels must be hung from the top of the
    paddle box to enable the shaft to be rove through them, and the cross
    stays between the engines should be fixed in when the vessel is afloat.
    To try whether the shafts are in a line, turn the paddle wheels, and
    try if the distance between the cranks is the same at the upper and
    under, and the two horizontal centres; if not, move the end of the
    paddle shaft up or down, backward or forward, until the distance
    between the cranks at all the four centres is the same.</P>

    <P>490. <EM>Q.</EM>--In what manner are the engines of a steam vessel
    secured to the hull?</P>

    <P><EM>A.</EM>--The engines of a steamer are secured to the hull by
    means of bolts called holding down bolts, and in wooden vessels a good
    deal of trouble is caused by these bolts, which are generally made of
    iron. Sometimes they go through the bottom of the ship, and at other
    times they merely go through the keelson,--a recess being made in the
    floor or timbers to admit of the introduction of a nut. The iron,
    however, wears rapidly away in both cases, even though the bolts are
    tinned; and it has been found the preferable method to make such of the
    bolts as pass through the bottom, or enter the bilge, of Muntz&#39;s
    metal, or of copper. In a side lever engine, four Muntz&#39;s metal
    bolts may be put through the bottom at the crank end of the framing of
    each engine, four more at the main centre, and four more at the
    cylinder, making twelve through bolts to each engine; and it is more
    convenient to make these bolts with a nut at each end, as in that case
    the bolts may be dropped down from the inside, and the necessity is
    obviated of putting the vessel on very high blocks in the dock, in
    order to give room to put the bolts up from the bottom. The remainder
    of the holding down bolts may be of iron, and may, by means of a square
    neck, be screwed into the timber of the keelsons as wood screws--the
    upper part being furnished with a nut which may be screwed down upon
    the sole plate, so soon as the wood screw portion is in its place. If
    the cylinder be a fixed one it should be bolted down to the sole plate
    by as many bolts as are employed to attach the cylinder cover, and they
    should be of copper or brass, in any situation that is not easily
    accessible.</P>

    <P>491. <EM>Q.</EM>--If the engines become loose, how do you refix
    them?</P>

    <P><EM>A.</EM>--It is difficult to fix engines effectually which have
    once begun to work in the ship, for in time the surface of the keelsons
    on which the engines bear becomes worn uneven, and the engines
    necessarily rock upon it. As a general rule, the bolts attaching the
    engines to the keelsons are too few and of too large a diameter: it
    would be preferable to have smaller bolts, and a greater number of
    them. In addition to the bolts going through the keelsons or the
    vessel&#39;s bottom, there should be a large number of wood screws
    securing the sole plate to the keelson, and a large number of bolts
    securing the various parts of the engine to the sole plate. In iron
    vessels, holding down bolts passing through the bottom are not
    expedient; and there the engine has merely to be secured to the iron
    plate of the keelsons, which are made hollow to admit of a more
    effectual attachment.</P>

    <P>492. <EM>Q.</EM>--What are the proper proportions of bolts?</P>

    <P><EM>A.</EM>--In well formed bolts, the spiral groove penetrates
    about one twelfth of the diameter of the cylinder round which it winds,
    so that the diameter of the solid cylinder which remains is five sixths
    of the diameter over the thread. If the strain to which iron may be
    safely subjected in machinery is one fifteenth of its utmost strength,
    or 4,000 lbs. on the square inch, then 2,180 lbs. may be sustained by a
    screw an inch in diameter, at the outside of the threads. The strength
    of the holding down bolts may easily be computed, when the elevating
    force of the piston or main centre is known; but it is expedient very
    much to exceed this strength in practice, on account of the elasticity
    of the keelsons, the liability to corrosion, and other causes.</P>

    <H4 CLASS="subhead"><A NAME="k08"></A>THE LOCOMOTIVE ENGINE.</H4>

    <P>493. <EM>Q.</EM>--What is the amount of tractive force requisite to
    draw carriages on railways?</P>

    <P><EM>A.</EM>--Upon well formed railways with carriages of good
    construction, the average tractive force required for low speeds is
    about 7-1/2 lbs. per ton, or 1/300th of the load, though in some
    experimental cases, where particular care was taken to obtain a
    favorable result, the tractive force has been reduced as low as 1/500th
    of the load. At low speeds the whole of the tractive force is expended
    in overcoming the friction, which is made up partly of the friction of
    attrition in the axles, and partly of the rolling friction, or the
    obstruction to the rolling of the wheels upon the rail. The rolling
    friction is very small when the surfaces are smooth, and in the case of
    railway carriages does not exceed 1/1000th. of the load; whereas the
    draught on common roads of good construction, which is chiefly made up
    of the rolling friction, is as much as 1/36th of the load.</P>

    <P>494.<EM>Q.</EM>--In reference to friction you have already stated
    that the friction of iron sliding upon brass, which has been oiled and
    then wiped dry, so that no film of oil is interposed, is about 1/11th
    of the pressure, but that in machines in actual operation, where there
    is a film of oil between the rubbing surfaces, the friction is only
    about one third of this amount, or 1/33d of the weight. How then can
    the tractive resistance of locomotives at low speeds, which you say is
    entirely made up of friction, be so little as 1/500th. of the
    weight?</P>

    <P><EM>A.</EM>--I did not state that the resistance to traction was
    1/500th of the weight upon an average--to which condition the answer
    given to a previous question must be understood to apply--but I stated
    that the average traction was about 1/300th of the load, which nearly
    agrees with my former statement. If the total friction be 1/300th of
    the load, and the rolling friction be 1/1000th of the load, then the
    friction of attrition must be 1/429th of the load; and if the diameter
    of the wheels be 36 in., and the diameter of the axles be 3 in., which
    are common proportions, the friction of attrition must be increased in
    the proportion of 36 to 3, or 12 times, to represent the friction of
    the rubbing surface when moving with the velocity of the carriage,
    12/429ths are about 1/35th of the load, which does not differ much from
    the proportion of 1/33d as previously determined.</P>

    <P>495. <EM>Q.</EM>--What is the amount of adhesion of the wheels upon
    the rails?</P>

    <P><EM>A.</EM>--The adhesion of the wheels upon the rails is about
    1/5th of the weight when the rails are clean, or either perfectly wet
    or perfectly dry; but when the rails are half wet or greasy, the
    adhesion is not more than 1/10th or 1/12th of the weight or pressure
    upon the wheels. The weight of a locomotive of modern construction
    varies from 20 to 25 tons.</P>

    <P>496. <EM>Q.</EM>--And what is its cost and average performance?</P>

    <P><EM>A.</EM>--The cost of a common narrow gauge locomotive, of
    average power, varies from &pound;1,900 to &pound;2,200; it will run on
    an average 130 miles per day, at a cost for repairs of 2-1/2d. per
    mile; and the cost of locomotive power, including repairs, wages, oil,
    and coke, does not much exceed 6d. per mile run, on economically
    managed railways. This does not include a sinking fund for the renewal
    of the engines when worn out, which may be taken as equivalent to 10
    per cent. on their original cost.</P>

    <P>497. <EM>Q.</EM>--Does the expense of traction increase much with an
    increased speed?</P>

    <P><EM>A.</EM>--Yes; it increases very rapidly, partly from the
    undulation of the earth when a heavy train passes over it at a high
    velocity, but chiefly from the resistance of the atmosphere and blast
    pipe, which constitute the greatest of the impediments to motion at
    high speeds. At a speed of 30 miles an hour, the atmospheric resistance
    has been found in some cases to amount to about 12 lbs. a ton; and in
    side winds the resistance even exceeds this amount, partly in
    consequence of the additional friction caused from the flanges of the
    wheels being forced against the rails, and partly because the wind
    catches to a certain extent the front of every carriage, whereby the
    efficient breadth of each carriage, in giving motion to the air in the
    direction of the train, is very much increased. At a speed of 30 miles
    an hour, an engine evaporating 200 cubic feet of water in the hour, and
    therefore exerting about 200 horses power, will draw a load of 110
    tons. Taking the friction of the train at 7-1/2 lbs. per ton, or 825
    lbs. operating at the circumference of the driving wheel--which, with 5
    ft. 6 in. wheels, and 18 in. stroke, is equivalent to 4,757 lbs. upon
    the piston--and taking the resistance of the blast pipe at 6 lbs. per
    square inch of the pistons, and the friction of the engine unloaded at
    1 lb. per square inch, which, with pistons 12 in. in diameter, amount
    together to 1,582 lbs., and reckoning the increased friction of the
    engine due to the load at 1/7th of the load, as in some cases it has
    been found experimentally to be, though a much less proportion than
    this would probably be a nearer average, we have 7018.4 lbs. for the
    total load upon the pistons. At 30 miles an hour the speed of the
    pistons will be 457.8 feet per minute, and 7018.4 lbs. multiplied by
    457.8 ft. per minute, are equal to 3213023.5 lbs. raised one foot high
    in the minute, which, divided by 33,000, gives 97.3 horses power as the
    power which would draw 110 tons upon a railway at a speed of 30 miles
    an hour, if there were no atmospheric resistance. The atmospheric
    resistance is at the rate of 12 lbs. a ton, with a load of 110 tons,
    equal to 1,320 lbs., moving at a speed of 30 miles an hour, which, when
    reduced, becomes 105.8 horses power, and this, added to 97.3, makes
    203.1, instead of 200 horses power, as ascertained by a reference to
    the evaporative power of the boiler. This amount of atmospheric
    resistance, however, exceeds the average, and in some of the
    experiments for ascertaining the atmospheric resistance, a part of the
    resistance due to the curves and irregularities of the line has been
    counted as part of the atmospheric resistance.</P>

    <P>498. <EM>Q.</EM>--Is the resistance per ton of the engine the same
    as the resistance per ton of the train?</P>

    <P><EM>A.</EM>--No; it is more, since the engine has not merely the
    resistance of the atmosphere and of the wheels to encounter, but the
    resistance of the machinery besides. According to Mr. Gooch&#39;s
    experiments upon a train weighing 100 tons, the resistance of the
    engine and tender at 13.1 miles per hour was found by the indicator to
    be 12.38 lbs.; the resistance per ton of the train, as ascertained by
    the dynamometer, was at the same speed 7.58 lbs., and the average
    resistance of locomotive and train was 9.04 lbs. At 20.2 miles per hour
    these resistances respectively became 19.0, 8.19, and 12.2 lbs. At 441
    miles per hour the resistances became 34.0, 21.10, and 25.5 lbs., and
    at 57.4 miles an hour they became 35.5, 17.81, and 23.8 lbs.</P>

    <P>499. <EM>Q.</EM>--Is it not maintained that the resistance of the
    atmosphere to the progress of railway trains increases as the square of
    the velocity?</P>

    <P><EM>A.</EM>--The atmospheric resistance, no doubt, increases as the
    square of the velocity, and the power, therefore, necessary to overcome
    it will increase as the cube of the velocity, since in doubling the
    speed four times, the power must be expended in overcoming the
    atmospheric resistance in half the time. At low speeds, the resistance
    does not increase very rapidly; but at high speeds, as the rapid
    increase in the atmospheric resistance causes the main resistance to be
    that arising from the atmosphere, the total resistance will vary nearly
    as the square of the velocity. Thus the resistance of a train,
    including locomotive and tender, will, at 15 miles an hour, be about
    9.3 lbs. per ton; at 30 miles an hour it will be 13.2 lbs. per ton; and
    at 60 miles an hour, 29 lbs. per ton. If we suppose the same law of
    progression to continue up to 120 miles an hour, the resistance at that
    speed will be 92.2 lbs. per ton, and at 240 miles an hour the
    resistance will be 344.8 lbs. per ton. Thus, in doubling the speed from
    60 to 120 miles per hour, the resistance does not fall much short of
    being increased fourfold, and the same remark applies to the increase
    of the speed from 120 to 240 miles an hour. These deductions and other
    deductions from Mr. Gooch&#39;s experiments on the resistance of
    railway trains, are fully discussed by Mr. Clark, in his Treatise on
    railway machinery, who gives the following rule for ascertaining the
    resistance of a train, supposing the line to be in good order, and free
    from curves:--To find the total resistance of the engine, tender, and
    train in pounds per ton, at any given speed. Square the speed in miles
    per hour; divide it by 171, and add 8 to the quotient. The result is
    the total resistance at the rails in lbs. per ton.</P>

    <P>500.<EM>Q.</EM>--How comes it, that the resistance of fluids
    increases as the square of the velocity, instead of the velocity
    simply?</P>

    <P><EM>A.</EM>--Because the height necessary to generate the velocity
    with which the moving object strikes the fluid, or the fluid strikes
    the object, increases as the <EM>square</EM> of the velocity, and the
    resistance or the weight of a column of any fluid varies as the height.
    A falling body, as has been already explained, to have acquired twice
    the velocity, must have fallen through four times the height; the
    velocity generated by a column of any fluid is equal to that acquired
    by a body falling through the height of the column; and it is therefore
    clear, that the pressure due to any given velocity must be as the
    square of that velocity, the pressure being in every case as twice the
    altitude of the column. The work done, however, by a stream of air or
    other fluid in a given time, will vary as the cube of the velocity; for
    if the velocity of a stream of air be doubled, there will not only be
    four times the pressure exerted per square foot, but twice the quantity
    of air will be employed; and in windmills, accordingly, it is found,
    that the work done varies nearly as the cube of the velocity of the
    wind. If, however, the work done by <EM>a given quantity</EM> of air
    moving at different speeds be considered, it will vary as the squares
    of the speeds.</P>

    <P>501. <EM>Q.</EM>--But in a case where there is no work done, and the
    resistance varies as the square of the speed, should not the power
    requisite to overcome that resistance vary as the square of the
    speed?</P>

    <P><EM>A.</EM>--It should if you consider the resistance over a given
    distance, and not the resistance during a given time. Supposing the
    resistance of a railway train to increase as the square of the speed,
    it would take four times the power, so far as atmospheric resistance is
    concerned, to accomplish a mile at the rate of 60 miles an hour, that
    it would take to accomplish a mile at 30 miles an hour; but in the
    former case there would be twice the number of miles accomplished in
    the same time, so that when the velocity of the train was doubled, we
    should require an engine that was capable of overcoming four times the
    resistance at twice the speed, or in other words, that was capable of
    exerting eight times the power, so far as regards the element of
    atmospheric resistance. We know by experience, however, that it is
    easier to attain high speeds on railways than in steam vessels, where
    the resistance does increase nearly as the square of the speed.</P>

    <P>502. <EM>Q.</EM>--Will you describe generally the arrangement of a
    locomotive engine?</P>

    <P><EM>A.</EM>--The boiler and engine are hung upon a framework set on
    wheels, and, together with this frame or carriage, constitute what is
    commonly called the locomotive. Behind the locomotive runs another
    carriage, called the tender, for holding coke and water. A common mode
    of connecting the engine and tender is by means of a rigid bar, with an
    eye at each end through which pins are passed. Between the engine and
    tender, however, buffers should always be interposed, as their pressure
    contributes greatly to prevent oscillation and other irregular motions
    of the engine.</P>

    <P>503. <EM>Q.</EM>--How is the framing of a locomotive usually
    constructed?</P>

    <P><EM>A.</EM>--All locomotives are now made with the framing which
    supports the machinery situated within the wheels; but for some years a
    vehement controversy was maintained respecting the relative merits of
    outside and inside framing, which has terminated, however, in the
    universal adoption of the inside framing. It is difficult, in engines
    intended for the narrow gauge, to get cylinders within the framing of
    sufficient diameter to meet the exigencies of railway locomotion; by
    casting both cylinders in a piece, however, a considerable amount of
    room may be made available to increase their diameters. It is very
    desirable that the cylinders of locomotives should be as large as
    possible, so that expansion may be adopted to a large extent; and with
    any given speed of piston, the power of an engine either to draw heavy
    loads, or achieve high velocities, will be increased with every
    increase of the dimensions of the cylinder. The framing of locomotives,
    to which the boiler and machinery are attached, and which rests upon
    the springs situated above the axles, is formed generally of malleable
    iron, but in some engines the side frames consist of oak with iron
    plates riveted on each side. The guard plates are in these cases
    generally of equal length, the frames being curved upward to pass over
    the driving axle. Hard cast iron blocks are riveted between the guard
    plates to serve as guides for the axle bushes. The side frames are
    connected across the ends, and cross stays are introduced beneath the
    boiler to stiffen the frame sideways, and prevent the ends of the
    connecting or eccentric rods from falling down if they should be
    broken.</P>

    <P>504. <EM>Q.</EM>--What is the nature and arrangement of the springs
    of locomotives?</P>

    <P><EM>A.</EM>--The springs are of the ordinary carriage kind, with
    plates connected at the centre, and allowed to slide on each other at
    their ends. The upper plate terminates in two eyes, through each of
    which passes a pin, which also passes through the jaws of the bridle,
    connected by a double threaded screw to another bridle, which is
    jointed to the framing; the centre of the spring rests upon the axle
    box. Sometimes the springs are placed between the guard plates, and
    below the framing which rests upon their extremities. One species of
    springs which has gained a considerable introduction, consists of a
    number of flat steel plates with a piece of metal or other substance
    interposed between them at the centre, leaving the ends standing apart.
    It would be preferable, perhaps, to make the plates of a common spring
    with different curves, so that the leaves, though in contact at the
    centre, would not be in contact with the ends with light loads, but
    would be brought into contact gradually, as the strain conies on: a
    spring would thus be obtained that was suitable for all loads.</P>

    <P>505. <EM>Q.</EM>--What is the difference between inside and outside
    cylinder engines?</P>

    <P><EM>A.</EM>--Outside cylinders are so designated when placed upon
    the outside of the framing, with their connecting rods operating upon
    pins in the driving wheels; while the inside cylinders are situated
    within the framing, and the connecting rods attach themselves to cranks
    in the driving axle.</P>

    <P>506. <EM>Q.</EM>--Whether are inside or outside cylinder engines to
    be preferred?</P>

    <P><EM>A.</EM>--A diversity of opinion obtains as to the relative
    merits of outside and inside cylinders. The chief objection to outside
    cylinders is, that they occasion a sinuous motion in the engine which
    is apt to send the train off the rails; but this action may be made
    less perceptible or be remedied altogether, by placing a weight upon
    one side of the wheels, the momentum of which will just balance the
    momentum of the piston and its connections. The sinuous or rocking
    motion of locomotives is traceable to the arrested momentum of the
    piston and its attachments at every stroke of the engine, and the
    effect of the pressure thus created will be more operative in inducing
    oscillation the farther it is exerted from the central line of the
    engine. If both cylinders were set at right angles in the centre of the
    carriage, and the pistons were both attached to a central crank, there
    would be no oscillation produced; or the same effect would be realized
    by placing one cylinder in the centre of the carriage, and two at the
    sides--the pistons of the side cylinders moving simultaneously: but it
    is impossible to couple the piston of an upright cylinder direct to the
    axle of a locomotive, without causing the springs to work up and down
    with every stroke of the engine: and the use of three cylinders, though
    adopted in some of Stephenson&#39;s engines, involves too much
    complication to be a beneficial innovation.</P>

    <P>507. <EM>Q.</EM>--Whether are four-wheeled or six-wheeled engines
    preferable?</P>

    <P><EM>A.</EM>--Much controversial ingenuity has been expended upon the
    question of the relative merits of the four and six-wheeled engines;
    one party maintaining that four-wheeled engines are most unsafe, and
    the other that six-wheeled engines are unmechanical, and are more
    likely to occasion accidents. The four-wheeled engines, however, appear
    to have been charged with faults that do not really attach to them when
    properly constructed; for it by no means follows that if the axle of a
    four-wheeled engine breaks, or even altogether comes away, that the
    engine must fall down or run off the line; inasmuch as, if the engine
    be properly coupled with the tender, it has the tender to sustain it.
    It is obvious enough, that such a connection may be made between the
    tender and the engine, that either the fore or hind axle of the engine
    may be taken away, and yet the engine will not fall down, but will be
    kept up by the support which the tender affords; and the arguments
    hitherto paraded against the four-wheeled engines are, so far as
    regards the question of safety, nothing more than arguments against the
    existence of the suggested connection. It is no doubt the fact, that
    locomotive engines are now becoming too heavy to be capable of being
    borne on four wheels at high speeds without injury to the rails; but
    the objection of damage to the rails applies with at least equal force
    to most of the six-wheeled engines hitherto constructed, as in those
    engines the engineer has the power of putting nearly all the weight
    upon the driving wheels; and if the rail be wet or greasy, there is a
    great temptation to increase the bite of those wheels by screwing them
    down more firmly upon the rails. A greater strain is thus thrown upon
    the rail than can exist in the case of any equally heavy four-wheeled
    engine; and the engine is made very unsafe, as a pitching motion will
    inevitably be induced at high speeds, when an engine is thus poised
    upon the central driving wheels, and there will also be more of the
    rocking or sinuous motion. Locomotives, however, intended to achieve
    high speeds or to draw heavy loads, are now generally made with eight
    wheels, and in some cases the driving wheels are placed at the end of
    the engine instead of in the middle.</P>

    <P>508. <EM>Q.</EM>--As the question of the locomotive boiler has been
    already disposed of in discussing the question of boilers in general,
    it now only remains to inquire into the subject of the engine, and we
    may commence with the cylinders. Will you state the arrangement and
    construction of the cylinders of a locomotive and their
    connections?</P>

    <P><EM>A.</EM>--The cylinders are placed in the same horizontal plane
    as the axle of the driving wheels, and the connecting rod which is
    attached to the piston rod engages either a crank in the driving axle
    or a pin in the driving wheel, according as the cylinders are inside or
    outside of the framework. The cylinders are generally made an inch
    longer than the stroke, or there is half an inch of clearance at each
    end of the cylinder, to permit the springs of the vehicle to act
    without causing the piston to strike the top or bottom of the cylinder.
    The thickness of metal of the cylinder ends is usually about a third
    more than the thickness of the cylinder itself, and both ends are
    generally made removable. The priming of the boiler, when it occurs, is
    very injurious to the cylinders and valves of locomotives, especially
    if the water be sandy, as the grit carried over by the steam wears the
    rubbing surfaces rapidly away. The face of the cylinder on which the
    valve works is raised a little above the metal around it, both to
    facilitate the operation of forming the face and with the view of
    enabling any foreign substance deposited on the face to be pushed aside
    by the valve into the less elevated part, where it may lie without
    occasioning any further disturbance. The valve casing is sometimes cast
    upon the cylinder, and it is generally covered with a door which may be
    removed to permit the inspection of the faces. In some valve casings
    the top as well as the back is removable, which admits of the valve and
    valve bridle being removed with greater facility. A cock is placed at
    each end of locomotive cylinders, to allow the water to be discharged
    which accumulates in the cylinder from priming or condensation; and the
    four cocks of the two cylinders are usually connected together, so that
    by turning a handle the whole are opened at once. In Stephenson&#39;s
    engines, however, with variable expansion, there is but one cock
    provided for this purpose, which is on the bottom of the valve
    chest.</P>

    <P>509. <EM>Q.</EM>--What kind of piston is used in locomotives?</P>

    <P><EM>A.</EM>--The variety of pistons employed in locomotives is very
    great, and sometimes even the more complicated kinds are found to work
    very satisfactorily; but, in general, those pistons which consist of a
    single ring and tongue piece, or of two single rings set one above the
    other, so as to break joint, are preferable to those which consist of
    many pieces. In Stephenson&#39;s pistons the screws were at one time
    liable to work slack, and the springs to break.</P>

    <P>510. <EM>Q.</EM>--Will you explain the connection of the piston rod
    with the connecting rod?</P>

    <P><EM>A.</EM>--The piston rods of all engines are now generally either
    case hardened very deeply, or are made of steel; and in locomotive
    engines the diameter of the piston rod is about one seventh of the
    diameter of the cylinder, and it is formed of tilted steel. The cone of
    the piston rod, by which it is attached to the piston, is turned the
    reverse way to that which is adopted in common engines, with the view
    of making the cutter more accessible from the bottom of the cylinder,
    which is made to come off like a door. The top of the piston rod is
    secured with a cutter into a socket with jaws, through the holes of
    which a cross head passes, which is embraced between the jaws by the
    small end of the connecting rod, while the ends of the cross head move
    in guides. Between the piston rod clutch and the guide blocks, the feed
    pump rod joins the cross head in some engines.</P>

    <P>511. <EM>Q.</EM>--What kind of guides is employed for the end of the
    piston rod?</P>

    <P><EM>A.</EM>--The guides are formed of steel plates attached to the
    framing, between which work the guide blocks, fixed on the ends of the
    cross head, which have flanges bearing against the inner edges of the
    guides. Steel or brass guides are better than iron ones: Stephenson and
    Hawthorn attach their guides at one end to a cross stay, at the other
    to lugs on the cylinder cover; and they are made stronger in the middle
    than at the ends. Stout guide rods of steel, encircled by stuffing
    boxes on the ends of the cross head, would probably be found superior
    to any other arrangement. The stuffing boxes might contain conical
    bushes, cut spirally, in addition to the packing, and a ring, cut
    spirally, might be sprung upon the rod and fixed in advance of the
    stuffing box, with lateral play to wipe the rod before entering the
    stuffing box, to prevent it from being scratched by the adhesion of
    dust.</P>

    <P>512. <EM>Q.</EM>--Is any provision made for keeping the connecting
    rod always of the same length?</P>

    <P><EM>A.</EM>--In every kind of locomotive it is very desirable that
    the length of the connecting rod should remain invariable, in spite of
    the wear of the brasses, for there is a danger of the piston striking
    against the cover of the cylinder if it be shortened, as the clearance
    is left as small as possible in order to economize steam. In some
    engines the strap encircling the crank pin is fixed immovably to the
    connecting rod by dovetailed keys, and a bolt passes through the keys,
    rod, and strap, to prevent the dovetailed keys from working out. The
    brass is tightened by a gib and cutter, which is kept from working
    loose by three pinching screws and a cross pin or cutter through the
    point. The effect of this arrangement is to lengthen the rod, but at
    the cross head end of the rod the elongation is neutralized by making
    the strap loose, so that in tightening the brass the rod is shortened
    by an amount equal to its elongation at the crank pin end. The
    tightening here is also effected by a gib and cutter, which is kept
    from working loose by two pinching screws pressing on the side of the
    cutter. Both journals of the connecting rod are furnished with oil
    cups, having a small tube in the centre with siphon wicks. The
    connecting rod is a thick flat bar, with its edges rounded.</P>

    <P>513. <EM>Q.</EM>--How is the cranked axle of locomotives
    constructed?</P>

    <P><EM>A.</EM>--The cranked axle of locomotives is always made of
    wrought iron, with two cranks forged upon it toward the middle of its
    length, at a distance from each other answerable to the distance
    between the cylinders. Bosses are made on the axle for the wheels to be
    keyed upon, and bearings for the support of the framing. The axle is
    usually forged in two pieces, which are afterward welded together.
    Sometimes the pieces for the cranks are put on separately, but the
    cranks so made are liable to give way. In engines with outside
    cylinders the axles are made straight-the crank pins being inserted in
    the naves of the wheels. The bearings to which the connecting rods are
    attached are made with very large fillets in the corners, so as to
    strengthen the axle in that part, and to obviate side play in the
    connecting rod. In engines which, have been in use for some time,
    however, there is generally a good deal of end play in the bearings of
    the axles themselves, and this slackness contributes to make the
    oscillation of the engine more violent; but this evil may be remedied
    by making the bearings spheroidal, whereby end play becomes
    impossible.</P>

    <P>514. <EM>Q.</EM>--How are the bearings of the axles arranged?</P>

    <P><EM>A.</EM>--The axles bear only against the top of the axle boxes,
    which are generally of brass; but a plate extends underneath the
    bearing, to prevent sand from being thrown upon it. The upper part of
    the box in most engines has a reservoir of oil, which is supplied to
    the journal by tubes with siphon wicks. Stephenson uses cast iron axle
    boxes with brasses, and grease instead of oil; and the grease is fed
    upon the journal by the heat of the bearing melting it, whereby it is
    made to flow down through a hole in the brass. Any engines constructed
    with outside bearings have inside bearings also, which are supported by
    longitudinal bars, which serve also in some cases to support the piston
    guides; these bearings are sometimes made so as not to touch the shafts
    unless they break.</P>

    <P>515. <EM>Q.</EM>--How are the eccentrics of a locomotive
    constructed?</P>

    <P><EM>A.</EM>--In locomotives the body of the eccentric is of cast
    iron, in inside cylinder engines the eccentrics are set on the axle
    between the cranks, and they are put on in two pieces held together by
    bolts; but in straight axle engines the eccentrics are cast in a piece,
    and are secured on the shaft by means of a key. The eccentric, when in
    two pieces, is retained at its proper angle on the shaft by a pinching
    screw, which is provided with a jam nut to prevent it from working
    loose. A piece is left out of the eccentric in casting it to allow of
    the screw being inserted, and the void is afterward filled by inserting
    a dovetailed piece of metal. Stephenson and Hawthorn leave holes in
    their eccentrics on each side of the central arm, and they apply
    pinching screws in each of these holes. The method of fixing the
    eccentric to the shaft by a pinching screw is scarcely sufficiently
    substantial; and cases are perpetually occurring, when this method of
    attachment is adopted, of eccentrics shifting from their place. In the
    modern engines the eccentrics are forged on the axles.</P>

    <P>516. <EM>Q.</EM>--How are the eccentric straps constructed?</P>

    <P><EM>A.</EM>--The eccentric hoops are generally of wrought iron, as
    brass hoops are found liable to break. When formed of malleable iron,
    one half of the strap is forged with the rod, the other half being
    secured to it by bolts, nuts, and jam nuts. Pieces of brass are, in
    some cases, pinned within the malleable iron hoop; but it appears to be
    preferable to put brasses within the hoop to encircle the eccentric, as
    in the case of any other bearing. When the brass straps are used, the
    lugs have generally nuts on both sides, so that the length of the
    eccentric rod may be adjusted by their means to the proper length; but
    it is better for the lugs of the hoops to abut against the necks of the
    screws, and, if any adjustment be necessary from the wear of the
    straps, washers can be interposed. In some engines the adjustment is
    effected by screwing the valve rod, and the cross head through which it
    passes has a nut on either side of it, by which its position upon the
    valve rod is determined.</P>

    <P>517. <EM>Q.</EM>--Will you describe the eccentric rod and valve
    levers?</P>

    <P><EM>A.</EM>--In the engines in use before the introduction of the
    link motion, the forks of the eccentric rod were of steel, and the
    length of the eccentric rod was the distance between the centre of the
    crank axle and the centre of the valve shaft; but in modern engines the
    use of the link motion is universal. The valve lever in locomotives is
    usually longer than the eccentric lever, to increase the travel of the
    valve, if levers are employed; but it is better to connect the valve
    rod to the link of the link motion without the intervention of levers.
    The pins of the eccentric lever in the old engines used to wear
    quickly; Stephenson used to put a ferule of brass on these pins, which
    being loose, and acting like a roller, facilitated the throwing in and
    out of gear, and when worn could easily be replaced, so that there was
    no material derangement of the motion of the valve from play in this
    situation.</P>

    <P>518. <EM>Q.</EM>--What is the arrangement of a starting lever?</P>

    <P><EM>A.</EM>--The starting lever travels between two iron segments,
    and can be fixed in any desired position. This is done by a small catch
    or bell crank, jointed to the bottom of the handle at the end of the
    lever, and coming up by the side of the handle, but pressed out from it
    by a spring. The smaller arm of this bell crank is jointed to a bolt,
    which shoots into notches, made in one of the segments between which
    the lever moves. By pressing the bell crank against the handle of the
    lever the bolt is withdrawn, and the lever may be shifted to any other
    point, when, the spring being released, the bolt flies into the nearest
    notch.</P>

    <P>519. <EM>Q.</EM>--In what way does the starting handle act on the
    machinery of the engine to set it in motion?</P>

    <P><EM>A.</EM>--Its whole action lies in raising or depressing the link
    of the link motion relatively with the valve rod. If the valve rod be
    attached to the middle of the link, the valve will derive no motion
    from, it at all, and the engine will stop. If the attachment be slipped
    to one end of the link the engine will go ahead, and if slipped to the
    other end it will go astern. The starting handle merely achieves this
    change of position.</P>

    <P>520. <EM>Q.</EM>--Will you explain the operation of setting the
    valve of a locomotive?</P>

    <P><EM>A.</EM>--In setting the valves of locomotives, place the crank
    in the position answerable to the end of the stroke of the piston, and
    draw a straight line, representing the centre line of the cylinder,
    through the centres of the crank shaft and crank pin. From the centre
    of the shaft describe a circle with the diameter equal to the throw of
    the valve; another circle to represent the crank shaft; and a third
    circle to represent the path of the crank pin. From the centre of the
    crank shaft, draw a line perpendicular to the centre line of the
    cylinder and crank shaft, and draw another perpendicular at a distance
    from the first equal to the amount of the lap and the lead of the
    valve: the points in which this line intersects the circle of the
    eccentric are the points in which the centre of the eccentric should be
    placed for the forward and reverse motions. When the eccentric rod is
    attached directly to the valve, the radius of the eccentric, which
    precedes the crank in its revolution, forms with the crank an obtuse
    angle; but when, by the intervention of levers, the valve has a motion,
    opposed to that of the eccentric rod, the angle contained by the crank
    and the radius of the eccentric must be acute, and the eccentric must
    follow the crank: in other words, with a direct attachment to the valve
    the eccentric is set <EM>more</EM> than one fourth of a revolution in
    advance of the crank, and with an indirect attachment the eccentric is
    set <EM>less</EM> than one fourth of a circle behind the crank. If the
    valve were without lead or lap the eccentric would be exactly one
    fourth of a circle in advance of the crank or behind the crank,
    according to the nature of the valve connection; but as the valve would
    thus cover the port by the amount of the lap and lead, the eccentric
    must be set forward so as to open the port to the extent of the lap and
    lead, and this is effected by the plan just described.</P>

    <P>521. <EM>Q.</EM>--In the event of the eccentrics slipping round upon
    the shaft, which you stated sometimes happens, is it necessary to
    perform the operation of setting the valve as you have just described
    it?</P>

    <P><EM>A.</EM>--If the eccentrics shift upon the shaft, they may be
    easily refixed by setting the valve open the amount of the lead,
    setting the crank at the end of the stroke, and bringing round the
    eccentric upon the shaft till the eccentric rod gears with the valve.
    It would often be troublesome in practice to get access to the valve
    for the purpose of setting it, and this may be dispensed with if the
    amount of lap on the valve and the length of the eccentric rod be
    known. To this end draw upon a board two straight lines at right angles
    to one another, and from their point of intersection as a centre
    describe two circles, one representing the circle of the eccentric, the
    other the crank shaft; draw a straight line parallel to one of the
    diameters, and distant from it the amount of the lap and the lead: the
    points in which his parallel intersects the circle of the eccentric are
    the positions of the forward and backward eccentrics. Through these
    points draw straight lines from the centre of the circle, and mark the
    intersection of these lines with the circle of the crank shaft; measure
    with a pair of compasses the chord of the arc intercepted between
    either of these points, and the diameter which is at right angles with
    the crank, and the diameters being first marked on the shaft itself,
    then by transferring with the compasses the distance found in the
    diagram, and marking the point, the eccentric may at any time be
    adjusted without difficulty.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig45.png" ALIGN="left" WIDTH="288"
    HEIGHT="500" ALT="Fig. 45"></P>

    <P>522. <EM>Q.</EM>--Will you describe the structure and arrangement of
    the feed pumps of locomotive engines?</P>

    <P><EM>A.</EM>--The feed pumps of locomotives are generally made of
    brass, but the plungers are sometimes made of iron, and are generally
    attached to the piston, cross head, though in Stephenson&#39;s engines
    they are worked by rods attached to eyes on the eccentric hoops. There
    is a ball valve, fig. 45, between the pump and the tender, and two
    usually in the pipe leading from the pump to the boiler, besides a cock
    close to the boiler, by which the pump may be shut off from the boiler
    in case of any accident to the valves. The ball valves are guided by
    four branches, which rise vertically, and join together at the top in a
    hemispherical form. The shocks of the ball against this cap have in
    some cases broken it after one week&#39;s work, from the top of the
    cage having been flat, and the branches not having had their junction
    at the top properly filleted. These valve guards are attached in
    different ways to the pipes; when one occurs at the junction of two
    pieces of pipe it has a flange, which along with the flanges of the
    pipes and that of the valve seat are held together by a union joint. It
    is sometimes formed with a thread at the under end, and screwed into
    the pipe. The balls are cast hollow to lessen the shock, as well as to
    save the metal. In some cases where the feed pump plunger has been
    attached to the cross head, the piston rod has been bent by the strain;
    and that must in all cases occur, if the communication between the pump
    and boiler be closed when the engine is started, and there be no escape
    valve for the water.</P>

    <P>523. <EM>Q.</EM>--Are none but ball valves used in the feed
    pump?</P>

    <P><EM>A.</EM>--Spindle valves have in some cases been used instead of
    ball valves, but they are more subject to derangement; but piston
    valves, so contrived as to shut a portion of water in the cage when
    about to close, might be adopted with a great diminution of the shock.
    Slide valves might be applied, and would probably be found preferable
    to any of the expedients at present in use. In all spindle valves
    opened and shut rapidly, it is advisable to have the lower surface
    conical, to take off the shock of the water; and a large lift of the
    valve should be prevented, else much of the water during the return
    stroke of the pump will flow out before the valve shuts.</P>

    <P>524. <EM>Q.</EM>--At what part of the boiler is the feed water
    admitted?</P>

    <P><EM>A.</EM>--The feed pipe of most locomotive engines enters the
    boiler near the bottom and about the middle of its length. In
    Stephenson&#39;s engine the water is let in at the smoke box end of the
    boiler, a little below the water level; by this means the heat is more
    fully extracted from the escaping smoke, but the arrangement is of
    questionable applicability to engines of which the steam dome and steam
    pipe are at the smoke box end, as in that case the entering cold water
    would condense the steam.</P>

    <P>525. <EM>Q.</EM>--How are the pipes connecting the tender and
    locomotive constructed, so as to allow of play between the engine and
    tender without leakage?</P>

    <P><EM>A.</EM>--The pipes connecting the tender with the pumps should
    allow access to the valves and free motion to the engine and tender.
    This end is attained by the use of ball and socket joints; and, to
    allow some end play, one piece of the pipe slides into the other like a
    telescope, and is kept tight by means of a stuffing box. Any pipe joint
    between the engine and tender must be made in this fashion.</P>

    <P>526. <EM>Q.</EM>--Have you any suggestion to make respecting the
    arrangement of the feed pump?</P>

    <P><EM>A.</EM>--It would be a material improvement if a feed pump was
    to be set in the tender and worked by means of a small engine, such as
    that now used in steam vessels for feeding the boilers. The present
    action of the feed pumps of locomotives is precarious, as, if the
    valves leak in the slightest degree, the steam or boiling water from
    the boiler will prevent the pumps from drawing. It appears expedient,
    therefore, that at least one pump should be far from the boiler and
    should be set among the feed water, so that it will only have to force.
    If a pump was arranged in the manner suggested, the boiler could still
    be fed regularly, though the locomotive was standing still; but it
    would be prudent to have the existing pumps still wrought in the usual
    way by the engine, in case of derangement of the other, or in case the
    pump in the tender might freeze.</P>

    <P>527. <EM>Q.</EM>--Will you explain the construction of locomotive
    wheels?</P>

    <P><EM>A.</EM>--The wheels of a locomotive are always made of malleable
    iron. The driving wheels are made larger to increase the speed; the
    bearing wheels also are easier on the road when large. In the goods
    engines the driving wheels are smaller than in the passenger engines,
    and are generally coupled together. Wheels are made with much variety
    in their constructive details: sometimes they are made with cast iron
    naves, with the spokes and rim of wrought iron; but in the best modern
    wheels the nave is formed of the ends of the spokes welded together at
    the centre. When cast iron naves are adopted, the spokes are forged out
    of flat bars with T-formed heads, and are arranged radially in the
    founder&#39;s mould, the cast iron, when fluid, being poured among
    them. The ends of the T heads are then welded together to constitute
    the periphery of the wheel or inner tire; and little wedge-form pieces
    are inserted where there is any deficiency of iron. In some cases the
    arms are hollow, though of wrought iron; the tire of wrought iron, and
    the nave of cast iron; and the spokes are turned where they are fitted
    into the nave, and are secured in their sockets by means of cutters.
    Hawthorn makes his wheels with cast iron naves and wrought iron rims
    and arms; but instead of welding the arms together, he makes palms on
    their outer end, which are attached by rivets to the rim. These rivets,
    however, unless very carefully formed, are apt to work loose; and it
    would probably be found an improvement if the palms were to be slightly
    indented into the rim, in cases in which the palms do not meet each
    other at the ends. When the rim is turned it is ready for the tire,
    which is now made of steel.</P>

    <P>528. <EM>Q.</EM>--How do you find the length of bar necessary for
    forming a tire?</P>

    <P><EM>A.</EM>--To find the proper length of bar requisite for the
    formation of a hoop of any given diameter, add the thickness of the bar
    to the required diameter, and the corresponding circumference in the
    table of circumferences of circles is the length of the bar. If the
    iron be bent edgewise the breadth of the bar must be added to the
    diameter, for it is the thickness of the bar measured radially that is
    to be taken into consideration. In the tires of railway wheels, which
    have a flange on one edge, it is necessary to add not only the
    thickness of the tire, but also two thirds of the depth of the flange;
    generally, however, the tire bars are sent from the forge so curved
    that the plain edge of the tire is concave, and the flange edge convex,
    while the side which is afterward to be bent into contact with the
    cylindrical surface of the wheel is a plane. In this case the addition
    of the diameter of two thirds of the depth of the flange is
    unnecessary, for the curving of the flange edge has the effect of
    increasing the real length of the bar. When the tire is thus curved, it
    is only necessary to add the thickness of the hoop to the diameter, and
    then to find the circumference from a table; or the same result will be
    obtained by multiplying the diameter thus increased by the thickness of
    the hoop by 3.1416.</P>

    <P>529. <EM>Q.</EM>--How are the tires attached to the wheels?</P>

    <P><EM>A.</EM>--The materials for wheel tires are first swaged
    separately, and then welded together under the heavy hammer at the
    steel works; after which they are bent to the circle, welded, and
    turned to certain gauges. The tire is now heated to redness in a
    circular furnace; during the time it is getting hot, the iron wheel,
    turned to the right diameter, is bolted down upon a face plate or
    surface; the tire expands with the heat, and when at a cherry red, it
    is dropped over the wheel, for which it was previously too small, and
    it is also hastily bolted down to the surface plate; the whole mass is
    then quickly immersed by a swing crane in a tank of water five feet
    deep, and hauled up and down till nearly cold; the tires are not
    afterward tempered. The tire is attached to the rim with rivets having
    countersunk heads, and the wheel is then fixed on its axle.</P>

    <P>530. <EM>Q.</EM>--Is it necessary to have the whole tire of
    steel?</P>

    <P><EM>A.</EM>--It is not indispensable that the whole tire should be
    of steel; but a dovetail groove, turned out of the tire at the place
    where it bears most on the rail, and fitted with a band of steel, will
    suffice. This band may be put in in pieces, and the expedient appears
    to be the best way of repairing a worn tire; but particular care must
    be taken to attach these pieces very securely to the tire by rivets,
    else in the rapid revolution of the wheel the steel may be thrown out
    by the centrifugal force. In aid of such attachment the steel, after
    being introduced, is well hammered, which expands it sideways until it
    fills the dovetail groove.</P>

    <P>531. <EM>Q.</EM>--Is any arrangement adopted to facilitate the
    passage of the locomotive round curves?</P>

    <P><EM>A.</EM>--The tire is turned somewhat conical, to facilitate the
    passage of the engine round curves--the diameter of the outer wheel
    being virtually increased by the centrifugal force of the engine, and
    that of the inner wheel being correspondingly diminished, whereby the
    curve is passed without the resistance which would otherwise arise from
    the inequality of the spaces passed over by wheels of the same diameter
    fixed upon the same axle. The rails, moreover, are not set quite
    upright, but are slightly inclined inward, in consequence of which the
    wheels must be either conical or slightly dished, to bear fairly upon
    the rails. One benefit of inclining the rails in this way, and coning
    the tires, is that the flange of the wheels is less liable to bear
    against the sides of the rail, and with the same view the flanges of
    all the wheels are made with large fillets in the corners. Wheels have
    been placed loose upon the axle, but they have less stability, and are
    not now much used. Nevertheless this plan appears to be a good one if
    properly worked out.</P>

    <P>532. <EM>Q.</EM>--Are any precautions taken to prevent engines from
    being thrown off the rails by obstructions left upon the line?</P>

    <P><EM>A</EM>.--In most engines a bar is strongly attached to the front
    of the carriage on each side, and projects perpendicularly downward to
    within a short distance of the rail, to clear away stones or other
    obstructions that might occasion accidents if the engine ran over
    them.</P>

    <H2 CLASS="chapter"><A NAME="ch09"></A>CHAPTER IX.</H2>

    <H3>STEAM NAVIGATION.</H3>

    <H4 CLASS="subhead"><A NAME="m01"></A>RESISTANCE OF VESSELS IN
    WATER.</H4>

    <P>533. <EM>Q.</EM>--How do you determine the resistance encountered by
    a vessel moving in water?</P>

    <P><EM>A.</EM>--The resistance experienced by vessels moving in water
    varies as the square of the velocity of their motion, or nearly so; and
    the power necessary to impart an increased velocity varies nearly as
    the cube of such increased velocity. To double the velocity of a steam
    vessel, therefore, will require four times the amount of tractive
    force, and as that quadrupled force must act through twice the distance
    in the same time, an engine capable of exerting eight times the
    original power will be required. <A NAME="fnr5"></A> <A HREF="#fn5"
    CLASS="fnsuper">1</A></P>

    <P>534. <EM>Q.</EM>--In the case of a board moving in water in the
    manner of a paddle float, or in the case of moving water impinging on a
    stationary board, what will be the pressure produced by the impact?</P>

    <P><EM>A.</EM>--The pressure produced upon a flat board, by striking
    water at right angles to the surface of the board, will be equal to the
    weight of a column of water having the surface struck as a base, and
    for its altitude twice the height due to the velocity with which the
    board moves through the water. If the board strike the water obliquely,
    the resistance will be less, but no very reliable law has yet been
    discovered to determine its amount.</P>

    <P>535. <EM>Q.</EM>--Will not the resistance of a vessel in moving
    through the water be much less than that of a flat board of the area of
    the cross section?</P>

    <P><EM>A.</EM>--It will be very much less, as is manifest from the
    comparatively small area of paddle board, and the small area of the
    circle described by the screw, relatively with the area of the immersed
    midship section of the vessel. The absolute speed of a vessel, with any
    given amount of power, will depend very much upon her shape.</P>

    <P>536. <EM>Q.</EM>--In what way is it that the shape of a vessel
    influences her speed, since the vessels of the same sectional area must
    manifestly put in motion a column of water of the same magnitude, and
    with the same velocity?</P>

    <P><EM>A.</EM>--A vessel will not strike the water with the same
    velocity when the bow lines are sharp as when they are otherwise; for a
    very sharp bow has the effect of enabling the vessel to move through a
    great distance, while the particles of water are moved aside but a
    small distance, or in other words, it causes the velocity with which
    the water is moved to be very small relatively with the velocity of the
    vessel; and as the resistance increases as the square of the velocity
    with which the water is moved, it is conceivable enough in what way a
    sharp bow may diminish the resistance.</P>

    <P>537. <EM>Q.</EM>--Is the whole power expended in the propulsion of a
    vessel consumed in moving aside the water to enable the vessel to
    pass?</P>

    <P><EM>A.</EM>--By no means; only a portion, and in well-formed vessels
    only a small portion, of the power is thus consumed. In the majority of
    cases, the greater part of the power is expended in overcoming the
    friction of the water upon the bottom of the vessel; and the problem
    chiefly claiming consideration is, in what way we may diminish the
    friction.</P>

    <P>538. <EM>Q.</EM>--Does the resistance produced by this friction
    increase with the velocity?</P>

    <P><EM>A.</EM>--It increases nearly as the square of the velocity. At
    two nautical miles per hour, the thrust necessary to overcome the
    friction varies as the 1.823 power of the velocity; and at eight
    nautical miles per hour, the thrust necessary to overcome the friction
    varies as the 1.713 power of the velocity. It is hardly proper,
    perhaps, to call this resistance by the name of friction; it is partly,
    perhaps mainly, due to the viscidity or adhesion of the water.</P>

    <P>539. <EM>Q.</EM>--Perhaps at high velocities this resistance may
    become less?</P>

    <P><EM>A</EM>.--That appears very probable. It may happen that at high
    velocities the adhesion is overcome, so that the water is dragged off
    the vessel, and the friction thereafter follows the law which obtains
    in the case of solid bodies. But any such conclusion is mere
    speculation, since no experiments illustrative of this question have
    yet been made.</P>

    <P>540. <EM>Q.</EM>--Will a vessel experience more resistance in moving
    in salt water than in moving in fresh?</P>

    <P><EM>A.</EM>--If the immersion be the same in both cases a vessel
    will experience more resistance in moving in salt water than in moving
    in fresh, on account of the greater density of salt water; but as the
    notation is proportionably greater in the salt water the resistance
    will be the same with the same weight carried.</P>

    <P>541. <EM>Q.</EM>--Discarding for the present the subject of
    friction, and looking merely to the question of bow and stern
    resistance, in what manner should the hull of a vessel be formed so as
    to make these resistances a minimum?</P>

    <P><EM>A.</EM>--The hull should be so formed that the water, instead of
    being away driven forcibly from the bow, is opened gradually, so that
    every particle of water may be moved aside slowly at first, and then
    faster, like the ball of a pendulum, until it reaches the position of
    the midship frame, at which point it will have come to a state of rest,
    and then again, like a returning pendulum, vibrate back in the same
    way, until it comes to rest at the stern. It is not difficult to
    describe mechanically the line which the water should pursue. If an
    endless web of paper be put into uniform motion, and a pendulum
    carrying a pencil or brush be hung in front of it, then such pendulum
    will trace on the paper the proper water line of the ship, or the line
    which the water should pursue in order that no power may be lost except
    that which is lost in friction. It is found, however, in practice, that
    vessels formed with water lines on this principle are not much superior
    to ordinary vessels in the facility with which they pass through the
    water: and this points to the conclusion that in ordinary vessels of
    good form, the amount of power consumed in overcoming the resistance
    due to the wave at the bow and the partial vacuity at the stern is not
    so great as has heretofore been supposed, and that, in fact, the main
    resistance is that due to the friction.</P>

    <P CLASS="footnote"><A NAME="fn5"></A> <A HREF="#fnr5">[1]</A> This
    statement supposes that there is no difference of level between the
    water at the bow and the water at the stern. In the experiments on the
    steamer Pelican, the resistance was found to vary, as the 2.28th power
    of the velocity, but the deviation from the recognized law was imputed
    to a difference in the level of the water at the bow and stern.</P>

    <H4 CLASS="subhead"><A NAME="m02"></A>EXPERIMENTS ON THE RESISTANCE OF
    VESSELS.</H4>

    <P>542. <EM>Q.</EM>--Have experiments been made to determine the
    resistance which steam vessels experience in moving through the
    waters?</P>

    <P><EM>A.</EM>--Experiments have been made both to determine the
    relative resistance of different classes of vessels, and also the
    absolute resistance in pounds or tons. The first experiments made upon
    this subject were conducted by Messrs. Boulton and Watt, and they have
    been numerous, long continued, and carefully performed. These
    experiments were made upon paddle vessels.</P>

    <P>543. <EM>Q.</EM>--Will you recount the chief results of these
    experiments?</P>

    <P><EM>A.</EM>--The purpose of the experiments was to establish a
    coefficient of performance, which with any given class of vessel would
    enable the speed, which would be obtained with any given power, to be
    readily predicted. This coefficient was obtained by multiplying the
    cube of the velocity of the vessels experimented upon, in miles per
    hour, by the sectional area of the immersed midship section in square
    feet, and dividing by the numbers of nominal horses power, and this
    coefficient will be large in the proportion of the goodness of the
    shape of the vessel.</P>

    <P>544. <EM>Q.</EM>--How many experiments were made altogether?</P>

    <P><EM>A.</EM>--There were five different sets of experiments on five
    different classes of vessels. The first set of experiments was made in
    1828, upon the vessels Caledonia, Diana, Eclipse, Kingshead, Moordyke,
    and Eagle-vessels of a similar form and all with square bilges and flat
    floors; and the result was to establish the number 925 as the
    coefficient of performance of such vessels. The second set of
    experiments was made upon the superior vessels Venus, Swiftsure,
    Dasher, Arrow, Spitfire, Fury, Albion, Queen, Dart, Hawk, Margaret, and
    Hero-all vessels having flat floors and round bilges, where the
    coefficient became 1160. The third set of experiments was made upon the
    vessels Lightning, Meteor, James Watt, Cinderella, Navy Meteor,
    Crocodile, Watersprite, Thetis, Dolphin, Wizard, Escape, and Dragon-all
    vessels with rising floors and round bilges, and the coefficient of
    performance was found to be 1430. The fourth set of experiments was
    made in 1834, upon the vessels Magnet, Dart, Eclipse, Flamer, Firefly,
    Ferret, and Monarch, when the coefficient of performance was found to
    be 1580. The fifth set of experiments was made upon the Red Rover, City
    of Canterbury, Herne, Queen, and Prince of Wales, and in the case of
    those vessels the coefficient rose to 2550. The velocity of any of
    these vessels, with any power or sectional area, may be ascertained by
    multiplying the coefficient of its class by the nominal horse power,
    dividing by the sectional area in square feet, and extracting the cube
    root of the quotient, which will be the velocity in miles per hour; or
    the number of nominal horse power requisite for the accomplishment of
    any required speed may be ascertained by multiplying the cube of the
    required velocity in miles per hour, by the sectional area in square
    feet, and dividing by the coefficient: the quotient is the number of
    nominal horse power requisite to realize the speed.</P>

    <P>545. <EM>Q.</EM>--Seeing, however, that the nominal power does not
    represent an invariable amount of dynamical efficiency, would it not be
    better to make the comparison with reference to the actual power?</P>

    <P><EM>A.</EM>--In the whole of the experiments recited, except in the
    case of one or two of the last, the pressure of steam in the boiler
    varied between 2-3/4 lbs. and 4 lbs. per square inch, and the effective
    pressure on the piston varied between 11 lbs. and 13 lbs. per square
    inch, so that the average ratio of the nominal to the actual power may
    be easily computed; but it will be preferable to state the nominal
    power of some of the vessels, and their actual power as ascertained by
    experiment.</P>

    <P>546. <EM>Q.</EM>--Then state this.</P>

    <P><EM>A.</EM>--Of the Eclipse, the nominal power was 76, and the
    actual power 144.4 horses; of the Arrow, the nominal power was 60, and
    the actual 119.5; Spitfire, nominal 40, actual 64; Fury, nominal 40,
    actual 65.6; Albion, nominal 80, actual 135.4; Dart, nominal 100,
    actual 152.4; Hawk, nominal 40, actual 73; Hero, nominal 100, actual
    171.4; Meteor, nominal 100, actual 160; James Watt, nominal 120, actual
    204; Watersprite, nominal 76, actual 157.6; Dolphin, nominal 140,
    actual 238; Dragon, nominal 80, actual 131; Magnet, nominal 140, actual
    238; Dart, nominal 120, actual 237; Flamer, nominal 120, actual 234;
    Firefly, nominal 52, actual 86.6; Ferret, nominal 52, actual 88;
    Monarch, nominal 200, actual 378. In the case of swift vessels of
    modern construction, such as the Red Rover, Herne, Queen, and Prince of
    Wales, the coefficient appears to be about 2550; but in these vessels
    there is a still greater excess of the actual over the nominal power
    than in the case of the vessels previously enumerated, and the increase
    in the coefficient is consequent upon the increased pressure of the
    steam in the boiler, as well as the superior form of the ship. The
    nominal power of the Red Rover, Herne, and City of Canterbury is, in
    each case, 120 horses, but the actual power of the Red Rover is 294, of
    the Herne 354, and of the City of Canterbury 306, and in some vessels
    the excess is still greater; so that with such variations it becomes
    necessary to adopt a coefficient derived from the introduction of the
    actual instead of the nominal power.</P>

    <P>547. <EM>Q.</EM>--What will be the average difference between the
    nominal and actual powers in the several classes of vessels you have
    mentioned and the respective coefficients when corrected for the actual
    power?</P>

    <P><EM>A.</EM>--In the first class of vessels experimented upon,
    the actual power was about 1.6 times greater than the nominal power; in
    the second class, 1.67 times greater; in the third class, 1.7 times
    greater; and in the fourth, 1.96 times greater; while in such vessels
    as the Red Rover and City of Canterbury, it is 2.65 times greater; so
    that if we adopt the actual instead of the nominal power in fixing the
    coefficients, we shall have 554 as the first coefficient, 694 as the
    second, 832 for the third, and 806 for the fourth, instead of 925,
    1160, 1430, and 1580 as previously specified; while for such vessels as
    the Red Rover, Herne, Queen, and Prince of Wales, we shall have 962
    instead of 2550. These smaller coefficients, then, express the relative
    merits of the different vessels without reference to any difference of
    efficacy in the engines, and it appears preferable, with such a
    variable excess of the actual over the nominal power, to employ them
    instead of those first referred to. From the circumstance of the third
    of the new coefficients being greater than the fourth, it appears that
    the superior result in the fourth set of experiments arose altogether
    from a greater excess of the actual over the nominal power.</P>

    <P>548. <EM>Q.</EM>--These experiments, you have already stated, were
    all made on paddle vessels. Have similar coefficients of performance
    been obtained in the case of screw vessels?</P>

    <P><EM>A.</EM>--The coefficients of a greater number of screw vessels
    have been obtained and recorded, but it would occupy too much time to
    enumerate them here. The coefficient of performance of the Fairy is
    464.8; of the Rattler 676.8; and of the Frankfort 792.3. This
    coefficient, however, refers to nautical and not to statute miles. If
    reduced to statute miles for the purpose of comparison with the
    previous experiments, the coefficients will respectively become 703,
    1033, and 1212; which indicate that the performance of screw vessels is
    equal to the performance of paddle vessels, but some of the superiority
    of the result may be imputed to the superior size of the screw
    vessels.</P>

    <H4 CLASS="subhead"><A NAME="m03"></A>INFLUENCE OF THE SIZE OF VESSELS
    UPON THEIR SPEED.</H4>

    <P>549. <EM>Q.</EM>--Will large vessels attain a greater speed than
    small, supposing each to be furnished with the same proportionate
    power?</P>

    <P><EM>A.</EM>--It is well known that large vessels furnished with the
    same proportionate power, will attain a greater speed than small
    vessels, as appears from the rule usual in yacht races of allowing a
    certain part of the distance to be run to vessels which are of inferior
    size. The velocity attained by a large vessel will be greater than the
    velocity attained by a small vessel of the same mould and the same
    proportionate power, in the proportion of the square roots of the
    linear dimensions of the vessels. A vessel therefore with four times
    the sectional area and four times the power of a smaller symmetrical
    vessel, and consequently of twice the length, will have its speed
    increased in the proportion of the square root of 1 to the square root
    of 2, or 1.4 times.</P>

    <P>550. <EM>Q.</EM>--Will you further illustrate this doctrine by an
    example?</P>

    <P><EM>A.</EM>--The screw steamer Fairy, if enlarged to three times the
    size while retaining the same form, would have twenty-seven times the
    capacity, nine times the sectional area, and nine times the power. The
    length of such a vessel would be 434 feet; her breadth 63 feet 4-1/2
    inches; her draught of water 16-1/2 feet; her area of immersed section
    729 square feet; and her nominal power 1080 horses. Now as the lengths
    of the Fairy and of the new vessel are in the proportion of 1 to 3, the
    speeds will be in the proportion of the square root of 1 to the square
    root of 3; or, in other words, the speed of the large vessel will be
    1.73 times greater than the speed of the small vessel. If therefore the
    speed of the Fairy be 13 knots, the speed of the new vessel will be
    22.49 knots, although the proportion of power to sectional area, which
    is supposed to be the measure of the resistance, is in both cases
    precisely the same. If the speed of the Fairy herself had to be
    increased to 22.29 knots, the power would have to be increased in the
    proportion of the cube of 13 to the cube of 22.49, or 5.2 times, which
    makes the power necessary to propel the Fairy at that speed equal to
    624 nominal horses power.</P>

    <H4 CLASS="subhead"><A NAME="m04"></A>STRUCTURE AND OPERATION OF PADDLE
    WHEELS.</H4>

    <P>551. <EM>Q.</EM>--Will you describe the configuration and mode of
    action of the paddle wheels in general use?</P>

    <P><EM>A.</EM>--There are two kinds of paddle wheels in extensive use,
    the one being the ordinary radial wheel, in which the floats are fixed
    on arms radiating from the centre; and the other the feathering wheel,
    in which each float is hung upon a centre, and is so governed by
    suitable mechanism as to be always kept in nearly the vertical
    position. In the radial wheel there is some loss of power from oblique
    action, whereas in the feathering wheel there is little or no loss from
    this cause; but in every kind of paddle there is a loss of power from
    the recession of the water from the float boards, or the <EM>slip</EM>
    as it is commonly called; and this loss is the necessary condition of
    the resistance for the propulsion of the vessel being created in a
    fluid. The slip is expressed by the difference between the speed of the
    wheel and the speed of the vessel, and the larger this difference is
    the greater the loss of power from slip must be--the consumption of
    steam in the engine being proportionate to the velocity of the wheel,
    and the useful effect being proportionate to the speed of the ship.</P>

    <P>552. <EM>Q.</EM>--The resistance necessary for propulsion will not
    be situated at the circumference of the wheel?</P>

    <P><EM>A.</EM>--In the feathering wheel, where every part of any one
    immerged float moves forward with the same horizontal velocity, the
    pressure or resistance may be supposed to be concentrated in the centre
    of the float; whereas, in the common radial wheel this cannot be the
    case, for as the outer edge of the float moves more rapidly than the
    edge nearest the centre of the wheel, the outer part of the float is
    the most effectual in propulsion. The point at which the outer and
    inner portions of the float just balance one another in propelling
    effect, is called the <EM>centre of pressure</EM>; and if all the
    resistances were concentrated in this point, they would have the same
    effect as before in resisting the rotation of the wheel. The resistance
    upon any one moving float board totally immersed in the water will,
    when the vessel is at rest, obviously vary as the square of its
    distance from the centre of motion--the resistance of a fluid varying
    with the square of the velocity; but, except when the wheel is sunk to
    the axle or altogether immersed in the water, it is impossible, under
    ordinary circumstances, for one float to be totally immersed without
    others being immersed partially, whereby the arc described by the
    extremity of the paddle arm will become greater than the arc described
    by the inner edge of the float; and consequently the resistance upon
    any part of the float will increase in a higher ratio than the square
    of its distance from the centre of motion--the position of the centre
    of pressure being at the same time correspondingly affected. In the
    feathering wheel the position of the centre of pressure of the entering
    and emerging floats is continually changing from the lower edge of the
    float--where it is when the float is entering or leaving the water--to
    the centre of the float, which is its position when the float is wholly
    immerged; but in the radial wheel the centre of pressure can never rise
    so high as the centre of the float.</P>

    <P>553. <EM>Q.</EM>--All this relates to the action of the paddle when
    the vessel is at rest: will you explain its action when the vessel is
    in motion?</P>

    <P><EM>A.</EM>--When the wheel of a coach rolls along the ground, any
    point of its periphery describes in the air a curve which is termed a
    cycloid; any point within the periphery traces a prolate or protracted
    cycloid, and any point exterior to the periphery traces a curtate or
    contracted cycloid--the prolate cycloid partaking more of the nature of
    a straight line, and the curtate cycloid more of the nature of a
    circle. The action of a paddle wheel in the water resembles in this
    respect that of the wheel of a carriage running along the ground: that
    point in the radius of the paddle of which the rotative speed is just
    equal to the velocity of the vessel will describe a cycloid; points
    nearer the centre, prolate cycloids, and points further from the
    centre, curtate cycloids. The circle described by the point whose
    velocity equals the velocity of the ship, is called the <EM>rolling
    circle</EM>, and the resistance due to the difference of velocity of
    the rolling circle and centre of pressure is that which operates in the
    propulsion of the vessel. The resistance upon any part of the float,
    therefore, will vary as the square of its distance from the rolling
    circle, supposing the float to be totally immerged; but, taking into
    account the greater length of time during which the extremity of the
    paddle acts, whereby the resistance will be made greater, we shall not
    err far in estimating the resistance upon any point at the third power
    of its distance from the rolling circle in the case of light
    immersions, and the 2.5 power in the case of deep immersions.</P>

    <P>554. <EM>Q.</EM>--How is the position of the centre of pressure to
    be determined?</P>

    <P><EM>A.</EM>--With the foregoing assumption, which accords
    sufficiently with experiment to justify its acceptation, the position
    of the centre of pressure may be found by the following rule:--from the
    radius of the wheel substract the radius of the rolling circle; to the
    remainder add the depth of the paddle board, and divide the fourth
    power of the sum by four times the depth; from the cube root of the
    quotient subtract the difference between the radii of the wheel and
    rolling circle, and the remainder will be the distance of the centre of
    pressure from the upper edge of the paddle.</P>

    <P>555. <EM>Q.</EM>--How do you find the diameter of the rolling
    circle?</P>

    <P><EM>A.</EM>--The diameter of the rolling circle is very easily
    found, for we have only to divide 5,280 times the number of miles per
    hour, by 60 times the number of strokes per minute, to get an
    expression for the circumference of the rolling circle, or the
    following rule may be adopted:--divide 88 times the speed of the vessel
    in statute miles per hour, by 3.1416 times the number of strokes per
    minute; the quotient will be the diameter in feet of the rolling
    circle. The diameter of the circle in which the centre of pressure
    moves or the effective diameter of the wheel being known, and also the
    diameter of the rolling circle, we at once find the excess of the
    velocity of the wheel over the vessel.</P>

    <P>556. <EM>Q.</EM>--Will you illustrate these rules by an example?</P>

    <P><EM>A.</EM>--A steam vessel of moderately good shape, and with
    engines of 200 horses power, realises, with 22 strokes per minute, a
    speed of 10.62 miles per hour. To find the diameter of the rolling
    circle, we have 88 times 10.62, equal to 934.66, and 22 times 3.1416,
    equal to 69.1152; then 934.66 divided by 69.1152 is equal to 13.52
    feet, which is the diameter of the rolling circle. The diameter of the
    wheel is 19 ft. 4 in., so that the diameter of the rolling circle is
    about 2/3ds of the diameter of the wheel, and this is a frequent
    proportion. The depth of the paddle board is 2 feet, and the difference
    between the diameters of the wheel and rolling circle will be 5.8133,
    which will make the difference of their radii 2.9067; and adding to
    this the depth of the paddle board, we have 4.9067, the fourth power of
    which is 579.64, which, divided by four times the depth of the paddle
    board, gives us 72.455, the cube root of which is 4.1689, which,
    diminished by the difference of the radii of the wheel and rolling
    circle, leaves 1.2622 feet for the distance of the centre of pressure
    from the upper edge of the paddle board in the case of light
    immersions. The radius of the wheel being 9.6667, the distance from the
    centre of the wheel to the upper edge of the float is 7.6667, and
    adding to this 1.2622, we get 8.9299 feet as the radius, or 17.8598
    feet as the diameter of the circle in which the centre of pressure
    revolves. With 22 strokes per minute, the velocity of the centre of
    pressure will be 20.573 feet per second, and with 10.62 miles per hour
    for the speed of the vessel, the velocity of the rolling circle will be
    15.576 feet per second. The effective velocity will be the difference
    between these quantities, or 4.997 feet per second. Now the height from
    which a body must fall by gravity, to acquire a velocity of 4.997 feet
    per second, is about .62 feet; and twice this height, or 1.24 feet,
    multiplied by 62-1/2, which is the number of Lbs. weight in a cubic
    foot of water, gives 77-1/2 Lbs. as the pressure on each square foot of
    the vertical paddle boards. As each board is of 20 square feet of area,
    and there is a vertical board on each side of the ship, the total
    pressure on the vertical paddle boards will be 2900 Lbs.</P>

    <P>557. <EM>Q.</EM>--What pressure is this equivalent to on each square
    inch of the pistons?</P>

    <P><EM>A.</EM>--A vessel of 200 horses power will have two cylinders,
    each 50 inches diameter, and 5 feet stroke, or thereabout. The area of
    a piston of 50 inches diameter is 1963.5 square inches, so that the
    area of the two pistons is 3927 square inches, and the piston will move
    through 10 feet every revolution; and with 22 strokes per minute this
    will be 220 feet per minute, or 3.66 feet per second. Now, if the
    effective velocity of the centre of pressure and the velocity of the
    pistons had been the same, then a pressure of 2900 Lbs. upon the
    vertical paddles would have been balanced by an equal pressure on the
    pistons, which would have been in this case about .75 Lbs. per square
    inch; but as the effective velocity of the centre of pressure is 4.997
    feet per second, while that of the pistons is only 3.66 feet per
    second, the pressure must be increased in the proportion of 4.997 to
    3.66 to establish an equilibrium of pressure, or, in other words, it
    must be 1.02 Lbs. per square inch. It follows from this investigation,
    that, in radial wheels, the greater part of the engine power is
    distributed among the oblique floats.</P>

    <P>558. <EM>Q.</EM>--How comes this to be the case?</P>

    <P><EM>A.</EM>--To understand how it happens that more power is
    expended upon the oblique than upon the vertical floats, it is
    necessary to remember that the only resistance upon the vertical paddle
    is that due to the difference of velocity of the wheel and the ship;
    but if the wheel be supposed to be immersed to its axle, so that the
    entering float strikes the water horizontally, it is clear that the
    resistance on such float is that due to the whole velocity of rotation;
    and that the resistance to the entering float will be the same whether
    the vessel is in motion or not. The resistance opposed to the rotation
    of any float increases from the position of the vertical float-where
    the resistance is that due to the difference of velocity of the wheel
    and vessel--until it reaches the plane of the axis, supposing the wheel
    to be immersed so far, where the resistance is that due to the whole
    velocity of rotation; and although in any oblique float the total
    resistance cannot be considered operative in a horizontal direction,
    yet the total resistance increases so rapidly on each side of the
    vertical float, that the portion of it which is operative in the
    horizontal direction, is in all ordinary cases of immersion very
    considerable. In the feathering wheel, where there is little of this
    oblique action, the resistance will be in the proportion of the square
    of the horizontal velocities of the several floats, which may be
    represented by the horizontal distances between them; and in the
    feathering wheel, the vertical float having the greatest horizontal
    velocity will have the greatest propelling effect.</P>

    <P>559. <EM>Q.</EM>--Should the floats in feathering wheels enter and
    leave the water vertically?</P>

    <P><EM>A.</EM>--The floats should be so governed by the central crank
    or eccentric, that the entering and emerging floats have a direction
    intermediate between a radius and a vertical line.</P>

    <P>560. <EM>Q.</EM>--Can you give any practical rules for proportioning
    paddle wheels?</P>

    <P><EM>A.</EM>--A common rule for the pitch of the floats is to allow
    one float for every foot of diameter of the wheel; but in the case of
    fast vessels a pitch of 2-1/2 feet, or even less, appears preferable,
    as a close pitch occasions less vibration. If the floats be put too
    close, however, the water will not escape freely from between them, and
    if set too far apart the stroke of the entering paddle will occasion an
    inconvenient amount of vibratory motion, and there will also be some
    loss of power. To find the proper area of a single float:--divide the
    number of actual horses power of both engines by the diameter of the
    wheel in feet; the quotient is the area of one paddle board in square
    feet proper for sea going vessels, and the area multiplied by 0.6 will
    give the length of the float in feet. In very sharp vessels, which
    offer less resistance in passing through the water, the area of paddle
    board is usually one-fourth less than the above proportion, and the
    proper length of the float may in such case be found by multiplying the
    area by 0.7. In sea going vessels about four floats are usually
    immersed, and in river steamers only one or two floats. There is more
    slip in the latter case, but there is also more engine power exerted in
    the propulsion of the ship, from the greater speed of engine thus
    rendered possible.</P>

    <P>561. <EM>Q.</EM>--Then is it beneficial to use small floats?</P>

    <P><EM>A.</EM>--Quite the contrary. If to permit a greater speed of the
    engine the floats be diminished in area instead of being raised out of
    the water, no appreciable accession to the speed of the vessel will be
    obtained; whereas there will be an increased speed of vessel if the
    accelerated speed of the engine be caused by diminishing the diameter
    of the wheels. In vessels intended to be fast, therefore, it is
    expedient to make the wheels small, so as to enable the engine to work
    with a high velocity; and it is expedient to make such wheels of the
    feathering kind, to obviate loss of power from oblique action. In no
    wheel must the rolling circle fall below the water line, else the
    entering and emerging floats will carry masses of water before them.
    The slip is usually equal to about one-fourth of the velocity of the
    centre of pressure in well proportioned wheels; but it is desirable to
    have the slip as small as is possible consistently with the observance
    of other necessary conditions. The speed of the engine and also the
    speed of the vessel being fixed, the diameter of the rolling circle
    becomes at once ascertainable, and adding to this the slip, we have the
    diameter of the wheel.</P>

    <H4 CLASS="subhead"><A NAME="m05"></A>CONFIGURATION AND ACTION OF THE
    SCREW.</H4>

    <P>562. <EM>Q.</EM>--Will you describe more in detail than you have yet
    done, the configuration and mode of action of the screw propeller?</P>

    <P><EM>A.</EM>--The ordinary form of screw propeller is represented in
    figs. 46 and 47; fig. 46 being a perspective view, and fig. 47 an end
    view, or view such as is seen when looking upon the end of the shaft.
    The screw here represented is one with two arms or blades. Some screws
    have three arms, some four and some six; but the screw with two arms is
    the most usual, and screws with more than three arms are not now much
    employed in this country. The screw on being put into revolution by the
    engine, preserves a spiral path in the water, in which it draws itself
    forward in the same way as a screw nail does when turned round in a
    piece of wood, whereas the paddle wheel more resembles the action of a
    cog wheel working in a rack.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig4647.png" ALIGN="right" WIDTH="380"
    HEIGHT="500" ALT=
    "Fig. 46. Fig. 47. ORDINARY FORM OF SCREW PROPELLER."></P>

    <P>563. <EM>Q.</EM>--But the screw of a steam vessel has no resemblance
    to a screw nail?</P>

    <P><EM>A.</EM>--It has in fact a very close resemblance if you suppose
    only a very short piece of the screw nail to be employed, and if you
    suppose, moreover, the thread of the screw to be cut nearly into the
    centre to prevent the wood from stripping. The original screw
    propellers were made with several convolutions of screw, but it was
    found advantageous to shorten them, until they are now only made
    one-sixth of a convolution in length.</P>

    <P>564. <EM>Q.</EM>--And the pitch you have already explained to be the
    distance in the line of the shaft from one convolution to the next,
    supposing the screw to consist of two or more convolutions?</P>

    <P><EM>A.</EM>--Yes, that is what is meant by the pitch. If a thread be
    wound upon a cylinder with an equal distance between the convolutions,
    it will trace a screw of a uniform pitch; and if the thread be wound
    upon the cylinder with an increasing distance between each convolution,
    it will trace a screw of an increasing pitch. But two or more threads
    may be wound upon the cylinder at the same time, instead of a single
    thread. If two threads be wound upon it they will trace a
    double-threaded screw; if three threads be wound upon it they will
    trace a treble-threaded screw; and so of any other number. Now if the
    thread be supposed to be raised up into a very deep and thin spiral
    feather, and the cylinder be supposed to become very small, like the
    newel of a spiral stair, then a screw will be obtained of the kind
    proper for propelling vessels, except that only a very short piece of
    such screw must be employed. Whatever be the number of threads wound
    upon a cylinder, if the cylinder be cut across all the threads will be
    cut. A slice cut out of the cylinder will therefore contain a piece of
    each thread. But the threads, in the case of a screw propeller, answer
    to the arms, so that in every screw propeller the number of threads
    entering into the composition of the screw will be the same as the
    number of arms. An ordinary screw with two blades is a short piece of a
    screw of two threads.</P>

    <P>565. <EM>Q.</EM>--In what part of the ship is the screw usually
    placed?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig48.png" ALIGN="left" WIDTH="362"
    HEIGHT="550" ALT="Fig. 48"></P>

    <P><EM>A.</EM>--In that part of the run of the ship called the dead
    wood, which is a thin and unused part of the vessel just in advance of
    the rudder. The usual arrangement is shown in fig. 48, which represents
    the application to a vessel of a species of screw which has the arms
    bent backwards, to counteract the centrifugal motion given to the water
    when there is a considerable amount of slip.</P>

    <P>566. <EM>Q.</EM>--How is the slip in a screw vessel determined?</P>

    <P><EM>A.</EM>--By comparing the actual speed of the vessel with the
    speed due to the pitch and number of revolutions of the screw, or, what
    is the same thing, the speed which the vessel would attain if the screw
    worked in a solid nut. The difference between the actual speed and this
    hypothetical speed, is the slip.</P>

    <P>567. <EM>Q.</EM>--In well formed screw propellers what is the amount
    of slip found to be?</P>

    <P><EM>A.</EM>--If the screw be properly proportioned to the resistance
    that the vessel has to overcome, the slip will not be more than 10 per
    cent., but in some cases it amounts to 30 per cent., or even more than
    this. In other cases, however, the slip is nothing at all, and even
    less than nothing; or, in other words the vessel passes through the
    water with a greater velocity than if the screw were working in a solid
    nut.</P>

    <P>568. <EM>Q.</EM>--Then it must be by the aid of the wind or some
    other extraneous force?</P>

    <P><EM>A.</EM>--No; by the action of the screw alone.</P>

    <P>569. <EM>Q.</EM>--But how is such a result possible?</P>

    <P><EM>A.</EM>--It appears to be mainly owing to the centrifugal action
    of the screw, which interposes a film or wedge of water between the
    screw itself and the water on which the screw reacts. This negative
    slip, as it is called, chiefly occurs when the pitch of the screw is
    less than its diameter, and when, consequently, the velocity of
    rotation is greater than if a coarser pitch had been employed. There
    is, moreover, in all vessels passing through the water with any
    considerable velocity, a current of water following the vessel, in
    which current, in the case of a screw vessel, the screw will revolve;
    and in certain cases the phenomenon of negative slip may be imputable
    in part to the existence of this current.</P>

    <P>570. <EM>Q.</EM>--Is the screw propeller as effectual an instrument
    of propulsion as the radial or feathering paddle?</P>

    <P><EM>A.</EM>--In all cases of deep immersion it appears to be quite
    as effectual as the radial paddle, indeed, more so; but it is scarcely
    as effectual as the feathering paddle, with any amount of immersion,
    and scarcely as effectual as the common paddle in the case of light
    immersions.</P>

    <H4 CLASS="subhead"><A NAME="m06"></A>COMPARATIVE ADVANTAGES OF PADDLE
    AND SCREW VESSELS.</H4>

    <P>571. <EM>Q.</EM>--Whether do you consider paddle or screw vessels to
    be on the whole the most advantageous?</P>

    <P><EM>A.</EM>--That is a large question, and can only receive a
    qualified answer. In some cases the use of paddles is indispensable,
    as, for example, in the case of river vessels of a limited draught of
    water, where it would not be possible to get sufficient depth below the
    water surface to enable a screw of a proper diameter to be got in.</P>

    <P>572. <EM>Q.</EM>--But how does the matter stand in the case of ocean
    vessels?</P>

    <P><EM>A.</EM>--In the case of ocean vessels, it is found that paddle
    vessels fitted with the ordinary radial wheels, and screw vessels
    fitted with the ordinary screw, are about equally efficient in calms
    and in fair or beam winds with light and medium immersions. If the
    vessels are loaded deeply, however, as vessels starting on a long
    voyage and carrying much coal must almost necessarily be, then the
    screw has an advantage, since the screw acts in its best manner when
    deeply immersed, and the paddles in their worst. When a screw and
    paddle vessel, however, of the same model and power are set to
    encounter head winds, the paddle vessel it is found has in all cases an
    advantage, not in speed, but in economy of fuel. For whereas in a
    paddle vessel, when her progress is resisted, the speed of the engine
    diminishes nearly in the proportion of the diminished speed of ship, it
    happens that in a screw vessel this is not so,--at least to an equal
    extent,--but the engines work with nearly the same rate of speed as if
    no increase of resistance had been encountered by the ship. It follows
    from this circumstance, that whereas in paddle vessels the consumption
    of steam, and therefore of fuel, per hour is materially diminished when
    head winds occur, in screw vessels a similar diminution in the
    consumption of steam and fuel does not take place.</P>

    <P>573. <EM>Q.</EM>--But perhaps under such circumstances the speed of
    the screw vessel will be the greater of the two?</P>

    <P><EM>A.</EM>--No; the speed of the two vessels will be the same,
    unless the strength of the head wind be so great as to bring the
    vessels nearly to a state of rest, and on that supposition the screw
    vessel will have the advantage. Such cases occur very rarely in
    practice; and in the case of the ordinary resistances imposed by head
    winds, the speed of the screw and paddle vessel will be the same, but
    the screw vessel will consume most coals.</P>

    <P>574. <EM>Q.</EM>--What is the cause of this peculiarity?</P>

    <P><EM>A.</EM>--The cause is, that when the screw is so proportioned in
    its length as to be most suitable for propelling vessels in calms, it
    is too short to be suitable for propelling vessels which encounter a
    very heavy resistance. It follows, therefore, that if it is prevented
    from pursuing its spiral course in the water, it will displace the
    water to a certain extent laterally, in the manner it does if the
    engine be set on when the vessel is at anchor; and a part of the engine
    power is thus wasted in producing a useless disturbance of the water,
    which in paddle vessels is not expended at all.</P>

    <P>575. <EM>Q.</EM>--If a screw and paddle vessel of the same mould and
    power be tied stern to stern, will not the screw vessel preponderate
    and tow the paddle vessel astern against the whole force of her
    engines?</P>

    <P><EM>A.</EM>--Yes, that will be so.</P>

    <P>576. <EM>Q.</EM>--And seeing that the vessels are of the same mould
    and power, so that neither can derive an advantage from a variation in
    that condition, does not the preponderance of the screw vessel show
    that the screw must be the most powerful propeller?</P>

    <P><EM>A.</EM>---No, it does not.</P>

    <P>577. <EM>Q.</EM>--Seeing that the vessels are the same in all
    respects except as regards the propellers, and that one of them
    exhibits a superiority, does not this circumstance show that one
    propeller must be more powerful than the other?</P>

    <P><EM>A.</EM>--That does not follow necessarily, nor is it the fact in
    this particular case. All steam vessels when set into motion, will
    force themselves forward with an amount of thrust which, setting aside
    the loss from friction and from other causes, will just balance the
    pressure on the pistons. In a paddle vessel, as has already been
    explained, it is easy to tell the tractive force exerted at the centre
    of pressure of the paddle wheels, when the pressure urging the pistons,
    the dimensions of the wheels and the speed of the vessel are known; and
    that force, whatever be its amount, must always continue the same with
    any constant pressure on the pistons. In a screw vessel the same law
    applies, so that with any given pressure on the pistons and discarding
    the consideration of friction, it will follow that whatever be the
    thrust exerted by a paddle or a screw vessel, it must remain uniform
    whether the vessel is in motion or at rest, and whether moving at a
    high or a low velocity through the water. Now to achieve an equal speed
    during calms in two vessels of the same model, there must be the same
    amount of propelling thrust in each; and this thrust, whatever be its
    amount, cannot afterward vary if a uniform pressure of steam be
    maintained. The thrusts, therefore, caused by their respective
    propelling instruments, when a screw and paddle vessel are tied stern
    to stern, must be the same as at other times; and as at other times
    those thrusts are equal, so must they be when the vessels are set in
    the antagonism supposed.</P>

    <P>578. <EM>Q.</EM>--How comes it then that the screw vessel
    preponderates?</P>

    <P><EM>A.</EM>--Not by virtue of a larger thrust exerted by the screw
    in pressing forward the shaft and with it the vessel, but by the
    gravitation against the stern of the wave of water which the screw
    raises by its rapid rotation. This wave will only be raised very high
    when the progress of the vessel through the water is nearly arrested,
    at which time the centrifugal action of the screw is very great; and
    the vessel under such circumstances is forced forward partly by the
    thrust of the screw, and partly by the hydrostatic pressure of the
    protuberance of water which the centrifugal action of the screw raises
    up at the stern.</P>

    <P>579. <EM>Q.</EM>--Can you state any facts in corroboration of this
    view?</P>

    <P><EM>A.</EM>--The screw vessel will not preponderate if a screw and
    paddle vessel be tied bow to bow and the engines of each be then
    reversed. In, some screw vessels the amount of thrust actually exerted
    by the screw under all its varying circumstances, has been ascertained
    by the application of a dynamometer to the end of the shaft. By this
    instrument--which is formed by a combination of levers like a weighing
    machine for carts--a thrust or pressure of several tons can be measured
    by the application of a small weight; and it has been found, by
    repeated experiment with the dynamometer, that the thrust of the screw
    in a screw vessel when towing a paddle vessel against the whole force
    of her engines, is just the same as it is when the two vessels are
    maintaining an equal speed in calms. The preponderance of the screw
    vessel must, therefore, be imputable to some other agency than to a
    superior thrust of the screw, which is found by experiment not to
    exist.</P>

    <P>580. <EM>Q.</EM>--Has the dynamometer been applied to paddle
    vessels?</P>

    <P><EM>A.</EM>--It has not been applied to the vessels themselves, as
    in the case of screw vessels, but it has been employed on shore to
    ascertain the amount of tractive force that a paddle vessel can exert
    on a rope.</P>

    <P>581. <EM>Q.</EM>--Have any experiments been made to determine the
    comparative performances of screw and paddle vessels at sea?</P>

    <P><EM>A.</EM>--Yes, numerous experiments; of which the best known are
    probably those made on the screw steamer Rattler and the paddle steamer
    Alecto, each vessel of the same model, size, and power,--each vessel
    being of about 800 tons burden and 200 horses power. Subsequently
    another set of experiments with the same object was made with the Niger
    screw steamer and the Basilisk paddle steamer, both vessels being of
    about 1000 tons burden and 400 horses power. The general results which
    were obtained in the course of these experiments are those which have
    been already recited.</P>

    <P>582. <EM>Q.</EM>--Will you recapitulate some of the main incidents
    of these trials?</P>

    <P><EM>A.</EM>--I may first state some of the chief dimensions of the
    vessels. The Rattler is 176 feet 6 inches long, 32 feet 8-1/2 inches
    broad, 888 tons burden, 200 horses power, and has an area of immersed
    midship section of 380 square feet at a draught of water of 11 feet
    5-1/2 inches. The Alecto is of the same dimensions in every respect,
    except that she is only of 800 tons burden, the difference in this
    particular being wholly owing to the Rattler having been drawn out
    about 15 feet at the stern, to leave abundant room for the application
    of the screw. The Rattler was fitted with a dynamometer, which enabled
    the actual propelling thrust of the screw shaft to be measured; and the
    amount of this thrust, multiplied by the distance through which the
    vessel passed in a given time, would determine the amount of power
    actually utilized in propelling the ship. Both vessels were fitted with
    indicators applied to the cylinders, so as to determine the amount of
    power exerted by the engines.</P>

    <P>583. <EM>Q.</EM>--How many trials of the vessels were made on this
    occasion?</P>

    <P><EM>A.</EM>--Twelve trials in all; but I need not refer to those in
    which similar or identical results were only repeated. The first trial
    was made under steam only, the weather was calm and the water smooth.
    At 54 minutes past 4 in the morning both vessels left the Nore, and at
    30-1/2 minutes past 2 the Rattler stopped her engines in Yarmouth
    Roads, where in 20-1/2 minutes afterward she was joined by the Alecto.
    The mean speed achieved by the Rattler during this trial was 9.2 knots
    per hour; the mean speed of the Alecto was 8.8 knots per hour. The slip
    of the screw was 10.2 per cent. The actual power exerted by the
    engines, as shown by the indicator, was in the case of the Rattler
    334.6 horses, and in the case of the Alecto 281.2 horses; being a
    difference of 53.4 horses in favor of the Rattler. The forward thrust
    upon the screw shaft was 3 tons, 17 cwt., 3 qrs., and 14 lbs. The horse
    power of the shaft--or power actually utilized--ascertained by
    multiplying the thrust in pounds by the space passed through by the
    vessel in feet per minute, and dividing by 33,000, was 247.8 horses
    power. This makes the ratio of the shaft to the engine power as 1 to
    1.3, or, in other words, it shows that the amount of engine power
    utilized in propulsion was 77 per cent. In a subsequent trial made with
    the vessels running before the wind, but with no sails set and the
    masts struck, the speed realized by the Rattler was 10 knots per hour.
    The slip of the screw was 11.2 per cent. The actual power exerted by
    the engines of the Rattler was 368.8 horses. The actual power exerted
    by the engines of the Alecto was 291.7 horses. The thrust of the shaft
    was equal to a weight of 4 tons, 4 cwt., 1 qr., 1 lb. The horse power
    of the shaft was 290.2 horses, and the ratio of the shaft to the engine
    power was 1 to 1.2. Here, therefore, the amount of the engine power
    utilized was 84 per cent.</P>

    <P>584. <EM>Q.</EM>--If in any screw vessel the power of the engine be
    diminished by shutting off the steam or otherwise, you will then have a
    larger screw relatively with the power of the engine than before?</P>

    <P><EM>A.</EM>--Yes.</P>

    <P>585. <EM>Q.</EM>--Was any experiment made to ascertain the effect of
    this modification?</P>

    <P><EM>A.</EM>--There was; but the result was not found to be better
    than before. The experiment was made by shutting off the steam from the
    engines of the Rattler until the number of strokes was reduced to 17 in
    the minute. The actual power was then 126.7 horses; thrust upon the
    shaft 2 tons, 2 cwt., 3 qrs., 14 lbs; horse power of shaft 88.4 horses;
    ratio of shaft to engine power 1 to 1.4; slip of the screw 18.7 per
    cent. In this experiment the power utilized was 71 per cent.</P>

    <P>586. <EM>Q.</EM>--Was any experiment made to determine the relative
    performances in head winds?</P>

    <P><EM>A.</EM>--The trial in which this relation was best determined
    lasted for seven hours, and was made against a strong head wind and
    heavy head sea. The speed of the Rattler by patent log was 4.2 knots;
    and at the conclusion of the trial the Alecto had the advantage by
    about half a mile. Owing to an accidental injury to the indicator, the
    power exerted by the engines of the Rattler in this trial could not be
    ascertained; but judging from the power exerted in other experiments
    with the same number of revolutions, it appears probable that the power
    actually exerted by the Rattler was about 300 horses. The number of
    strokes per minute made by the engines of the Rattler was 22, whereas
    in the Alecto the number of strokes per minute was only 12; so that
    while the engines of the Alecto were reduced, by the resistance
    occasioned by a strong head wind, to nearly half their usual speed, the
    engines of the Rattler were only lessened about one twelfth of their
    usual speed. The mean thrust upon the screw shaft during this
    experiment, was 4 tons, 7 cwt., 0 qr., 16 lbs. The horse power of the
    shaft was 125.9 horses, and the slip of the screw was 56 per cent.
    Taking the power actually exerted by the Rattler at 300 horses, the
    power utilized in this experiment is only 42 per cent.</P>

    <P>587. <EM>Q.</EM>--What are the dimensions of the screw in the
    Rattler?</P>

    <P><EM>A.</EM>--Diameter 10 feet, length 1 foot 3 inches, pitch 11
    feet. The foregoing experiments show that with a larger screw a better
    average performance would be obtained. The best result arrived at, was
    when the vessel was somewhat assisted by the wind, which is equivalent
    to a reduction of the resistance of the hull, or to a smaller hull,
    which is only another expression for a larger proportionate screw.</P>

    <P>588. <EM>Q.</EM>--When you speak of a larger screw, what increase of
    dimension do you mean to express?</P>

    <P><EM>A.</EM>--An increase of the diameter. The amount of reacting
    power of the screw upon the water is hot measured by the number of
    square feet of surface of the arms, but by the area of the disc or
    circle in which the screw revolves. The diameter of the screw of the
    Rattler being 10 feet, the area of its disc is 78.5 square feet; and
    with the amount of thrust already mentioned as existing in the first
    experiment, viz. 8722 lbs., the reacting pressure on each square foot
    of the screw&#39;s disc will be 108-1/2 lbs. The immersed midship
    section being 380 square feet, this is equivalent to 23 lbs. per square
    foot of immersed midship section at a speed of 9.2 knots per hour.</P>

    <P>589. <EM>Q.</EM>--In smaller vessels of similar form, will the
    resistance per square foot of midship section be more than this?</P>

    <P><EM>A.</EM>--It will be considerably more. In the Pelican, a vessel
    of 109- 3/4 square feet of midship section, I estimate the resistance
    per square foot of midship section at 30 lbs., when the speed of the
    vessel is 9.7 knots per hour. In the Minx with an immersed midship
    section of 82 square feet, the resistance per square foot of immersed
    midship section was found by the dynamometer to be 41 lbs. at a speed
    of 8-1/2 knots; and in the Dwarf, a vessel with 60 square feet of
    midship section, I estimate the resistance per square foot of midship
    section at 46 lbs. at a speed of 9 knots per hour, which is just double
    the resistance per square foot of the Rattler. The diameter of the
    screw of the Minx is 4-1/2 feet, so that the area of its disc is 15.9
    square feet, and the area of immersed midship section is about 5 times
    greater than that of the screw&#39;s disc. The diameter of the screw of
    the Dwarf is 5 feet 8 inches, so that the area of its disc is 25.22
    square feet, and the area of immersed midship section is 2.4 times
    greater than that of the screw&#39;s disc. The pressure per square foot
    of the screw&#39;s disc is 214 lbs. in the case of the Minx, and
    109-1/2 lbs. in the case of the Dwarf.</P>

    <P>590. <EM>Q.</EM>--From the greater proportionate resistance of small
    vessels, will not they require larger proportionate screws than large
    vessels?</P>

    <P><EM>A.</EM>--They will.</P>

    <P>591. <EM>Q.</EM>--Is there any ready means of predicting what the
    amount of thrust of a screw will be?</P>

    <P><EM>A.</EM>--When we know the amount of pressure on the pistons, and
    the velocity of their motion relatively with the velocity of advance
    made by the screw, supposing it to work in a solid nut, it is easy to
    tell what the thrust of the screw would be if it were cleared of the
    effects of friction and other irregular sources of disturbance. The
    thrust, in fact, would be at once found by the principle of virtual
    velocities; and if we take this theoretical thrust and diminish it by
    one fourth to compensate for friction and lateral slip, we shall have a
    near approximation to the amount of thrust that will be actually
    exerted. <A NAME="fnr6"></A> <A HREF="#fn6" CLASS="fnsuper">1</A></P>

    <P CLASS="footnote"><A NAME="fn6"></A> <A HREF="#fnr6">[1]</A> See
    Treatise on the Screw Propeller, by J. Bourne, C. E.</P>

    <H4 CLASS="subhead"><A NAME="m07"></A>COMPARATIVE ADVANTAGES OF
    DIFFERENT SCREWS.</H4>

    <P>592. <EM>Q.</EM>--What species of screw do you consider the
    best?</P>

    <P><EM>A.</EM>--In cases in which a large diameter of screw can be
    employed, the ordinary screw or helix with two blades seems to be as
    effective as any other, and it is the most easily constructed. If,
    however, the screw is restricted in diameter, or if the vessel is
    required to tow, or will have to encounter habitually strong head
    winds, it will be preferable to employ a screw with an increasing
    pitch, and also of such other configuration that it will recover from
    the water some portion of the power that has been expended in slip.</P>

    <P>593. <EM>Q.</EM>--How can this be done?</P>

    <P><EM>A.</EM>--There are screws which are intended to accomplish, this
    object already in actual use. When there is much slip a centrifugal
    velocity is given to the water, and the screw, indeed, if the engine be
    set on when the vessel is at rest, acts very much as a centrifugal fan
    would do if placed in the same situation. The water projected outward
    by the centrifugal force escapes in the line of least resistance, which
    is to the surface; and if there be a high column of water over the
    screw, or, in other words, if the screw is deeply immersed, then the
    centrifugal action is resisted to a greater extent, and there will be
    less slip produced. The easiest expedient, therefore, for obviating
    loss by slip is to sink the screw deeply in the water; but as there are
    obvious limits to the application of this remedy, the next best device
    is to recover and render available for propulsion some part of the
    power which has been expended in giving motion to the water. One device
    for doing this consists in placing the screw well forward in the dead
    wood, so that it shall be overhung by the stern of the ship. The water
    forced upward by the centrifugal action of the screw will, by impinging
    on the overhanging stern, press the vessel forward in the water, just
    in the same way as is done by the wind when acting on an oblique sail.
    I believe, the two revolving vanes without any twist or obliquity on
    them at all, would propel a vessel if set well forward in the dead wood
    or beneath the bottom, merely by the ascent of the water up the
    inclined plane of the vessel&#39;s run; and, at all events, a screw so
    placed would, in my judgment, aid materially in propelling the vessel
    when her progress was resisted by head winds.</P>

    <P>594. <EM>Q.</EM>--But you said there are some kinds of screws which
    profess to accomplish this?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig49.png" WIDTH="622" HEIGHT="500" ALT=
    "Fig. 49. THE EARL OF DUNDONALD&#39;S PROPELLER."></P>

    <P><EM>A.</EM>--There are screws which profess to counteract the
    centrifugal velocity given to the water by imparting to it an equal
    centripetal force, the consequence of which will be, that the water
    projected backward by the screw, instead of taking the form of the
    frustum of a cone, with its small end next the screw, will take the
    form of a cylinder. One of these forms of screw is that patented by the
    Earl of Dundonald in 1843, and which is represented in fig. 49. Another
    is the form of screw already represented in fig. 48, and which was
    patented by Mr. Hodgson in 1844. Mr. Hodgson bends the arms of his
    propellers backward, not into the form of a triangle, but into the form
    of a parabola, to the end that the impact of the screw on the particles
    of the water may cause them to converge to a focus, as the rays of
    light would do in a parabolic reflector. But this particular
    configuration is not important, seeing that the same convergence which
    is given to the particles of the water, with a screw of uniform pitch
    bent back into the form of a parabola, will be given with a screw bent
    back into the form of a triangle, if the pitch be suitably varied
    between the centre and the circumference.</P>

    <P>595. <EM>Q.</EM>--Then the pitch may be varied in two ways?</P>

    <P><EM>A.</EM>--Yes: a screw may have a pitch increasing in the
    direction of the length, as would happen in the case of a spiral stair,
    if every successive step in the ascent was thicker than the one below
    it; or it may increase from the centre to the circumference, as would
    happen in the case of a spiral stair, if every step were thinner at the
    centre of the lower than at its outer wall. When the pitch of a screw
    increases in the direction of its length, the leading edge of the screw
    enters the water without shock or impact, as the advance of the leading
    edge per revolution will not be greater than the advance of the vessel.
    When the pitch of a screw increases in the direction of its diameter,
    the central part of the screw will advance with only the same velocity
    as the water, so that it cannot communicate any centrifugal velocity to
    the water; and the whole slip, as well as the whole propelling
    pressure, will occur at the outer part of the screw blades.</P>

    <P>596. <EM>Q.</EM>--Is there any advantage derived from these forms of
    screws?</P>

    <P><EM>A.</EM>--There is a slight advantage, but it is so slight as
    hardly to balance the increased trouble of manufacture, and,
    consequently, they are not generally or widely adopted.</P>

    <P>597. <EM>Q.</EM>--What other kinds of screw are there proposing to
    themselves the same or similar objects?</P>

    <P><EM>A.</EM>--There is the corrugated screw, the arms of which are
    corrugated, so as it were to gear with the water during its revolution,
    and thereby prevent it from acquiring a centrifugal velocity. Then
    there is Griffith&#39;s screw, which has a large ball at its centre,
    which, by the suction it creates at its hinder part, in passing through
    the water, produces a converging force, which partly counteracts the
    divergent action of the arms. Finally, there is Holm&#39;s screw, which
    has now been applied to a good number of vessels with success.</P>

    <P>598. <EM>Q.</EM>--Will you describe the configuration and action of
    Holm&#39;s screw?</P>

    <P><EM>A.</EM>--First, then, the screw increases in the direction of
    its length, and this increase is very rapid at the following edge, so
    that, in fact, the following edge stands in the plane of the shaft, or
    in the vertical longitudinal plane of the vessel. Then the ends of the
    arms are bent over into a curved flange, the edge of which points
    astern, and the point where this curved flange joins the following edge
    of the screw is formed, not into an angle, but into a portion of a
    sphere, so that this corner resembles the bowl of a spoon. When the
    screw is put into revolution, the water is encountered by the leading
    edge of the screw without shock, as its advance is only equal to the
    advance of the vessel, and before the screw leaves the water it is
    projected directly astern. At the same time, the curved flange at the
    rim of the screw prevents the dispersion of the water in a radial
    direction, and it consequently assumes the form of a column or cylinder
    of water, projected backward from the ship.</P>

    <P>599. <EM>Q.</EM>--What is the nature of Beattle&#39;s screw?</P>

    <P><EM>A.</EM>--Beattie&#39;s screw is an arrangement of the screw
    propeller whereby it is projected beyond the rudder, and the main
    object of the arrangement is to take away the vibratory motion at the
    stern,--an intention which it accomplishes in practice. There is an
    oval eye in the rudder, to permit the screw shaft to pass through
    it.</P>

    <P>600. <EM>Q.</EM>--When the diameter of the cylinder of water
    projected backward by a screw, and the force urging it into motion are
    known, may not the velocity it will acquire be approximately
    determined?</P>

    <P><EM>A.</EM>--That will not be very difficult; and I will take for
    illustration the case of the Minx, already referred to, which will show
    how such a computation is to be conducted. The speed of this vessel, in
    one of the experiments made with her, was 8.445 knots; the number of
    revolutions of the screw per minute, 231.32; and the pressure on each
    square foot of area of the screw&#39;s disc, 214 lbs. If a knot be
    taken to be 6075.6 feet, then the distance advanced by the vessel, when
    the speed is 8.445 knots, will be 3.7 feet per revolution, and this
    advance will be made in about .26 of a second of time. Now the distance
    which a body will fall by gravity, in .26 of a second, is 1.087 feet;
    and a weight of 214 lbs. put into motion by gravity, or by a pressure
    of 214 lbs., would, therefore, acquire a velocity of 1.087 feet during
    the time one revolution of the screw is being performed. The weight to
    be moved, however, is 3.7 cubic feet of water, that being the new water
    seized by the screw each revolution for every square foot of surface in
    the screw&#39;s disc; and 3.7 cubic feet of water weigh 231.5 lbs., so
    that the urging force of 214 lbs. is somewhat less than the force of
    gravity, and the velocity of motion communicated to the water will be
    somewhat under 1.087 feet per revolution, or we may say it will be in
    round numbers 1 foot per revolution. This, added to the progress of the
    vessel, will make the distance advanced by the screw through the water
    4.7 feet per revolution, leaving the difference between this and the
    pitch, namely 1.13 feet, to be accounted for on the supposition that
    the screw blades had broken laterally through the water to that extent.
    It would be proper to apply some correction to this computation, which
    would represent the increased resistance due to the immersion of the
    screw in the water; for a column of water cannot be moved in the
    direction of its axis beneath the surface, without giving motion to the
    superincumbent water, and the inertia of this superincumbent water
    must, therefore, be taken into the account. In the experiment upon the
    Minx, the depth of this superincumbent column was but small. The total
    amount of the slip was 36.53 per cent.; and there will not be much
    error in setting down about one half of this as due to the recession of
    the water in the direction of the vessel&#39;s track, and the other
    half as due to the lateral penetration of the screw blades.</P>

    <P>601. <EM>Q.</EM>--Is it not important to make the stern of screw
    vessels very fine, with the view of diminishing the slip, and
    increasing the speed?</P>

    <P><EM>A.</EM>--It is most important. The Rifleman, a vessel of 486
    tons, had originally engines of 200 horses power, which propelled her
    at a speed of 8 knots an hour. The Teazer, a vessel of 296 tons, had
    originally engines of 100 horses power, which propelled her at a speed
    of 6-1/2 knots an hour. The engines of the Teazer were subsequently
    transferred to the Rifleman, and new engines of 40 horse power were put
    into the Teazer. Both vessels were simultaneously sharpened at the
    stern, and the result was, that the 100 horse engines drove the
    Rifleman, when sharpened, as fast as she had previously been driven by
    the 200 horse engines; and the 40 horse engines drove the Teazer, when
    sharpened, a knot an hour faster than she had previously been driven by
    the 100 horse engines. The immersion of both vessels was kept unchanged
    in each case; and the 100 horse engines of the Teazer, when transferred
    to the Rifleman, drove that vessel, after she had been sharpened, 2
    knots an hour faster than they had previously driven a vessel not much
    more than half the size. These are important facts for every one to be
    acquainted with who is interested in the success of screw vessels, and
    who seeks to obtain the maximum of efficiency with the minimum of
    expense. <A NAME="fnr7"></A> <A HREF="#fn7" CLASS="fnsuper">1</A></P>

    <P CLASS="footnote"><A NAME="fn7"></A> <A HREF="#fnr7">[1]</A> See
    Treatise on the Screw Propeller, by John Bourne, C. E.</P>

    <H4 CLASS="subhead"><A NAME="m08"></A>PROPORTIONS OF SCREWS.</H4>

    <P>602. <EM>Q.</EM>--In fixing upon the proportions of a screw proper
    to propel any given vessel, how would you proceed?</P>

    <P><EM>A.</EM>--I would first compute the probable resistance of the
    vessel, and I would be able to find the relative resistances of the
    screw and hull, and in every case it is advisable to make the screw as
    large in diameter as possible. The larger the screw is, the greater
    will be the efficiency of the engine in propelling the vessel; the
    larger will be the ratio of the pitch to the diameter, which produces a
    maximum effect; and the smaller will be the length of the screw or the
    fraction of a convolution to produce a maximum effect.</P>

    <P>603. <EM>Q.</EM>--Will you illustrate this doctrine by a practical
    example?</P>

    <P><EM>A.</EM>--The French screw steamer Pelican was fitted
    successively with two screws of four blades, but the diameter of the
    first screw was 98.42 inches, and the diameter of the second 54 inches.
    If the efficiency of the first screw by represented by 1, that of the
    second screw will be represented by .823, or, in other words, if the
    first screw would give a speed of 10 knots, the second would give
    little more than 8. The most advantageous ratio of pitch to diameter
    was found to be 2.2 in the case of the large screw, and 1.384 in the
    case of the small. The fraction of a convolution which was found to be
    most advantageous was .281 in the case of the large screw, and .450 in
    the case of the small screw.</P>

    <P>604. <EM>Q</EM>--Were screws of four blades found to be more
    efficient than screws with two? <EM>A</EM>They were found to have less
    slip, but not to be more efficient, the increased slip in those of two
    blades being balanced by the increased friction in those of four.
    Screws of two blades, to secure a maximum efficiency, must have a finer
    pitch than screws of four.</P>

    <P>605. <EM>Q.</EM>--Are the proportions found to be most suitable in
    the case of the Pelican applicable to the screws of other vessels?</P>

    <P><EM>A.</EM>-Only to those which have the same relative resistance of
    screw and hull. Taking the relative resistance to be the area of
    immersed midship section, divided by the square of the screw&#39;s
    diameter, it will in the case of the Rattler be 380/100 or 3.8. From
    the experiments made by MM. Bourgois and Moll on the screw steamer
    Pelican, they have deduced the proportions of screws proper for all
    other classes of vessels, whether the screws are of two, four, or six
    blades.</P>

    <P>606. <EM>Q.</EM>--Will you specify the nature of their
    deductions?</P>

    <P><EM>A.</EM>--I will first enumerate those which bear upon screws
    with two blades. When the relative resistance is 5.5 the ratio of pitch
    to diameter should be 1.006, and the fraction of the pitch or
    proportion of one entire convolution should be 0.454. When the relative
    resistance is 5, the ratio of pitch to diameter should be 1.069, and
    fraction of pitch 0.428; relative resistance 4.5, pitch 1.135, fraction
    0.402; relative resistance 4, pitch 1.205, fraction 0.378; relative
    resistance 3.5, pitch 1.279, fraction 0.355; relative resistance 3,
    pitch 1.357, fraction 0.334; relative resistance 2.5, pitch 1.450,
    fraction 0.313; relative resistance 2, pitch 1.560, fraction 0.294;
    relative resistance 1.5, pitch 1.682, fraction 0.275. The relative
    resistance of 4 is that which is usual in an auxiliary line of battle
    ship, 3.5 in an auxiliary frigate, 3 in a high speed line of battle
    ship, 2.5 in a high speed frigate, 2 in a high speed corvette, and 1.5
    in a high speed despatch boat.</P>

    <P>607. <EM>Q.</EM>--What are the corresponding proportions of screws
    of four blades?</P>

    <P><EM>A.</EM>--The ratios of the pitches to the diameter being for
    each of the relative resistances enumerated above, 1.342, 1.425, 1.513,
    1.607, 1.705, 1.810, 1.933, 2.080, and 2.243, the respective fractions
    of pitch or fractions of a whole convolution will be 0.455, 0.428,
    0.402, 0.378, 0.355, 0.334, 0.313, 0.294, and 0.275.</P>

    <P>608. <EM>Q.</EM>--And what are the corresponding proportions proper
    for screws of six blades?</P>

    <P><EM>A.</EM>--Beginning with the relative resistance of 5.5 as
    before, the proper ratio of pitch to diameter for that and each of the
    successive resistances in the case of screws with six blades, will be
    1.677, 1.771, 1.891, 1.2009, 2.131, 2.262, 2.416, 2.600, 2.804; and the
    respective fractions of pitch will be 0.794, 0.749, 0.703, 0.661,
    0.621, 0.585, 0.548, 0.515, and 0.481. These are the proportions which
    will give a maximum performance in every case. <A NAME="fnr8"></A> <A
    HREF="#fn8" CLASS="fnsuper">1</A></P>

    <P CLASS="footnote"><A NAME="fn8"></A> <A HREF="#fnr8">[1]</A> In my
    Treatise on the Screw Propeller I have gone into these various
    questions more fully than would consort with the limits of this
    publication.</P>

    <H4 CLASS="subhead"><A NAME="m09"></A>SCREW VESSELS WITH FULL AND
    AUXILIARY POWER.</H4>

    <P>609. <EM>Q.</EM>--Do you consider that the screw propeller is best
    adapted for vessels of full power, or for vessels with auxiliary
    power?</P>

    <P><EM>A.</EM>--It is, in my opinion, best adapted for vessels with
    auxiliary power, and it is a worse propeller than paddle wheels for
    vessels which have habitually to encounter strong head winds. Screw
    vessels are but ill calculated--at least as constructed heretofore--to
    encounter head winds, and the legitimate sphere of the screw is in
    propelling vessels with auxiliary power.</P>

    <P>610. <EM>Q.</EM>--Does the screw act well in conjunction with
    sails?</P>

    <P><EM>A.</EM>--I cannot say it acts better than paddles, except in so
    far as it is less in the way and is less affected by the listing or
    heeling over of the ship. A small steam power, however, acts very
    advantageously in aid of sails, for not only does the operation of the
    sails in reducing the resistance of the hull virtually increase the
    screw&#39;s diameter, but the screw, by reducing the resistance which
    has to be overcome by the sails and by increasing the speed of the
    vessel, enables the sails to act with greater efficiency, as the wind
    will not rebound from them with as great a velocity as it would
    otherwise do, and a larger proportion of the power of the wind will
    also be used up. In the case of beam winds, moreover, the action of the
    screw, by the larger advance it gives to the vessel will enable the
    sails to intercept a larger column of wind in a given time. It appears,
    therefore, that the sails add to the efficiency of the screw, and that
    the screw also adds to the efficiency of the sails.</P>

    <P>611. <EM>Q.</EM>--What is the comparative cost of transporting
    merchandise in paddle steamers of full power, in screw steamers of
    auxiliary power, and in sailing ships?</P>

    <P><EM>A.</EM>--That will depend very much upon the locality where the
    comparison is made. In the case of vessels performing distant ocean
    voyages, in which they may reckon upon the aid of uniform and constant
    winds, such as the trade winds or the monsoon, sailing ships of large
    size will be able to carry more cheaply than any other species of
    vessel. But where the winds are irregular and there is not much sea
    room, or for such circumstances as exist in the Channel or
    Mediterranean trades, screw vessels with auxiliary power will
    constitute the cheapest instrument of conveyance.</P>

    <P>612. <EM>Q.</EM>--Are there any facts recorded illustrative of the
    accuracy of this conclusion?</P>

    <P><EM>A.</EM>--A full paddle vessel of 1000 tons burden and 350 horses
    power, will carry about 400 tons of cargo, besides coal for a voyage of
    500 miles, and the expense of such a voyage, including wear and tear,
    depreciation, &amp;c., will be about 190<EM>l</EM>. The duration of the
    voyage will be about 45-1/2 hours. A screw vessel of 400 tons burden
    and 100 horses power, will carry the same amount of cargo, besides her
    coals, on the same voyage, and the expense of the voyage, including
    wear and tear, depreciation, &amp;c., will be not much more than
    60<EM>l</EM>. An auxiliary screw vessel, therefore, can carry
    merchandise at one third of the cost of a full-powered paddle vessel.
    By similar comparisons made between the expense of conveying
    merchandise in auxiliary screw steamers and sailing ships on coasting
    voyages, it appears that the cost in screw steamers is about one third
    less than in the sailing ships; the greater expedition of the screw
    steamers much more than compensating for the expense which the
    maintenance of the machinery involves.</P>

    <H4 CLASS="subhead"><A NAME="m10"></A>SCREW AND PADDLES COMBINED.</H4>

    <P>613. <EM>Q.</EM>--Would not a screw combined with paddles act in a
    similarly advantageous way as a screw or paddles when aided by the
    wind?</P>

    <P><EM>A.</EM>--If in any given paddle vessel a supplementary screw be
    added to increase her power and speed, the screw will act in a more
    beneficial manner than if it had the whole vessel to propel itself, and
    for a like reason the paddles will act in a more beneficial manner.
    There will be less slip both upon the paddles and upon the screw than
    if either had been employed alone; but the same object would be
    attained by giving the vessel larger paddles or a larger screw.</P>

    <P>614. <EM>Q.</EM>--Have any vessels been constructed with combined
    screw and paddles?</P>

    <P><EM>A.</EM>--Not any that I know of, except the great vessel built
    under the direction of Mr. Brunel. The Bee many years since was fitted
    with both screw and paddles, but this was for the purpose of
    ascertaining the relative efficiency of the two modes of propulsion,
    and not for the purpose of using both together.</P>

    <P>615. <EM>Q.</EM>--What would be the best means of accelerating the
    speed of a paddle vessel by the introduction of a supplementary
    screw?</P>

    <P><EM>A.</EM>--If the vessel requires new boilers, the best course of
    procedure would be to work a single engine giving motion to the screw
    with high pressure steam, and to let the waste steam from the high
    pressure engine work the paddle engines. In this way the power might be
    doubled without any increased expenditure of fuel per hour, and there
    would be a diminished expenditure per voyage in the proportion of the
    increased speed.</P>

    <P>616. <EM>Q.</EM>--What would the increased speed be by doubling the
    power?</P>

    <P><EM>A.</EM>--The increase would be in the proportion of the cube
    root of 1 to the cube root of 2, or it would be 1.25 times greater. If,
    therefore, the existing speed were 10 miles, it would be increased to
    12-1/2 miles by doubling the power, and the vessel would ply with about
    a fourth less coals by increasing the power in the manner
    suggested.</P>

    <P>617. <EM>Q.</EM>--Is not high pressure steam dangerous in steam
    vessels?</P>

    <P><EM>A.</EM>--Not necessarily so, and it has now been introduced into
    a good number of steam vessels with satisfactory results. In the case
    of locomotive engines, where it is used so widely, very few accidents
    have occurred; and in steam vessels the only additional source of
    danger is the salting of the boiler. This may be prevented either by
    the use of fresh water in the boiler, or by practising a larger amount
    of blowing off, to insure which it should be impossible to diminish the
    amount of water sent into the boiler by the feed pump, and the excess
    should be discharged overboard through a valve near the water level of
    the boiler, which valve is governed by a float that will rise or fall
    with the fluctuating level of the water. If the float be a copper ball,
    a little water should be introduced into it before it is soldered or
    brazed up, which will insure an equality of pressure within and without
    the ball, and a leakage of water into it will then be less likely to
    take place. A stone float, however, is cheaper, and if properly
    balanced will be equally effective. All steam vessels should have a
    large excess of boiling feed water constantly flowing into the boiler,
    and a large quantity of water constantly blowing off through the
    surface valves, which being governed by floats will open and let the
    superfluous water escape whenever the water level rises too high. In
    this way the boiler will be kept from salting, and priming will be much
    less likely to occur. The great problem of steam navigation is the
    economy of fuel, since the quantity of fuel consumed by a vessel will
    very much determine whether she is profitable or otherwise.
    Notwithstanding the momentous nature of this condition, however, the
    consumption of fuel in steam vessels is a point to which very little
    attention has been paid, and no efficient means have yet been adopted
    in steam vessels to insure that measure of economy which is known to be
    attainable, and which has been attained already in other departments of
    engineering in which the benefits of such economy are of less weighty
    import. It needs nothing more than the establishment of an efficient
    system of registration in steam vessels, to insure a large and rapid
    economy in the consumption of fuel, as this quality would then become
    the test of an engineer&#39;s proficiency, and would determine the
    measure of his fame. In the case of the Cornish engines, a saving of
    more than half the fuel was speedily effected by the introduction of
    the simple expedient of registration. In agricultural engines a like
    economy has speedily followed from a like arrangement; yet in both of
    these cases the benefits of a large saving are less eminent than they
    would be in the case of steam navigation; and it is to be hoped that
    this expedient of improvement will now be speedily adopted.</P>

    <H2 CLASS="chapter"><A NAME="ch10"></A>CHAPTER X.</H2>

    <H3>EXAMPLES OF ENGINES.</H3>

    <H4 CLASS="subhead"><A NAME="p01"></A>OSCILLATING PADDLE ENGINES.</H4>

    <P>618. <EM>Q.</EM>--Will you describe the structure of an oscillating
    engine as made by Messrs. Penn?</P>

    <P><EM>A.</EM>--To do this it will be expedient to take an engine of a
    given power, and then the sizes may be given as well as an account of
    the configuration of the parts: we may take for an example a pair of
    engines of 21-1/2 inches diameter of cylinder, and 22 inches stroke,
    rated by Messrs. Penn at 12 horses power each. The cylinders of this
    oscillating engine are placed beneath the cranks, and, as in all
    Messrs. Penn&#39;s smaller engines, the piston rod is connected to the
    crank pin by means of a brass cap, provided with a socket, by means of
    which it is cuttered to the piston rod. There is but one air pump,
    which is situated within the condenser between the cylinders, and it is
    wrought by means of a crank in the intermediate shaft--this crank being
    cut out of a solid piece of metal as in the formation of the cranked
    axles of locomotive engines. The steam enters the cylinder through the
    outer trunnions, or the trunnions adjacent to the ship&#39;s sides, and
    enters the condenser through the two midship trunnions--a short three
    ported valve being placed on the front of the cylinder to regulate the
    flow of steam to and from the cylinder in the proper manner. The weight
    of this valve on one side of the cylinder is balanced by a weight hung
    upon the other side of the cylinder; but in the most recent engines
    this weight is discarded, and two valves are used, which balance one
    another. The framing consists of an upper and lower frame of cast iron,
    bound together by eight malleable iron columns: upon the lower frame
    the pillow blocks rest which carry the cylinder trunnions, and the
    condenser and the bottom frame are cast in the same piece. The upper
    frame supports the paddle shaft pillow blocks; and pieces are bolted on
    in continuation of the upper frame to carry the paddle wheels, which
    are overhung from the journal.</P>

    <P>619. <EM>Q.</EM>--What are the dimensions and arrangement of the
    framing?</P>

    <P><EM>A.</EM>--The web, or base plate of the lower frame is 3/4 of an
    Inch thick, and a cooming is earned all round the cylinder, leaving an
    opening of sufficient size to permit the necessary oscillation. The
    cross section of the upper frame is that of a hollow beam 6 inches
    deep, and about 3-1/2 inches wide, with holes at the sides to take out
    the core; and the thickness of the metal is 13/16ths of an inch. Both
    the upper and the lower frame is cast in a single piece, with the
    exception of the continuations of the upper frame, which support the
    paddle wheels. An oval ring 3 inches wide is formed in the upper frame,
    of sufficient size to permit the working of the air pump crank; and
    from this ring feathers run to the ends of the cross portions of the
    frame which supports the intermediate shaft journals. The columns are
    1-1/2 inches in diameter; they are provided with collars at the lower
    ends, which rest upon bosses in the lower frame, and with collars at
    the upper ends for supporting the upper frame; but the upper collars of
    two of the corner columns are screwed on, so as to enable the columns
    to be drawn up when it is required to get the cylinders out. The cross
    section of the bottom frame is also of the form of a hollow beam, 7
    inches deep, except in the region of the condenser, where it is, of
    course, of a different form. The depth of the boss for the reception of
    the columns is a little more than 7 inches deep on the lower frame, and
    a little more than 6 inches deep on the upper frame; and the holes
    through them are so cored out, that the columns only bear at the upper
    and lower edges of the hole, instead of all through it--a formation by
    which the fitting of the columns is facilitated.</P>

    <P>620. <EM>Q.</EM>--What are the dimensions of the condenser?</P>

    <P><EM>A.</EM>--The condenser, which is cast upon the lower frame,
    consists of an oval vessel 22-1/2 inches wide, by 2 feet 4-1/4 inches
    long, and 1 foot 10-1/2 inches deep; it stands 9 inches above the upper
    face of the bottom frame, the rest projecting beneath it; and it is
    enlarged at the sides by being carried beneath the trunnions.</P>

    <P>621. <EM>Q.</EM>--What are the dimensions of the air pump?</P>

    <P><EM>A.</EM>--The air pump, which is set in the centre of the
    condenser, is 15-1/4 inches in diameter, and has a stroke of 11 inches.
    The foot valve is situated in the bottom of the air pump, and its seat
    consists of a disc of brass, in which there is a rectangular flap
    valve, opening upwards, but rounded on one side to the circle of the
    pump, and so balanced as to enable the valve to open with facility. The
    balance weight, which is formed of brass cast in the same piece as the
    valve itself, operates as a stop, by coming into contact with the disc
    which constitutes the bottom of the pump; the disc being recessed
    opposite to the stop to enable the valve to open sufficiently. This
    disc is bolted to the barrel of the pump by means of an internal
    flange, and before it can be removed the pump must be lifted out of its
    place. The air pump barrel is of brass to which is bolted a cast iron
    mouth piece, with a port for carrying the water to the hot well; within
    the hot well the delivery valve, which consists of a common flap valve,
    is situated. The mouth piece and the air pump barrel are made tight to
    the condenser, and to one another, by means of metallic joints
    carefully scraped to a true surface, so that a little white or red lead
    interposed makes an air tight joint. The air pump bucket is of brass,
    and the valve of the bucket is of the common pot lid or spindle kind.
    The injection water enters through a single cock in front of the
    condenser--the jet striking against the barrel of the air pump. The air
    pump rod is maintained in its vertical position by means of guides, the
    lower ends of which are bolted to the mouth of the pump, and the upper
    to the oval in the top frame, within which the air pump crank works;
    and the motion is communicated from this crank to the pump rod by means
    of a short connected rod. The lower frame is not set immediately below
    the top frame, but 2-1/2 inches behind it, and the air pump and
    condenser are 2-1/2 inches nearer one edge of the lower frame than the
    other.</P>

    <P>622. <EM>Q.</EM>--What are the dimensions of the cylinder?</P>

    <P><EM>A.</EM>--The thickness of the metal of the cylinder is 9/16ths
    of an inch; the depth of the belt of the cylinder is 9-1/2 inches, and
    its greatest projection from the cylinder is 2-1/2 inches. The distance
    from the lower edge of the belt to the bottom of the cylinder is 11-1/2
    inches, and from the upper edge of the belt to the top flange of the
    cylinder is 9 inches. The trunnions are 7-1/4 inches diameter in the
    bearings, and 3-1/2 inches in width; and the flanges to which the
    glands are attached for screwing in the trunnion packings are 1-1/2
    inch thick, and have 7/8ths of an inch of projection. The width of the
    packing space round the trunnions is 5/8ths of an inch, and the
    diameter of the pipe passing through the trunnion 4-5/8ths, which
    leaves 11/16ths for the thickness of the metal of the bearing. Above
    and below each trunnion a feather runs from the edge of the belt or
    bracket between 3 and 4 inches along the cylinder, for the sake of
    additional support; and in large engines the feather is continued
    through the interior of the belt, and cruciform feathers are added for
    the sake of greater stiffness. The projection of the outer face of the
    trunnion flange from the side of the cylinder is 6-1/2 inches; the
    thickness of the flange round the mouth of the cylinder is 3/4 of an
    inch, and its projection 1-3/8 inch; the height of the cylinder
    stuffing box above the cylinder cover is 4-1/8 inches, and its external
    diameter 4-3/8 inches--the diameter of the piston rod being 2-1/8
    inches. The thickness of the stuffing box flange is 1-1/8 inch.</P>

    <P>623. <EM>Q.</EM>--Will you describe the nature of the communication
    between the cylinder and condenser?</P>

    <P><EM>A.</EM>--The pipe leading to the condenser from the cylinder is
    made somewhat bell mouthed where it joins the condenser, and the gland
    for compressing the packing is made of a larger internal diameter in
    every part except at the point at which the pipe emerges from it, where
    it accurately fits the pipe so as to enable the gland to squeeze the
    packing. By this construction the gland may be drawn back without being
    jammed upon the enlarged part of the pipe; and the enlargement of the
    pipe toward the condenser prevents the air pump barrel from offering
    any impediment to the free egress of the steam. The gland is made
    altogether in four pieces: the ring which presses the packing is made
    distinct from the flange to which the bolts are attached which force
    the gland against the packing, and both ring and flange are made in two
    pieces, to enable them to be got over the pipe. The ring is half
    checked in the direction of its depth, and is introduced without any
    other support to keep the halves together, than what is afforded by the
    interior of the stuffing box; and the flange is half checked in the
    direction of its thickness, so that the bolts which press down the ring
    by passing through this half-checked part, also keep the segments of
    the flange together. The bottom of the trunnion packing space is
    contracted to the diameter of the eduction pipe, so as to prevent the
    packing from being squeezed into the jacket; but the eduction pipe does
    not fit quite tight into this contracted part, but, while in close
    contact on the lower side, has about 1/32nd of an inch of space between
    the top of the pipe and the cylinder, so as to permit the trunnions to
    wear to that extent without throwing a strain upon the pipe. The
    eduction pipe is attached to the condenser by a flange joint, and the
    bolt holes are all made somewhat oblong in the perpendicular direction,
    so as to permit the pipe to be slightly lowered, should such an
    operation be rendered necessary by the wear of the trunnion bearings;
    but in practice the wear of the trunnion bearings is found to be so
    small as to be almost inappreciable.</P>

    <P>624. <EM>Q.</EM>--Will you describe the valve and valve casing?</P>

    <P><EM>A.</EM>--The length of the valve casing is 16-1/2 inches, and
    its projection from the cylinder is 3-1/2 inches at the top, 4-1/4
    inches at the centre, and 2-1/2 inches at the bottom, so that the back
    of the valve casing is not made flat, but is formed in a curve. The
    width of the valve casing is 9 inches, but there is a portion of the
    depth of the belt 1-1/2 inch wider, to permit the steam to enter from
    the belt into the casing. The valve casing is attached to the cylinder
    by a metallic joint; the width of the flange of this joint is 1-1/4
    inch, the thickness of the flange on the casing 1/2 inch, and the
    thickness of the flange on the cylinder 5/8ths of an inch. The
    projection from the cylinder of the passage for carrying the steam
    upwards, and downwards, from the valve to the top and bottom of the
    cylinder, is 2-1/4 inches, and its width externally 8-5/8 inches. The
    valve is of the ordinary three ported description, and both cylinder
    and valve faces are of cast iron.</P>

    <P>625. <EM>Q.</EM>--What description of piston is used?</P>

    <P><EM>A.</EM>--The piston is packed with hemp, but the junk ring is
    made of malleable iron, as cast iron junk rings have been found liable
    to break: there are four plugs screwed into the cylinder cover, which,
    when removed, permit a box key to be introduced, to screw down the
    piston packing. The screws in the junk ring are each provided with a
    small ratchet, cut in a washer fixed upon the head, to prevent the
    screw from turning back; and the number of clicks given by these
    ratchets, in tightening up the bolts, enables the engineer to know when
    they have all been tightened equally. In more recent engines, and
    especially in those of large size, Messrs. Penn employ for the piston
    packing a single metallic ring with tongue piece and indented plate
    behind the joint; and this ring is packed behind with hemp squeezed by
    the junk ring as in ordinary hemp-packed pistons.</P>

    <P>626. <EM>Q.</EM>--Will you describe the construction of the cap for
    connecting the piston rod with the crank pin?</P>

    <P><EM>A.</EM>--The cap for attaching the piston rod to the crank pin,
    is formed altogether of brass, which brass serves to form the bearing
    of the crank pin. The external diameter of the socket by which this cap
    is attached to the piston rod is 3-5/16 inches. The diameter of the
    crank pin is 3 inches, and the length of the crank pin bearing 3-7/8
    inches. The thickness of the brass around the crank pin bearing is 1
    inch, and the upper portion of the brass is secured to the lower
    portion, by means of lugs, which are of such a depth that the
    perpendicular section through the centre of the bearing has a square
    outline measuring 7 inches in the horizontal direction, 3-7/8 inches
    from the centre of the pin to the level of the top of the lugs, and
    2-1/2 inches from the centre of the pin to the level of the bottom of
    the lugs. The width of the lugs is 2 inches, and the bolts passing
    through them are 1-1/4 inch in diameter. The bolts are tapped into the
    lower portion of the cap, and are fitted very accurately by scraping
    where they pass through the upper portion, so as to act as steady pins
    in preventing the cover of the crank pin bearing from being worked
    sideways by the alternate thrust on each side. The distance between the
    centres of the bolts is 5 inches, and in the centre of the cover, where
    the lugs, continued in the form of a web, meet one another, an oil cup
    1-5/8 inch in diameter, 1-1/8 inch high, and provided with an internal
    pipe, is cast upon the cover, to contain oil for the lubrication of the
    crank pin bearing. The depth of the cutter for attaching the cap to the
    piston rod is 1-1/4 inch and its thickness is 3/8ths of an inch.</P>

    <P>627. <EM>Q.</EM>--Will you describe the means by which the air pump
    rod is connected with the crank which works the air pump?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig50.png" WIDTH="417" HEIGHT="550" ALT=
    "Fig. 50. AIR PUMP CONNECTING ROD AND CROSS HEAD. Messrs. Penn."></P>

    <P><EM>A.</EM>--A similar cap to that of the piston rod attaches the
    air pump crank to the connecting rod by which the air pump rod is
    moved, but in this instance the diameter of the bearing is 5 inches,
    and the length of the bearing is about 3 inches. The air pump
    connecting rod and cross head are shown in perspective in fig. 50. The
    thickness of the brass encircling the bearing of the shaft is three
    fourths of an inch upon the edge, and 1-1/8 inch in the centre, the
    back being slightly rounded; the width of the lugs is 1-5/8 inch, and
    the depth of the lugs is 2 inches upon the upper brass, and 2 inches
    upon the lower brass, making a total depth of 4 inches. The diameter of
    the bolts passing through the lugs is 1 inch, and the bolts are tapped
    into the lower brass, and accurately fitted into the upper one, so as
    to act as steady pins, as in the previous instance. The lower eye of
    the connecting rod is forked, so as to admit the eye of the air pump
    rod; and the pin which connects the two together is prolonged into a
    cross head, as shown in fig. 50. The ends of this cross head move in
    guides. The forked end of the connecting rod is fixed upon the cross
    head by means of a feather, so that the cross head partakes of the
    motion of the connecting rod, and a cap, similar to that attached to
    the piston rod, is attached to the air pump rod, for connecting it with
    the cross head. The diameter of the air pump rod is 1-1/2 inch, the
    external diameter of the socket encircling the rod is 2-1/8 inches, and
    the depth of the socket 4-1/2 inches from the centre of the cross head.
    The depth of the cutter for attaching the socket to the rod is 1 inch,
    and its thickness 5/16 inch. The breadth of the lugs is 1-3/8 inch, the
    depth 1-1/4 inch, making a total depth of 2-1/2 inches; and the
    diameter of the bolts seven eighths of an inch. The diameter of the
    cross head at the centre is 2 inches, the thickness of each jaw around
    the bearing 1 inch, and the breadth of each 9/16 inch.</P>

    <P>628. <EM>Q.</EM>--What are the dimensions of the crank shaft and
    cranks?</P>

    <P><EM>A.</EM>--The diameter of the intermediate shaft journal is
    4-3/16 inches, and of the paddle shaft journal 4-3/8 inches; the length
    of the journal in each case is 5 inches. The diameter of the large eye
    of the crank is 7 inches, and the diameter of the hole through it is
    4-3/8 inches; the diameter of the small eye of the crank is 5-1/4
    inches, the diameter of the hole through it being 3 inches. The depth
    of the large eye is 4-1/4 inches, and of the small eye 3-3/4 inches;
    the breadth of the web is 4 inches at the shaft end, and 3 inches at
    the pin end, and the thickness of the web is 2-5/8 inches. The width of
    the notch forming the crank in the intermediate shaft for working the
    air pump is 3-1/2 inches, and the width of each of the arms of this
    crank is 3-15/16 inches. Both the outer and inner corners of the crank
    are chamfered away, until the square part of the crank meets the round
    of the shaft. The method of securing the cranks pins into the crank
    eyes of the intermediate shaft consists in the application of a nut to
    the end of each pin, where it passes through the eye, the projecting
    end of the pin being formed with a thread upon which the nut is
    screwed.</P>

    <P>629. <EM>Q.</EM>--Will you describe the eccentric and eccentric
    rod?</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig51.png" ALIGN="right" WIDTH="192"
    HEIGHT="550" ALT="Fig. 51. ECCENTRIC AND ROD. Messrs. Penn."></P>

    <P><EM>A.</EM>--The eccentric and eccentric rod are shown in fig. 51.
    The eccentric is put on the crank shaft in two halves, joined in the
    diameter of largest eccentricity by means of a single bolt passing
    through lugs on the central eye, and the back balance is made in a
    separate piece five eighths of an inch thick, and is attached by means
    of two bolts, which also help to bind the halves of the eccentric
    together. The eccentric strap is half an inch thick, and 1-1/4 inch
    broad, and the flanges of the eccentric, within which the strap works,
    are each three eighths of an inch thick. The eccentric rod is attached
    to the eccentric hoop by means of two bolts passing through lugs upon
    the rod, and tapped into a square boss upon the hoop; and pieces of
    iron, of a greater or less thickness, are interposed between the
    surfaces in setting the valve, to make the eccentric rod of the right
    length. The eccentric rod is kept in gear by the push of a small
    horizontal rod, attached to a vertical blade spring, and it is thrown
    out of gear by means of the ordinary disengaging apparatus, which acts
    in opposition to the spring, as, in cases where the eccentric rod is
    not vertical, it acts in opposition to the gravity of the rod.</P>

    <P>630. <EM>Q.</EM>--Will you explain in detail the construction of the
    valve gearing, or such parts of it as are peculiar to the oscillating
    engine?</P>

    <P><EM>A.</EM>--The eccentric rod is attached by a pin, 1 inch in
    diameter, to an open curved link or sector with a tail projecting
    upward and passing through an eye to guide the link in a vertical
    motion. The link is formed of iron case-hardened, and is 2-3/4 inches
    deep at the middle, and 2-3/8 inches deep at the ends, and 1 inch
    broad. The opening in the link, which extends nearly its entire length,
    is 1-5/16 inch broad; and into this opening a brass block 2 inches long
    is truly fitted, there being a hole through the block 3/4 inch
    diameter, for the reception of the pin of the valve shaft lever. The
    valve shaft is 1-3/4 inch diameter at the end next the link or segment,
    and diminishes regularly to the other end, but its cross section
    assumes the form of an octagon in its passage round the cylinder,
    measuring mid-way 1-1/4 inch deep, by about 3/4 inch thick, and the
    greatest depth of the finger for moving the valve is about 1 inch. The
    depth of the lever for moving the valve shaft is 2 inches at the broad,
    and 1-1/4 inch at the narrow end. The internal breadth of the mortice
    in which the valve finger moves is 5/16 inch, and its external depth is
    1-3/4 inch, which leaves three eighths of an inch as the thickness of
    metal round the hole; and the breadth, measuring in the direction of
    the hole, is 1-1/2 inch. The valve rod is three fourths of an inch in
    diameter, and the mortice is connected to the valve rod by a socket 1
    inch long, and 1-1/8 inch diameter, through which a small cutter
    passes. A continuation of the rod, eleven sixteenths of an inch
    diameter, passes upward from the mortice, and works through an eye,
    which serves the purpose of a guide. In addition to the guide afforded
    to the segment by the ascending tail, it is guided at the ends upon the
    columns of the framing by means of thin semicircular brasses, 4 inches
    deep, passing round the columns, and attached to the segment by two 3/8
    inch bolts at each end, passing through projecting feathers upon the
    brasses and segment, three eighths of an inch in thickness. The
    curvature of the segment is such as to correspond with the arc swept
    from the centre of the trunnion to the centre of the valve lever pin
    when the valve is at half stroke as a radius; and the operation of the
    segment is to prevent the valve from being affected by the oscillation
    of the cylinder, but the same action, would be obtained by the
    employment of a smaller eccentric with more lead. In some engines the
    segment is not formed in a single piece, but of two curved blades, with
    blocks interposed at the ends, which may be filed down a little, to
    enable the sides of the slot to be brought nearer, as the metal wears
    away.</P>

    <P>631. <EM>Q.</EM>--What kind of plummer blocks are used for the
    paddle shaft bearings?</P>

    <P><EM>A.</EM>--The paddle shaft plummer blocks are altogether of
    brass, and are formed in much the same manner as the cap of the piston
    rod, only that the sole is flat, as in ordinary plummer blocks, and is
    fitted between projecting lugs of the framing, to prevent side motion.
    In the bearings fitted on this plan, however, the upper brass will
    generally acquire a good deal of play after some amount of wear. The
    bolts are worked slack in the holes, though accurately fitted at first;
    and it appears expedient, therefore, either to make the bolts very
    large, and the sockets through which they pass very deep, or to let one
    brass fit into the other.</P>

    <P>632. <EM>Q.</EM>--How are the trunnion plummer blocks made?</P>

    <P><EM>A.</EM>--The trunnion plummer blocks are formed in the same
    manner as the crank shaft plummer blocks; the nuts are kept from
    turning back by means of a pinching screw passing through a stationary
    washer. It is not expedient to cast the trunnion plummer blocks upon
    the lower frame, as is sometimes done; for the cylinders, being pressed
    from the steam trunnions by the steam, and drawn in the direction of
    the condenser by the vacuum, have a continual tendency to approach one
    another; and as they wear slightly toward midships, there would be no
    power of readjustment unless the plummer blocks were movable. The
    flanges of the trunnions should always fit tight against the plummer
    block sides, but there should be a little play sideways at the necks of
    the trunnions, so that the cylinder may be enabled to expand when
    heated, without throwing an undue strain upon the trunnion
    supports.</P>

    <P>633. <EM>Q.</EM>--What kind of paddle wheel is supplied with these
    oscillating engines?</P>

    <P><EM>A.</EM>--The wheels are of the feathering kind, 9 feet 8 inches
    in diameter, measuring to the edges of the floats; and there are 10
    floats upon each wheel, measuring 4 feet 6 inches long each, and 18-1/2
    inches broad. There are two sets of arms to the wheel, which converge
    to a cast iron centre, formed like a short pipe with large flanges, to
    which the arms are affixed. The diameter of the shaft, where the centre
    is put on, is 4- 1/2 inches, the external diameter of the pipe is 8
    inches, and the diameter of the flanges is 20 inches, and their
    thickness 1-1/4 inch. The flanges are 12 inches asunder at the outer
    edge, and they partake of the converging direction of the arms. The
    arms are 2-1/4 inches broad and half an inch thick; the heads are made
    conical, and each is secured into a recess upon the side of the flange
    by means of three bolts. The ring which connects together the arms,
    runs round at a distance of 3 feet 6 inches from the centre, and the
    projecting ends of the arms are bent backward the length of the lever
    which moves the floats, and are made very wide and strong at the point
    where they cross the ring, to which they are attached by four rivets.
    The feathering action of the floats is accomplished by means of a pin
    fixed to the interior of the paddle box, set 3 inches in advance of the
    centre of the shaft, and in the same horizontal line. This pin is
    encircled by a cast iron collar, to which rods are attached 1-3/8 inch
    diameter in the centre, proceeding to the levers, 7 inches long, fixed
    on the back of the floats in the line of the outer arms. One of these
    rods, however, is formed of nearly the same dimensions as one of the
    arms of the wheel, and is called the driving arm, as it causes the cast
    iron collar to turn round with the revolution of the wheel, and this
    collar, by means of its attachments to the floats, accomplishes the
    feathering action. The eccentricity in this wheel is not sufficient to
    keep the floats in the vertical position, but in the position between
    the vertical and the radial. The diameter of the pins upon which the
    floats turn is 1-3/8 inch, and between the pins and paddle ring two
    stud rods are set between each of the projecting ends of the arms, so
    as to prevent the two sets of arms from being forced nearer or further
    apart; and thus prevent the ends of the arms from hindering the action
    of the floats, by being accidentally jammed upon the sides of the
    joints. Stays, crossing one another, proceed from the inner flange of
    the centre to the outer ring of the wheel, and from the outer flange of
    the centre to the inner ring of the wheel, with the view of obtaining
    greater stiffness. The floats are formed of plate iron, and the whole
    of the joints and joint pins are steeled, or formed of steel. For
    sea-going vessels the most approved practice is to make the joint pins
    of brass, and also to bush the eyes of the joints with brass; and the
    surface should be large to diminish wear.</P>

    <P>634. <EM>Q.</EM>--Can you give the dimensions of any other
    oscillating engines?</P>

    <P><EM>A.</EM>--In Messrs. Penn&#39;s 50 horse power oscillating
    engine, the diameter of the cylinder is 3 feet 4 inches, and the length
    of the stroke 3 feet. The thickness of the metal of the cylinder is 1
    inch, and the thickness of the cylinder bottom is 1-3/4 inch, crossed
    with feathers, to give it additional stiffness. The diameter of the
    trunnion bearings is 1 foot 2 inches, and the breadth of the trunnion
    bearings 5-1/2 inches. Messrs. Penn, in their larger engines, generally
    make the area of the steam trunnion less than that of the eduction
    trunnion, in the proportion of 32 to 37; and the diameter of the
    eduction trunnion is regulated by the internal diameter of the eduction
    pipe, which is about 1/5th of the diameter of the cylinder. But a
    somewhat larger proportion than this appears to be expedient: Messrs.
    Rennie make the area of their eduction pipes, in oscillating engines,
    1/22d of the area of the cylinder. In the oscillating engines of the
    Oberon, by Messrs. Rennie, the cylinder is 61 inches diameter, and
    1-1/2 inch thick above and below the belt, but in the wake of the belt
    it is 1-1/4 inch thick, which is also the thickness of metal of the
    belt itself. The internal depth of the belt is 2 feet 6 inches, and its
    internal breadth is 4 inches. The piston rod is 6-3/4 inches in
    diameter, and the total depth of the cylinder stuffing box is 2 feet 4
    inches, of which 18 inches consists of a brass bush--this depth of
    bearing being employed to prevent the stuffing box or cylinder from
    wearing oval.</P>

    <P>635. <EM>Q.</EM>--Can you give any other examples?</P>

    <P><EM>A.</EM>--The diameter of cylinder of the oscillating engines of
    the steamers Pottinger, Ripon, and Indus, by Miller &amp; Ravenhill, is
    76 inches, and the length of the stroke 7 feet. The thickness of the
    metal of the cylinder is 1-11/16 inch; diameter of the piston rod 8-3/4
    inches; total depth of cylinder stuffing box 3 feet; depth of bush in
    stuffing box 4 inches; the rest of the depth, with the exception of the
    space for packing, being occupied with a very deep gland, bushed with
    brass. The internal diameter of the steam pipe is 13 inches; diameter
    of steam trunnion journal 25 inches; diameter of eduction trunnion
    journal 25 inches; thickness of metal of trunnions 2-1/4 inches; length
    of trunnion bearings 11 inches; projection of cylinder jacket, 8
    inches; depth of packing space in trunnions, 10 inches; width of
    packing space in trunnions, or space round the pipes, 1-1/2 inch;
    diameter of crank pin 10-1/4 inches; length of bearing of crank pin
    15-1/2, inches. There are six boilers on the tubular plan in each of
    these vessels; the length of each boiler is 10 feet 6 inches, and the
    breadth 8 feet; and each boiler contains 62 tubes 3 inches in diameter,
    and 6 feet 6 inches long, and two furnaces 6 feet 4-1/2 inches long,
    and 3 feet 1-1/2 inch broad.</P>

    <P>636. <EM>Q.</EM>--Is it the invariable practice to make the piston
    rod cap of brass in the way you have described?</P>

    <P><EM>A.</EM>--In all oscillating engines of any considerable size,
    the cover of the connecting brass, which attaches the crank pin to the
    connecting rod, is formed of malleable iron; and the socket also, which
    is cuttered to the end of the piston rod, is of malleable iron, and is
    formed with a T head, through which bolts pass up through the brass, to
    keep the cover of the brass in its place.</P>

    <P>637. <EM>Q.</EM>--Is the piston of an oscillating engine made deeper
    than in common engines?</P>

    <P><EM>A.</EM>--It is expedient, in oscillating engines, to form the
    piston with a projecting rim round the edge above and below, and a
    corresponding recess in the cylinder cover and cylinder bottom, whereby
    the breadth of bearing of the solid part of the metal will be
    increased, and in many engines this is now done.</P>

    <P>638. <EM>Q.</EM>--Would any difficulty be experienced in keeping the
    trunnions tight in a high pressure oscillating engine?</P>

    <P><EM>A.</EM>--It is very doubtful whether the steam trunnions of a
    high pressure oscillating engine will continue long tight if the
    packing consists of hemp; and it appears preferable to introduce a
    brass ring, to embrace the pipe, cut spirally, with an overlap piece to
    cover the cut, and packed behind with hemp.</P>

    <P>639. <EM>Q.</EM>--How is the packing of the trunnions usually
    effected?</P>

    <P><EM>A.</EM>--The packing of the trunnions, after being plaited as
    hard as possible, and cut to the length to form one turn round the
    pipe, is dipped into boiling tallow, and is then compressed in a mould,
    consisting of two concentric cylinders, with a gland forced down into
    the annular space by three to six screws in the case of large
    diameters, and one central screw in the case of small diameters. Unless
    the trunnion packings be well compressed, they will be likely to leak
    air, and it is, therefore, necessary to pay particular attention to
    this condition. It is also very important that the trunnions be
    accurately fitted into their brasses by scraping, so that there may not
    be the smallest amount of play left upon them; for if any upward motion
    is permitted, it will be impossible to prevent the trunnion packings
    from leaking.</P>

    <H4 CLASS="subhead"><A NAME="p02"></A>DIRECT ACTING SCREW ENGINE.</H4>

    <P>640. <EM>Q.</EM>--Will you describe the configuration and
    construction of a direct acting screw engine?</P>

    <P><EM>A.</EM>--I will take as an example of this species of engine,
    the engine constructed by Messrs. John Bourne &amp; Co., for the screw
    steamer Alma, a vessel of 500 tons burden. This engine is a single
    steeple engine laid on its side, and in its general features it
    resembles the engines of the Amphion already described, only that there
    is one cylinder instead of two. The cylinder is of 42 inches diameter
    and 42 inches stroke, and the vessel has been propelled by this single
    engine at the rate of fourteen miles an hour.</P>

    <P>641. <EM>Q.</EM>--Is not a single engine liable to stick upon the
    centre so that it cannot be started or reversed with facility?</P>

    <P><EM>A.</EM>--A single engine is no doubt more liable to stick upon
    the centre than two engines, the cranks of which are set at right
    angles with one another; but numerous paddle vessels are plying
    successfully that are propelled by a single engine, and the screw
    offers still greater facility than paddles for such a mode of
    construction. In the screw engine referred to, as the cylinder is laid
    upon its side, there is no unbalanced weight to be lifted up every
    stroke, and the crank, whereby the screw shaft is turned round,
    consists of two discs with a heavy side intended to balance the
    momentum of the piston and its connections; but these counter-weights
    by their gravitation also prevent the connecting rod and crank from
    continuing in the same line when the engine is stopped, and in fact
    they place the crank in the most advantageous position for starting
    again when it has to be set on.</P>

    <P>642. <EM>Q.</EM>--Will you explain the general arrangement of the
    parts of this engine?</P>

    <P><EM>A.</EM>--The cylinder lies on its side near one side of the
    vessel, and from the end of the cylinder two piston rods extend to a
    cross head sliding athwartships, in guides, near the other side of the
    vessel. To this cross head the connecting rod is attached, and one end
    of it partakes of the motion of the cross head or piston, while the
    other end is free to follow the revolution of the crank on the screw
    shaft.</P>

    <P>643. <EM>Q.</EM>--What is the advantage of two discs entering into
    the composition of the crank instead of one?</P>

    <P><EM>A.</EM>--A double crank, such as two discs form with the crank
    pin, is a much steadier combination than would result if only one disc
    were employed with an over-hung pin. Then the friction on the neck of
    the shaft is made one half less by being divided between the two
    bearings, and the short prolongation of the shaft beyond the journal is
    convenient for the attachment of the eccentrics to work the valves.</P>

    <P>644. <EM>Q.</EM>--Will you enumerate some of the principal
    dimensions of this engine?</P>

    <P><EM>A.</EM>--The bottom frame, on which also the condenser is cast,
    forms the base of the engine: on one end of it the cylinder is set; on
    the other end are the guides for the cross head, and in the middle are
    the bearings for the crank shaft. The part where the cylinder stands is
    two feet high above the engine platform, and the elevation to the
    centre of the guides or the centre of the shaft is 10 inches higher
    than this. The metal both of the side frames and bottom flange is 1-1/4
    inch thick. The cylinder has flanges cast on its sides, upon which it
    rests on the bottom frame, and it is sunk between the sides of the
    frame so as to bring the centre of the cylinder in the same plane as
    the centre of the screw shaft. The opening left at the guides for the
    reception of the guide blocks is 6 inches deep, and the breadth of the
    bearing surface is 11 inches. The cover of the guides is 8 inches deep
    at the middle, and about half the depth at the ends, and holes are
    cored through the central web for two oil cups on each guide. The brass
    for each of the crank shaft bearings is cut into four pieces so that it
    may be tightened in the up and down direction by the bolts, which
    secure the plummer block cap, and tightened in the athwartship
    direction, which is the direction of the strain, by screwing up a
    wedge-formed plate against the side of the brass, a parallel plate
    being applied to the other side of the brass, which may be withdrawn to
    get out the wedge piece when the shaft requires to be lifted out of its
    place. The air pump is bolted to one side of the bottom frame, and a
    passage is cast on it conducting from the condenser to the air pump. In
    this passage the inlet and outlet valves at each end of the air pump
    are situated, and appropriate doors are formed above them to make them
    easily accessible. The outlet passage leading from the air pump
    communicates with the waste water pipe, through which the water
    expelled by the air pump is discharged overboard.</P>

    <P>645. <EM>Q.</EM>--Is the cylinder of the usual strength and
    configuration?</P>

    <P><EM>A.</EM>--The cylinder is formed of cast iron in the usual way,
    and is 1-1/8 inch thick in the barrel. The ends are of the same
    thickness, but are each stiffened with six strong feathers. The piston
    is cast open. The bottom of it is 5/8ths of an inch thick, and it is
    stiffened by six feathers 3/4 of an inch thick; but the feather
    connecting the piston rod eyes is 1-1/4 inch thick, and the metal round
    the eyes is 2 inches thick. The piston is closed by a disc or cover
    5/8ths of an inch thick, secured by 15 bolts, and this cover answers
    also the purpose of a junk ring. The piston packing consists of a
    single cast iron ring 3-1/2 inches broad, and 1/2 inch thick, packed
    behind with hemp. This ring is formed with a tongue piece, with an
    indented plate behind the cut; and the cut is oblique to prevent a
    ridge forming in the cylinder. The total thickness of the piston is
    5-1/2 inches. The piston rods are formed with conical ends for fitting
    into the piston, but are coned the reverse way as in locomotives, and
    are secured in the piston by nuts on the ends of the rods, these nuts
    being provided with ratchets to prevent them from unscrewing
    accidentally.</P>

    <P>646. <EM>Q.</EM>--What species of slide valve is employed?</P>

    <P><EM>A.</EM>--The ordinary three ported valve, and it is set on the
    top of the cylinder. The cylinder ports are 4-1/2 inches broad by 24
    inches long; and to relieve the valve from the great friction due to
    the pressure on so large a surface, a balance piston is placed over the
    back of the valve, to which it is connected by a strong link; and the
    upward pressure on this piston being nearly the same as the downward
    pressure on the valve, it follows that the friction is extinguished,
    and the valve can be moved with great case with one hand. The balance
    piston is 21 inches in diameter. In the original construction of this
    balance piston two faults were committed. The passage communicating
    between the condenser and the top of the balance piston was too small,
    and the pins at the ends of the link connecting the valve and balance
    piston were formed with an inadequate amount of bearing surface. It
    followed from this misproportion that the balance piston, being
    adjusted to take off nearly the whole of the pressure, lifted the valve
    off the face at the beginning of each stroke. For the escape of the
    steam into the eduction passage momentarily impaired the vacuum
    subsisting there, and owing to the smallness of the passage leading to
    the space above the balance piston, the vacuum subsisting in that space
    could not be impaired with equal rapidity. The balance piston,
    therefore, rose by the upward pressure upon it momentarily
    predominating over the downward pressure on the valve; but this fault
    was corrected by enlarging the communicating passage between the top of
    the balance piston and the eduction pipe. The smallness of the pins at
    the ends of the link connecting the valve and balance piston, caused
    the surfaces to cut into one another, and to wear very rapidly, and the
    pins and eyes in this situation should be large in diameter, and as
    long as they can be got, as they are not so easily lubricated as the
    other bearings about the engine, and are moreover kept at a high
    temperature by the steam. The balance piston is packed in the same way
    as the main piston of the engine. Its cylinder, which is only a few
    inches in length, is set on the top of the valve casing, and a trunk
    projects upwards from its centre to enable the connecting link to rise
    up in it to attain the necessary length.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig52.png" ALIGN="left" WIDTH="106"
    HEIGHT="500" ALT=
    "Fig 52. CONNECTING ROD. Messrs. Bourne &amp; Co."></P>

    <P>647. <EM>Q.</EM>--What is the diameter of the piston rods and
    connecting rod?</P>

    <P><EM>A.</EM>--The piston rods, which are two in number, are 3 inches
    diameter, and 12 feet 10 inches long over all. They were, however,
    found to be rather small, and have since been made half an inch
    thicker. The connecting rod consists of two rods, which are
    prolongations of the bolts that connect the sides of the brass bushes
    which encircle the crank pin and cross head. The connecting rod is
    shown in perspective in fig. 52. The rods composing it are each 2-3/4
    inches in diameter.</P>

    <P>648. <EM>Q.</EM>--Will you describe the configuration of the cross
    head.</P>

    <P><EM>A.</EM>--The cross head, exhibited in fig. 53, is a round piece
    of iron like a short shaft, with two unequal arms keyed upon it, the
    longer of which <EM>b</EM> works the air pump, and the shorter
    <EM>c</EM> works the feed pump. The piston rods enter these arms at
    <EM>a A.</EM> The cross head is 8 inches diameter where it is embraced
    by the connecting rod at <EM>e</EM>, and 7 inches diameter where the
    air pump and feed pump arms are fixed on. The ends of the cross head
    <EM>d d</EM>, for a length of 12 inches, are reduced to 3 inches
    diameter where they fit into round holes in the centre of the guide
    blocks. Those blocks are of cast iron 6 inches deep, 11 inches wide,
    and 14 inches long, and they are formed with flanges 1 inch thick on
    the inner sides of the blocks. The projection of the air pump lever
    from the centre of the cross head is 1 foot 9 inches, and it is bent
    5-3/4 inches to one side to enable it to engage the air pump rod. The
    eye of this arm is 6 inches broad and about 2 inches thick. At the part
    where one of the piston rods passes through it, the arm is 8 inches
    deep and 6 inches wide; but the width thereafter narrows to 3 inches,
    and finally to 2 inches; and the depth of the web of the arm reduces
    from 8 inches at the piston rod, to 4 inches at the eye, which receives
    the end of the air pump rod. The feed pump arm is only 3 inches thick,
    and has 9 inches of projection from the centre of the cross head; but
    the eye attached to it on the opposite side of the cross head for the
    reception of the other piston rod is of the same length as that part of
    the air pump arm which one of the piston rods passes through. The
    piston rods have strong nuts on each side of each of these arms to
    attach them to the arms, and also to enable the length of the piston
    rods to be suitably adjusted, to leave equal clearance between the
    piston and each end of the cylinder at the termination of the
    stroke.</P>

    <P>649. <EM>Q.</EM>--Will you recapitulate the main particulars of the
    air pump?</P>

    <P><EM>A.</EM>--The air pump is made of brass 12-1/2 inches diameter
    and 42 inches stroke, and the metal of the barrel is 9/16ths of an inch
    thick. The air pump bucket is a solid piston of brass, 6-1/2 inches
    deep at the edge, and 7 inches deep at the eye; and in the edge three
    grooves are turned to hold water which answers the purpose of packing.
    The inlet and outlet valves of the air pump consist of brass plates 1/2
    inch with strong feathers across them, and in each plate there are six
    grated perforations covered by india rubber discs 7 inches in diameter.
    These six perforations afford collectively an area for the passage of
    the water equal to the area of the pump. The air pump rod is of brass,
    2-1/2 inches diameter.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig53.png" WIDTH="700" HEIGHT="452" ALT=
    "Fig. 53. CROSS HEAD AND PUMP ARMS. Messrs. Bourne &amp; Co."></P>

    <P>650. <EM>Q.</EM>--What are the constructive peculiarities of the
    discs and crank pin?</P>

    <P><EM>A.</EM>--The discs, which are 64 inches diameter, are formed of
    cast iron, and are 2-1/2 inches thick in the body, and 5 inches broad
    at the rim. The crank shaft is 8-1/2 inches diameter, and the central
    boss of the disc which receives the shaft measures 10 inches through
    the eye, and the metal of the eye is 3 inches thick. In the part of the
    disc opposite to the crank pin, the web is thickened to 10 inches for
    nearly the whole semicircle, with the view of making that side of the
    disc heavier than the other side; and when the engine is stopped, the
    gravitation of this heavy side raises the crank pin to the highest
    point it can attain, whereby it is placed in mid stroke, and cannot
    rest with the piston rods and connecting rod in a horizontal line. The
    crank pin is 8-1/2 inches diameter, and the length of the bearing or
    rubbing part of it is 16 inches. It is secured at the ends to the discs
    by flanges 18 inches diameter, and 2 inches thick. These flanges are
    indented into thickened parts of the discs, and are each attached to
    its corresponding disc by six bolts 2 inches diameter, countersunk in
    the back of the disc, and tapped into the malleable iron flange.
    Besides this attachment, each end of the pin, reduced to 4-1/2 inches
    diameter, passes through a hole in its corresponding disc, and the ends
    of the pin are then riveted over. The crank pin is perforated through
    the centre by a small hole about 3/4 of an inch in diameter, and three
    perforations proceed from this central hole to the surface of the pin.
    Each crank shaft bearing is similarly perforated, and pipes are cast in
    the discs connecting these perforations together. The result of this
    arrangement is, that a large part of the oil or water fed into the
    bearings of the shaft is driven by the centrifugal action of the discs
    to the surface of the crank pin, and in this way the crank pin may be
    oiled or cooled with water in a very effectual manner. To intercept the
    water or oil which the discs thus drive out by their centrifugal
    action, a light paddle box or splash board of thin sheet brass is made
    to cover the upper part of each of the discs, and an oil cup with
    depending wick is supported by the tops of these paddle boxes, which
    wick is touched at each revolution of the crank by a bridge standing in
    the middle of an oil cup attached to the crank pin. The oil is wiped
    from the wick by the projecting bridge at each revolution, and subsides
    into the cup from whence it proceeds to lubricate the crank pin
    bearing. This is the expedient commonly employed to oil the crank pins
    of direct acting engines; but in the engine now described, there are
    over and above this expedient, the communicating passages from the
    shaft bearings to the surface of the pin, by which means any amount of
    cooling or lubrication can be administered to the crank pin bearing,
    without the necessity of stopping or slowing the engine.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig54.png" WIDTH="603" HEIGHT="550" ALT=
    "Fig. 54. DOUBLE DISC CRANK. Messrs. Bourne &amp; Co."></P>

    <P>651. <EM>Q.</EM>--What is the diameter of the screw shaft?</P>

    <P><EM>A.</EM>--The screw shaft is 7-1/2 inches diameter, but the
    bearings on each side of the disc are 8-1/2 inches diameter, and 16
    inches long. Between the side of the disc and the side of the
    contiguous bearings there is a short neck extending 4-3/4 inches in the
    length of the shaft, and hollowed out somewhat to permit the passage of
    the piston rod; for one piston rod passes immediately above the shaft
    on the one side of the discs, and the other piston rod passes
    immediately below the shaft on the other side of the discs. A short
    piece of one piston rod is shown in fig. 54.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig55.png" WIDTH="384" HEIGHT="500" ALT=
    "Fig. 55. THRUST BEARING. Messers. Bourne &amp; Co."></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig56.png" WIDTH="431" HEIGHT="500" ALT=
    "Fig. 56. COUPLING CRANKS. Messers. Bourne &amp; Co."></P>

    <P>652. <EM>Q.</EM>--How is the thrust of the screw shaft received?</P>

    <P><EM>A.</EM>--The thrust of the screw shaft is received upon 7
    collars, each 1 inch thick, and with 1 inch of projection above the
    shaft. The plummer block for receiving the thrust of the shaft is shown
    in fig. 55, and the coupling to enable the screw propeller to be
    disconnected from the engine, so that it may revolve freely when the
    vessel is under sail, is shown in fig. 56. When it is required to
    disengage the propeller from the engine, the pins passing through the
    opposite eyes shown fig. 56, are withdrawn by means of screws provided
    for that purpose, and the propeller and the engine are thenceforth
    independent of one another.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig57.png" ALIGN="left" WIDTH="227"
    HEIGHT="500" ALT="Fig. 57. LINK MOTION. Messrs. Bourne &amp; Co."></P>

    <P>653. <EM>Q.</EM>--Will you describe the arrangement of the valve
    gearing?</P>

    <P><EM>A.</EM>--The end of the screw shaft, after emerging from the
    bearing beside the disc, is reduced to a diameter of 4 inches, and is
    prolonged for 4-1/2 inches to give attachment to the cam or curved
    plate which gives motion to the expansion valve. This plate is 3-1/2
    inches thick, and a stud 3-1/2 inches diameter is fixed in the plate at
    a distance of 5 inches from the centre of the shaft. To this stud an
    arm is attached which extends to a distance of 2 inches from the centre
    of the shaft in the opposite direction, and the end of this arm carries
    a pin of 2-1/2 inches diameter. From the pin most remote from the
    centre of the shaft, a rod 2-1/2 inches broad and 1 inch thick extends
    to the upper end of the link of the link motion; and from the pin least
    remote from the centre of the shaft, a similar rod extends to the lower
    end of the link of the link motion. This link, which is represented in
    fig. 57, is 2-1/4 inches broad, 1 inch thick, and is capable of being
    raised or lowered 25 inches in all. In the open part of the link is a
    brass block, which, by raising or lowering the link, takes either the
    position in which it is represented at the centre of the link, or a
    position at either end of it. Through the hole in the brass block a pin
    passes to attach the brass to the end of a lever fixed on the valve
    shaft; so that whatever motion is imparted to the brass block is
    communicated to the valve through the medium of this lever. If the
    brass block be set in the middle of the link, no motion is communicated
    to it, and the valve being consequently kept stationary and covering
    both ports, the engine stops. If the link be lowered until the brass
    block comes to the upper end of the link, the valve receives the motion
    of the eccentric for going ahead, and the engine moves ahead; whereas
    if the link be raised until the brass block comes to the lower end of
    the link, the valve receives the motion of the backing eccentric, and
    the engine moves astern. Instead of eccentrics, however, pins at the
    end of the shaft are employed in this engine, the arrangement partaking
    of the nature of a double crank; but the backing pin has less throw
    than the going ahead pin, whereby the efficient length of the link for
    going ahead is increased; and the operation of backing, which does not
    require to be performed at the highest rate of speed, is sufficiently
    accommodated by about half the throw being given to the valve that is
    given in going ahead. A valve shaft extends across the end of the
    cylinder with two levers standing up, which engage horizontal side rods
    extending from a small cross head on the end of the valve rod. A lever
    extends downwards from the end of the valve shaft, which is connected
    by a pin to the brass block within the link; and the link is moved up
    or down by the starting handle, which, by means of a spring bolt
    shooting into a quadrant, holds the starting handle at any position in
    which it may be set.</P>

    <P>654. <EM>Q.</EM>--What is the diameter and pitch of the screw
    propeller?</P>

    <P><EM>A.</EM>--The diameter is 7 feet and the pitch 14 feet. The
    propeller is Holm&#39;s conchoidal propeller. Its diameter is smaller
    than is advisable, being limited by the draught of water of the vessel;
    and the vessel was required to have a small draught of water to go over
    a bar. This engine makes, under favorable circumstances, 100 strokes
    per minute. The speed of piston with this number of strokes is 700 feet
    per minute, and the engine works steadily at this speed, the shock and
    tremor arising from the arrested momentum of the moving parts being
    taken away by the counterbalance applied at the discs.</P>

    <H4 CLASS="subhead"><A NAME="p03"></A>LOCOMOTIVE ENGINE.</H4>

    <P>655. <EM>Q.</EM>--Will you describe the principal features of a
    modern locomotive engine?</P>

    <P><EM>A.</EM>--I will take for this purpose the
    locomotive Snake, constructed by John V. Gooch for the London and South
    Western Railway, as an example of a modern locomotive of good
    construction, adapted for the narrow gauge. The length of the wheel
    base of this engine is 12 feet 8-1/2 inches. There are two cylinders,
    each 14&frac14; inches diameter and 21 inches stroke. The total weight
    of the engine is 19 tons; and this weight is so distributed on the
    wheels as to throw 8 tons on the leading wheels, 6 tons on the driving
    wheels, and 5 tons on the hind wheels. The engine is made with outside
    cylinders, and the cylinders are raised somewhat out of the horizontal
    line to enable them better to clear the leading wheels.</P>

    <P>656. <EM>Q.</EM>--What are the dimensions of the boiler?</P>

    <P><EM>A.</EM>--The interior of the fire box is 3 feet 7-1/4 inches
    wide by 3 feet 5-1/2 inches long, measuring in the direction of the
    rails. The area of the fire grate is consequently 12.4 square feet. The
    bars are somewhat lower on the side next the fire door than at the side
    next the tubes, and the mean height of the crown of the fire box above
    the bars is 3 feet 10 inches. The top edge of the fire door is about 7
    inches lower than the crown of the fire box. The fire box is divided
    transversely by a corrugated feather or bridge of plate iron,
    containing water, about 3-1/2 inches wide, and of about one-third of
    the height of the fire box in the centre of the feather, and about
    two-thirds the height of the fire box at the sides where it joins the
    sides of the fire box. The internal shell of the fire box tapers
    somewhat upwards to facilitate the disengagement of the steam. It is
    about 2 inches narrower and shorter at the top than at the bottom; the
    water space between the external and internal shell of the fire box
    being 2 inches at the bottom and 3 inches at the top.</P>

    <P>657. <EM>Q.</EM>--Of what material is the fire box composed?</P>

    <P><EM>A.</EM>--The external shell of the fire box is formed of iron
    plates 3/8ths of an inch thick, and the internal shell is formed of
    copper plates 1/4 inch thick, but the tube plate is &frac34; inch
    thick. The fire grate is rectangular, and the internal and external
    shells are tied together by iron stay bolts 3/4 inch diameter, and
    pitched about 4 inches apart. The roof of the fire box is stiffened by
    six strong bars extending from side to side of the fire box like beams,
    and the top of the fire box is secured to these bars, so that it cannot
    be forced down without breaking or bending them.</P>

    <P>658. <EM>Q.</EM>--What are the dimensions of the barrel of the
    boiler?</P>

    <P><EM>A.</EM>--The barrel of the boiler is 3 feet 7-1/2 inches in
    diameter, and 10 feet long. It is formed of iron plates 3/8ths of an
    inch thick, riveted together. It is furnished with 181 brass tubes
    1-7/8 inch diameter and 10 feet long, secured at the ends by ferules.
    The tube plate at the smoke box end is 5/8ths of an inch thick, and the
    tube plates above the tubes are tied together by eight iron rods 7/8ths
    of an inch thick, extending from end to end of the boiler. The metal of
    the tubes is somewhat thicker at the end next the fire, being 13 wire
    gauge at fire box end, and 14 wire gauge at smoke box end. The rivets
    of the boiler are 3/4 inch diameter and 1-1/2 inch pitch. The plating
    of the ash pan is 5/16ths of an inch thick, and the plating of the
    smoke box is 3/16ths of an inch thick.</P>

    <P>659. <EM>Q.</EM>--Will you describe the structure of the framework
    on which the boiler and its attachments rest, and in which the wheels
    are set?</P>

    <P><EM>A.</EM>--The framework or framing consists of a rectangular
    structure of plate iron circumscribing the boiler, with projecting lugs
    or arms for the reception of the axles of the wheels. In this engine
    the sides of the rectangle are double, or, as far as regards the sides,
    there are virtually two framings, one for the reception of the driving
    axles, and the other for the reception of the axles not connected with
    the engine. The whole of the parts of the outer and inner framings are
    connected together by knees at the corners, and the double sides are
    elsewhere connected by intervening brackets and stays, so as to
    constitute the whole into one rigid structure. The whole of the plating
    of the inside frame is 3/4 inch thick and 9 inches deep. The plating of
    the outside frame is of the same thickness and depth at the fore part,
    until it reaches abaft the position of the cylinders and guides, where
    it reduces to 1/2 inch thick. The axle guard of the leading wheels is
    formed of 3/4 plate bolted to the frame with angle iron guides. The
    axle guards of the trailing wheels are formed of two 1/2 inch plates,
    with cast iron blocks between them to serve as guides. The ends of the
    rectangular frame are formed of plates 3/4 thick, and at the front end
    there is a buffer beam of oak 4-1/2 inches thick and 15 inches deep.
    The draw bolt is 2 inches diameter. There are two strong stays on each
    side, joining the barrel of the boiler to the inside framing, and one
    angle iron on each side joining the bottom of the smoke box to the
    inside framing.</P>

    <P>660. <EM>Q.</EM>--Of what construction are the wheels?</P>

    <P><EM>A.</EM>--The wheels and axles are of wrought iron, and the tires
    of the wheels are of steel. The driving wheels are 6 feet 6-1/2 inches
    in diameter, and the diameter of crank pin is 3-1/2 inches. The
    diameter of the smaller wheels is 48-1/2 inches. The axle boxes are of
    cast iron with bushes of Fenton&#39;s metal, and the leading axle has
    four bearings. The springs are formed of steel plates, 3 feet long, 4
    inches broad, and 1\2 inch thick. The axle of the driving wheel has two
    eccentrics, forged solid upon it, for working the pumps.</P>

    <P>661. <EM>Q.</EM>--Will you specify the dimensions of the principal
    parts of the engine?</P>

    <P><EM>A.</EM>--Each of the cylinders which is 14-1/4 inches diameter,
    has the valve casing cast upon it. The steam ports are 13 inches long
    and 1-5/8 inches broad, and the exhaust port is 2-1/2 inches broad. The
    travel of the valve is 4-1/8 inches, the lap 1 inch, and the lead 1/4
    inch. The piston is 4 inches thick: its body is formed of brass with a
    cover of cast iron, and between the body and the cover two flanges,
    forged on the piston rod, are introduced to communicate the push and
    pull of the piston to the rod. The piston rod is of iron, 2-1/2 inches
    diameter. The guide bars for guiding the top of the piston rod are of
    steel, 4 inches broad, fixed to rib iron bearers, with hard wood 1/4 of
    an inch thick, interposed. The connecting rod is 6 feet long between
    the centres, and is fitted with bushes of white metal. The eccentrics
    are formed of wrought iron, and have 4-1/8 inches of throw. The link of
    the link motion is formed of wrought iron. It is hung by a link from a
    pin attached to the framing; and instead of being susceptible of upward
    and downward motion, as in the case of the link represented in fig. 57
    a rod connecting the valve rod with the movable block in the link, is
    susceptible of this motion, whereby the same result is arrived at as if
    the link were moved and the block was stationary. One or the other
    expedient is preferable, according to the general nature of the
    arrangements adopted. The slide valve is of brass, and the regulator
    consists of two brass slide valves worked over ports in a chest in the
    steam pipe, set in the smoke box. The steam pipe is of brass, No. 14.
    wire gauge, perforated within the boiler barrel with holes 1/12th of an
    inch in diameter along its upper side. The blast pipe, which is of
    copper, has an orifice of 4-1/4 inches diameter. There is a damper,
    formed like a Venetian blind, with the plates running athwartships at
    the end of the tubes.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig58.png" ALIGN="right" WIDTH="112"
    HEIGHT="550" ALT="Fig. 58. SAFETY VALVE. Gooch."></P>

    <P>662. <EM>Q.</EM>--Of what construction is the safety valve?</P>

    <P><EM>A.</EM>--There are two safety valves, consisting of pistons
    1-3/16 inch in diameter, and which are kept down by spiral springs
    placed immediately over them. A section of this valve is given in fig.
    58.</P>

    <P>663. <EM>Q.</EM>--What are the dimensions of the feed pumps?</P>

    <P><EM>A.</EM>--The feed pumps are of brass, with plungers 4 inches
    diameter and 3-1/4 inches stroke. The feed pipe is of copper, 2 inches
    diameter. A good deal of trouble has been experienced in locomotives
    from the defective action of the feed pump, partly caused by the
    leakage of steam into the pumps, which prevented the water from
    entering them, and partly from the return of a large part of the water
    through the valves at the return stroke of the pump, in consequence of
    the valve lifting too high. The pet cock--a small cock communicating
    with the interior of the pump--will allow any steam to escape which
    gains admission, and the air which enters by the cock cools down the
    barrel of the pump, so that in a short time it will be in a condition
    to draw. The most ordinary species of valve in the feed pumps of
    locomotives, is the ball valve.</P>

    <P>Notwithstanding the excellent performance of the best examples of
    locomotive engines, it is quite certain that there is still much room
    for improvement; and indeed various sources of economy are at present
    visible, which, if properly developed, would materially reduce the
    expense of the locomotive power. In all engines the great source of
    expense is the fuel; and although the consumption of fuel has been
    greatly reduced within the last ten or fifteen years, it is capable of
    being still further reduced by certain easy expedients of improvement,
    which therefore it is important should be universally applied. One of
    these expedients consists in heating the feed water by the waste steam;
    and the feed water should in every case be sent into the boiler
    <EM>boiling hot</EM>, instead of being quite cold, as is at present
    generally the case. The ports of the cylinders should be as large as
    possible; the expansion of the steam should be carried to a greater
    extent; and in the case of engines with outside cylinders, the waste
    steam should circulate entirely round the cylinders before escaping by
    the blast pipe. The escape of heat from the boiler should be more
    carefully prevented; and the engine should be balanced by weights on
    the wheels to obviate a waste of power by yawing on the rails. The most
    important expedient of all, however, lies in the establishment of a
    system of registering the performance of all new engines, in order that
    competition may stimulate the different constructors to the attainment
    of the utmost possible economy; and under the stimulus of comparison
    and notoriety, a large measure of improvement would speedily ensue. The
    benefits consequent on public competition are abundantly illustrated by
    the rapid diminution of the consumption of fuel in the case of
    agricultural engines, when this stimulus was presented.</P>

    <H2 CLASS="chapter"><A NAME="ch11"></A>CHAPTER XI</H2>

    <H3>OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF
    THE STEAM ENGINE.</H3>

    <P>In the English edition of this work, the first part of this chapter
    is devoted to examples of Portable and fixed Agricultural engines, of
    different makers and styles of workmanship, but not in sufficient
    detail, nor illustrated on large enough scale to be of practical value
    as models, forming rather in fact an illustrated catalogue of the
    manufacturer, than a study for the mechanic. On this account, they have
    been entirely omitted, and their place supplied by a few illustrations
    from American workmanship, not only of Steam Engines, of various forms
    and applications, but also of various machines, or appliances,
    connected with the working of engines, as for the determination, or
    regulation of pressure, of the boilers; for the supply or feed of the
    boilers, the regulation of the speed of the engine, and the like.</P>

    <P>The Gauges used in this country to show the pressures of steam in
    boilers are of various constructions, but perhaps the most common is
    the Bourdon, or, as it is known here, the Ashcroft gauge, from the
    party introducing it, and holding the patent. Fig. 59 represents its
    interior construction. It consists of a thin metallic tube, <EM>a</EM>,
    bent into nearly a complete circle closed at one end, the steam being
    introduced at the other, at <EM>b</EM>. The effect of the pressure of
    the steam on the interior of the tube is to expand the circle, more or
    less according to the pressure, the elasticity of the metal returning
    the circle to its original position, when the pressure is removed. The
    free or closed end of the tube is connected by a link <EM>c</EM> with a
    lever <EM>d</EM>, at the opposite end of which is segmental gear, in
    gear with a pinion, on which is a hand, which marks the pressure on a
    dial. The dial and hand are not shown on the cut, but are on the
    exterior case removed to show the construction.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig59.png" WIDTH="511" HEIGHT="550" ALT=
    "Fig. 59."></P>

    <P>Fig. 60 is an elevation of a boiler with Clark&#39;s Patent Steam
    and Fire Regulator attached, for the control of the draft of the
    chimney by the pressure of steam in the boiler. It consists of a
    chamber, <EM>a</EM>, with a flexible diaphragm or cover on top, in
    communication with the boiler. On this diaphragm rests a plunger or
    piston, which is held down like a safety valve, by a lever and weight,
    <EM>b</EM>. The end of the lever is connected with a balanced damper,
    <EM>c</EM>, in the chimney. The weight, <EM>b</EM>, is placed at any
    required position on the lever, and when the pressure of steam in the
    boiler, exerted on the diaphragm, becomes sufficient to raise the
    weight, the lever rises, and the damper begins to close, and to check
    the draft in the chimney. When properly adjusted, the machine works on
    a variation of from, one to two pounds between the extremes of motion.
    When the dampers are very large, say 3 feet or over, they should be set
    on rollers, like common grindstone rollers; the regulator should be
    attached directly to the damper, the length of the pipe connecting the
    regulator with the boiler being of no account.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig60.png" WIDTH="750" HEIGHT="435" ALT=
    "Fig. 60."></P>

    <P>Porter&#39;s Patent Governor, fig. 61, is a modification of the
    ordinary centrifugal governor. Very small balls are employed, from
    2-1/4 to 2-5/8 inches in diameter. These swing from a single joint at
    the axis of the spindle, which is the most sensitive arrangement, and
    make from 300 to 350 revolutions per minute, at which speed their
    centrifugal force lifts the counterpoise. The lower arms are jointed to
    the upper ones at the centres of the balls, and connect with the slide
    by joints about two inches apart. The counterpoise may be attached to
    the slide in any manner; for the sake of elegance, it is put in the
    form of a vase rising between the arms, its stem forming the slide. The
    vase is hollow and filled with lead, and weighs from 60 lbs. to 175
    lbs. It moves freely on the spindle, through nearly twice the vertical
    distances traversed by the balls, and is capable of rising from 2-1/2
    to 3 inches, before its rim will touch the arms. It is represented in
    the figure as lifted through about one half of its range of action.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig61.png" WIDTH="294" HEIGHT="550" ALT=
    "Fig. 61."></P>

    <P>The standard is bored out of the solid, forming a long and perfect
    bearing for the spindle; the arms and balls are of gun metal, the joint
    pins of steel; every part of the governor is finished bright, except
    the bracket carrying the lever, and the square base of the standard,
    which are painted. The pulley is from 3 to 10 inches in diameter, and
    makes in the larger sizes about 125 revolutions, and in the smaller 230
    revolutions per minute; the higher speed of the governor being got up
    by gearing.</P>

    <P>Mr. Porter warrants the following action in this governor, operating
    any regulating valve or cut-off which is in reasonably good order. The
    engine should be run with the stop-valve wide open, and, except the
    usual oiling, will require no attention from the engineer, under any
    circumstances, after it is started, until it is to be stopped. No
    increase in the pressure of steam will affect its motion perceptibly.
    The extreme possible variation in the speed, between that at which the
    regulating valve will be held wide open, and that at which it will be
    closed, is from 3 to 5 per cent., being least in the largest governors.
    This is less than 1/6 of the variation required by the average of
    ordinary governors, and is with difficulty detected by the senses. The
    entire load which the engine is capable of driving may be thrown on or
    off at once, and one watching the revolutions cannot tell when it is
    done. The governor will be sensibly affected by a variation in the
    motion of the engine of 1 revolution in 800. Notwithstanding this
    extreme sensitiveness, or rather by reason of it, it will not
    oscillate, but when the load is uniform will stand quite, or nearly,
    motionless.</P>

    <P>For the supply of the water to the boiler, in many positions, it is
    very convenient to have a pump unconnected with the engine. On this
    account it is very usual in this country to have what are called donkey
    pumps or engines independent of the main engines, which can be used to
    feed the boilers, or for supplying water for many other purposes.</P>

    <P>Fig. 62 is a longitudinal section of the Worthington Steam Pump, the
    first of its kind, and for many years in successful operation.</P>

    <P>The general arrangement is that of a Steam Cylinder, the piston rod
    of which, carried through into the water cylinder and attached directly
    to the water plunger, works back and forth without rotary motion, and
    of course without using either crank or fly wheel.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig62.png" WIDTH="690" HEIGHT="550" ALT=
    "Fig. 62."></P>

    <P>In the figures, <EM>a</EM> is the Steam Cylinder--<EM>b</EM>, the
    Steam Chest-- <EM>d</EM>, a handle for regulating the steam
    valve--<EM>f</EM>, the starting bar <EM>g, g</EM>, tappets attached to
    the valve rod, which is moved by the contact of the arm <EM>e</EM>, on
    the piston rod with said tappets--<EM>h</EM>, the double-acting water
    plunger working through a packing ring--<EM>o, o</EM>, force
    valves--<EM>o&#39;, o&#39;</EM>, suction valves. The pump piston is
    represented as moving from right to left, the arrows indicating the
    course of the water through the passages. The suction valves
    <EM>&ouml;&#39;</EM>, on the right side, and the force valves
    <EM>o</EM>, on the left side, are show open; <EM>x</EM>, is an air
    chamber made of copper; <EM>s</EM>, the suction pipe terminating in a
    vacuum chamber; made by prolonging the suction pipe, and closing it
    perfectly tight at the top, the connection being made to the pump by a
    branch as shown; <EM>m, m</EM>, are hand-hole plates, affording easy
    access to the water valves; <EM>n, n</EM>, small holes through the
    plunger, which relieve the pressure near the end of the stroke, to give
    momentum to throw the valves when working at slow speed.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig63.png" WIDTH="700" HEIGHT="529" ALT=
    "Fig. 63."></P>

    <P>Fig. 63 is a perspective view of H.R. Worthington&#39;s Duplex Steam
    Pump. The prominent peculiarity of this pump is its valve motion. As
    seen in the cut, two steam pumps are placed side by side (or end to
    end, if desired). Each pump, by a rock shaft connected with its piston
    rod, gives a constant and easy motion to the steam valve of the other.
    Each pump therefore gives steam to and starts its neighbor, and then
    finishes its own stroke, pausing an instant till its own steam valve,
    being opened by the other pump, allows it to make the return
    stroke.</P>

    <P>This combined action produces a perfectly positive valve motion
    without dead points, great regularity and ease of motion, and entire
    absence of noise or shock of any kind. Both kinds of pumps are made by
    Mr. Worthington, of various size according to the requirements, the
    duplex being used for boiler feed and for the supply of cities with
    water.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig64.png" WIDTH="700" HEIGHT="442" ALT=
    "Fig. 64."></P>

    <P>Fig. 64 is a side elevation of the Woodward Steam Pump. The pump is
    direct acting. The steam and water piston being on the same rod, but
    momentum is obtained to throw the valves by means of a fly wheel,
    placed beyond the pump, and connected with the piston rod by a cross
    head and a yoke. The machine is simple in its construction and action,
    and is extensively used.</P>

    <P>Giffard&#39;s Injector, both in Europe and this country, is quite
    extensively used to supply the place of a pump, as independent feed for
    all classes of boilers. It is represented in elevation and section,
    figs. 65 and 66.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig6566.png" WIDTH="352" HEIGHT="550"
    ALT="Fig. 65. Fig. 66."></P>

    <P><EM>A</EM>, steam pipe leading from the boiler. <EM>B</EM>, a
    perforated tube or cylinder, through which the steam passes into the
    space <EM>b</EM>. <EM>C</EM> screwed rod for regulating the passage of
    steam through the annular conical space <EM>c</EM>, and worked by the
    handle <EM>d/</EM>. <EM>E</EM>, suction pipe, leading from the tank or
    hot well to small chamber <EM>m</EM>. <EM>F</EM>, annular conical
    opening or discharge pipe, the size of which is regulated by the
    movement of the tube or cylinder <EM>B</EM>. <EM>G</EM>, hand wheel for
    actuating the cylinder <EM>B</EM>. <EM>H</EM>, opening, in connection
    with the atmosphere, intervening between discharge pipe <EM>F</EM> and
    the receiving pipe through which the water is forced. <EM>I</EM>, tube
    through which the water passes to the boiler. <EM>K</EM>, valve for
    preventing the return of the water from the boiler when the injector is
    not working. <EM>L</EM>, waste or overflow pipe. <EM>M</EM>, nut to
    tighten the packing rings <EM>g</EM> and upper packing <EM>i</EM> in
    cylinder <EM>B</EM>. <EM>N</EM>, lock nut to hold <EM>M</EM>.</P>

    <P>The pipe <EM>A</EM> is connected with the steam space of the boiler
    at its highest part, to obtain as dry steam as possible. The passage of
    the steam into <EM>A</EM> is controlled by a cock, as is also the feed
    pipe to the boiler. In working, both are opened, the steam passes
    through <EM>A</EM> into the space <EM>b</EM>, and issuing through the
    nozzle <EM>c</EM> with the pressure due to its head, and a partial
    vacuum by its contact with the feed water, it drives this water in
    connection with the jet through the pipe <EM>F</EM> into the pipe
    <EM>I</EM> in connection with the water space of the boiler.</P>

    <P><EM>Method of Working.</EM>--Turn the wheel so as to permit a small
    quantity of water to flow to the instrument. Open the steam cock
    connecting the apparatus with the boiler. Turn slightly the handle,
    which will admit a small quantity of steam to the apparatus; a partial
    vacuum is thus produced, causing the water to enter through the supply
    pipe. As soon as this happens, which can be observed at the overflow
    pipe, the supply of steam or water may be increased as required, up to
    the capacity of the instrument, regulating either by means of the wheel
    and handle, so as to prevent any overflow. The quantity of water
    delivered into the boiler, may be varied by means of the stop cocks on
    the steam and water pipes, without altering the handles on the
    injector; a graduated cock on the water supply pipe is very convenient
    for this purpose.</P>

    <P>The machines are manufactured by Wm. Sellers &amp; Co.
    Philadelphia.</P>

    <P>As an example of Portable Steam Engines, of which there are large
    numbers in this country of different manufacturers, we give the
    representation (fig. 67) of one made by J.C. Hoadley, of Lawrence,
    Mass.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig67.png" WIDTH="700" HEIGHT="477" ALT=
    "Fig. 67."></P>

    <P>In these machines, the rules and proportions of the locomotive
    engine are adapted to the requirements of stationary power, for all
    purposes under forty horse power. The leading ideas are: high velocity,
    high pressure, good valve motion, large fire-box, numerous and short
    flues, and steam blast. The characteristic features are: great strength
    of boiler, fully adequate to bear with safety 200. lbs. pressure per
    sq. in., great compactness and simplicity, large and adjustable wearing
    surfaces, and the entire absence of all finish, or polish, for mere
    show.</P>

    <P>The cylinder is placed over the centre of the boiler, at the
    fire-box end, so that the strain due to the engine is central to the
    boiler (which serves as bed plate); the starting valve is under the
    hand of the engineer when at the fire door; and both ends of the crank
    shaft are available for driving pulleys.</P>

    <P>For the sake of compactness, the cylinders are set low, by means of
    a depression in the boiler between the stands of the crank shaft, to
    admit of the play of the crank and connecting rod. All the parts are
    attached to the boiler, which is made of sufficient strength to bear
    all extra strain due to the working of the engine.</P>

    <P>They have feed water heater, force pumps, Jackson&#39;s governor and
    valve, belt for governor, belt pulley, turned on the face, steam gauge;
    everything, in short, necessary to the convenient working of a steam
    engine. All engines are fired up and tried before they leave the shop,
    and they are warranted tight, safe, and complete.</P>

    <P>A strong and convenient running gear, so arranged as to be easily
    attached and detached at pleasure, is furnished, if desired; forming,
    when separate, a useful wagon.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig68.png" WIDTH="345" HEIGHT="550" ALT=
    "Fig. 68."></P>

    <P>Fig. 68 is a compact vertical engine, as built by R. Hoe &amp; Co.,
    of this city. It is intended to drive printing presses, but is adapted
    to any kind of work, and is especially suited to such places as require
    economy of space. Although the value of expansion has been called in
    question by some of the engineers of the United States Navy, and under
    an appropriation from Congress is now to be made the subject of
    experiment; yet, in almost all the manufactories and workshops of the
    United States, no matter what the form of steam engine, or the purposes
    to which it is applied, whether stationary, locomotive, or marine, some
    form of cut-off, by which expansion of the steam can be availed of, is
    considered indispensable. Many varieties are in use, but those engines
    are most popular in which the cut-off is applied directly to the valves
    on the cylinder, opening them quickly and shutting off almost
    instantly, avoiding all wire drawing of the steam at the ports, and
    regulating the speed of the engine promptly. Of this class of engines,
    those manufactured by the Corliss Steam Engine Company, of Providence,
    R.I., are perhaps the widest known, not only for their extensive
    introduction, but also from having, by a long and successful
    litigation, established the claims of the patentee, Mr. George H.
    Corliss.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig70.png" WIDTH="317" HEIGHT="550" ALT=
    "Fig. 70."></P>

    <P>Fig. 70 is a section of the cylinder and valve chests of a
    horizontal Corliss engine. <EM>S</EM> is the steam connection, and
    <EM>E</EM> the exhaust; there are two distinct sets of valves, the
    steam <EM>s, s&#39;</EM>, and the exhaust <EM>e, e&#39;</EM>, operated
    independently of each other. In their construction the valves may be
    considered cylindrical plugs, of which portions near the ports are cut
    away to admit the steam and reduce the bearing surface; the valves are
    fitted on the lathe and the seats by boring. The motion given to the
    valves is rocking, but it will be observed that the valves are not
    firmly connected to the rocking shaft or cylinder; in the figure the
    valves are shown shade lined, and the shaft or stem plain; in this way
    the valves are not affected by the packing of the valve stem, but
    always rest upon the face of the ports. In the figure the piston is
    just about to commence its outstroke, the movement of the steam is
    supposed to be represented by the arrows; the inner steam valve
    <EM>s</EM>, and the outer exhaust <EM>e&#39;</EM>, are just beginning
    to open. It will be observed that the outer steam <EM>s&#39;</EM> is
    fully closed, whilst the inner exhaust valve <EM>e</EM> is but barely
    so, showing that there has been a cut- off on the steam valve, but no
    lead to the exhaust, that it was left fully open till the completion of
    the stroke.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig71a.png" WIDTH="700" HEIGHT="427"
    ALT="Fig. 71."></P>

    <P>Fig. 71 is a side elevation of the cylinder, with the valve
    connections with the governor. <EM>S</EM> is the steam pipe; <EM>s,
    s&#39;</EM> handles to the steam valves, and <EM>e, e&#39;</EM> to the
    exhaust valves, shown in dotted line in fig. 70. The handles to the
    exhaust valves are connected directly to a rocking plate <EM>R</EM>, to
    which motion is given by a connection <EM>x</EM>, with an eccentric on
    the engine shaft. When once set, therefore the movement of the exhaust
    valves is constant, and they will always be opened and closed at the
    same point of the stroke. Connected with the rocking plate <EM>R</EM>,
    and on opposite sides of its centre, the same as the exhaust valve
    connections, there are two levers, vibrating on a centre <EM>c</EM>, of
    which one only is shown, as it covers the other; to the upper ends of
    these levers pawls are attached, one end of which rests on the stems or
    rods connected with the handles <EM>s, s&#39;</EM>, of the steam
    valves; on these stems there are notches against which the pawls
    strike, and as the levers vibrate inward they push back the stems and
    thereby open the valves, and this continues for the whole length of the
    inward motion of the levers, or till the outer extremities of the pawls
    come in contact with the end of the short lever <EM>l</EM>, which,
    pushing down the outer end of the pawls, relieves the stems at the
    other ends, and the valve stem returns to its place through the force
    of springs attached to the outer extremities of the valve stems
    <EM>a</EM>, are cylindrical guides to the valve stems, at the inner
    extremities of which are air cushions. The lever <EM>l</EM> is
    connected directly with the governor. As the balls rise, they depress
    the extremity, which comes in contact with the pawls sooner, and
    thereby shut the valves earlier; and on the contrary when the balls are
    depressed, the valves remain open longer; as the pawls come in contact
    with the stems always at one point, the steam valves open constantly,
    but are closed at any point by the relief of the pawls, according to
    the speed of the governor.</P>

    <P>Fig. 71 represents, partly in section and partly in plan, the
    cylinder, steam chests, valves, &amp;c., of one of the Woodruff &amp;
    Beach high pressure Engines, Wright&#39;s patent.</P>

    <P>Fig. 72 represents, in elevation, the cam shaft, to the upper end of
    which, not shown in the drawing, is attached the ordinary centrifugal
    governor. The cylinder, steam chests, valves, &amp;c., being similar to
    those of other engines, need no special notice; but the cam for opening
    and closing the steam valves, fig. 72, requires particular attention,
    as it embodies a beautiful and simple device for cutting off the steam
    with certainty at any part of the stroke, the motion being produced
    automatically by the action of the governor on this cam, throwing it
    more or less out of centre with the spindle of the governor, as the
    rotation of the balls is less or more rapid, the eccentricity of the
    cam determining the amount of steam admitted to the working cylinder of
    the engine. To produce this effect the cam is made as follows:</P>

    <P><EM>C</EM> is a hollow cylinder or shell, with a part of one end
    formed into a cam proper. Throughout the whole length of this piece,
    upon the inside, there is a spiral groove cut to receive one end of a
    feather, by which its pitch or eccentricity is regulated.
    <EM>C&#39;</EM> is also a hollow cylinder or shell, of the same length
    and diameter as <EM>C</EM>, with a similar spiral groove cut on the
    inside, the outside being perfectly smooth and plain, upon which the
    toe (<EM>t</EM>) for closing the valves is fastened. The inside piece
    consists of two hubs <EM>D, D&#39;</EM>, eccentric with each other, and
    made in one piece, <EM>D</EM> being turned to exactly fit the inside of
    the shell <EM>C</EM>, and <EM>D&#39;</EM> to fit the shell
    <EM>C&#39;</EM>, the hub <EM>D&#39;</EM> having a socket (<EM>c</EM>)
    into which the spindle (<EM>s</EM>) of the governor is screwed; the end
    (<EM>d</EM>) of the hub <EM>D</EM> forming a journal or bearing, with a
    bevel wheel on its extremity to convey motion from the crank-shaft
    gearing to the governor and cut-off. There is a hole throughout the
    length of the inside hubs <EM>D</EM> and <EM>D&#39;</EM>, which is
    continued through the spindle of the governor, and contains the rod
    (<EM>r</EM>) that connects the cam with the governor. This hole is
    eccentric to the outside surface of the hub <EM>D</EM>, as well as to
    the shell <EM>C</EM>, and concentric with the hub <EM>D&#39;</EM> and
    shell <EM>C&#39;</EM>, and with the governor rod (<EM>r</EM>).</P>

    <P>The shell <EM>C</EM> and hub <EM>D</EM>, and shell <EM>C&#39;</EM>
    and hub <EM>D&#39;</EM>, are connected together by feathers; one piece
    of each feather is of a spiral form, and the other a straight or
    rectangular piece, the two being connected together by a stub on the
    rectangular piece, which fits into a hole or bearing in the other or
    spiral piece, so that the latter can turn on the stub and accommodate
    itself to the groove in which it has to work. The spiral part of each
    feather works in the spiral groove on the inside of its corresponding
    shell <EM>C</EM> and <EM>C&#39;</EM> respectively, and the rectangular
    pieces work in a straight groove cut in the hubs <EM>D</EM> and
    <EM>D&#39;</EM>, the inner parts of the rectangular pieces being
    fastened to the governor rod (<EM>r</EM>), so that the feathers are
    permanently connected with the governor.</P>

    <P>The shell <EM>C&#39;</EM> revolves inside of two yokes (<EM>y</EM>)
    and (<EM>y&#39;</EM>), one attached to each steam-valve toe,
    (<EM>a</EM>) and (<EM>a&#39;</EM>) respectively.</P>

    <P>On the inside of each yoke, and opposite to its valve-toe, is a
    raised piece, against which the closing piece (<EM>t</EM>) on the shell
    (<EM>C&#39;</EM>) acts to close the valves.</P>

    <P>This shell (<EM>C&#39;</EM>), as before noticed, has a spiral groove
    on its inside, similar in all respects to that in the cam-shell
    (<EM>C</EM>); and being acted upon in the same manner and through the
    same rod by the governor, it is evident that the closing piece
    (<EM>t</EM>) on its outside will always hold the same relation to the
    opening toe on the lower or cam-shell (<EM>C</EM>); and whatever
    alteration is made in the one, a corresponding alteration takes place
    in the other, thereby insuring the closing of the valves at the proper
    time at every point of the variation of the cut-off.</P>

    <P>When the several pieces above described are put together, the
    apparatus for opening and closing the valves and producing the cut-off
    is complete, as shown in fig. 72, and it operates as follows:</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig71.png" WIDTH="700" HEIGHT="413" ALT=
    "Fig. 71."></P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig72.png" WIDTH="421" HEIGHT="550" ALT=
    "Fig. 72"></P>

    <P>Motion is communicated by gearing from the crank-shaft to the bevel
    wheel on the piece (<EM>d</EM>) on the end of the hub <EM>D</EM>, and
    is communicated to the spindle of the governor, which is screwed into
    the socket on <EM>D&#39;</EM>. As the balls rise or fall, through
    change of centrifugal force due to the variation in the speed of
    rotation, they raise or depress the governor-rod, which passes through
    the spindle and the hubs <EM>D&#39;</EM> and <EM>D</EM>, and is
    attached to the feathers, thereby raising or depressing the feathers,
    which, acting on their respective spiral grooves, instantly alters the
    lift of the cam on the shell (<EM>C</EM>), and brings the closing toe
    (<EM>t</EM>) on the shell (<EM>C&#39;</EM>) into proper position for
    closing, and so regulates the amount of steam admitted to the
    cylinder.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig71b.png" WIDTH="700" HEIGHT="439"
    ALT="Fig. 71."></P>

    <P>Consequently, any speed may be selected at which the load of the
    engine is to move, and any variation from that will be instantly felt
    by the governor, and corrected by this simple and beautiful device.
    There is no jar in the working of the parts; the feathers move
    noiselessly in their grooves; the governor rod moves up and down
    through the spindle and the hubs <EM>D</EM> and <EM>D&#39;</EM>, and
    can be regulated by hand to give any required opening of the steam
    ports to suit the work to be done. Any change in the amount of work
    will then alter the speed of the engine, and so affect the governor and
    cam, as before said.</P>

    <P>It is unnecessary to insist on the great economy attained by using
    steam with a well-regulated cut-off, for practical men know now that
    the essential points of excellence in the steam engine are a good
    boiler, which generates the greatest quantity of steam for the least
    consumption of fuel; and, secondly, a reliable cut-off, which uses the
    steam to the best advantage, by admitting the proper quantity for the
    work required.</P>

    <P>STEAM FIRE ENGINES.--Portable engines for the extinguishment of
    fires, are an American invention, and to Messrs. A.B. &amp; E. Latta,
    of Cincinnati, working on the right principles, is due the credit which
    they claim in their circular, as follows:</P>

    <P>&quot;We claim to be the <EM>original</EM> and first
    <EM>projectors</EM> of the <EM>first successful steam fire engine</EM>
    in the world&#39;s history. There have been many attempts at making a
    machine of such construction as would answer to extinguish fires; but
    none of them proved to be available in a sufficiently short space of
    time to warrant their use as a fire apparatus. We hold that a steam
    fire engine should be of such nature as to be brought into requisition
    in as short a space of time as is necessary to get the machine on the
    ground, and the hose laid and ready to work: that is, supposing the
    fire to be within one square of the place where the steamer is located.
    The object in locating a machine at any point is to protect that
    immediate vicinity; and it is therefore absolutely necessary to have it
    available in the shortest space of time, and that with unerring
    certainty. We think that reliability is of the greatest importance to
    the protection of a city from fire, as everything is dependent on the
    <EM>working</EM> of such apparatus in time; and for this reason no
    expense should be spared on this kind of machinery.&quot;</P>

    <P>Fig. 73 is a representation of one of the Messrs. Latta&#39;s fire
    engines, of which there are many of different classes, according to the
    requirements; they say that they can furnish engines as low as $1,000,
    and have made some for $10,000.</P>

    <P>The first peculiar feature of this engine is the boiler; it differs
    entirely from all boilers now in use.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig73.png" WIDTH="740" HEIGHT="515" ALT=
    "Fig. 73."></P>

    <P>The fire box or furnace is simply a square box or furnace of any
    required dimensions; it is nothing more than a water space surrounding
    the fire, stay-bolted as all water spaces are. It is made of boiler
    plate in the usual manner. The water space extends only 2/3 of the
    height, the balance being a single sheet. The bottom of this fire box
    is crossed by grate bars to support the fuel; in its rear side are fire
    doors, inserted for firing. The internal arrangements of the boiler are
    composed of a large number of tubes, lying across in a horizontal
    position, put together in sections with return bends resembling the
    coils for heating buildings. These coils are of small pipe (say one
    inch in diameter), and as numerous as may be necessary. They give the
    required amount of steam. They are secured to wrought-iron plates at
    each end by rivets. These plates lie close to the box, and are secured
    to it, top and bottom. These tubes are wrought iron, firmly screwed
    into the bends, so as to prevent any possible breaking.</P>

    <P>The box has a hole through both sheets, in the same manner as a
    hollow stay-bolt, through which the coil pipe passes, having no
    connection with the box. After passing into the box it divides into two
    pipes, then subdivides into four, and so on, until its numbers equal
    the number of coils in the box, and to which each limb is attached. The
    upper ends of these coils are the same in number, and are carried
    through at the top or nearly the top of the box. They then run down
    outside to the steam chamber, or rather water space, as the box is both
    steam chamber and water space. These pipes empty their contents into
    the box, steam and water, as it may come, all together. It will be
    observed that these coils of tube are sufficiently separated to allow
    the fire to pass between them freely, and cover their whole
    surface.</P>

    <P>The mode of operation of this boiler is this: The fire box is filled
    2/3 full of water. The coils are dry at starting; the space for fuel
    being filled with good wood, the fire is lighted, and in a few moments
    the engineer moves his hand pump, which takes its water from the box to
    which it is attached, and forces it through the coils. By this means
    steam is generated in from 3 to 5 minutes, so as to start the
    engine.</P>

    <P>It will be seen that the water performs a complete circuit; it is
    taken from the box and passed through the coils; what is steam remains
    in the steam chamber, and what is not (if any) drops back into the box
    from where it started. Hence it will be seen that a large surface is
    exposed to a small quantity of water, and in a way that it is entirely
    controllable. All the engineer has to do to surcharge his steam, is to
    reduce the speed of the pump (which is independent of the main engine).
    By raising the heat and quantity of water, any degree of elasticity can
    be given to the steam, and that, too, with the least amount of waste
    heat in giving a natural draft. Hence the great economy of this
    boiler.</P>

    <P>The next feature of this engine is, it has no wood work about it to
    perish with the heat and roughness of the streets. All the wheels are
    wrought iron; and, as yet, these are the only ones that have stood a
    steam fire engine. The frame is wrought iron; truck, on which the front
    wheel is hung, wrought iron. The axles are cast steel. The engine and
    pump is a double- acting piston pump direct, without any rotary motion;
    with a perfect balance valve, it is balanced at all times, and hence
    the engine remains quiet without blocking, when at work. The engine is
    mounted on three wheels, which enables it to be turned in a very short
    space.</P>

    <P>Many engines have been constructed by the Messrs. Latta for the fire
    companies, of different cities, and have been in successful competition
    with other engines; the farthest throw ever made by one of their
    first-class engines was 310 feet from a 1-5/8 inch nozzle; steaming
    time, starting from cold water, 3-1/2 minutes.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig74.png" WIDTH="740" HEIGHT="418" ALT=
    "Fig. 74 AMOSKEAG STEAM FIRE ENGINE."></P>

    <P>Fig. 74 is a representation of one class of steam fire engine, as
    built by the Amoskeag Manufacturing Company, at Manchester, N.H. The
    boiler is an upright tubular boiler, of a peculiar construction, the
    patent right to which is vested in the Amoskeag Manufacturing Company.
    This boiler is very simple in its combination, and for safety,
    strength, durability, and capacity for generating steam is unsurpassed.
    No fan or artificial blower is ever used or needed, the natural draft
    of the boiler being always sufficient. Starting with cold water in the
    boiler, a working head of steam can be generated in <EM>less than five
    minutes</EM> from the time of kindling the fire. The engine
    &quot;Amoskeag,&quot; owned by the city of Manchester, has played two
    streams in <EM>three minutes and forty seconds</EM> after touching the
    match, at the same time drawing her own water. The boilers are made and
    proved so as to be safely run at a steam pressure of 140 to 150 lbs. to
    the square inch; but the engines are constructed so as to give the best
    streams at a pressure of about 100 lbs. to the square inch, and for
    service at fires a steam pressure of about 60 lbs. to the square inch
    is all that is required.</P>

    <P>The various styles of engine are all <EM>vertical</EM> in their
    action, and in all the pumps and steam cylinders are firmly and
    directly fastened to the boiler, the steam cylinders being attached
    directly to the steam dome. This arrangement obviates the necessity of
    carrying steam to the cylinders through pipes of considerable length,
    and the machine has very little vibratory motion when in operation--so
    little that it is not necessary to block its wheels to keep it in its
    place, or to take the weight off the springs before commencing
    work.</P>

    <P>The pumps are placed on the engines as near the ground as they can
    be with safety, and are arranged so as to attach the suction and
    leading hose to either or both sides of the machine, as may be most
    convenient or desirable, so that less difficulty will be found in
    placing an engine for work, and when required to draw its own water, it
    has only to draw it the shortest possible distance.</P>

    <P>Each engine has two &quot;feed pumps&quot; for supplying the boiler,
    and also a connection between the main forcing pumps and the boiler, so
    that it can be supplied from that source if desirable. The tank which
    carries the water for supplying the boiler is so placed that the water
    in it is always above the &quot;feed pumps,&quot; an advantage that
    insures the almost certain working of these pumps. These pumps are of
    brass, the best locomotive pattern, and one of them running with the
    engine, when at work, furnishes an ample supply of water to the
    boiler.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig75.png" WIDTH="740" HEIGHT="484" ALT=
    "Fig. 75."></P>

    <P>The engines are exceedingly portable; they can be turned about or
    placed for service in as contracted a space as any hand engine, and two
    good horses will draw a first-class engine with the greatest ease,
    carrying at the same time water for the boiler, a supply of fuel
    sufficient to run the engine two hours, the driver, the engineer, and
    the fireman.</P>

    <P>Fig. 75 is a representation of the class of steam fire engine built
    by Silsbee, Mynderse &amp; Co., Seneca Falls, N. Y. under Holly&#39;s
    patent.</P>

    <P>The boiler is vertical, with vertical water tubes passing directly
    through the fire. These tubes are closed at the bottom and open at the
    top, where they pass through a water-tight plate, and communicate with
    the water in the boiler. The arrangement of the tubes causes a constant
    current, the water rising on the outside of the tubes as they are
    heated, and its place being supplied by a current flowing downward
    through the tube to the boiler. The smoke and flame pass among the
    tubes up through flues.</P>

    <P>Both engine and pump are rotary, and of the same type. They consist
    essentially of two elliptical rotary pistons, cogged and working into
    one another in an air-tight case. The pistons fit close to the inside
    of the case, and gear into each on the line of their conjugate
    diameters. The action is somewhat similar to the old-fashioned rotary
    pump, consisting of two cog wheels in gear with, each other, the spaces
    at the side of the case being filled with water, which at the centre
    are occupied by the teeth in gear. In Holly&#39;s pump, instead of
    uniform teeth, and depending on the fit of the teeth with the side of
    the case and with each other for the packing, there are two large teeth
    in each piston opposite each other, which have slide pistons, and
    intermediate with these large teeth are small cogs, which continue the
    motion of the rotary pistons. The machine works very smoothly, and
    performs the work necessary, in ordinary service, under a pressure of
    50 to 60 lbs.</P>

    <P>There are many other makers of fire engines in this country; but
    sufficient examples are given to illustrate the class; so successful
    have they been, that they are fast superseding hand engines, even in
    the smaller cities.</P>

    <P>Under a paid department, the following is, in the city of Boston,
    Mass., the comparative cost of running the two kinds of engines,
    viz.:</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "STEAM FIRE ENGINE">
      <TR>
        <TD COLSPAN="2" ALIGN="center">
          <P>STEAM FIRE ENGINE.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 engineer</P>
        </TD>

        <TD ALIGN="right">
          <P>$720 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 fireman</P>
        </TD>

        <TD ALIGN="right">
          <P>600 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 driver</P>
        </TD>

        <TD ALIGN="right">
          <P>600 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 foreman of hose</P>
        </TD>

        <TD ALIGN="right">
          <P>150 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>8 hosemen, at $125 each</P>
        </TD>

        <TD ALIGN="right">
          <P>375 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>-</P>
        </TD>

        <TD ALIGN="right">
          <P>--------</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>7 men</P>
        </TD>

        <TD ALIGN="right">
          <P>$2,445 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Keeping of 2 horses</P>
        </TD>

        <TD ALIGN="right">
          <P>315 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>-</P>
        </TD>

        <TD ALIGN="right">
          <P>--------</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>Total</P>
        </TD>

        <TD ALIGN="right">
          <P>$2,760 00</P>
        </TD>
      </TR>
    </TABLE>

    <P>&nbsp;</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "HAND ENGINE">
      <TR>
        <TD COLSPAN="2" ALIGN="center">
          <P>HAND ENGINE.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 foreman</P>
        </TD>

        <TD ALIGN="right">
          <P>$150 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 assistant foreman</P>
        </TD>

        <TD ALIGN="right">
          <P>125 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 clerk</P>
        </TD>

        <TD ALIGN="right">
          <P>125 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 steward</P>
        </TD>

        <TD ALIGN="right">
          <P>125 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>3 leading hosemen, at $125 each</P>
        </TD>

        <TD ALIGN="right">
          <P>375 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>33 men, at $100 each</P>
        </TD>

        <TD ALIGN="right">
          <P>3,300 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>--</P>
        </TD>

        <TD ALIGN="right">
          <P>---------</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>40 men</P>
        </TD>

        <TD ALIGN="right">
          <P>$4,200 00</P>
        </TD>
      </TR>
    </TABLE>

    <P>Here the engineer, fireman, and driver are constantly employed, the
    hosemen have other employment in the neighborhood, but all the company
    sleep in the engine house.</P>

    <P>In the city of Manchester, N.H., a steam fire engine company is
    composed of fourteen men, all told, one of whom, acting as driver and
    steward, is constantly employed, remaining at the engine house with a
    pair of horses always ready to run out with the engine in case of an
    alarm of fire. The other members of the company have other employments,
    and turn out only on an alarm of fire.</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "STEAM FIRE ENGINES">
      <TR>
        <TD COLSPAN="3" ALIGN="center">
          <P>STEAM FIRE ENGINES.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;Amoskcag,&quot;&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="center">
          <P>&nbsp;Expenditures&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="right">
          <P>$864 32</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;Fire King,&quot;&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="center">
          <P>&nbsp;&quot;&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="right">
          <P>855 78</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>&quot;E.W. Harrington, &quot;&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="center">
          <P>&nbsp;&quot;&nbsp;&nbsp;</P>
        </TD>

        <TD ALIGN="right">
          <P>496 09</P>
        </TD>
      </TR>
    </TABLE>

    <P>The above expense includes pay of members, team expenses, cost of
    gas, wood, coal, and all necessities incident to service. The
    &quot;E.W. Harrington&quot; is a second-class engine, stationed in the
    outskirts of the city, and was run cheaper from the fact that no horses
    were kept for it by the city.</P>

    <P>A first-class hand-engine company is allowed to number, all told,
    fifty men, and the members of the company are paid as follows:</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" SUMMARY=
    "FIRST-CLASS HAND-ENGINE COMPANY.">
      <TR>
        <TD COLSPAN="3" ALIGN="center">
          <P>FIRST-CLASS HAND-ENGINE COMPANY.</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 foreman</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>$35 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 assistant foreman</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>28 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 clerk</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>28 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>1 steward</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>68 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>46 men, at $18 each</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>828 00</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>--</P>
        </TD>

        <TD>
        </TD>

        <TD ALIGN="right">
          <P>--------</P>
        </TD>
      </TR>

      <TR>
        <TD>
          <P>50 men.</P>
        </TD>

        <TD>
          <P>Total</P>
        </TD>

        <TD ALIGN="right">
          <P>$987 00</P>
        </TD>
      </TR>
    </TABLE>

    <P>By this it will be seen, that in a city like Manchester, with from
    twenty to twenty-five thousand inhabitants, a first-class steam fire
    engine can be run at an expense not to exceed that of a first-class
    hand engine, while in service it will do at least <EM>four times</EM>
    the work. The cost of repairs is found by experience to be no greater
    on the steam fire engines than on hand engines.</P>

    <P>The Excavator, fig. 76, is the invention of the late Mr. Otis, an
    application of the spoon dredging machine of the docks to railway
    purposes, with very important modifications. The machine consists of a
    strong truck, <EM>A</EM>, <EM>A</EM>, mounted on railway wheels, on
    which is placed the boiler <EM>C</EM>, the crane <EM>E</EM>, and the
    requisite gearing. The excavator or shovel, <EM>D</EM>, is a box of
    wrought iron, with strong points in front to act as picks in loosening
    the earth, and its bottom hung by a hinge at <EM>d</EM>, so that, by
    detaching a catch, it may fly open and discharge the material raised.
    To operate the machine, suppose the shovel <EM>D</EM> to be in the
    position shown in the cut; it is lowered by the chains <EM>o</EM>,
    <EM>o</EM>, and thrown forward or backward, if necessary, by the drum
    <EM>B</EM>, and handle <EM>S</EM>, till the picks in the front of the
    shovel are brought in proper contact with the face of the cut; motion
    forward is now given to the shovel by the drum <EM>B</EM> and handle
    <EM>S</EM>, and at the same time it is raised by the chains <EM>o</EM>,
    <EM>o</EM>. These two motions can be so adjusted to each other, as to
    give movement to the shovel to enable it to loosen and scrape up a
    shovelful of earth. The handle <EM>S</EM> is now left free, and the
    shovel <EM>D</EM> is raised vertically by the chains <EM>o</EM>,
    <EM>o</EM>. The crane is now turned round, till the shovel comes over a
    rail car on a side track; the bottom of the shovel is opened, and the
    dirt deposited in the car. All these motions are performed by the aid
    of a steam engine, and are controlled by a man who stands on a platform
    at <EM>f</EM>.</P>

    <P><IMG BORDER="0" SRC="https://brian.carnell.com/wiki/_media/etext:c:ce-john-bourne-catechism-steam-engine-fig76.png" WIDTH="740" HEIGHT="424" ALT=
    "Fig 76."></P>

    <P>692. <EM>Q.</EM>--Having now described the most usual and approved
    forms of engines applicable to numerous miscellaneous purposes for
    which a moderate amount of steam power is required, will you briefly
    recapitulate what amount of work of different kinds an engine of a
    given power will perform, so that any one desiring to employ an engine
    to perform a given amount of work, will be able to tell what the power
    of such engine should be?</P>

    <P><EM>A.</EM>--It will of course be impossible to recapitulate all the
    purposes to which engines are applicable, or to specify for every case
    the amount of power necessary for the accomplishment of a given amount
    of work; but some examples may be given which will be applicable to the
    bulk of the cases occurring in practice.</P>

    <P>693. <EM>Q.</EM>--Beginning, then, with the power necessary for
    threshing,--a 4 horse power engine, with cylinder 6 inches diameter,
    pressure of steam 45 lbs., per square inch, and making 140 revolutions
    per minute, will thresh out 40 quarters of wheat in 10 hours with a
    consumption of 3 cwt. of coals.</P>

    <P><EM>A.</EM>--Although this may be done, it is probably too much to
    say that it can be done on an average, and about three fourths of a
    quarter of wheat per horse power would probably be a nearer average.
    The amount of power consumed varies with the yield.</P>

    <P>Messrs. Barrett, Exall, and Andrewes give the following table as
    illustrative of the work done, and the fuel consumed by their portable
    engines; but this must be regarded as a maximum performance:--</P>

    <TABLE CELLSPACING="0" CELLPADDING="4" BORDER="0" WIDTH="100%" SUMMARY=
    "Horse power; Weight of engine; Corn thrashed; Coals consumed; Water required">
      <TR>
        <TD>
          <P>Number of horse power.</P>
        </TD>

        <TD COLSPAN="2">
          <P>Weight of engine.</P>
        </TD>

        <TD>
          <P>Quarters of corn thrashed in 10 hours.</P>
        </TD>

        <TD>
          <P>Quantity of coals consumed in 10 hours.</P>
        </TD>

        <TD>
          <P>Quantity of water required for 10 hours in gallons.</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
        </TD>

        <TD ALIGN="center">
          <P>Tons.</P>
        </TD>

        <TD ALIGN="center">
          <P>Cwts.</P>
        </TD>

        <TD ALIGN="center">
        </TD>

        <TD ALIGN="center">
          <P>Cwts.</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>4</P>
        </TD>

        <TD ALIGN="center">
          <P>2</P>
        </TD>

        <TD ALIGN="center">
          <P>0</P>
        </TD>

        <TD ALIGN="center">
          <P>40</P>
        </TD>

        <TD ALIGN="center">
          <P>3</P>
        </TD>

        <TD ALIGN="center">
          <P>360</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>5</P>
        </TD>

        <TD ALIGN="center">
          <P>2</P>
        </TD>

        <TD ALIGN="center">
          <P>5</P>
        </TD>

        <TD ALIGN="center">
          <P>50</P>
        </TD>

        <TD ALIGN="center">
          <P>4</P>
        </TD>

        <TD ALIGN="center">
          <P>380</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>6</P>
        </TD>

        <TD ALIGN="center">
          <P>2</P>
        </TD>

        <TD ALIGN="center">
          <P>10</P>
        </TD>

        <TD ALIGN="center">
          <P>60</P>
        </TD>

        <TD ALIGN="center">
          <P>5</P>
        </TD>

        <TD ALIGN="center">
          <P>460</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>7</P>
        </TD>

        <TD ALIGN="center">
          <P>2</P>
        </TD>

        <TD ALIGN="center">
          <P>15</P>
        </TD>

        <TD ALIGN="center">
          <P>70</P>
        </TD>

        <TD ALIGN="center">
          <P>6</P>
        </TD>

        <TD ALIGN="center">
          <P>540</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>8</P>
        </TD>

        <TD ALIGN="center">
          <P>3</P>
        </TD>

        <TD ALIGN="center">
          <P>0</P>
        </TD>

        <TD ALIGN="center">
          <P>80</P>
        </TD>

        <TD ALIGN="center">
          <P>7</P>
        </TD>

        <TD ALIGN="center">
          <P>620</P>
        </TD>
      </TR>

      <TR>
        <TD ALIGN="center">
          <P>10</P>
        </TD>

        <TD ALIGN="center">
          <P>3</P>
        </TD>

        <TD ALIGN="center">
          <P>10</P>
        </TD>

        <TD ALIGN="center">
          <P>100</P>
        </TD>

        <TD ALIGN="center">
          <P>9</P>
        </TD>

        <TD ALIGN="center">
          <P>780</P>
        </TD>
      </TR>
    </TABLE>

    <P>694. <EM>Q.</EM>--In speaking of horses power, I suppose you mean
    indicator horse power?</P>

    <P><EM>A.</EM>--Yes; or rather the dynamometer horse power, which is
    the same, barring the friction of the engine. At the shows of the Royal
    Agricultural Society, the power actually exerted by the different
    engines is ascertained by the application of a friction wheel or
    dynamometer.</P>

    <P>695. <EM>Q.</EM>--Can you give any other examples of the power
    necessary for grinding corn?</P>

    <P><EM>A.</EM>--An engine exerting 23-1/3 horses power by the indicator
    works two pairs of flour stones of 4 feet 8 inches diameter, two pairs
    of stones grinding oatmeal of 4 feet 8 inches diameter, one dressing
    machine, one pair of fanners, one dust screen, and one sifting machine.
    One of the flour stones makes 85, and the other 90 revolutions in the
    minute. One of the oatmeal stones makes 120, and the other 140
    revolutions in the minute. To take another case:--An engine exerting
    26-1/2 indicator horses power works two pairs of flour stones, one
    dressing machine, two pairs of stones grinding oatmeal, and one pair of
    shelling stones. The flour stones, one pair of the oatmeal stones, and
    shelling stones, are 4 feet 8 inches diameter. The diameter of the
    other pair of oatmeal stones is 3 feet 8 inches. The length of the
    cylinder of the dressing machine is 7 feet 6 inches. The flour stones
    make 87 revolutions in the minute, and the larger oatmeal stone 111
    revolutions, but the smaller oatmeal stone and the shelling stone
    revolve faster than this. At the time the indicator diagram was taken,
    each pair of flour stones was grinding at the rate of 5 bushels an
    hour; each pair of oatmeal stones about 24 bushels an hour; and the
    shelling stones were shelling at the rate of about 54 bushels an hour.
    The fanners and screen were also in operation.</P>

    <P>696. <EM>Q.</EM>--Have you any other case to enumerate?</P>

    <P><EM>A.</EM>--I may mention one in which the power of the same engine
    was increased by giving it a larger supply of steam. The engine when
    working with 8.65 horses power, gives motion to one pair of oatmeal
    stones of 4 feet 6 inches diameter, and one pair of flour stones 4 feet
    8 inches diameter. The oatmeal stone makes 100 revolutions in the
    minute, and the flour stone 89. The oatmeal stones grind about 36
    bushels in the hour, and the flour stones 5 bushels in the hour. The
    engine when working to 12 horses power drives one pair of flour stones,
    4 feet 8 inches diameter, at 89 revolutions per minute and one pair of
    stones of the same diameter at 105 revolutions, grinding beans for
    cattle. The flour mill stones with this proportion of power, being more
    largely fed, ground 6 bushels per hour, and the other stones also
    ground 6 bushels per hour. When the power was increased to 18 horses,
    and the engine was burdened in addition with a dressing machine having
    a cylinder of 19 inches diameter, the speed of the flour stone fell to
    85, and of the beans stone to 100 revolutions per minute, and the yield
    was also reduced. The dressing machine dressed 24 bushels per hour.</P>

    <P>697. <EM>Q.</EM>--What is the power necessary to work a sugar mill
    such as is used to press the juice from canes in the West Indies?</P>

    <P><EM>A.</EM>--Twenty horses power will work a sugar mill having
    rollers about 5 feet long and 28 inches diameter; the rollers making
    2-1/3 turns in a minute. If the rollers be 26 inches diameter and 4-1/2
    feet long, 18 horses power will suffice to work them at the same speed,
    and 16 horses power if the length be reduced to 3 feet 8 inches. 12
    horses power will be required to work a sugar mill with rollers 24
    inches diameter and 4 feet 2 inches long; and 10 horses power will
    suffice if the rollers be 3 feet 10 inches long and 23 inches diameter.
    The speed of the surface of sugar mill rollers should not be greater
    than 16 feet per minute, to allow time for the canes to part with their
    juice. In the old mills the speed was invariably too great. The
    quantity of juice expressed will not be increased by increasing the
    speed of the rollers, but more of the juice will pass away in the
    begass or woody refuse of the cane.</P>

    <P>698. <EM>Q.</EM>--What is the amount of power necessary to drive
    cotton mills?</P>

    <P><EM>A.</EM>--An indicator or actual horse power will drive 305 hand
    mule spindles, with proportion of preparing machinery for the same; or
    230 self- acting mule spindles with preparation; or 104 throstle
    spindles with preparation; or 10-1/2 power looms with common sizing.
    The throstles referred to are the common throstles spinning 34&#39;s
    twist for power loom weaving, and the spindles make 4000 turns per
    minute. The self-acting mules are Robert&#39;s, about one half spinning
    36&#39;s weft, and spindles revolving 4800 turns per minute; and the
    other half spinning 36&#39;s twist, with the spindles revolving 5200
    times per minute. Half the hand mules were spinning 36&#39;s weft, at
    4700 revolutions, and the other half 36&#39;s twist at 5000 revolutions
    per minute. The average breadth of the looms was 37 inches, weaving 37
    inch cloth, making 123 picks per minute,--all common calicoes about 60
    reed, Stockport count, and 68 picks to the inch. To take another
    example in the case of a mill for twisting cotton yarn into thread:--In
    this mill there are 27 frames with 96 common throstle spindles in each,
    making in all 2592 spindles. The spindles turn 2200 times in a minute;
    the bobbins are 1-7/8 inches diameter, and the part which holds the
    thread is 2-3/16 inches long. In addition to the twisting frames the
    steam engine works 4 turning lathes, 3 polishing lathes, 2 American
    machines for turning small bobbins, two circular saws, one of 22 and
    the other of 14 inches diameter, and 24 bobbin heads or machines for
    filling the bobbins with finished thread. The power required to drive
    the whole of this machinery is 28-1/2 horses. When all the machinery
    except the spindles is thrown off, the power required is 21 horses, so
    that 2592, the total number of spindles, divided by 21, the total
    power, is the number of twisting spindles worked by each actual horse
    power. The number is 122.84.</P>

    <P>699. <EM>Q.</EM>--What work will be done by a given engine in sawing
    timber, pressing cotton, blowing furnaces, driving piles, and dredging
    earth out of rivers?</P>

    <P><EM>A.</EM>--A high pressure cylinder 10 inches diameter, 4 feet
    stroke, making 35 revolutions with steam of 90 to 100 lbs. on the
    square inch, supplied by three cylindrical boilers 30 inches diameter
    and 20 feet long, works two vertical saws of 34 inches stroke, which
    are capable of cutting 30 feet of yellow pine, 18 inches deep, in the
    minute. A high pressure cylinder 14 inches diameter and 4 feet stroke,
    making 60 strokes per minute with steam of 40 lbs. on the square inch,
    supplied by three cylindrical boilers without flues, 30 inches diameter
    and 26 feet long, with 32 square feet of grate surface, works four
    cotton presses geared 6 to 1, with two screws in each, of 7-1/2 inches
    diameter and 1-5/8 pitch, which presses will screw 1000 bales of cotton
    in the twelve hours. Also one high pressure cylinder of 10 inches
    diameter and 3 feet stroke, making 45 to 60 revolutions per minute,
    with steam of 45 to 50 lbs. per square inch, with two hydraulic presses
    having 13 inch rams of 41 feet stroke, and force pumps 2 inches
    diameter and 6 inches stroke, presses 30 bales of cotton per hour. One
    condensing engine with cylinder 56 inches diameter, 10 feet stroke, and
    making 15 strokes per minute with steam of 60 lbs. pressure per square
    inch, cut off at 1/4th of the stroke, supplied by six boilers, each 5
    feet diameter, and 24 feet long, with a 22-inch double-return flue in
    each, and 198 square feet of fire grate, works a blast cylinder of 126
    inches diameter, and 10 feet stroke, at 15 strokes per minute. The
    pressure of the blast is 4 to 5 lbs. per square inch; the area of pipes
    2300 square inches, and the engine blows four furnaces of 14 feet
    diameter, each making 100 tons of pig iron per week. Two high pressure
    cylinders, each of 6 inches diameter and 18 inches stroke, making 60 to
    80 strokes per minute, with steam of 60 Lbs. per square inch, lift two
    rams, each weighing 1000 lbs., five times in a minute, the leaders for
    the lift being 24 feet long. One high pressure cylinder of 12 inches
    diameter and 5 feet stroke, making 20 strokes per minute, with steam of
    60 to 70 lbs. pressure per square inch, lifts 6 buckets full of
    dredging per minute from a depth of 30 feet below the water, or lifts
    10 buckets full of mud per minute from a depth of 18 feet below the
    water.</P>

    <H2 CLASS="chapter"><A NAME="ch12"></A>CHAPTER XII.</H2>

    <H3>MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.</H3>

    <H4 CLASS="subhead"><A NAME="r01"></A>CONSTRUCTION OF ENGINES.</H4>

    <P>700. <EM>Q.</EM>--What are the qualities which should be possessed
    by the iron of which the cylinder of steam engines are made?</P>

    <P><EM>A.</EM>--The general ambition in making cylinders is to make
    them sound and hard; but it is expedient also to make them tough, so as
    to approach as nearly as possible to the state of malleable iron. This
    may be done by mixing in the furnace as many different kinds of iron as
    possible; and it may be set down as a general rule in iron founding,
    that the greater the number of the kinds of metal entering into the
    composition of any casting, the denser and tougher it will be. The
    constituent atoms of the different kinds of iron appear to be of
    different sizes, and the mixture of different kinds maintains the
    toughness, while it adds to the density and cohesive power. Hot blast
    iron was at one time generally believed to be weaker than cold blast
    iron, but it is now questioned whether it is not the stronger of the
    two. The cohesive strength of unmixed iron is not in proportion to its
    specific gravity, and its elasticity and power to resist shocks appear
    to become greater as the specific gravity becomes less. Nos. 3 and 4
    are the strongest irons. In most cases, iron melted in a cupola is not
    so strong as when remelted in an air furnace, and when run into green
    sand it is not reckoned so strong as when run into dry sand, or loam.
    The quality of the fuel, and even the state of the weather, exerts an
    influence on the quality of the iron: smelting furnaces, on the cold
    blast principle, have long been known to yield better iron in winter
    than in summer, probably from the existence of less moisture in the
    air; and it would probably be found to accomplish an improvement in the
    quality of the iron if the blast were made to pass through a vessel
    containing muriate of lime, by which the moisture of the air would be
    extracted. The expense of such a preparation would not be considerable,
    as, by subsequent evaporation, the salt might be used over and over
    again for the same purpose.</P>

    <P>701. <EM>Q.</EM>--Will you explain the process of casting
    cylinders?</P>

    <P><EM>A.</EM>--The mould into which the metal is poured is built up of
    bricks and loam, the loam being clay and sand ground together in a
    mill, with the addition of a little horse-dung to give it a fibrous
    structure and prevent cracks. The loam board, by which the circle of
    the cylinder is to be swept, is attached to an upright iron bar, at the
    distance of the radius of the cylinder, and a cylindrical shell of
    brick is built up, which is plastered on the inside with loam, and made
    quite smooth by traversing the perpendicular loam board round it. A
    core is then formed in a similar manner, but so much smaller as to
    leave a space between the shell and the core equal to the thickness of
    the cylinder, and into this space the melted metal is poured. Whatever
    nozzles or projections are required upon the cylinder, must be formed
    by means of wooden patterns, which are built into the shell, and
    subsequently withdrawn; but where a number of cylinders of the same
    kind are required, it is advisable to make these patterns of iron,
    which will not be liable to warp or twist while the loam is being
    dried. Before the iron is cast into the mould, the interior of the
    mould must be covered with finely powdered charcoal--or blackening, as
    it is technically termed; and the secret of making finely skinned
    castings lies in using plenty of blackening. In loam and dry sand
    castings the charcoal should be mixed with thick clay water, and
    applied until it is an eighth of an inch thick, or more; the surface
    should be then very carefully smoothed or sleeked, and if the metal has
    been judiciously mixed, and the mould thoroughly dried, the casting is
    sure to be a fine one. Dry sand and loam castings should be, as much as
    possible, made in boxes; the moulds may thereby be more rapidly and
    more effectually dried, and better castings will be got with a less
    expense.</P>

    <P>702. <EM>Q.</EM>--Will you explain the next operation which a
    cylinder undergoes?</P>

    <P><EM>A.</EM>--The next stage is the boring; and in boring cylinders
    of 74 inches diameter, the boring bar must move so as to make one
    revolution in about 4-1/2 minutes, at which speed the cutters will move
    at the rate of about 5 feet per minute. In boring brass, the speed must
    be slower; the common rate at which the tool moves in boring brass air
    pumps is about 3 feet per minute. If this speed be materially exceeded
    the tool will be spoiled, and the pump made taper. The speed proper for
    boring a cylinder will answer for boring the brass air pump of the same
    engine. A brass air pump of 36-1/2 inches diameter requires the bar to
    make one turn in about three minutes, which is also the speed proper
    for a cylinder 60 inches in diameter. To bore a brass air pump 36-1/2
    inches in diameter requires a week, an iron one requires 48 hours, and
    a copper one 24 hours. In turning a malleable iron shaft 12-3/4 inches
    in diameter, the shaft should make about five turns per minute, which
    is equivalent to a speed in the tool of about 16 feet per minute; but
    this speed may be exceeded if soap and water be plentifully run on the
    point of the tool. A boring mill, of which the speed may be varied from
    one turn in six minutes to twenty-five turns in one minute, will be
    suitable for all ordinary wants that can occur in practice.</P>

    <P>703. <EM>Q.</EM>--Are there any precautions necessary to be observed
    in order that the boring may be truly effected?</P>

    <P><EM>A.</EM>--In fixing a cylinder into the boring mill, great care
    must be taken that it is not screwed down unequally; and indeed it will
    be impossible to bore a large cylinder in a horizontal mill without
    being oval, unless the cylinder be carefully gauged when standing on
    end, and be set up by screws when laid in the mill until it again
    assumes its original form. A large cylinder will inevitably become oval
    if laid upon its side; and if while under the tension due to its own
    weight it be bored round, it will become oval again when set upon end.
    If the bottom be cast in, the cylinder will be probably found to be
    round at one end and oval at the other, unless a vertical boring mill
    be employed, or the precautions here suggested be adopted.</P>

    <P>704. <EM>Q.</EM>--Does the boring tool make the cylinder
    sufficiently smooth for the reception of the piston?</P>

    <P><EM>A.</EM>--Many engine makers give no other finish to their
    cylinders; but Messrs. Penn grind their cylinders after they are bored,
    by laying them on their side, and rubbing a piece of lead, with a cross
    iron handle like that of a rolling stone, and smeared with emery and
    oil, backward and forward-- the cylinder being gradually turned round
    so as to subject every part successively to the operation. The lead by
    which this grinding is accomplished is cast in the Cylinder, whereby it
    is formed of the right curve; but the part of the cylinder in which it
    is cast should be previously heated by a hot iron, else the metal may
    be cracked by the sudden heat.</P>

    <P>705. <EM>Q.</EM>--How are the parts of a piston fitted together so
    as to be perfectly steam tight?</P>

    <P><EM>A.</EM>--The old practice was to depend chiefly upon grinding as
    the means of making the rings tight upon the piston or upon one
    another; but scraping is now chiefly relied on. Some makers, however,
    finish their steam surfaces by grinding them with powdered Turkey stone
    and oil. A slight grinding, or polishing, with powdered Turkey stone
    and oil, appears to be expedient in ordinary cases, and may be
    conveniently accomplished by setting the piston on a revolving table,
    and holding the ring stationary by a cross piece of wood while the
    table turns round. Pieces of wood may be interposed between the ring
    and the body of the piston, to keep the ring nearly in its right
    position; but these pieces of wood should be fitted so loosely as to
    give some side play, else the disposition would arise to wear the
    flange of the piston into a groove.</P>

    <P>706. <EM>Q.</EM>--What kind of tool is used for finishing surfaces
    by scraping?</P>

    <P><EM>A.</EM>--A flat file bent, and sharpened at the end, makes an
    eligible scraper for the first stages; or a flat file sharpened at the
    end and used like a chisel for wood. A three-cornered file, sharpened
    at all the corners, is the best instrument for finishing the operation.
    The scraping tool should be of the best steel, and should be carefully
    sharpened at short intervals on a Turkey stone, so as to maintain a
    fine edge.</P>

    <P>707. <EM>Q.</EM>--Will you explain the method of fitting together
    the valve and cylinder faces?</P>

    <P><EM>A.</EM>--Both faces must first be planed, then filed according
    to the indications of a metallic straight edge, and subsequently of a
    thick metallic face plate, and finally scraped very carefully until the
    face plate bears equally all over the surface. In planing any surface,
    the catches which retain the surface on the planing machine should be
    relaxed previously to the last cut, to obviate distortion from
    springing. To ascertain, whether the face plate bears equally, smear it
    over with a little red ochre and oil, and move the face plate slightly,
    which will fix the color upon the prominent points. This operation is
    to be repeated frequently; and as the work advances, the quantity of
    coloring matter is to be diminished, until finally it is spread over
    the face plate in a thin film, which only dims the brightness of the
    plate. The surfaces at this stage must be rubbed firmly together to
    make the points of contact visible, and the higher points will become
    slightly clouded, while the other parts are left more or less in shade.
    If too small a quantity of coloring matter be used at first, it will be
    difficult to form a just conception of the general state of the
    surface, as the prominent points will alone be indicated, whereas the
    use of a large quantity of coloring matter in the latter stages would
    destroy the delicacy of the test the face plate affords. The number of
    bearing points which it is desirable to establish on the surface of the
    work, depends on the use to which the surface is to be applied; but
    whether it is to be finished with great elaboration, or otherwise, the
    bearing points should be distributed equally over the surface. Face
    plates, or planometers, as they are sometimes termed, are supplied by
    most of the makers of engineering tools. Every factory should be
    abundantly supplied with them, and also with steel straight edges; and
    there should be a master face plate, and a master straight edge, for
    the sole purpose of testing, from time to time, the accuracy of those
    in use.</P>

    <P>708. <EM>Q.</EM>--Is the operation of surfacing, which you have
    described, necessary in the case of all slide valves?</P>

    <P><EM>A.</EM>--Yes; and in fitting the faces of a D valve, great care
    must, in addition, be taken that the valve is not made conical; for
    unless the back be exactly parallel with the face, it will be
    impossible to keep the packing from being rapidly cut away. When the
    valve is laid upon the face plate, the back must be made quite fair
    along the whole length, by draw filing, according to the indications of
    a straight edge; and the distance from the face to the extreme height
    of the back must be made identical at each extremity.</P>

    <P>709. <EM>Q.</EM>--When you described the operation of boring the
    cylinder, you stated that the cylinder, when laid upon its side, became
    oval; will not this change of figure distort the cylinder face?</P>

    <P><EM>A.</EM>--It is not only in the boring of the cylinder that it is
    necessary to be careful that there is no change of figure, for it will
    be impossible to face the valves truly in the case of large cylinders,
    unless the cylinder be placed on end, or internal props be introduced
    to prevent the collapse due to the cylinder&#39;s weight. It may be
    added, that the change of figure is not instantaneous, but becomes
    greater after some continuance of the strain than it was at first, so
    that in gauging a cylinder to ascertain the difference of diameter when
    it is placed on its side, it should have lain some days upon its side
    to ensure the accuracy of the operation.</P>

    <P>710. <EM>Q.</EM>--How is any flaw in the valve or cylinder face
    remedied?</P>

    <P><EM>A.</EM>--Should a hole occur either in the valve, in the
    cylinder, or any other part where the surface requires to be smooth, it
    may be plugged up with a piece of cast iron, as nearly as possible of
    the same texture. Bore out the faulty part, and afterward widen the
    hole with an eccentric drill, so that it will be of the least diameter
    at the mouth. The hole may go more than half through the iron: fit then
    a plug of cast iron roughly by filing, and hammer it into the hole,
    whereby the plug will become riveted in it, and its surface may then be
    filed smooth. Square pieces may be let in after the same fashion, the
    hole being made dovetailed, and the pieces thus fitted will never come
    out.</P>

    <P>711. <EM>Q.</EM>--When cylinders are faced with brass, how is the
    face attached to the cylinder?</P>

    <P><EM>A.</EM>--Brass faces are put upon valves or cylinders by means
    of small brass screws tapped into the iron, with conical necks for the
    retention of the brass: they are screwed by means of a square head,
    which, when the screw is in its place, is cut off and filed smooth. In
    some cases the face is made of extra thickness, and a rim not so thick
    runs round it, forming a step or recess for the reception of brass
    rivets, the heads of which are clear of the face.</P>

    <P>712. <EM>Q.</EM>--What is the best material for valve faces?</P>

    <P><EM>A.</EM>--Much trouble is experienced with every modification of
    valve face; but cast iron working upon cast iron is, perhaps, the best
    combination yet introduced. A usual practice is to pin brass faces on
    the cylinder, allowing the valve to retain its cast iron face. Some
    makers employ brass valves, and others pin brass on the valves, leaving
    the cylinder with a cast iron face. If brass valves are used, it is
    advisable to plane out two grooves across the face, and to fill them up
    with hard cast iron to prevent rutting. Speculum metal and steel have
    been tried for the cylinder faces, but only with moderate success. In
    some cases the brass gets into ruts; but the most prevalent affection
    is a degradation of the iron, owing to the action of the steam, and the
    face assuming a granular appearance, something like loaf sugar. This
    action shows itself only at particular spots, and chiefly about the
    angles of the port or valve face. At first the action is slow; but when
    once the steam has worked a passage for itself, the cutting away
    becomes very rapid, and, in a short time, it will be impossible to
    prevent the engine from heating when stopped, owing to the leakage of
    steam through the valve into the condenser. Copper steam pipes seem to
    have some galvanic action on valve faces, and malleable iron pipes have
    sometimes been substituted; but they are speedily worn out by
    oxidation, and the scales of rust which are carried on by the steam
    scratch the valves and cylinders, so that the use of copper pipes is
    the least evil.</P>

    <P>713. <EM>Q.</EM>--Will you explain in what manner the joints of an
    engine are made?</P>

    <P><EM>A.</EM>--Rust joints are not now much used in engines of any
    kind, yet it is necessary that the engineer should be acquainted with
    the manner of their formation. One ounce of sal-ammoniac in powder is
    mingled with 18 ounces or a pound of borings of cast iron, and a
    sufficiency of water is added to wet the mixture thoroughly, which
    should be done some hours before it is wanted for use. Some persons add
    about half an ounce of flowers of brimstone to the above proportions,
    and a little sludge from the grindstone trough. This cement is caulked
    into the joints with a caulking iron, about three quarters of an inch
    wide and one quarter of an inch thick, and after the caulking is
    finished the bolts of the joints may be tried to see if they cannot be
    further tightened. The skin of the iron must, in all cases, be broken
    where a rust joint is to be made; and, if the place be greasy, the
    surface must be well rubbed over with nitric acid, and then washed with
    water, till no grease remains. The oil about engines has a tendency to
    damage rust joints by recovering the oxide. Coppersmiths staunch the
    edges of their plates and rivets by means of a cement formed of pounded
    quicklime, with serum of blood, or white of egg; and in copper boilers
    such a substance may be useful in stopping the impalpable leaks which
    sometimes occur, though Roman, cement appears to be nearly as
    effectual.</P>

    <P>714. <EM>Q.</EM>--Will you explain the method of case hardening the
    parts of engines?</P>

    <P><EM>A.</EM>--The most common plan for case hardening consists in the
    insertion of the articles to be operated upon among horn or leather
    cuttings, hone dust, or animal charcoal, in an iron box provided with a
    tight lid, which is then put into a furnace for a period answerable to
    the depth of steel required. In some cases the plan pursued by the
    gunsmiths may be employed with convenience. The article is inserted in
    a sheet iron case amid bone dust, often not burned; the lid of the box
    is tied on with wire, and the joint luted with clay; the box is heated
    to redness as quickly as possible and kept half an hour at a uniform
    heat: its contents are then suddenly immersed in cold water. The more
    unwieldy portions of an engine may be case hardened by prussiate of
    potash--a salt made from animal substances, composed of two atoms of
    carbon and one of nitrogen, and which operates on the same principle as
    the charcoal. The iron is heated in the fire to a dull red heat, and
    the salt is either sprinkled upon it or rubbed on in a lump, or the
    iron is rubbed in the salt in powder. The iron is then returned to the
    fire for a few minutes, and finally immersed in water. By some persons
    the salt is supposed to act unequally, as if there were greasy spots
    upon the iron which the salt refused to touch, and the effect under any
    circumstances is exceedingly superficial; nevertheless, upon all parts
    not exposed to wear, a sufficient coating of steel may be obtained by
    this process.</P>

    <P>715. <EM>Q.</EM>--What kind of iron is most suitable for the working
    parts of an engine?</P>

    <P><EM>A.</EM>--In the malleable iron work of engines scrap iron has
    long been used, and considered preferable to other kinds; but if the
    parts are to be case hardened, as is now the usual practice, the use of
    scrap iron is to be reprehended, as it is almost sure to make the parts
    twist in the case hardening process. In case hardening, iron absorbs
    carbon, which causes it to swell; and as some kinds of iron have a
    greater capacity for carbon than other kinds, in case hardening they
    will swell more, and any such unequal enlargement in the constituent
    portions of a piece of iron will cause it to change its figure. In some
    cases, case hardening has caused such a twisting of the parts of an
    engine, that they could not afterward be fitted together; it is
    preferable, therefore, to make such parts as are to be case hardened to
    any considerable depth of Lowmoor, Bowling, or Indian iron, which being
    homogeneous will absorb carbon equally, and will not twist.</P>

    <P>716. <EM>Q.</EM>--What is the composition of the brass used for
    engine bearings?</P>

    <P><EM>A.</EM>--The brass bearings of an engine are composed
    principally of copper and tin. A very good brass for steam engine
    bearings consists of old copper 112 lbs., tin 12-1/2 lbs., zinc 2 or 3
    oz.; and if new tile copper be used, there should be 13 lbs. of tin
    instead of 12-1/2 lbs. A tough brass for engine work consists of 1-1/2
    lb. tin, 1-1/2 lb. zinc, and 10 lbs. copper; a brass for heavy
    bearings, 2-1/2 oz. tin, 1/2 oz. zinc, and 1 lb. copper. There is a
    great difference in the length of time brasses wear, as made by
    different manufacturers; but the difference arises as much from a
    different quantity of surface, as from a varying composition of the
    metal. Brasses should always be made strong and thick, as when thin
    they collapse upon the bearing and increase the friction and the
    wear.</P>

    <P>717. <EM>Q.</EM>--How is Babbitt&#39;s metal for lining the bushes
    of machinery compounded?</P>

    <P><EM>A.</EM>--Babbitt&#39;s patent lining metal for bushes has been
    largely employed in the bushes of locomotive axles and other machinery:
    it is composed of 1 lb. of copper, 1 lb. regulus of antimony, and 10
    lbs. of tin, or other similar proportions, the presence of tin being
    the only material condition. The copper is first melted, then the
    antimony is added, with a small proportion of tin-charcoal being
    strewed over the surface of the metal in the crucible to prevent
    oxidation. The bush or article to be lined, having been cast with a
    recess for the soft metal, is to be fitted to an iron mould, formed of
    the shape and size of the bearing or journal, allowing a little in size
    for the shrinkage. Drill a hole for the reception of the soft metal,
    say 1/2 to 3/4 inch diameter, wash the parts not to be tinned with a
    clay wash to prevent the adhesion of the tin, wet the part to be tinned
    with alcohol, and sprinkle fine sal-ammoniac upon it; heat the article
    until fumes arise from the ammonia, and immerse it in a kettle of Banca
    tin, care being taken to prevent oxidation. When sufficiently tinned,
    the bush should be soaked in water, to take off any particles of
    ammonia that may remain upon it, as the ammonia would cause the metal
    to blow. Wash with pipe clay, and dry; then heat the bush to the
    melting point of tin, wipe it clean, and pour in the metal, giving it
    sufficient head as it cools; the bush should then be scoured with fine
    sand, to take off any dirt that may remain upon it, and it is then fit
    for use. This metal wears for a longer time than ordinary gun metal,
    and its use is attended with very little friction. If the bearing
    heats, however, from the stopping of the oil hole or otherwise, the
    metal will be melted out. A metallic grease, containing particles of
    tin in the state of an impalpable powder, would probably be preferable
    to the lining of metal just described.</P>

    <P>718. <EM>Q.</EM>--Can you state the composition of any other alloys
    that are used in engine work?</P>

    <P><EM>A.</EM>--The ordinary range of good yellow brass that files and
    turns well, is about 4-1/2 to 9 ounces of zinc to the pound of copper.
    Flanges to stand brazing may be made of copper 1 lb., zinc 1/2 oz.,
    lead 3/8 oz. Brazing solders when stated in the order of their hardness
    are:-three parts copper and one part zinc (very hard), eight parts
    brass and one part zinc (hard), six parts brass, one part tin, and one
    part zinc (soft); a very common solder for iron, copper, and brass,
    consists of nearly equal parts of copper and zinc. Muntz&#39;s metal
    consists of forty parts zinc and sixty of copper; any proportions
    between the extremes of fifty parts of zinc and fifty parts copper, and
    thirty-seven zinc and sixty-three copper, will roll and work at a red
    heat, but forty zinc to sixty copper are the proportions preferred.
    Bell metal, such as is used for large bells, consists of 4-1/2 ounces
    to 5 ounces of tin to the pound of copper; speculum metal consists of
    from 7-1/2 ounces to 8-1/2 ounces of tin to the pound of copper.</P>

    <H4 CLASS="subhead"><A NAME="r02"></A>ERECTION OF ENGINES.</H4>

    <P>719. <EM>Q.</EM>--Will you explain the operation of erecting a pair
    of side lever engines in the workshop?</P>

    <P>A.--In beginning the erection of side lever marine engines in the
    workshop, the first step is to level the bed plate lengthways and
    across, and strike a line up the centre, as near as possible in the
    middle, which indent with a chisel in various places, so that it may at
    any time be easily found again. Strike another line at right angles
    with this, either at the cylinder or crank centre, by drawing a
    perpendicular in the usual manner. Lay the other sole plate alongside
    at the right distance, and strike a line at the cylinder or crank
    centre of it also, shifting either sole plate a little endways until
    these two transverse lines come into the same line, which may be
    ascertained by applying a straight edge across the two sole plates.
    Strike the rest of the centres across, and drive a pin into each corner
    of each sole plate, which file down level, so as to serve for points of
    reference at any future stage; next, try the cylinder, or plumb it on
    the inside roughly, and see how it is for height, in order to ascertain
    whether much will be required to be chipped off the bottom, or whether
    more requires to be chipped off the one side than the other. Chip the
    cylinder bottom fair; set it in its place, plumb the cylinder very
    carefully with a straight edge and silk thread, and scribe it so as to
    bring the cylinder mouth to the right height, then chip the sole plate
    to suit that height. The cylinder must then be tried on again, and the
    parts filed wherever they bear hard, until the whole surface is well
    fitted. Next, chip the place for the framing; set up the framing, and
    scribe the horizontal part of the jaw with the scriber used for the
    bottom of the cylinder, the upright part being set to suit the shaft
    centres, and the angular flange of cylinder, where the stay is
    attached, having been previously chipped plumb and level. The stake
    wedges with which the framing is set up preparatorily to the operation
    of scribing, must be set so as to support equally the superincumbent
    weight, else the framing will spring from resting unequally, and it
    will be altogether impossible to fit it well. These directions
    obviously refer exclusively to the old description of side lever engine
    with cast iron framing; but there is more art in erecting an engine of
    that kind with accuracy, than in erecting one of the direct action
    engines, where it is chiefly turned or bored surfaces that have to be
    dealt with.</P>

    <P>720. <EM>Q.</EM>--How do you lay out the positions of the centres of
    a side lever engine?</P>

    <P><EM>A.</EM>--In fixing the positions of the centres in side lever
    engines, it appears to be the most convenient way to begin with the
    main centre. The height of the centre of the cross head at half stroke
    above the plane of the main centre is fixed by the drawing of the
    engine, which gives the distance from the centre of cross head at half
    stroke to the flange of the cylinder; and from thence it is easy to
    find the perpendicular distance from the cylinder flange to the plane
    of the main centre, merely by putting a straight edge along level, from
    the position of the main centre to the cylinder, and measuring from the
    cylinder flauge down to it, raising or lowering the straight edge until
    it rests at the proper measurement. The main centre is in that plane,
    and the fore and aft position is to be found by plumbing up from the
    centre line on the sole plate. To find the paddle shaft centre, plumb
    up from the centre line marked on the edge of the sole plate, and on
    this line lay off from the plane of the main centre the length of the
    connecting rod, if that length be already fixed, or otherwise the
    height fixed in the drawing of the paddle shaft above the main centre.
    To fix the centre for the parallel motion shaft, when the parallel bars
    are connected with the cross head, lay off from the plane of main
    centre the length of the parallel bar from the centre of the cylinder,
    deduct the length of the radius crank, and plumb up the central line of
    motion shaft; lay off on this line, measuring from the plane of main
    centre, the length of the side rod; this gives the centre of parallel
    motion shaft when the radius bars join the cross head, as is the
    preferable practice where parallel motions are used. The length of the
    connecting rod is the distance from the centre of the beam when level,
    or the plane of the main centre, to the centre of the paddle shaft. The
    length of the side rods is the distance from the centre line of the
    beam when level, to the centre of the cross head when the piston is at
    half stroke. The length of the radius rods of the parallel motion is
    the distance from the point of attachment on the cross head or side
    rod, when the piston is at half stroke, to the extremity of the radius
    crank when the crank is horizontal; or in engines with the parallel
    motion attached to the cross head, it is the distance from the centre
    of the pin of the radius crank when horizontal to the centre of the
    cylinder. Having fixed the centre of the parallel motion shaft in the
    manner just described, it only remains to put the parts together when
    the motion is attached to the cross head; but when the motion is
    attached to the side rod, the end of the parallel bar must not move in
    a perpendicular line, but in an arc, the versed sine of which bears the
    same ratio to that of the side lever, that the distance from the top of
    the side rod to the point of attachment bears to the total length of
    the side rod.</P>

    <P>721. <EM>Q.</EM>--How do you ascertain the accuracy of the parallel
    motion?</P>

    <P><EM>A.</EM>--The parallel motion when put in its place should be
    tested by raising and lowering the piston by means of the crane. First,
    set the beams level, and shift in or out the motion shaft plummer
    blocks or bearings, until the piston rod is upright. Then move the
    piston to the two extremes of its motion. If at both ends the cross
    head is thrown too much out, the stud in the beam to which the motion
    side rod is attached is too far out, and must be shifted nearer to the
    main centre; if at the extremities the cross head is thrown too far in,
    the stud in the beam is not out far enough. If the cross head be thrown
    in at the one end, and out equally at the other, the fault is in the
    motion side rod, which must be lengthened or shortened to remedy the
    defect.</P>

    <P>722. <EM>Q.</EM>--Will you describe the method pursued in erecting
    oscillating engines?</P>

    <P><EM>A.</EM>--The columns here are of wrought iron, and in the case
    of small engines there is a template made of wood and sheet iron, in
    which the holes are set in the proper positions, by which the upper and
    lower frames are adjusted; but in the case of large engines, the holes
    are set off by means of trammels. The holes for the reception of the
    columns are cast in the frames, and are recessed out internally: the
    bosses encircling the holes are made quite level across, and made very
    true with a face plate, and the pillars which have been turned to a
    gauge are then inserted. The top frame is next put on, and must bear
    upon the collars of the columns so evenly, that one of the columns will
    not be bound by it harder than another. If this point be not attained,
    the surfaces must be further scraped, until a perfect fit is
    established. The whole of the bearings in the best oscillating engines
    are fitted by means of scraping, and on no other mode of fitting can
    the same reliance be placed for exactitude.</P>

    <P>723. <EM>Q.</EM>--How do you set out the trunnions of oscillating
    engines, so that they shall be at right angles with the interior of the
    cylinder?</P>

    <P><EM>A.</EM>--Having bored the cylinder, faced the flange, and bored
    out the hole through which the boring bar passes, put a piece of wood
    across the mouth of the cylinder, and jam it in, and put a similar
    piece in the hole through the bottom of the cylinder. Mark the centre
    of the cylinder upon each of these pieces, and put into the bore of
    each trunnion an iron plate, with a small indentation in the middle to
    receive the centre of a lathe, and adjusting screws to bring the centre
    into any required position. The cylinder must then be set in a lathe,
    and hung by the centres of the trunnions, and a straight edge must be
    put across the cylinder mouth and levelled, so as to pass through the
    line in which the centre of the cylinder lies. Another similar straight
    edge, and similarly levelled, must be similarly placed across the
    cylinder bottom, so as to pass through the central line of the
    cylinder; and the cylinder is then to be turned round in the trunnion
    centres-the straight edges remaining stationary, which will at once
    show whether the trunnions are in the same horizontal plane as the
    centre of the cylinder, and if not, the screws of the plates in the
    trunnions must be adjusted until the central point of the cylinder just
    comes to the straight edge, whichever end of the cylinder is presented.
    To ascertain whether the trunnions stand in a transverse plane,
    parallel to the cylinder flange, it is only necessary to measure down
    from the flange to each trunnion centre; and if both these conditions
    are satisfied, the position of the centres may be supposed to be right.
    The trunnion bearings are then turned, and are fitted into blocks of
    wood, in which they run while the packing space is being turned out.
    Where many oscillating engines are made, a lathe with four centres is
    used, which makes the use of straight edges in setting out the
    trunnions superfluous.</P>

    <P>724. <EM>Q.</EM>--Will you explain how the slide valve of a marine
    engine is set?</P>

    <P><EM>A.</EM>--Place the crank in the position corresponding to the
    end of the stroke, which can easily be done in the shop with a level,
    or plumb line; but in a steam vessel another method becomes necessary.
    Draw the transverse centre line, answering to the centre line of the
    crank shaft, on the sole plate of the engine, or on the cylinder mouth
    if the engine be of the direct action kind; describe a circle of the
    diameter of the crank pin upon the large eye of the crank, and mark off
    on either side of the transverse centre line a distance equal to the
    semi-diameter of the crank pin. From the point thus found, stretch a
    line to the edge of the circle described on the large eye of the crank,
    and bring round the crank shaft till the crank pin touches the
    stretched line; the crank may thus be set at either end of its stroke.
    When the crank is thus placed at the end of the stroke, the valve must
    be adjusted so as to have the amount of lead, or opening on the steam
    side, which it is intended to give at the beginning of the stroke; the
    eccentric must then be turned round upon the shaft until the notch in
    the eccentric rod comes opposite the pin on the valve lever, and falls
    into gear: mark upon the shaft the situation of the eccentric, and put
    on the catches in the usual way. The same process must be repeated for
    going astern, shifting round the eccentric to the opposite side of the
    shaft, until the rod again falls into gear. In setting valves, regard
    must of course be had to the kind of engine, the arrangements of the
    levers, and the kind of valve employed; and in any general instructions
    it is impossible to specify every modification in the procedure that
    circumstances may render advisable.</P>

    <P>725. <EM>Q.</EM>--Is a similar method of setting the valve adopted
    when the link motion is employed.</P>

    <P><EM>A.</EM>--Each end of the link of the link motion has the kind of
    motion communicated to it that is due to the action of the particular
    eccentric with which that end is in connection. In that form of the
    link motion in which the link itself is moved up or down, there is a
    different amount of lead for each different position of the link, since
    to raise or lower the link is tantamount to turning the eccentric round
    on the shaft. In that form of the link motion in which the link itself
    is not raised or lowered, but is susceptible of a motion round a centre
    in the manner of a double ended lever, the lead continues uniform. In
    both forms of the link motion, as the stroke of the valve may be varied
    to any required extent while the lap is a constant quantity, the
    proportion of the lap relatively to the stroke of the valve may also be
    varied to any required extent, and the amount of the lap relatively
    with the stroke of the valve determines the amount of the expansion. In
    setting the valve when fitted with the link motion, the mode of
    procedure is much the same as when it is moved by a simple eccentric.
    The first thing is to determine if the eccentric rods are of the proper
    length, and this is done by setting the valve at half stroke and
    turning round the eccentric, marking each extremity of the travel of
    the end of the rod. The valve attachment should be midway between these
    extremes; and if it is not so, it must be made so by lengthening or
    shortening the rod. The forward and backward eccentric rods are to be
    adjusted in this way, and this being done, the engine is to be put to
    the end of the stroke, and the eccentric is to be turned round until
    the amount of lead has been given that is desired. The valve must be
    tried by turning the engine round to see that it is right at both
    centres, for going ahead and also for going astern. In some examples of
    the link motion, one of the eccentric rods is made a little longer than
    the other, and the position of the point of suspension or point of
    support powerfully influences the action of the link in certain cases,
    especially if the link and this point are not in the same vertical
    line. To reconcile all the conditions proper to the satisfactory
    operation of the valve in the construction of the link motion, is a
    problem requiring a good deal of attention and care for its
    satisfactory solution; and to make sure that this result is attained,
    the engine must be turned round a sufficient number of times to enable
    us to ascertain if the valve occupies the desired position, both at the
    top and bottom centres, whether the engine is going ahead or astern.
    This should also be tried with the starting handle in the different
    notches, or, in other words, with the sliding block in the slot or
    opening of the link in different positions.</P>

    <H4 CLASS="subhead"><A NAME="r03"></A>MANAGEMENT OF MARINE
    BOILERS.</H4>

    <P>726. <EM>Q.</EM>--You have already stated that the formation of salt
    or scale in marine boilers is to be prevented by blowing out into the
    sea at frequent intervals a portion of the concentrated water. Will you
    now explain how the proper quantity of water to be blown out is
    determined?</P>

    <P><EM>A.</EM>--By means of the salinometer, which is an instrument for
    determining the density of the water, constructed on the principle of
    the hydrometer for telling the strength of spirits. Some of the water
    is drawn off from the boiler from time to time, and the salinometer is
    immersed in it after it has been cooled. By the graduations of the
    salinometer the saltness of this water is at once discovered; and if
    the saltness exceeds 8 ounces of salt in the gallon, more water should
    be blown out of the boiler to be replenished with fresher water from
    the sea, until the prescribed limit of freshness is attained. Should
    the salinometer be accidentally broken, a temporary one may be
    constructed of a phial weighted with a few grains of shot or other
    convenient weight. The weighted phial is first to be floated in fresh
    water, and its line of floatation marked; then to be floated in salt
    water, and its line of floatation marked; and another mark of an equal
    height above the salt water mark will be the blow off point.</P>

    <P>727. <EM>Q.</EM>--HOW often should boilers be blown off in order to
    keep them free from incrustation?</P>

    <P><EM>A.</EM>--Flue boilers generally require to be blown off about
    twice every watch, or about twice in the four hours; but tubular
    boilers may require to be blown off once every twenty minutes, and such
    an amount of blowing off should in every case be adopted, as will
    effectually prevent any injurious amount of incrustation.</P>

    <P>728. <EM>Q.</EM>--In the event of scale accumulating on the flues of
    a boiler, what is the best way of removing it?</P>

    <P><EM>A.</EM>--If the boilers require to be scaled, the best method of
    performing the operation appears to be the following:--Lay a train of
    shavings along the flues, open the safety valve to prevent the
    existence of any pressure within the boiler, and light the train of
    shavings, which, by expanding rapidly the metal of the flues, while the
    scale, from its imperfect conducting power, can only expand slowly,
    will crack off the scale; by washing down the flues with a hose, the
    scale will be carried to the bottom of the boiler, or issue, with the
    water, from the mud-hole doors. This method of scaling must be
    practised only by the engineer himself, and must not be intrusted to
    the firemen who, in their ignorance, might damage the boiler by
    overheating the plates. It is only where the incrustation upon the
    flues is considerable that this method of removing it need be
    practised; in partial cases the scale may be chipped off by a hatched
    faced hammer, and the flues may then be washed down with the hose in
    the manner before described.</P>

    <P>729. <EM>Q.</EM>--Should the steam be let out of the boiler, after
    it has blown out the water, when the engine is stopped?</P>

    <P><EM>A.</EM>--No; it is better to retain the steam in the boiler, as
    the heat and moisture it occasions soften any scale adhering to the
    boiler, and cause it to peel off. Care must, however, be taken not to
    form a vacuum in the boiler; and the gauge cocks, if opened, will
    prevent this.</P>

    <P>730. <EM>Q.</EM>--Are tubular boilers liable to the formation of
    scale in certain places, though generally free from it?</P>

    <P><EM>A.</EM>--In tubular boilers a good deal of care is required to
    prevent the ends of the tubes next the furnace from becoming coated
    with scale. Even when the boiler is tolerably clean in other places the
    scale will collect here; and in many cases where the amount of blowing
    off previously found to suffice for flue boilers has been adopted, an
    incrustation five eighths of an inch in thickness has formed in twelve
    months round the furnace ends of the tubes, and the stony husks
    enveloping them have actually grown together in some parts so as
    totally to exclude the water.</P>

    <P>731. <EM>Q.</EM>--When a tubular boiler gets incrusted in the manner
    you have described, what is the best course to be adopted for the
    removal of the scale?</P>

    <P><EM>A.</EM>--When a boiler gets into this state the whole of the
    tubes must be pulled out, which may be done by a Spanish windlass
    combined with a pair of blocks; and three men, when thus provided, will
    be able to draw out from 50 to 70 tubes per day,--those tubes with the
    thickest and firmest incrustations being, of course, the most difficult
    to remove. The act of drawing out the tubes removes the incrustation;
    but the tubes should afterward be scraped by drawing them backward and
    forward between the old files, fixed in a vice, in the form of the
    letter V. The ends of the tube should then be heated and dressed with
    the hammer, and plunged while at a blood heat into a bed of sawdust to
    make them cool soft, so that they may be riveted again with facility. A
    few of the tubes will be so far damaged at the ends by the act of
    drawing them out, as to be too short for reinsertion: this result might
    be to a considerable extent obviated by setting the tube plates at
    different angles, so that the several horizontal rows of tubes would
    not be originally of the same length, and the damaged tubes of the long
    rows would serve to replace the short ones; but the practice would be
    attended with other inconveniences.</P>

    <P>732. <EM>Q.</EM>--Is there no other means of keeping boilers free
    from scale than by blowing off?</P>

    <P><EM>A.</EM>--Muriatic acid, or muriate of ammonia, commonly called
    sal-ammoniac, introduced into a boiler, prevents scale to a great
    extent; but it is liable to corrode the boiler internally, and also to
    damage the engine, by being carried over with the steam; and the use of
    such intermixtures does not appear to be necessary, if blowing off from
    the surface of the water is largely practised. In old boilers, however,
    already incrusted with scale, the use of muriate of ammonia may
    sometimes be advantageous.</P>

    <P>733. <EM>Q.</EM>--Are not the tubes of tubular boilers liable to be
    choked up by deposits of soot?</P>

    <P><EM>A.</EM>--The soot which collects in the inside of the tubes of
    tubular boilers is removed by means of a brush, like a large bottle
    brush; and the carbonaceous scale, which remains adhering to the
    interior of the tubes, is removed by a circular scraper. Ferules in the
    tubes interfere with the action of this scraper, and in the case of
    iron tubes ferules are now generally discarded; but it will sometimes
    be necessary to use ferules for iron tubes, where the tubes have been
    drawn and reinserted, as it may be difficult to refix the tubes without
    such an auxiliary. Tubes one tenth of an inch in thickness are too
    thin: one eighth of an inch is a better thickness, and such tubes will
    better dispense with the use of ferules, and will not so soon wear into
    holes.</P>

    <P>734. <EM>Q.</EM>--If the furnace or flue of a boiler be injured, how
    do you proceed to repair it?</P>

    <P><EM>A.</EM>--If from any imperfection in the roof of a furnace or
    flue a patch requires to be put upon it, it will be better to let the
    patch be applied upon the upper, rather than upon the lower, surface of
    the plate; as if applied within the furnace a recess will be formed for
    the lodgment of deposit, which will prevent the rapid transmission of
    the heat in that part; and the iron will be very liable to be again
    burned away. A crack in a plate may be closed by boring holes in the
    direction of the crack, and inserting rivets with large heads, so as to
    cover up the imperfection. If the top of the furnace be bent down, from
    the boiler having been accidentally allowed to get short of water, it
    may be set up again by a screw jack,--a fire of wood having been
    previously made beneath the injured plate; but it will in general be
    nearly as expeditious a course to remove the plate and introduce a new
    one, and the result will be more satisfactory.</P>

    <P>735. <EM>Q.</EM>--In the case of the chimney being carried away by
    shot or otherwise, what course would you pursue?</P>

    <P><EM>A.</EM>--In some cases of collision, the funnel is carried away
    and lost overboard, and such cases are among the most difficult for
    which a remedy can be sought. If flame come out of the chimney when the
    funnel is knocked away, so as to incur the risk of setting the ship on
    fire, the uptake of the boiler must be covered over with an iron plate,
    or be sufficiently covered to prevent such injury. A temporary chimney
    must then be made of such materials as are on board the ship. If there
    are bricks and clay or lime on board, a square chimney may be built
    with them, or, if there be sheet iron plates on board, a square chimney
    may be constructed of them. In the absence of such materials, the
    awning stanchions may be set up round the chimney, and chain rove in
    through among them in the manner of wicker work, so as to make an iron
    wicker chimney, which may then be plastered outside with wet ashes
    mixed with clay, flour, or any other material that will give the ashes
    cohesion. War steamers should carry short spare funnels, which may
    easily be set up should the original funnel be shot away; and if a jet
    of steam be let into the chimney, a very short and small funnel will
    suffice for the purpose of draught.</P>

    <H4 CLASS="subhead"><A NAME="r04"></A>MANAGEMENT OF MARINE
    ENGINES.</H4>

    <P>736. <EM>Q.</EM>--What are the most important of the points which
    suggest themselves to you in connection with the management of marine
    engines?</P>

    <P><EM>A.</EM>--The attendants upon engines should prepare themselves
    for any casualty that may arise, by considering possible cases of
    derangement, and deciding In what way they would act should certain
    accidents occur. The course to be pursued must have reference to
    particular engines, and no general rules can therefore be given; but
    every marine engineer should be prepared with the measures to be
    pursued in the emergencies in which he may be called upon to act, and
    where everything may depend upon his energy and decision.</P>

    <P>737. <EM>Q.</EM>--What is the first point of a marine engineer&#39;s
    duty?</P>

    <P><EM>A.</EM>--The safe custody of the boiler. He must see that the
    feed is maintained, being neither too high nor too low, and that
    blowing out the supersalted water is practised sufficiently. The
    saltness of the water at every half hour should be entered in the log
    book, together with the pressure of steam, number of revolutions of the
    engine, and any other particulars which have to be recorded. The
    economical use of the fuel is another matter which should receive
    particular attention. If the coal is very small, it should be wetted
    before being put on the fire. Next to the safety of the boiler, the
    bearings of the engine are the most important consideration. These
    points, indeed, constitute the main parts of the duty of an engineer,
    supposing no accident to the machinery to have taken place.</P>

    <P>738. <EM>Q.</EM>--If the eccentric catches or hoops were disabled,
    how would you work the valve?</P>

    <P><EM>A.</EM>--If the eccentric catches or hoops break or come off,
    and the damage cannot readily be repaired, the valve may be worked by
    attaching the end of the starting handle to any convenient part of the
    other engine, or to some part in connection with the connecting rod of
    the same engine. In side lever engines, with the starting bar hanging
    from the top of the diagonal stay, as is a very common arrangement, the
    valve might be wrought by leading a rope from the side lever of the
    other engine through blocks so as to give a horizontal pull to the
    hanging starting bar, and the bar could be brought back by a weight.
    Another plan would be, to lash a piece of wood to the cross tail butt
    of the damaged engine, so as to obtain a sufficient throw for working
    the valve, and then to lead a piece of wood or iron, from a suitable
    point in the piece of wood attached to the cross tail, to the starting
    handle, whereby the valve would receive its proper motion. In
    oscillating engines it is easy to give the required motion to the
    valve, by deriving it from the oscillation of the cylinder.</P>

    <P>739. <EM>Q.</EM>--What would you do if a crank pin broke?</P>

    <P><EM>A.</EM>--If the crank pin breaks in a paddle vessel with two
    engines, the other engine must be made to work one wheel. In a screw
    vessel the same course may be pursued, provided the broken crank is not
    the one through which the force of the other engine is communicated to
    the screw. In such a case the vessel will be as much disabled as if she
    broke the screw shaft or screw.</P>

    <P>740. <EM>Q.</EM>--Will the unbroken engine, in the case of
    disarrangement of one of the two engines of a screw or paddle vessel,
    be able of itself to turn the centre?</P>

    <P><EM>A.</EM>--It will sometimes happen, when there is much lead upon
    the slide valve, that the single engine, on being started, cannot be
    got to turn the centre if there be a strong opposing wind and sea; the
    piston going up to near the end of the stroke, and then coming down
    again without the crank being able to turn the centre. In such cases,
    it will be necessary to turn the vessel&#39;s head sufficiently from
    the wind to enable some sail to be set; and if once there is weigh got
    upon the vessel the engine will begin to work properly, and will
    continue to do so though the vessel be put head to wind as before.</P>

    <P>741. <EM>Q.</EM>--What should be done if a crack shows itself in any
    of the shafts or cranks?</P>

    <P><EM>A.</EM>--If the shafts or cranks crack, the engine may
    nevertheless be worked with moderate pressure to bring the vessel into
    port; but if the crack be very bad, it will be expedient to fit strong
    blocks of wood under the ends of the side levers, or other suitable
    part, to prevent the cylinder bottom or cover from being knocked out,
    should the damaged part give way. The same remark is applicable when
    flaws are discovered in any of the main parts of the engine, whether
    they be malleable or cast iron; but they must be carefully watched, so
    that the engines may be stopped if the crack is extending further.
    Should fracture occur, the first thing obviously to be done is to throw
    the engines out of gear; and should there be much weigh on the vessel,
    the steam should at once be thrown on the reverse side of the piston,
    so as to counteract the pressure of the paddle wheel.</P>

    <P>742. <EM>Q.</EM>--Have you any information to offer relative to the
    lubrication of engine bearings?</P>

    <P><EM>A.</EM>--A very useful species of oil cup is now employed in a
    number of steam vessels, and which, it is said, accomplishes a
    considerable saving of oil, at the same time that it more effectually
    lubricates the bearings. A ratchet wheel is fixed upon a little shaft
    which passes through the side of the oil cup, and is put into slow
    revolution by a pendulum attached to its outside and in revolving it
    lifts up little buckets of oil and empties them down a funnel upon the
    centre of the bearing. Instead of buckets a few short pieces of wire
    are sometimes hung on the internal revolving wheel, the drops of oil
    which adhere on rising from the liquid being deposited. upon a high
    part set upon the funnel, and which, in their revolution, the hanging
    wires touch. By this plan, however, the oil is not well supplied at
    slow speeds, as the drops fall before the wires are in proper position
    for feeding the journal. Another lubricator consists of a cock or plug
    inserted in the neck of the oil cup, and set in revolution by a
    pendulum and ratchet wheel, or any other means. There is a small cavity
    in one side of the plug, which is filled with oil when that side is
    uppermost, and delivers the oil through the bottom pipe when it comes
    opposite to it.</P>

    <P>743. <EM>Q.</EM>--What are the prevailing causes of the heating of
    bearings?</P>

    <P><EM>A.</EM>--Bad fitting, deficient surface, and too tight screwing
    down. Sometimes the oil hole will choke, or the syphon wick for
    conducting the oil from the oil cup into the central pipe leading to
    the bearing will become clogged with mucilage from the oil. In some
    cases bearings heat from the existence of a cruciform groove on the top
    brass for the distribution of the oil, the effect of which is to leave
    the top of the bearings dry. In the case of revolving journals the plan
    for cutting a cruciform channel for the distribution of the oil does
    not do much damage; but in other cases, as in beam journals, for
    instance, it is most injurious, and the brasses cannot wear well
    wherever the plan is pursued. The right way is to make a horizontal
    groove along the brass where it meets the upper surface of the bearing,
    so that the oil may be all deposited on the highest point of the
    journal, leaving the force of gravity to send it downward. This channel
    should, of course, stop short a small distance from each flange of the
    brass, otherwise the oil would run out at the ends.</P>

    <P>744. <EM>Q.</EM>--If a bearing heats, what is to be done?</P>

    <P><EM>A.</EM>--The first thing is to relax the screws, slow or stop
    the engine, and cool the bearing with water, and if it is very hot,
    then hot water may be first employed to cool it, and then cold. Oil
    with sulphur intermingled is then to be administered, and as the parts
    cool down, the screws may be again cautiously tightened, so as to take
    any jump off the engine from the bearing being too slack. The bearings
    of direct acting screw engines require constant watching, as, if there
    be any disposition to heat manifested by them, they will probably heat
    with great rapidity from the high velocity at which the engines work.
    Every bearing of a direct acting screw engine should have a cock of
    water laid on to it, which may be immediately opened wide should
    heating occur; and it is advisable to work the engine constantly,
    partly with water, and partly with oil applied to the bearings. The
    water and oil are mixed by the friction into a species of soap which
    both cools and lubricates, and less oil moreover is used than if water
    were not employed. It is proper to turn off the water some time before
    the engine is stopped, so as to prevent the rusting of the
    bearings.</P>

    <H4 CLASS="subhead"><A NAME="r05"></A>MANAGEMENT OF LOCOMOTIVES.</H4>

    <P>745. <EM>Q.</EM>--What are the chief duties of the engine driver of
    a locomotive?</P>

    <P><EM>A.</EM>--His first duties are those which concern the safety of
    the train; his next those which concern the safety and right management
    of the engine and boiler. The engine driver&#39;s first solicitude
    should be relative to the observation and right interpretation of the
    signals; and it is only after these demands upon his attention have
    been satisfied, that he can look to the state of his engine.</P>

    <P>746. <EM>Q.</EM>--As regards the engine and boiler, what should his
    main duties be?</P>

    <P><EM>A.</EM>--The engineer of a locomotive should constantly be upon
    the foot board of the engine, so that the regulator, the whistle or the
    reversing handle may be used instantly, if necessary; he must see that
    the level of the water in the boiler is duly maintained, and that the
    steam is kept at a uniform pressure. In feeding the boilers with water,
    and the furnaces with fuel, a good deal of care and some tact are
    necessary, as irregularity in the production of steam will often
    occasion priming, even though the water be maintained at a uniform
    level; and an excess of water will of itself occasion priming, while a
    deficiency is a source of obvious danger. The engine is generally
    furnished with three gauge cocks, and water should always come out of
    the second gauge cock, and steam out of the top one when the engine is
    running: but when the engine is at rest, the water in the boiler is
    lower than when in motion, so that when the engine is at rest, the
    water will be high enough if it just reaches to the middle gauge cock.
    In all boilers which generate steam rapidly, the volume of the water is
    increased by the mingled steam, and in feeding with cold water the
    level at first falls; but it rises on opening the safety valve, which
    causes the steam in the water to swell to a larger volume. In
    locomotive boilers, the rise of the water level due to the rapid
    generation of steam is termed &quot;false water.&quot; To economize
    fuel, the variable expansion gear, if the engine has one, should be
    adjusted to the load, and the blast pipe should be worked with the
    least possible contraction; and at stations the damper should be closed
    to prevent the dissipation of heat.</P>

    <P>747. <EM>Q.</EM>--In starting from a station, what precautions
    should be observed with respect to the feed?</P>

    <P><EM>A.</EM>--In starting from a station, and also in ascending
    inclined planes, the feed water is generally shut off; and therefore
    before stopping or ascending inclined planes, the boiler should be well
    filled up with water. In descending inclined planes an extra supply of
    water may be introduced into the boiler, and the fire may be fed, as
    there, is at such times a superfluity of steam. In descending inclined
    planes the regulator must be partially closed, and it should be
    entirely closed if the plane be very steep. The same precaution should
    be observed in the case of curves, or rough places on the line, and in
    passing over points or crossings.</P>

    <P>748. <EM>Q.</EM>--In approaching a station, how should the supply of
    water and fuel be regulated?</P>

    <P><EM>A.</EM>--The boiler should be well filled with water on
    approaching a station, as there is then steam to spare, and additional
    water cannot be conveniently supplied when the engine is stationary.
    The furnace should be fed with small quantities of fuel at a time, and
    the feed should be turned off just before a fresh supply of fuel is
    introduced. The regulator may, at the same time, be partially closed;
    and if the blast pipe be a variable one, it will be expedient to open
    it widely while the fuel is being introduced, to check the rush of air
    in through the furnace door, and then to contract it very much so soon
    as the furnace door is closed, in order to recover the fire quickly.
    The proper thickness of coke upon the grate depends upon the intensity
    of the draught; but in heavily loaded engines it is usually kept up to
    the bottom of the fire door. Care, however, must be taken that the coke
    does not reach up to the bottom row of tubes so as to choke them up.
    The fuel is usually disposed on the grate like a vault; and if the fire
    box be a square one, it is heaped high in the corners, the better to
    maintain the combustion.</P>

    <P>749. <EM>Q.</EM>--How can you tell whether the feed pumps are
    operating properly?</P>

    <P><EM>A.</EM>--To ascertain whether the pumps are acting well, the pet
    cock must be turned, and if any of the valves stick they will sometimes
    be induced to act again by working with the pet cock open, or
    alternately open and shut. Should the defect arise from a leakage of
    steam into the pump, which prevents the pump from drawing, the pet cock
    remedies the evil by permitting the steam to escape.</P>

    <P>750. <EM>Q.</EM>--What precautions should be taken against priming
    in locomotives?</P>

    <P><EM>A.</EM>--Should priming occur from the water in the boiler being
    dirty, a portion of it may be blown out; and should there be much
    boiling down through the glass gauge tube, the stop cock may be
    partially closed. The water should be wholly blown out of locomotive
    boilers three times a week, and at those times two mud-hole doors at
    opposite corners of the boiler should be opened, and the boiler be
    washed internally by means of a hose. If the boiler be habitually fed
    with dirty water, the priming will be a constant source of trouble.</P>

    <P>751. <EM>Q.</EM>--What measures should the locomotive engineer take,
    to check the velocity of the train, on approaching a station where he
    has to stop?</P>

    <P><EM>A.</EM>--On approaching a station the regulator should be
    gradually closed, and it should be completely shut about half a mile
    from the station if the train be a very heavy one: the train may then
    be brought to rest by means of the breaks. Too much reliance, however,
    must not be put upon the breaks, as they sometimes give way, and in
    frosty weather are nearly inoperative. In cases of urgency the steam
    may be thrown upon the reverse side of the piston, but it is desirable
    to obviate this necessity as far as possible. At terminal stations the
    steam should be shut off earlier than at roadside stations, as a
    collision will take place at terminal stations if the train overshoots
    the place where it ought to stop. There should always be a good supply
    of water when the engine stops, but the fire may be suffered gradually
    to burn low toward the conclusion of the journey.</P>

    <P>752. <EM>Q.</EM>--What is the duty of an engine man on arriving at
    the end of his journey?</P>

    <P><EM>A.</EM>--So soon as the engine stops it should be wiped down,
    and be then carefully examined: the brasses should be tried, to see
    whether they are slack or have been heating; and, by the application of
    a gauge, it should be ascertained occasionally whether the wheels are
    square on their axles, and whether the axles have end play, which
    should be prevented. The stuffing boxes must be tightened, and the
    valve gear examined, and the eccentrics be occasionally looked at to
    see that they have not shifted on their axles, though this defect will
    be generally intimated by the irregular beating of the engines. The
    tubes should also be examined and cleaned out, and the ashes emptied
    out of the smoke box through the small ash door at the end. If the
    engine be a six-wheeled one, with the driving wheels in the middle, it
    will be liable to pitch, and oscillate if too much weight be thrown
    upon the driving wheels; and where such faults are found to exist, the
    weight upon the drivings wheels should be diminished. The practice of
    blowing off the boiler by the steam, as is always done in marine
    boilers, should not be permitted as a general rule in locomotive
    boilers, when the tubes are of brass and the fire box of copper; but
    when the tubes and fire boxes are of iron, there will not be an equal
    risk of injury. Before starting on a journey, the engine man should
    take a summary glance beneath the engine--but before doing so he ought
    to assure himself that no other engine is coming up at the time. The
    regulator, when the engine is standing, should be closed and locked,
    and the eccentric rod be fixed out of gear, and the tender break
    screwed down; the cocks of the oil vessels should at the same time be
    shut, but should all be opened a short time before the train
    starts.</P>

    <P>753. <EM>Q.</EM>--What should be done if a tube bursts in the
    boiler?</P>

    <P><EM>A.</EM>--When a tube bursts, a wooden or iron plug must be
    driven into each end of it, and if the water or steam be rushing out so
    fiercely that the exact position of the imperfection cannot be
    discovered, it will be advisable to diminish the pressure by increasing
    the supply of feed water. Should the leak be so great that the level of
    the water in the boiler cannot be maintained, it will be expedient to
    drop the bars and quench the fire, so as to preserve the tubes and fire
    box from injury.</P>

    <P>754. <EM>Q.</EM>--If any of the working parts of a locomotive break
    or become deranged, what should be done?</P>

    <P><EM>A.</EM>--Should the piston rod or connecting rod break, or the
    cutters fall out or be clipped off--as sometimes happens to the piston
    cutter when the engine is suddenly reversed upon a heavy train--the
    parts should be disconnected, if the connection cannot be restored, so
    as to enable one engine to work; and of course the valve of the faulty
    engine must be kept closed. If one engine has not power enough to
    enable the train to proceed with the blast pipe full open, the engine
    may perhaps be able to take on a part of the carriages, or it may run
    on by itself to fetch assistance. The same course must be pursued if
    any of the valve gearing becomes deranged, and the defects cannot be
    rectified upon the spot.</P>

    <P>755. <EM>Q.</EM>--What are the most usual causes of railway
    collisions?</P>

    <P><EM>A.</EM>--Probably fogs and inexactness in the time kept by the
    trains. Collisions have sometimes occurred from carriages having been
    blown from a siding on to the rails by a high wind; and the slippery
    state of the rails, or the fracture of a break, has sometimes
    occasioned collisions at terminal stations. Collision has also
    repeatedly taken place from one engine having overtaken another, from
    the failure of a tube in the first engine, or from some other slight
    disarrangement; and collision has also taken place from the switches
    having been accidentally so left as to direct the train into a siding,
    instead of continuing it on the main line. Every train now carries fog
    signals, which are detonating packets, which are fixed upon the rails
    in advance or in the rear of a train which, whether from getting off
    the rails or otherwise, is stopped upon the line, and which are
    exploded by the wheels of any approaching train.</P>

    <P>756. <EM>Q.</EM>--What other duties of an engine-driver are there
    deserving attention?</P>

    <P><EM>A.</EM>--They are too various to be all enumerated here, and
    they also vary somewhat with the nature of the service. One rule,
    however, of universal application, is for the driver to look after
    matters himself, and not delegate to the stoker the duties which the
    person in charge of the engine should properly perform. Before leaving
    a station, the engine-driver should assure himself that he has the
    requisite supply of coke and water. Besides the firing tools and rakes
    for clearing the tubes, he should have with him in the tender a set of
    signal lamps and, torches, for tunnels and for night, detonating
    signals, screw keys, a small tank of oil, a small cask of tallow, and a
    small box of waste, a coal hammer, a chipping hammer, some wooden and
    iron plugs for the tubes, and an iron tube holder for inserting them,
    one or two buckets, a screw jack, wooden and iron wedges, split wire
    for pins, spare cutters, some chisels and files, a pinch bar, oil cans
    and an oil syringe, a chain, some spare bolts, and some cord, spun
    yarn, and rope.</P>

    <H2 CLASS="chapter">INDEX.</H2>

    <P CLASS="indented">Accidents in steam vessels, proper preparation
    for.<BR>
     Admiralty rule for horse power.<BR>
     Adhesion of wheels of locomotives to rails.<BR>
     Air, velocity of, entering a vacuum,<BR>
     &nbsp;&nbsp;required for combustion of coal;<BR>
     &nbsp;&nbsp;law of expansion of, by heat;<BR>
     Air pump, description of,<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;proper dimensions of.<BR>
     Air pump of marine engines, details of.<BR>
     Air pump of oscillating engine.<BR>
     Air pump of direct acting screw engines.<BR>
     Air pumps made both single and double acting,<BR>
     &nbsp;&nbsp;difference of, explained.<BR>
     Air pumps, double acting valves of,<BR>
     &nbsp;&nbsp;bad vacuum in;<BR>
     &nbsp;&nbsp;causes and remedy.<BR>
     Air pump rods, brass or copper, in marine engines.<BR>
     Air pump bucket, valves of.<BR>
     Air pump, connecting rod and cross head of oscillating engine.<BR>
     Air pump rod of oscillating engine.<BR>
     Air pump arm.<BR>
     Air vessels applied to suction side of pumps.<BR>
     &quot;Alma,&quot; engine of, by Messrs. John Bourne &amp; Co.<BR>
     &quot;Amphion,&quot; engines of.<BR>
     Amoskeag steam fire engine.<BR>
     Angle iron in boilers, precautions respecting.<BR>
     Apparatus for raising screw propeller.<BR>
     Atmospheric valve.<BR>
     Atmospheric resistance to railway trains.<BR>
     Auxiliary power, screw vessels with.<BR>
     Axle bearings of locomotives.<BR>
     Axle guards.<BR>
     Axles and wheels of modern locomotives.<BR>
     &quot;Azof,&quot; slide valve of.<BR>
    </P>

    <P CLASS="indented">Babbitt&#39;s metal, how to compound.<BR>
     Balance piston to take pressure off slide valve.<BR>
     Ball valves.<BR>
     Barrel of boiler of modern locomotives.<BR>
     Beam, working of land engine,<BR>
     &nbsp;&nbsp;main or working strength proper for.<BR>
     Bearings of engines or other machinery,<BR>
     &nbsp;&nbsp;rule for determining proper surface of.<BR>
     Bearings, heating of, how to prevent or remedy,<BR>
     &nbsp;&nbsp;journals should always bottom, as, if they grip<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;on the sides, the pressure is infinite.<BR>
     Beattie&#39;s screw.<BR>
     Belidor&#39;s valves might be used for foot and delivery valves.<BR>
     Bell-metal, composition of.<BR>
     Blast pipe of locomotives, description of.<BR>
     Blast in locomotives, exhaustion produced by,<BR>
     &nbsp;&nbsp;proper construction of the blast pipe;<BR>
     &nbsp;&nbsp;the blast pipe should be set below the root of<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;the chimney so much that the cone of escaping
    steam shall just fill the<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;chimney.<BR>
     Blast pipe with variable orifice, at one time much used.<BR>
     Blow-off cock of locomotives.<BR>
     Blow-off cocks of marine boilers, proper construction of.<BR>
     Blow-off cocks, description of.<BR>
     Blowing off supersalted water from marine boilers.<BR>
     Blowing off, estimate of heat lost by,<BR>
     &nbsp;&nbsp;mode of.<BR>
     Blow through valve, description of.<BR>
     Blowing furnaces, power necessary for.<BR>
     Bodies, falling, laws of.<BR>
     Bodmer, expansion valve by.<BR>
     Boilers, general description of: the wagon boiler,<BR>
     &nbsp;&nbsp;the Cornish boiler;<BR>
     &nbsp;&nbsp;the marine flue boiler;<BR>
     &nbsp;&nbsp;the marine tubular boiler;<BR>
     &nbsp;&nbsp;locomotive boiler--<EM>see</EM> Locomotives.<BR>
     Boilers proportions of: heating surface of,<BR>
     &nbsp;&nbsp;fire grate, surface of;<BR>
     &nbsp;&nbsp;consumption of fuel on each square foot of fire bars in
    wagon,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;Cornish, and locomotive boilers;<BR>
     &nbsp;&nbsp;calorimmeter and vent of boilers;<BR>
     &nbsp;&nbsp;comparison of proportions of wagon, flue, and tubular
    boilers;<BR>
     &nbsp;&nbsp;evaporative power of boilers;<BR>
     &nbsp;&nbsp;power generated by evaporation of a cubic foot of
    water;<BR>
     &nbsp;&nbsp;proper proportions of modern marine boilers both flue and
    tubular;<BR>
     &nbsp;&nbsp;modern locomotive boilers;<BR>
     &nbsp;&nbsp;exhaustion produced by blast in locomotives;<BR>
     &nbsp;&nbsp;increased evaporation from increased exhaustion;<BR>
     &nbsp;&nbsp;strength of boilers;<BR>
     &nbsp;&nbsp;experiments on, by Franklin Institute;<BR>
     &nbsp;&nbsp;by Mr. Fairbairn;<BR>
     &nbsp;&nbsp;mode of computing strength of boilers;<BR>
     &nbsp;&nbsp;staying of.<BR>
     Boilers, marine, prevented from salting by blowing off,<BR>
     &nbsp;&nbsp;early locomotive and contemporaneous marine boilers
    compared;<BR>
     &nbsp;&nbsp;chimneys of land;<BR>
     &nbsp;&nbsp;rules for proportions of chimneys;<BR>
     &nbsp;&nbsp;chimneys of marine boilers.<BR>
     Boilers, constructive details of: riveting and caulking of land
    boilers,<BR>
     &nbsp;&nbsp;proving of;<BR>
     &nbsp;&nbsp;seams payed with mixture of whiting and linseed oil;<BR>
     &nbsp;&nbsp;setting of wagon boilers;<BR>
     &nbsp;&nbsp;riveting of marine boilers;<BR>
     &nbsp;&nbsp;precautions respecting angle iron;<BR>
     &nbsp;&nbsp;how to punch the rivet holes and shear edges of
    plates;<BR>
     &nbsp;&nbsp;setting of marine boilers in wooden vessels;<BR>
     &nbsp;&nbsp;mastic cement for setting marine boilers;<BR>
     &nbsp;&nbsp;composition of mastic cement;<BR>
     &nbsp;&nbsp;best length of furnace;<BR>
     &nbsp;&nbsp;configuration of furnace bars;<BR>
     &nbsp;&nbsp;advantages and construction of furnace bridges;<BR>
     &nbsp;&nbsp;various forms of dampers;<BR>
     &nbsp;&nbsp;precautions against injury to boilers from intense
    heat;<BR>
     &nbsp;&nbsp;tubing of boilers;<BR>
     &nbsp;&nbsp;proper mode of staying tube plates;<BR>
     &nbsp;&nbsp;proper mode of constructing steamboat chimneys;<BR>
     &nbsp;&nbsp;waste steam-pipe and funnel casing;<BR>
     &nbsp;&nbsp;telescope chimneys;<BR>
     &nbsp;&nbsp;formation of scale in marine boilers;<BR>
     &nbsp;&nbsp;injury of such incrustations;<BR>
     &nbsp;&nbsp;amount of salt in sea water;<BR>
     &nbsp;&nbsp;saltness permissible in boilers;<BR>
     &nbsp;&nbsp;amount of heat lost by blowing off;<BR>
     &nbsp;&nbsp;mode of discharging the supersalted water;<BR>
     &nbsp;&nbsp;Lamb&#39;s scale preventer;<BR>
     &nbsp;&nbsp;internal corrosion of marine boilers;<BR>
     &nbsp;&nbsp;causes of internal corrosion;<BR>
     &nbsp;&nbsp;surcharged steam produced from salt water;<BR>
     &nbsp;&nbsp;stop valves between boilers;<BR>
     &nbsp;&nbsp;safety or escape valve on feed pipe;<BR>
     &nbsp;&nbsp;locomotive boilers consist of the fire box, barrel for<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;holding tubes, and smoke box;<BR>
     &nbsp;&nbsp;dimensions of the barrel and thickness of plates;<BR>
     &nbsp;&nbsp;mode of staying fire box and furnace crown;<BR>
     &nbsp;&nbsp;fire bars, ash box, and chimney;<BR>
     &nbsp;&nbsp;steam dome used only in old engines;<BR>
     &nbsp;&nbsp;manhole, mudholes, and blow-oft cock;<BR>
     &nbsp;&nbsp;tube plate, and mode of securing tubes;<BR>
     &nbsp;&nbsp;expanding mandrels;<BR>
     &nbsp;&nbsp;various forms of regulator.<BR>
     Boilers of modern locomotives.<BR>
     Boiler, the, proper care of, the first duty of the engineer.<BR>
     Bolts, proper proportions of.<BR>
     Boring of cylinders.<BR>
     Boulton and Watt&#39;s rules for fly wheel,<BR>
     &nbsp;&nbsp;proportions of marine flue boilers;<BR>
     &nbsp;&nbsp;rule for proportions of chimneys of land boilers;<BR>
     &nbsp;&nbsp;of marine boilers;<BR>
     &nbsp;&nbsp;experiments on the resistance of vessels in water.<BR>
     Bourdon&#39;s steam and vacuum gauges.<BR>
     Bourne, expansion valves by.<BR>
     Bourne, Messrs. J. &amp; Co., direct acting screw engines by.<BR>
     Brass for bearings, composition of.<BR>
     Brazing solders.<BR>
     Bridges in furnaces, benefits of.<BR>
     Burning of boilers, precautions against.<BR>
     Bursting velocity of fly wheel,<BR>
     &nbsp;&nbsp;and of railway wheels.<BR>
     Bursting of boilers,<BR>
     &nbsp;&nbsp;causes of;<BR>
     &nbsp;&nbsp;precautions against;<BR>
     &nbsp;&nbsp;may be caused by accumulations of salt.<BR>
     Butterfly valves of air pump.<BR>
    </P>

    <P CLASS="indented">Cabrey, expansion valve by.<BR>
     Calorimeter of boilers, definition of.<BR>
     Cams, proper forms of.<BR>
     Cast iron, strength of,<BR>
     &nbsp;&nbsp;proportions of cast iron beams;<BR>
     &nbsp;&nbsp;effects of different kinds of strains on beams;<BR>
     &nbsp;&nbsp;strength to resist shocks not proportional to strength to
    resist<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;strains;<BR>
     &nbsp;&nbsp;to attain maximum strength should be combined with wrought
    iron.<BR>
     Casting of cylinders.<BR>
     Case-hardening, how to accomplish.<BR>
     Cataract, explanation of nature and uses of.<BR>
     Caulking of land boilers.<BR>
     Cement, mastic, for setting marine boilers.<BR>
     Central forces.<BR>
     Centre of pressure of paddle wheels.<BR>
     Centres of gravity, gyration and oscillation.<BR>
     Centres for fixing arms of paddle wheel.<BR>
     Centres of an engine, how to lay off.<BR>
     Centrifugal force, nature of,<BR>
     &nbsp;&nbsp;rule for determining;<BR>
     &nbsp;&nbsp;bursting velocity of fly wheel;<BR>
     &nbsp;&nbsp;and of railway wheels.<BR>
     Centrifugal pump will supersede common pump.<BR>
     Centripetal force, nature of.<BR>
     Chimney of locomotives.<BR>
     Chimney of steam vessels, what to do if carried away.<BR>
     Chimneys of land boilers,<BR>
     &nbsp;&nbsp;Boulton and Watt&#39;s rule for proportions of;<BR>
     &nbsp;&nbsp;of marine boilers.<BR>
     Chimneys, exhaustion produced by,<BR>
     &nbsp;&nbsp;high and wide chimneys in locomotives injurious.<BR>
     Chimneys of steamboats,<BR>
     &nbsp;&nbsp;telescope.<BR>
     Clark&#39;s patent steam fire regulator.<BR>
     Coal, constituents of,<BR>
     &nbsp;&nbsp;combustion of air required for;<BR>
     &nbsp;&nbsp;evaporative efficacy of;<BR>
     &nbsp;&nbsp;of wood, turf, and coke.<BR>
     Cocks, proper construction of.<BR>
     Cog wheels for screw engines.<BR>
     Coke, evaporative efficacy of.<BR>
     Cold water pump, description of,<BR>
     &nbsp;&nbsp;rule for size of.<BR>
     Combustion, nature of.<BR>
     Combustion of coal, air required for.<BR>
     Combustion, slow and rapid, comparative merits of,<BR>
     &nbsp;&nbsp;rapid combustion necessary in steam vessels, and enables
    less heating,<BR>
     &nbsp;&nbsp;surface in the boiler to suffice.<BR>
     Conchoidal propeller.<BR>
     Condensation of steam, water required for.<BR>
     Condenser, description of,<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;proper dimensions of.<BR>
     Condenser of oscillating engine.<BR>
     Condenser of direct acting screw engine.<BR>
     Condensing engine, definition of.<BR>
     Condensing water, how to provide when deficient.<BR>
     Conical pendulum or governor.<BR>
     Connecting rod, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Connecting rod of direct acting screw engines,<BR>
     &nbsp;&nbsp;of locomotives.<BR>
     Consumption of fuel on each square foot of fire bars in wagon,
    Cornish,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;and locomotive boilers.<BR>
     Copper, strength of.<BR>
     Corliss&#39;s steam engine.<BR>
     Corrosion produced by surcharged steam.<BR>
     Corrosion of marine boilers,<BR>
     &nbsp;&nbsp;causes of.<BR>
     Cost of locomotives.<BR>
     Cotton spinning, power necessary for.<BR>
     Counter for counting strokes of an engine.<BR>
     Crank, description of,<BR>
     &nbsp;&nbsp;unequal leverage of, corrected by fly wheel;<BR>
     &nbsp;&nbsp;no power lost by;<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Crank of direct acting screw engines.<BR>
     Crank pin, strength proper for.<BR>
     Crank pin of direct acting screw engines.<BR>
     Cranked axle of locomotives.<BR>
     Cross head, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Cross head of direct acting screw engines.<BR>
     Cross tail, description of.<BR>
     Cylinder, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Cylinder of oscillating engine,<BR>
     &nbsp;&nbsp;of direct acting screw engine.<BR>
     Cylinders should have a steam jacket, and be felted and planted,<BR>
     &nbsp;&nbsp;should have escape valves.<BR>
     Cylinders of locomotives should be large,<BR>
     &nbsp;&nbsp;proper arrangement of.<BR>
     Cylinders, how to cast,<BR>
     &nbsp;&nbsp;how to bore;<BR>
     &nbsp;&nbsp;how to grind.<BR>
     Cylinder jacket, advantages of.<BR>
    </P>

    <P CLASS="indented">Damper.<BR>
     Dampers, various forms of.<BR>
     Deadwood, hole in, for screw.<BR>
     Delivery valve, description of.<BR>
     Delivery or discharge valves, proper dimensions of.<BR>
     Delivery valves might be made on Belidor&#39;s plan.<BR>
     Delivery valves in mouth of air pump,<BR>
     &nbsp;&nbsp;of india rubber.<BR>
     Direct acting screw engines should be balanced.<BR>
     Direct acting screw engine by Messrs. John Bourne &amp;, Co.,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;cylinder;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;discs;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;guides;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;screw shaft brasses;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;air pump;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;slide valve;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;balance piston;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;connecting rod;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;piston rods;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;cross head;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;air pump arm;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;feed pump;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;crank pin;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;screw shaft;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;thrust plummer block;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;link motion;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;screw propeller.<BR>
     Discharge valves.<BR>
     Disc valves of india rubber for air pumps.<BR>
     Discs of direct acting screw engine instead of crank.<BR>
     Dodds, expansion valve by.<BR>
     Double acting engines, definition of.<BR>
     Double acting air pumps,<BR>
     &nbsp;&nbsp;valves of;<BR>
     &nbsp;&nbsp;faults of.<BR>
     Draw bolt.<BR>
     Dredging earth out of rivers, power necessary for.<BR>
     Driving wheels of locomotives.<BR>
     Driving piles, power necessary for.<BR>
     Duplex pump, Worthington&#39;s.<BR>
     Dundonald, Earl of, screw by.<BR>
     Duty of engines and boilers,<BR>
     &nbsp;&nbsp;how the duty is ascertainable.<BR>
     Dynamometer, description of.<BR>
     Dynamometric power of screw vessels.<BR>
    </P>

    <P CLASS="indented">Eccentric, description of,<BR>
     &nbsp;&nbsp;sometimes made loose for backing.<BR>
     Eccentric and eccentric rod of oscillating engine.<BR>
     Eccentric notch should be fitted with a brass bush.<BR>
     Eccentric straps of locomotives,<BR>
     &nbsp;&nbsp;rods of locomotives.<BR>
     Eccentrics of locomotives,<BR>
     &nbsp;&nbsp;how to readjust.<BR>
     Economy of fuel in steam vessels.<BR>
     Edwards, expansion valve by.<BR>
     Elasticity, limits of.<BR>
     Engine, high pressure, definition of,<BR>
     &nbsp;&nbsp;low pressure, definition of.<BR>
     Engines, classification of,<BR>
     &nbsp;&nbsp;rotative, definition of;<BR>
     &nbsp;&nbsp;rotatory, definition of;<BR>
     &nbsp;&nbsp;single acting, definition of;<BR>
     &nbsp;&nbsp;double acting, definition of;<BR>
     &nbsp;&nbsp;mode of erecting in a vessel;<BR>
     &nbsp;&nbsp;how to refix if they have become loose.<BR>
     Engineers of steam vessels should make proper preparation for
    accidents.<BR>
     Equilibrium slide valve,<BR>
     &nbsp;&nbsp;grid-iron valve.<BR>
     Erecting engines in a vessel.<BR>
     Erection of engines in the workshop.<BR>
     Escape valve on feed pipe.<BR>
     Escape valves for letting water out of cylinders.<BR>
     Evaporative efficacy of coal,<BR>
     &nbsp;&nbsp;of wood, turf, and coke.<BR>
     Evaporative power of boilers,<BR>
     &nbsp;&nbsp;power generated by evaporation of a cubic foot of
    water;<BR>
     &nbsp;&nbsp;increase of evaporation due to increased exhaustion in
    locomotives.<BR>
     Excavator, Otis&#39;s.<BR>
     Exhaustion produced by chimneys,<BR>
     &nbsp;&nbsp;by the blast in locomotives;<BR>
     &nbsp;&nbsp;increased evaporation from increased exhaustion.<BR>
     Expanding mandrels for tubing boilers.<BR>
     Expansion of air by heat.<BR>
     Expansion of surcharged steam by heat.<BR>
     Expansion of steam,<BR>
     &nbsp;&nbsp;pressure of steam inversely as the space occupied;<BR>
     &nbsp;&nbsp;law of expansion;<BR>
     &nbsp;&nbsp;rule for computing the increase of efficiency produced by
    working<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;expansively;<BR>
     &nbsp;&nbsp;necessity of efficient provisions against refrigeration in
    working<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;expansively;<BR>
     &nbsp;&nbsp;advantages of steam jacket;<BR>
     &nbsp;&nbsp;Forms of apparatus for working expansively: lap on the
    slide valve<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;wire drawing the steam;<BR>
     &nbsp;&nbsp;Cornish expansion valve,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;in rotative engines worked by a cam;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;mode of varying the degree of expansion;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;proper forms of cams;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;the link motion;<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;expansion valves, by Cabrey, Fenton, Dodds,
    Farcot, Edwards,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Lavagrian, Bodmer, Meyer,
    Hawthorn, Gonzenbach, and Bourne.<BR>
     Expansion joint in valve casing.<BR>
     Expansion valves, Cornish,<BR>
     &nbsp;&nbsp;the link motion;<BR>
     &nbsp;&nbsp;by Cabrey, Fenton, Dodds, Farcot, Edwards, Lavagrian,
    Bodmer, Meyer,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;Hawthorn, Gouzenbach, and Bourne.<BR>
     Explosions of boilers,<BR>
     &nbsp;&nbsp;causes of explosions;<BR>
     &nbsp;&nbsp;precautions against;<BR>
     &nbsp;&nbsp;dangers of accumulations of salt.<BR>
    </P>

    <P CLASS="indented">Face plates or planometers.<BR>
     Falling bodies, laws of.<BR>
     Farcot, expansion valve by.<BR>
     Feathering paddle wheels, description of,<BR>
     &nbsp;&nbsp;details of.<BR>
     Feed pump, description of,<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;proper dimensions of;<BR>
     &nbsp;&nbsp;rule for proportioning.<BR>
     Feed pump plunger,<BR>
     &nbsp;&nbsp;and valves.<BR>
     Feed pumps of locomotives, details of.<BR>
     Feed pumps of direct acting screw engines.<BR>
     Fenton, expansion valve by.<BR>
     Fire bars of locomotives.<BR>
     Fire box of locomotives, mode of staying.<BR>
     Fire box of modern locomotives.<BR>
     Fire engines, cost of running.<BR>
     Fire grate surface of boilers.<BR>
     Fire grate in locomotives should be of small area,<BR>
     &nbsp;&nbsp;coke proper to be burned per hour on each square foot of
    bars.<BR>
     Firing furnaces, proper mode of.<BR>
     Flaws in valves or cylinders, how to remedy.<BR>
     Float for regulating water level in boilers.<BR>
     Floats of paddle.<BR>
     Floats of paddle wheels, increased resistance of, if oblique,<BR>
     &nbsp;&nbsp;floats should be large.<BR>
     Fly wheel corrects unequal leverage of crank,<BR>
     &nbsp;&nbsp;proper energy for;<BR>
     &nbsp;&nbsp;Boulton and Watt&#39;s rule for;<BR>
     &nbsp;&nbsp;bursting velocity of;<BR>
     &nbsp;&nbsp;description of;<BR>
     &nbsp;&nbsp;action of, in redressing irregularities of motion.<BR>
     Foot valve, description of,<BR>
     &nbsp;&nbsp;proper dimensions of.<BR>
     Foot valves might be made on Belidor&#39;s plan,<BR>
     &nbsp;&nbsp;of india rubber.<BR>
     Frame at stern for holding screw propeller.<BR>
     Framing of locomotives.<BR>
     Framing of oscillating engine.<BR>
     Franklin Institute, experiments on steam by.<BR>
     French Academy, experiments on steam by.<BR>
     Friction, nature of,<BR>
     &nbsp;&nbsp;does not vary as the rubbing surfaces, but as the
    retaining pressure;<BR>
     &nbsp;&nbsp;does not increase with the velocity per unit of distance,
    but increases<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;with the velocity per unit of time;<BR>
     &nbsp;&nbsp;measures of friction;<BR>
     &nbsp;&nbsp;effect of unguents;<BR>
     &nbsp;&nbsp;kind of unguent should vary with the pressure;<BR>
     &nbsp;&nbsp;Morin&#39;s experiments;<BR>
     &nbsp;&nbsp;rule for determining proper surfaces of bearings;<BR>
     &nbsp;&nbsp;friction of rough surfaces.<BR>
     Friction of the water the main cause of the resistance of vessels of
    good<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;shape.<BR>
     Fuel burnt on each square foot of fire bars in wagon, Cornish, and<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;locomotive boilers,<BR>
     &nbsp;&nbsp;economy of, in steam vessels.<BR>
     Funnel casing.<BR>
     Funnel, what to do if carried away.<BR>
     Funnels of steam boats. <EM>See</EM> Chimneys.<BR>
     Furnaces, proper mode of firing,<BR>
     &nbsp;&nbsp;smoke burning: Williams&#39;s argand;<BR>
     &nbsp;&nbsp;Prideaux&#39;s;<BR>
     &nbsp;&nbsp;Boulton and Watt&#39;s dead plate;<BR>
     &nbsp;&nbsp;revolving crate;<BR>
     &nbsp;&nbsp;Juckes&#39;s;<BR>
     &nbsp;&nbsp;Maudslay&#39;s;<BR>
     &nbsp;&nbsp;Hull&#39;s, Coupland&#39;s, Godson&#39;s, Robinson&#39;s,
    Stevens&#39;s, Hazeldine&#39;s,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;&amp;c..<BR>
     Furnaces of marine boilers, proper length of.<BR>
     Furnace bridges, benefits of.<BR>
     Fusible metal plugs useless as antidotes to explosions.<BR>
    </P>

    <P CLASS="indented">Gauges, vacuum,<BR>
     &nbsp;&nbsp;steam;<BR>
     &nbsp;&nbsp;gauge cocks and glass tubes for showing level of water in
    boiler,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;description of.<BR>
     Gauge cocks for showing level of water in boiler.<BR>
     Gearing for screw engines.<BR>
     Gibs and cutters, strengths proper for.<BR>
     Giffard&#39;s injector.<BR>
     Glass tubes for showing water level in boilers.<BR>
     Glass tube cocks.<BR>
     Gonzeubach, expansion valve by.<BR>
     Gooch&#39;s indicator.<BR>
     Gooch&#39;s locomotive.<BR>
     Governor or conical pendulum,<BR>
     &nbsp;&nbsp;description of.<BR>
     Governor, Porter&#39;s patent.<BR>
     Gravity, centre of.<BR>
     &quot;Great Western,&quot; boilers of, by Messrs. Maudslay.<BR>
     Gridiron valve.<BR>
     Griffith&#39;s screw.<BR>
     Grinding corn, power necessary for.<BR>
     Grinding of cylinders.<BR>
     Gudgeons, strength proper for.<BR>
     Guides of locomotives.<BR>
     Guides of direct acting screw engine.<BR>
     Gun metal, strength of.<BR>
     Gyration, centre of.<BR>
    </P>

    <P CLASS="indented">Harvey and West&#39;s pump valves.<BR>
     Hawthorn, expansion valve by.<BR>
     Heat, latent, definition of.<BR>
     Heat, specific, definition of.<BR>
     Heat, Regnault&#39;s experiments on.<BR>
     Heat, loss of, by blowing off marine boilers.<BR>
     Heating surface of boilers.<BR>
     Heating surface per square foot of fire bars in locomotives,<BR>
     &nbsp;&nbsp;a cubic foot of water evaporates by five square feet of
    heating surface.<BR>
     Heating of bearings, causes of,<BR>
     &nbsp;&nbsp;bearings should always be slack at the sides, else the
    pressure is<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;infinite.<BR>
     High pressure engine, definition of.<BR>
     High pressure engines, power of.<BR>
     High speed engines,<BR>
     &nbsp;&nbsp;arrangements proper for high speeds.<BR>
     Hoadley&#39;s portable engine.<BR>
     Hodgson&#39;s screw.<BR>
     Hoe &amp; Co.&#39;s steam engine.<BR>
     Holding down bolts of marine engines,<BR>
     &nbsp;&nbsp;or bolts for securing engines to hull.<BR>
     Holms&#39;s screw propeller.<BR>
     Horses power, definition of,<BR>
     &nbsp;&nbsp;nominal horse power;<BR>
     &nbsp;&nbsp;actual power ascertained by the indictator;<BR>
     &nbsp;&nbsp;Admiralty rule for.<BR>
     Hot water or feed pump, description of.<BR>
     Hot well, description of.<BR>
    </P>

    <P CLASS="indented">Increasing pitch of screw.<BR>
     Incrustation in boilers. <EM>See</EM> also Salt.<BR>
     India rubber valves for air pump.<BR>
     Indicator, description of the,<BR>
     &nbsp;&nbsp;by McNaught, structure and mode of using;<BR>
     &nbsp;&nbsp;Gooch&#39;s continuous indicator.<BR>
     Injection cock.<BR>
     Injection cocks of marine engines at ship&#39;s sides.<BR>
     Injection orifice, proper area of.<BR>
     Injector, Giffard&#39;s.<BR>
     Injection valve.<BR>
     Inside cylinder locomotives.<BR>
     Iron, strength of,<BR>
     &nbsp;&nbsp;limits of elasticity of;<BR>
     &nbsp;&nbsp;proper strain to be put upon iron in engines and
    machines;<BR>
     &nbsp;&nbsp;aggravation of strain by being intermittent;<BR>
     &nbsp;&nbsp;increase of strain due to deflection;<BR>
     &nbsp;&nbsp;strength of pillars and tubes,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;combination of malleable and cast iron.<BR>
     Iron, cast, strength of,<BR>
     &nbsp;&nbsp;cast iron beams;<BR>
     &nbsp;&nbsp;may be strong to resist strains, but not strong to resist
    shocks;<BR>
     &nbsp;&nbsp;should be combined with wrought iron to obtain maximum
    strength.<BR>
     Iron, if to be case hardened, should be homogeneous.<BR>
    </P>

    <P CLASS="indented">Jacket of cylinder, advantages of.<BR>
     Joints, rust, how to make.<BR>
    </P>

    <P CLASS="indented">Kingston&#39;s valves.</P>

    <P CLASS="indented">Lamb&#39;s scale preventer.<BR>
     Lantern brass in stuffing boxes.<BR>
     Lap and lead of the valve, meaning of.<BR>
     Large vessels have least proportionate resistance.<BR>
     Latent heat, definition of.<BR>
     Latta&#39;s steam fire engine.<BR>
     Lavagrian, expansion valve by.<BR>
     Lead and lap of the valve, meaning of.<BR>
     Lead of the valve, benefits of.<BR>
     Lever,<BR>
     &nbsp;&nbsp;futility of plans for deriving power from a lever.<BR>
     Lifting apparatus for screw propeller.<BR>
     Limits of elasticity.<BR>
     Links, main description of.<BR>
    </P>

    <P CLASS="indented">Link motion of direct acting screw engine.<BR>
     Link motion, how to set.<BR>
     Locomotive engines,<BR>
     &nbsp;&nbsp;general description of the locomotive;<BR>
     &nbsp;&nbsp;Stephenson&#39;s locomotive;<BR>
     &nbsp;&nbsp;Gooch&#39;s locomotive for the wide gauge;<BR>
     &nbsp;&nbsp;Crampton&#39;s locomotive for the narrow gauge.<BR>
     Locomotives, adhesion of wheels of,<BR>
     &nbsp;&nbsp;cost and performance of;<BR>
     &nbsp;&nbsp;framing of;<BR>
     &nbsp;&nbsp;cylinders of;<BR>
     &nbsp;&nbsp;springs of;<BR>
     &nbsp;&nbsp;outside and inside cylinders;<BR>
     &nbsp;&nbsp;sinuous motion of;<BR>
     &nbsp;&nbsp;rocking motion of;<BR>
     &nbsp;&nbsp;pitching motion of;<BR>
     &nbsp;&nbsp;pistons;<BR>
     &nbsp;&nbsp;piston rods;<BR>
     &nbsp;&nbsp;guides;<BR>
     &nbsp;&nbsp;cranked axle;<BR>
     &nbsp;&nbsp;axle bearings;<BR>
     &nbsp;&nbsp;eccentrics;<BR>
     &nbsp;&nbsp;eccentric rod;<BR>
     &nbsp;&nbsp;starting handle;<BR>
     &nbsp;&nbsp;link motion;<BR>
     &nbsp;&nbsp;valves, how to set;<BR>
     &nbsp;&nbsp;eccentrics, how to readjust;<BR>
     &nbsp;&nbsp;feed pumps;<BR>
     &nbsp;&nbsp;connection of engine and tender,<BR>
     &nbsp;&nbsp;driving wheels;<BR>
     &nbsp;&nbsp;wheel tires.<BR>
     Locomotive engine of modern construction, example of,<BR>
     &nbsp;&nbsp;fire box;<BR>
     &nbsp;&nbsp;barrel of boiler;<BR>
     &nbsp;&nbsp;tubes;<BR>
     &nbsp;&nbsp;tube plate;<BR>
     &nbsp;&nbsp;framing;<BR>
     &nbsp;&nbsp;axle guards;<BR>
     &nbsp;&nbsp;draw bolt;<BR>
     &nbsp;&nbsp;wheels and axles;<BR>
     &nbsp;&nbsp;cylinders;<BR>
     &nbsp;&nbsp;valve;<BR>
     &nbsp;&nbsp;piston;<BR>
     &nbsp;&nbsp;piston rod;<BR>
     &nbsp;&nbsp;guides;<BR>
     &nbsp;&nbsp;connecting rod;<BR>
     &nbsp;&nbsp;eccentrics;<BR>
     &nbsp;&nbsp;link motion;<BR>
     &nbsp;&nbsp;regulator;<BR>
     &nbsp;&nbsp;blast pipe;<BR>
     &nbsp;&nbsp;safety valve;<BR>
     &nbsp;&nbsp;feed pump;<BR>
     &nbsp;&nbsp;tendencies of improvement in locomotives.<BR>
     Locomotives, management of.<BR>
     Locomotive boilers, examples of modern proportions.<BR>
     Locomotive boilers, details of.<BR>
     Low pressure or condensing engine, definition of.<BR>
     Lubrication of rubbing surfaces,<BR>
     &nbsp;&nbsp;the friction depends mainly on the nature of
    lubricant;<BR>
     &nbsp;&nbsp;oil forced out of bearings, if the pressure exceeds
    800<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;lbs. per square inch longitudinal section;<BR>
     &nbsp;&nbsp;water a good lubricant if the surfaces are large
    enough.<BR>
     Lubrication of engine bearings.<BR>
    </P>

    <P CLASS="indented">McNaught&#39;s indicator.<BR>
     Main beam, strength proper for.<BR>
     Main centre, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Main links, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Mandrels, expanding, for tubing boilers.<BR>
     Manhole door.<BR>
     Manhole of locomotives.<BR>
     Marine flue boilers, proportions of.<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;<EM>See</EM> also Boilers.<BR>
     Marine boilers of modern construction, proper proportions of.<BR>
     Marine engines. <EM>See</EM> Steam Engines, marine.<BR>
     Mastic cement for setting marine boilers.<BR>
     Maudslay, Messrs., boilers of &quot;Retribution&quot; and &quot;Great
    Western,&quot; by,<BR>
     Mechanical powers,<BR>
     &nbsp;&nbsp;misconceptions respecting.<BR>
     Mechanical power, definition of,<BR>
     &nbsp;&nbsp;indestructible and eternal;<BR>
     &nbsp;&nbsp;the sun the source of mechanical power.<BR>
     Metallic packing for pistons.<BR>
     Metallic packing for stuffing boxes.<BR>
     Meyer, expansion valve by.<BR>
     Miller, Ravenhill &amp; Co.&#39;s mode of fixing piston rod to
    piston.<BR>
     Modern locomotives.<BR>
     Momentum, or <EM>vis viva</EM>.<BR>
     Morin, experiments on friction by.<BR>
     Mudholes of locomotives.<BR>
     Muntz&#39;s metal, composition of.<BR>
    </P>

    <P CLASS="indented">&quot;Niger&quot; and &quot;Basilisk,&quot; trials
    of.<BR>
     &quot;Nile,&quot; boilers of the, by Boulton and Watt.<BR>
     Notch of eccentric should be fitted with brass bush.<BR>
    </P>

    <P CLASS="indented">Oils for lubrication. <EM>See</EM> Lubrication.<BR>
     Oscillation, centre of.<BR>
     Oscillating paddle engine, description of.<BR>
     Oscillating engine, advantages of,<BR>
     &nbsp;&nbsp;futility of objections to;<BR>
     &nbsp;&nbsp;details of cylinder;<BR>
     &nbsp;&nbsp;framing;<BR>
     &nbsp;&nbsp;condenser;<BR>
     &nbsp;&nbsp;air pump;<BR>
     &nbsp;&nbsp;trunnions;<BR>
     &nbsp;&nbsp;valve and valve casing;<BR>
     &nbsp;&nbsp;piston;<BR>
     &nbsp;&nbsp;piston rod;<BR>
     &nbsp;&nbsp;air pump connecting rod and cross head;<BR>
     &nbsp;&nbsp;air pump rod;<BR>
     &nbsp;&nbsp;eccentric and eccentric rod;<BR>
     &nbsp;&nbsp;valve gear;<BR>
     &nbsp;&nbsp;valve sector;<BR>
     &nbsp;&nbsp;shaft plummer blocks;<BR>
     &nbsp;&nbsp;trunnion plummer blocks;<BR>
     &nbsp;&nbsp;feathering paddle wheels;<BR>
     &nbsp;&nbsp;packing of trunnions.<BR>
     Oscillating engines, how to erect.<BR>
     Otis&#39;s excavator.<BR>
     Outside and inside cylinder locomotives.<BR>
    </P>

    <P CLASS="indented">Packing for stuffing box of Watt&#39;s engine.<BR>
     Packing of piston of pumping engines, how to accomplish.<BR>
     Packing of trunnions.<BR>
     Paddle bolts, proper mode of forming.<BR>
     Paddle centres.<BR>
     Paddle floats.<BR>
     Paddle shaft, description of.<BR>
     Paddle shaft, details of.<BR>
     Paddle shaft plummer blocks of oscillating engines.<BR>
     Paddle wheels, details of,<BR>
     &nbsp;&nbsp;structure and operation of;<BR>
     &nbsp;&nbsp;slip of;<BR>
     &nbsp;&nbsp;centre of pressure of;<BR>
     &nbsp;&nbsp;rolling circle;<BR>
     &nbsp;&nbsp;action of oblique floats;<BR>
     &nbsp;&nbsp;rule for proportioning paddle wheels;<BR>
     &nbsp;&nbsp;benefits of large floats.<BR>
     Paddle wheels, feathering, description of;<BR>
     &nbsp;&nbsp;details of.<BR>
     Paddles and screw combined.<BR>
     Parallel motion, description of,<BR>
     &nbsp;&nbsp;how to lay off centres of.<BR>
     Pendulum,<BR>
     &nbsp;&nbsp;cause of vibrations of;<BR>
     &nbsp;&nbsp;relation of vibrations of pendulum to velocity of falling
    bodies;<BR>
     &nbsp;&nbsp;conical pendulum or governor.<BR>
     Penn, Messrs., engines of &quot;Great Britain,&quot; by,<BR>
     &nbsp;&nbsp;direct acting screw engines by;<BR>
     &nbsp;&nbsp;trunk engines by.<BR>
     Performance of locomotives.<BR>
     Pillars, hollow, strength of,<BR>
     &nbsp;&nbsp;law of strength varies with thickness of metal.<BR>
     Pipe for receiving screw shaft.<BR>
     Pipes of marine engines.<BR>
     Piston, description of,<BR>
     &nbsp;&nbsp;how to pack with hemp.<BR>
     Pistons, metallic packing for.<BR>
     Pistons for oscillating engines.<BR>
     Pistons, how to fit and finish.<BR>
     Pistons of locomotives.<BR>
     Piston rod, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Piston rods of locomotives.<BR>
     Piston rod of oscillating engine.<BR>
     Piston rods of direct acting screw engine.<BR>
     Pitch of the screw.<BR>
     Pitch, increasing or expanding.<BR>
     Pitching motion in locomotives.<BR>
     Planometers, or face plates.<BR>
     Plummer blocks of shafts and trunnions of oscillating engines.<BR>
     Plummer blocks for receiving thrust of screw propeller.<BR>
     Plunger of feed pump.<BR>
     Portable engine, Hoadley&#39;s.<BR>
     Porter&#39;s patent governor.<BR>
     Ports of the cylinder, area of.<BR>
     Pot-lid valves of air pump.<BR>
     Powers, mechanical,<BR>
     &nbsp;&nbsp;misconception respecting.<BR>
     Power, horses, definition of,<BR>
     &nbsp;&nbsp;nominal and actual power;<BR>
     &nbsp;&nbsp;power of high pressure engines.<BR>
     Power necessary for thrashing and grinding corn, working sugar
    mills,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;spinning cotton, sawing timber, grossing
    cotton, blowing furnaces,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;driving piles, and dredging earth out of
    rivers.<BR>
     Pressing cotton, power necessary for.<BR>
     Priming, nature and causes of.<BR>
     Priming, if excessive, may occasion explosion.<BR>
     Propeller, screw, description of.<BR>
     Proportions of screws with, two, four, and six blades.<BR>
     Proving of boilers.<BR>
     Prussiate of potash for case hardening.<BR>
     Pumping engines, mode of erecting,<BR>
     &nbsp;&nbsp;mode of starting.<BR>
     Pumps, loss of effect in, at high speed and with hot water,<BR>
     &nbsp;&nbsp;causes of this loss;<BR>
     &nbsp;&nbsp;remedy for.<BR>
     Pumps used for mines.<BR>
     Pump, air, description, of,<BR>
     &nbsp;&nbsp;action of.<BR>
     Pumps, air, proper proportions of,<BR>
     &nbsp;&nbsp;single and double acting.<BR>
     Pump, centrifugal, better than common pump.<BR>
     Pump, cold water, description of.<BR>
     Pump, feed, description of,<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;proper dimensions of;<BR>
     &nbsp;&nbsp;rule for proportioning;<BR>
     &nbsp;&nbsp;plunger of;<BR>
     &nbsp;&nbsp;valves of;<BR>
     &nbsp;&nbsp;independent.<BR>
     Pump valves for mines, &amp;c.<BR>
     Punching and shearing boiler plates.<BR>
    </P>

    <P CLASS="indented">Railway wheels, bursting velocity of.<BR>
     Railway trains, resistance of.<BR>
     Rarefaction or exhaustion produced by chimneys.<BR>
     &quot;Rattler&quot; and &quot;Alecto,&quot; trials of.<BR>
     Registration, benefits of.<BR>
     Regnault, experiments on heat by.<BR>
     Regulator, a valve for regulating the admission of steam in
    locomotives,<BR>
     &nbsp;&nbsp;description of;<BR>
     &nbsp;&nbsp;various forms of.<BR>
     Regulator, Clark&#39;s, patent steam and fire.<BR>
     Rennie, experiments on friction by.<BR>
     Resistance, experienced by railway trains.<BR>
     Resistance of vessels in water,<BR>
     &nbsp;&nbsp;mainly made up of friction;<BR>
     &nbsp;&nbsp;experiments on.<BR>
     Resistance and speed of vessels influenced by their size.<BR>
     &quot;Retribution,&quot; boilers of, by Messrs. Mandslay.<BR>
     Riveting and caulking of land boilers.<BR>
     Rocking motion of locomotives.<BR>
     Rolling circle of paddle wheels.<BR>
     Rotatory engines, definition of.<BR>
     Rotative engines, definition of.<BR>
     Rust joints, how to make.<BR>
    </P>

    <P CLASS="indented">Safety valve, area of, in low pressure engines,<BR>
     &nbsp;&nbsp;in locomotives.<BR>
     Salinometer, or salt gauge, how to use,<BR>
     &nbsp;&nbsp;how to construct.<BR>
     Salt, accumulation of, prevented in marine boilers by blowing off,<BR>
     &nbsp;if allowed to accumulate in boilers may occasion explosion;<BR>
     &nbsp;&nbsp;amount of, in sea water.<BR>
     Salt water produces surcharged steam.<BR>
     Salting of boilers, what to do if this takes place.<BR>
     Sawing timber, power necessary for.<BR>
     Scale in marine boilers. <EM>See</EM> also Salt.<BR>
     Scale preventer, Lamb&#39;s.<BR>
     Scrap iron, unsuitable for case hardening.<BR>
     Scraping tools for metal surfaces.<BR>
     Screw.<BR>
     Screw engine, geared oscillating, description of,<BR>
     &nbsp;&nbsp;direct acting, description of.<BR>
     Screw engine, direct acting, by Messrs. John Bourne &amp; Co.<BR>
     Screw engines, best forms of.<BR>
     Screw frame in deadwood.<BR>
     Screw propeller, description of.<BR>
     Screw propeller, mode of fixing on shaft,<BR>
     &nbsp;&nbsp;modes of receiving thrust;<BR>
     &nbsp;&nbsp;apparatus for lifting;<BR>
     &nbsp;&nbsp;configuration of;<BR>
     &nbsp;&nbsp;action of;<BR>
     &nbsp;&nbsp;pitch of the screw;<BR>
     &nbsp;&nbsp;screws of increasing or expanding pitch;<BR>
     &nbsp;&nbsp;slip of the screw;<BR>
     &nbsp;&nbsp;positive and negative slip;<BR>
     &nbsp;&nbsp;screw and paddles compared;<BR>
     &nbsp;&nbsp;test of the dynamometer;<BR>
     &nbsp;&nbsp;trials of &quot;Rattler&quot; and &quot;Alecto,&quot; and
    &quot;Niger&quot; and &quot;Basilisk&quot;;<BR>
     &nbsp;&nbsp;indicator and dynamometer power;<BR>
     &nbsp;&nbsp;loss of power in screw vessels in head winds;<BR>
     &nbsp;&nbsp;the screw should be deeply immersed;<BR>
     &nbsp;&nbsp;screws of the Earl of Dundonald, Hodgson, Griffith, Holm,
    and Beattie;<BR>
     &nbsp;&nbsp;lateral and retrogressive slip;<BR>
     &nbsp;&nbsp;sterns of screw vessels should be sharp;<BR>
     &nbsp;&nbsp;proportions of screws with two, four, and six blades;<BR>
     &nbsp;&nbsp;screw vessels with auxiliary power;<BR>
     &nbsp;&nbsp;screw and paddles combined;<BR>
     &nbsp;&nbsp;economy of fuel in steam vessels;<BR>
     &nbsp;&nbsp;benefits of registration.<BR>
     Screw propeller, Holm&#39;s conchoidal.<BR>
     Screw shaft, details of.<BR>
     Screw shaft pipe at stern.<BR>
     Screw shaft brasses of direct acting screw engines.<BR>
     Sea water, amount of salt in.<BR>
     Sea injection cocks.<BR>
     Setting of wagon boilers,<BR>
     &nbsp;&nbsp;of marine boilers.<BR>
     Setting the valves of locomotives.<BR>
     Shaft, paddle, details of.<BR>
     Shaft of screw propeller, details of.<BR>
     Shafts, strength of.<BR>
     Shank&#39;s steam gauge.<BR>
     Shocks may not be well resisted by iron that can well resist
    strains,<BR>
     &nbsp;&nbsp;effect of inertia in resisting shocks.<BR>
     Side levers or beams, description of.<BR>
     Side lever marine engines, description of.<BR>
     Side lever engines, how to erect.<BR>
     Side rods, description of,<BR>
     &nbsp;&nbsp;strength proper for.<BR>
     Silsbee, Mynderse &amp; Co.&#39;s steam fire engine.<BR>
     Single acting engines, definition of.<BR>
     Single acting or pumping engines,<BR>
     &nbsp;&nbsp;mode of erecting;<BR>
     &nbsp;&nbsp;mode of starting.<BR>
     Sinuous motion of locomotives.<BR>
     Slide valve,<BR>
     &nbsp;&nbsp;various forms of;<BR>
     &nbsp;&nbsp;long D and three ported valve, description of;<BR>
     &nbsp;&nbsp;action of the slide valve;<BR>
     &nbsp;&nbsp;lead and lap of the valve;<BR>
     &nbsp;&nbsp;rules for determining the proportions of valves;<BR>
     &nbsp;&nbsp;advantages of lead in swift moving engines.<BR>
     Slide valve, equilibrium.<BR>
     Slide valve with balance piston of direct acting screw engine.<BR>
     Slide valve, how to finish.<BR>
     Slide valves of marine engines, how to set.<BR>
     Slip of paddle wheels.<BR>
     Slip of the screw,<BR>
     &nbsp;&nbsp;positive and negative slip;<BR>
     &nbsp;&nbsp;lateral and retrogressive slip.<BR>
     Smoke, modes of consuming.<BR>
     Smoke burning furnaces,<BR>
     &nbsp;&nbsp;Williams&#39;s argand;<BR>
     &nbsp;&nbsp;Prideaux&#39;s;<BR>
     &nbsp;&nbsp;Boulton and Watt&#39;s dead plate;<BR>
     &nbsp;&nbsp;revolving grate;<BR>
     &nbsp;&nbsp;Juckes&#39;s;<BR>
     &nbsp;&nbsp;Maudslay&#39;s;<BR>
     &nbsp;&nbsp;Hall&#39;s, Coupland&#39;s, Godson&#39;s, Robinson&#39;s,
    Stevens&#39;s, Hazeldine&#39;s, &amp;c.<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;&quot;Snake&quot; locomotive.<BR>
     Southern,<BR>
     &nbsp;&nbsp;experiments on friction by;<BR>
     &nbsp;&nbsp;experiments on steam by.<BR>
     Specific heat, definition of.<BR>
     Speed of vessels influenced by their size.<BR>
     Spheroidal condition of water in boilers.<BR>
     Springs of locomotives.<BR>
     Stand pipe for low pressure boilers.<BR>
     Starting handle of locomotives.<BR>
     Staying of boilers.<BR>
     Staying tube plates, mode of.<BR>
     Staying fire boxes of locomotives.<BR>
     Steam, experiments on by Southern, French Academy, Franklin
    Institute,<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;and M. Regnault.<BR>
     Steam pump,<BR>
     &nbsp;&nbsp;Worthington&#39;s;<BR>
     &nbsp;&nbsp;Woodward&#39;s.<BR>
     Steam and water, relative bulks of.<BR>
     Steam,<BR>
     &nbsp;&nbsp;expansion of;<BR>
     &nbsp;&nbsp;pressure of;<BR>
     &nbsp;&nbsp;inversely as space occupied;<BR>
     &nbsp;&nbsp;<EM>See also</EM> Expansion of Steam.<BR>
     Steam engine, applications and appliances of the.<BR>
     Steam engine,<BR>
     &nbsp;&nbsp;general description of Watt&#39;s double acting
    engine;<BR>
     &nbsp;&nbsp;R. Hoe &amp; Co.&#39;s;<BR>
     &nbsp;&nbsp;Corliss&#39;s;<BR>
     &nbsp;&nbsp;Woodruff &amp; Beach&#39;s.<BR>
     Steam engine,<BR>
     &nbsp;&nbsp;various forms of, for propelling vessels;<BR>
     &nbsp;&nbsp;paddle engines and screw engines;<BR>
     &nbsp;&nbsp;principal varieties of paddle engines;<BR>
     &nbsp;&nbsp;different kinds of paddle wheels;<BR>
     &nbsp;&nbsp;the side lever engine;<BR>
     &nbsp;&nbsp;description of the side lever engine;<BR>
     &nbsp;&nbsp;oscillating paddle engine;<BR>
     &nbsp;&nbsp;description of feathering paddle wheels;<BR>
     &nbsp;&nbsp;direct acting screw engine.<BR>
     Steam dome of locomotives.<BR>
     Steam fire engine,<BR>
     &nbsp;&nbsp;Latta&#39;s.<BR>
     &nbsp;&nbsp;Amoskeag.<BR>
     &nbsp;&nbsp;Silsbee, Mynderse &amp; Co.&#39;s.<BR>
     Steam gauge,<BR>
     &nbsp;&nbsp;Bourdon&#39;s;<BR>
     &nbsp;&nbsp;Shank&#39;s.<BR>
     Steam jacket, benefits of;<BR>
     Steam passages, area of;<BR>
     Steam room in boilers;<BR>
     Steam, surcharged, law of expansion by heat;<BR>
     Steel, strength of;<BR>
     Stephenson, link motion by;<BR>
     Stop valves between boilers;<BR>
     Straight edges;<BR>
     Strains subsisting in machines;<BR>
     Strain proper to be put upon iron in engines;<BR>
     Strains in machines,<BR>
     &nbsp;&nbsp;vary inversely as the velocity of the part to which the
    strain is<BR>
     applied.<BR>
     &nbsp;&nbsp;aggravated by being intermittent.<BR>
     &nbsp;&nbsp;increase of strain due to deflection.<BR>
     &nbsp;&nbsp;effects of alternate strains in opposite directions.<BR>
     Strength of materials.<BR>
     Strength of hollow pillars,<BR>
     &nbsp;&nbsp;law of;<BR>
     &nbsp;&nbsp;strength varies with thickness of metal.<BR>
     Strength of cast iron to resist shocks does not vary as the
    strength<BR>
     &nbsp;&nbsp;&nbsp;&nbsp;to resist strains,<BR>
     &nbsp;&nbsp;increase of strength by combination with cast iron.<BR>
     Strength of boilers,<BR>
     &nbsp;&nbsp;experiments on, by Franklin Institute;<BR>
     &nbsp;&nbsp;by Mr. Fairbairn;<BR>
     &nbsp;&nbsp;mode of computing;<BR>
     &nbsp;&nbsp;mode of staying for strength.<BR>
     Strength of engines: cylinder,<BR>
     &nbsp;&nbsp;trunnions;<BR>
     &nbsp;&nbsp;piston rod;<BR>
     &nbsp;&nbsp;main links;<BR>
     &nbsp;&nbsp;connecting rod;<BR>
     &nbsp;&nbsp;studs of the beam;<BR>
     &nbsp;&nbsp;gudgeons;<BR>
     &nbsp;&nbsp;working beam;<BR>
     &nbsp;&nbsp;cast iron shaft;<BR>
     &nbsp;&nbsp;malleable iron shaft;<BR>
     &nbsp;&nbsp;teeth of wheels;<BR>
     &nbsp;&nbsp;side rods;<BR>
     &nbsp;&nbsp;crank;<BR>
     &nbsp;&nbsp;crank pin;<BR>
     &nbsp;&nbsp;cross head;<BR>
     &nbsp;&nbsp;main centre;<BR>
     &nbsp;&nbsp;gibs and cutter.<BR>
     Studs, strength proper for.<BR>
     Stuffing box, description of.<BR>
     Stuffing boxes with metallic packing,<BR>
     &nbsp;&nbsp;with sheet brass packed behind with hemp;<BR>
     &nbsp;&nbsp;sometimes fitted with a lantern, brass.<BR>
     Sugar mills, power necessary to work.<BR>
     Summers&#39; experiments on the friction of rough surfaces.<BR>
     Surcharged steam, law of expansion of, by heat.<BR>
     Surcharged steam produced by salt water,<BR>
     &nbsp;&nbsp;corrosive action of.<BR>
     Surfaces, how to make true.<BR>
     Sweeping the tubes of boilers clean of soot.<BR>
    </P>

    <P CLASS="indented">Teeth of wheels.<BR>
     Telescope chimneys.<BR>
     Tender of a locomotive, description of,<BR>
     &nbsp;&nbsp;attachment of, to engine.<BR>
     Thrashing corn, power necessary for.<BR>
     Throttle valve, description of.<BR>
     Thrust of the screw propeller, modes of receiving.<BR>
     Thrust plummer block.<BR>
     Tires of locomotive wheels.<BR>
     Traction on railways.<BR>
     Trunk engine by Messrs. Rennie, disadvantages of.<BR>
     Trunk engines by Messrs. Penn.<BR>
     Trunnions of oscillating engines, description of,<BR>
     &nbsp;&nbsp;strength proper for;<BR>
     &nbsp;&nbsp;details of.<BR>
     Trunnion packing.<BR>
     Trunnion plummer blocks.<BR>
     Tube plates, mode of staying.<BR>
     Tube plates of modern locomotives.<BR>
     Tubes of modern locomotive boilers.<BR>
     Tubes of boilers, how to sweep clean of soot.<BR>
     Tubing of boilers.<BR>
     Tubing locomotive boilers.<BR>
    </P>

    <P CLASS="indented">Valve, atmospheric.<BR>
     Valve casing, description of.<BR>
     Valve casing should have expansion joint.<BR>
     Valve and valve casing of oscillating engine.<BR>
     Valve delivery, description of,<BR>
     &nbsp;&nbsp;action of<BR>
     Valve, equilibrium slide.<BR>
     Valve, foot, description of,<BR>
     &nbsp;&nbsp;action of.<BR>
     Valve gear of Watt&#39;s engine,<BR>
     &nbsp;&nbsp;action of.<BR>
     Valve gear of oscillating engine.<BR>
     Valve, gridiron.<BR>
     Valve, slide. <EM>See</EM> Slide Valve.<BR>
     Valve, slide, how to finish.<BR>
     Valves, ball,<BR>
     &nbsp;&nbsp;Belidor&#39;s might be used for foot and delivery
    valves;<BR>
     &nbsp;&nbsp;butterfly, of air pump;<BR>
     &nbsp;&nbsp;concentric ring, for air pump bucket.<BR>
     Valves, equilibrium.<BR>
     Valves, escape, for cylinders.<BR>
     Valves, expansion. <EM>See</EM> Expansion Valves.<BR>
     Valves of feed pumps.<BR>
     Valves, india rubber, for air pump.<BR>
     Valves, Kingston&#39;s.<BR>
     Valves of locomotives, how to set.<BR>
     Valves, pot-lid, of air pump.<BR>
     Vacuum, meaning of,<BR>
     &nbsp;&nbsp;nature and uses of;<BR>
     &nbsp;&nbsp;how maintained in engines.<BR>
     Vacuum sometimes occurs in boilers,<BR>
     &nbsp;&nbsp;evils of a vacuum in boilers.<BR>
     Vacuum, velocity with which air rushes into a.<BR>
     Vacuum gauge,<BR>
     &nbsp;&nbsp;Bourdon&#39;s.<BR>
     Velocity of air entering a vacuum.<BR>
     Velocity of falling bodies.<BR>
     Vent of boilers, definition of.<BR>
     Vessels, resistance of,<BR>
     &nbsp;&nbsp;mainly made up of friction in good forms;<BR>
     &nbsp;&nbsp;experiments on;<BR>
     &nbsp;&nbsp;influence of size.<BR>
     <EM>Vis viva</EM>, or mechanical power.<BR>
    </P>

    <P CLASS="indented">Waste steam pipe.<BR>
     Waste water pipe.<BR>
     Water required for condensation,<BR>
     &nbsp;&nbsp;pumps for supplying.<BR>
     Watt&#39;s double acting engine, description of.<BR>
     Wedge.<BR>
     Wheels, toothed, for screw engines.<BR>
     Wheels, teeth of.<BR>
     Wheels of locomotives, adhesion of.<BR>
     Wheels, driving, of locomotives.<BR>
     Wheel tires.<BR>
     Wheels and axles of modern locomotives.<BR>
     Wood, experiments on friction by.<BR>
     Wood, evaporative efficacy of.<BR>
     Woodman&#39;s steam pump.<BR>
     Woodruff &amp; Beach&#39;s steam engine.<BR>
     Working beam of land engine, description of.<BR>
     Worthington&#39;s steam pump,<BR>
     &nbsp;&nbsp;duplex pump.<BR>
    </P>

    <H4 CLASS="centered">THE END.</H4>

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