UC-NRLF 
 
USEFUL WORKS OF GENERAL 
 
 late of the Legacy-Duty Office. New Edition. Fcp. Svo. 5s. 
 *** These two works may be had in One Volume, price 7s. 
 
 LONDON: LONGMAN, BROWN, GREEN", AND LONGMANS. 
 

 , 
 
 flh 
 
CATECHISM 
 
 STEAM ENGINE, 
 
 ILLUSTRATIVE OF THE 
 
 SCIENTIFIC PRINCIPLES UPON WHICH ITS OPERATION DEPENDS, 
 
 AND THE PRACTICAL DETAILS OF ITS STRUCTURE, IN 
 
 ITS APPLICATION TO MINES, MILLS, STEAM 
 
 NAVIGATION AND RAILWAYS. 
 
 fcarurutf )U%se3tian3 at 
 
 BY JOHN BOURNE, C.E. 
 
 THIRD EDITION. 
 
 LONDON : 
 LONGMAN, BROWN, GREEN, AND LONGMANS, 
 
 PATERNOSTER-ROW. 
 1850. 
 
LONDON : 
 
 SPOTTISWOODES and SHAW, 
 New-Street-Square. 
 
TO 
 
 COLONEL WILLIAM HENRY SYKES, 
 
 VICE PRESIDENT OF THE ROYAL SOCIETY, 
 F.G.S., M.R.A.S., ETC. 
 
 THIS THIRD EDITION IS INSCRIBED BY 
 
 THE AUTHOR, 
 
 AS A SLIGHT TESTIMONY OF THE RESPECT WHICH 
 VARIED ATTAINMENTS, LIBERALITY OF SENTIMENT, AND 
 ENERGY AND INTEGRITY OF CHARACTER, 
 MUST UNIVERSALLY INSPIRE. 
 
 283 
 
PREFACE. 
 
 THE present work is not intended as a substitute 
 for the quarto Treatise on the Steam Engine, 
 which I lately published, but is rather to be re- 
 garded as an introduction and in some measure 
 also as a supplement to that work. Notwith- 
 standing the existence, therefore, of the larger 
 Treatise, it appeared to me that a work upon the 
 steam engine, which in a moderate compass should 
 give an outline of the whole subject in its practical 
 aspect, would still be of much utility. There are 
 no doubt many compendiums already existing 
 which profess to accomplish this object; but I 
 have not met with any which were calculated to 
 satisfy even the most moderate expectations. 
 Most of them are mere compilations from theo- 
 retical authors, and abound even with scientific 
 errors, whilst indicating the absence of any prac- 
 tical acquaintance with the subject ; so that they 
 possess but slender claims upon the attention of 
 the engineer, or indeed of any one desirous of ob- 
 
VI PREFACE. 
 
 taining accurate information on the subject of 
 which they treat. I hold it to be the first quality 
 of an introductory work that it should at least be 
 sound that the doctrines it inculcates, and the 
 lessons it conveys, shall not all have to be unlearned 
 again at a subsequent stage of progress and 
 whatever be its other characteristics, I believe 
 that the present work will at least be found to 
 conform to this standard of utility. It embodies, 
 I believe, the best information now existing upon 
 the subjects of which it treats not taken from 
 books, nor deduced from mere theoretical consi- 
 derations, but derived from my own practice or 
 from the personal communications of the most 
 experienced engineers of the present time. 
 
 JOHN BOURNE. 
 
 ERRATUM. 
 Page 171. line 2. for "page 62." read "page 64." 
 
A CATECHISM 
 
 THE STEAM ENGINE. 
 
 PART I. 
 
 MECHANICAL PRINCIPLES. 
 
 1. Q. What is meant by a vacuum ? 
 
 A. A vacuum means an empty space ; a space in 
 which there is neither water nor air, nor any thing else 
 that we know of. 
 
 2. Q. Wherein does a high pressure differ from a 
 low pressure engine ? 
 
 A. 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 con- 
 densing 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 
 
 v * B 
 
2 A CATECHISM OP 
 
 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. 
 
 3. Q. How can the pressure of a vacuum be said 
 to be nothing, when the existence of a vacuum occasions 
 a pressure of 151bs. on the square inch ? 
 
 A Because it is not the vacuum which exerts this 
 pressure, but the atmosphere, which, like a head of 
 water, presses on every thing 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 a balance 
 retains its equilibrium though an equal weight be 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 va- 
 cuum, but rather to the. existence of an unbalanced 
 plenum, that the pressure made manifest by exhaustion 
 is due, and every one knows that a vacuum of itself 
 would not work an engine. 
 
 4. Q. How is the vacuum maintained in a con- 
 densing engine ? 
 
 A. 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 
 
THE STEAM ENGINE. 3 
 
 falls in the form of hot water to the bottom of the con- 
 denser. The water, which would else be accumulated 
 in the condenser, is continually being pumped out by 
 a pump worked by the engine. 
 
 5. Q. If a vacuum be an empty space, and there 
 be water in the condenser, how can there be a vacuum 
 there ? 
 
 A. There is a vacuum above the water, the water 
 being only like so much iron or lead lying at the 
 bottom. 
 
 6. Q. Is the vacuum in the condenser a perfect 
 vacuum ? 
 
 A. Not quite perfect ; for the cold water entering 
 for the purpose of condensation, is heated by the steam, 
 and emits a vapour 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 con- 
 denser, will stand at about 27 inches. 
 
 7. Q. Is a barometer sometimes applied to the 
 condensers of steam engines ? 
 
 A. Yes; and it is called the vacuum gauge, be- 
 cause 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. 
 
 8. Q. Can a condensing engine be worked with a 
 pressure less than that of the atmosphere ? 
 
 A. Yes, if once it be started ; but it will be a dif- 
 ficult thing to start an engine, if the pressure of the 
 steam be not greater than that of the atmosphere, Be- 
 
 B 2 
 
4 A CATECHISM OF 
 
 fore 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, which are cocks applied for telling the 
 height of water within the boiler, 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 cir- 
 cumstances, 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. 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 that 
 of the atmosphere ; but it is preferable in such cases, 
 partially to close the throttle valve in the steam pipe, 
 whereby the issue of the steam is resisted ; and the 
 pressure in the boiler is thus maintained, though the 
 cylinder only receives its former supply. 
 
 9. Q. In what way would you class the various 
 kinds of condensing engines ? 
 
 A. 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 
 
THE STEAM ENGINE. 5 
 
 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 rectili- 
 near motion. Rotatory engines have not hitherto 
 been successful, so that only the single acting or 
 pumping engine and the double acting or rotative en- 
 gine, can be said to be in actual use. For some pur- 
 poses, 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. 
 
 10. Q. 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 ? 
 
 A. No; rotative engines are generally provided 
 with a fly-wheel to correct such irregularities by its 
 momentum; but where two engines, with their re- 
 spective 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 pur- 
 poses requiring great regularity of motion, its use with 
 common engines is indispensable, though it is not im- 
 possible to supersede the necessity by new contrivances. 
 
 11. Q. You implied that there is some other dif- 
 
 E 3 
 
6 A CATECHISM OF 
 
 ference between single acting and double acting 
 engines, than that which lies in the use or exclusion 
 of the crank ? 
 
 A. 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 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 neces- 
 sary to know that there are some deviations from the 
 usual practice. 
 
 12. Q. With what velocity does air rush into a 
 vacuum ? 
 
 A. With the velocity which a body would acquire 
 by falling from the height of a homogeneous atmo- 
 sphere. The weight of air being known, as well as the 
 pressure it exerts on the earth'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 151bs. The height would be 27,818 
 feet. 
 
 13. Q. And what velocity would the fall of a body 
 from such a height produce ? 
 
 A. About 1,338 feet per second. All bodies fall 
 
THE STEAM ENGINE. 7 
 
 with the same velocity, when there is no resistance 
 from the atmosphere, as is shown by the experiment 
 of letting fall a feather and a guinea from the top of a 
 tall exhausted receiver, when they reach the bottom at 
 the same time. The velocity of falling bodies is one 
 that is accelerated uniformly, according to a known 
 law ; and when the height from which a body falls is 
 given, the velocity acquired at the end of the descent 
 can be easily computed. The square root of the 
 height in feet multiplied by 8 '021 will give the 
 velocity. 
 
 14. Q. But the velocity in what terms? 
 
 A. In feet per second. The distance through 
 which a body falls by gravity in one second is 16 T ^ 
 feet, in two seconds, 64^ feet, in three seconds, 144 T 9 
 feet, in four seconds, 257 T % 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 : 
 
 Number of seconds . . . 
 
 Units of space passed through 
 
 .3 
 
 2536 
 
 so that it appears that the spaces passed through by a 
 falling body are as the squares of the times of falling. 
 The velocity acquired by a falling body at the end of 
 the 1st second is 32 J feet per second, and the end of 
 the 2d second 64f feet, at the end of the 3d, 96| feet, 
 at the end of the 4th, 128J feet, and so on. These 
 numbers proceed in the progression 1, 2, 3, 4, &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 
 
 B 4 
 
8 A CATECHISM OF 
 
 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 vis viva or me- 
 chanical power inherent in a falling body, of any given 
 weight, is measureable by the height through which it 
 descends, it follows that the vis viva 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 energy it possessed before such energy 
 being measurable by a reference to the height through 
 which a body must have fallen, to acquire the velocity 
 given. 
 
 15. Q. By what considerations is the momentum 
 proper for the fly-wheel of an engine determined ? 
 
 A. 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 momentum 
 inherent in the machinery the engine has to drive 
 and the equability of motion required the engine 
 will work with sufficient regularity for all ordinary 
 purposes. 
 
THE STEAM ENGINE. 9 
 
 16. Q, What do you understand by the centre of 
 gravity of a body ? 
 
 A. That point within it, in which the whole of 
 the weight may be supposed to be concentrated, and 
 which continually endeavours to gain the lowest pos- 
 sible position. A body hung in the centre of gravity 
 will remain at rest in any position. 
 
 17. Q. What do you understand by centrifugal 
 and centripetal forces ? 
 
 A. 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 ver- 
 tical 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. 
 
 18. Q. What is meant by the centre of gyration ? 
 
 A. The centre of gyration is that point in a re- 
 volving 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 quicker than 
 
10 A CATECHISM OF 
 
 the part nearest to it, the momentum cannot be sup- 
 posed 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. 
 
 19. Q. What is the centre of oscillation ? 
 
 A. The centre of oscillation is a point in a pendu- 
 lum 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 sus- 
 pension 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. 
 
 20. Q. By what circumstance is the velocity of 
 vibration of a pendulous body determined ? 
 
 A. 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 pendulums of clocks, therefore, a small arc is pre- 
 ferred, 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. 
 
 21. Q. If then the length of a pendulum be given, 
 can the number of vibrations in a given time be de- 
 termined ? 
 
 A. Yes; the time of vibration bears the same re- 
 
THE STEAM ENGINE. 11 
 
 lation 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 dia- 
 meter. The number of vibrations made in a given 
 time by pendulums of different lengths, is inversely 
 as the square roots of their lengths. 
 
 22. Q. Then when the length of the second's pen- 
 dulum is known, the proper length of a pendulum to 
 make any given number of vibrations in the minute 
 can readily be computed ? 
 
 A. Yes; the length of the second'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 : mul- 
 tiply 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 pen- 
 dulum were required that would make 70 vibra- 
 tions per minute in the latitude of London, then 
 
 ^39^1393-^-60 = 5-363* = 2875 in. which is the 
 
 length required. 
 
 23. Q. What measures are there of the centrifugal 
 force of bodies revolving in a circle ? 
 
 A 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 dia- 
 meter of one be double that of the other, the larger 
 will have double the amount of centrifugal force. The 
 
12 A CATECHISM OF 
 
 centrifugal force of the same wheel, 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. 
 
 24. Q. 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 ? 
 
 A. 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. 
 
 25. Q. Can you explain how it comes that the 
 length of a pendulum determines the number of vibra- 
 tions it makes in a given time ? 
 
 A. 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 ra- 
 pidly 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 dis- 
 tance descended, and if the velocity due to the descent 
 of a body through a given height be spread over a 
 
THE STEAM ENGINE. 13 
 
 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 pendu- 
 lum determines the steepness of the arc, it must also 
 determine the velocity of vibration. 
 
 26. Q. 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's 
 pendulum ? 
 
 A. And so there is ; the length of the second's 
 pendulum at the level of the sea in London, is 39*1393 
 inches, and it is from the length of the second's pen- 
 dulum 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 pen- 
 dulum, 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 and 1-12 ft. very nearly, which is the space through 
 which a body falls by gravity in a second. 
 
 27. Q. Are the motions of the conical pendulum 
 or governor reducible to the same laws which apply to 
 the common pendulum ? 
 
 A. Yes ; the motion of the conical pendulum may 
 
14 A CATECHISM OF 
 
 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. A steam engine go- 
 vernor may, it is true, be driven round with any speed, 
 and therefore it may be supposed that the length of 
 the arms cannot aifect the time of revolution ; but 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 revo- 
 lution of the governor. If therefore, a certain expan- 
 sion 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 revolu- 
 tions 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 ball, you must divide the constant 
 number 187*68 by the number of revolutions per 
 minute, and the square of the quotient will be the ver- 
 tical height in inches of the centre of suspension above 
 the plane of the ball's revolution. Deduct the square 
 of the vertical height in inches from the square of the 
 
THE STEAM ENGINE. 15 
 
 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. 
 
 28. Q. Cannot the operation of a governor be de- 
 duced merely from the consideration of centrifugal and 
 centripetal forces ? 
 
 A. 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 centri- 
 petal 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 then 
 you make the speed or number of revolutions such, 
 that the centrifugal force will keep the balls in the 
 desired position. 
 
 29. Q. Does not the weight of the balls affect the 
 question ? 
 
 A. 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 over- 
 come 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 pro- 
 portion. 
 
16 A CATECHISM OF 
 
 30. Q. What do you understand by the mechanical 
 powers ? 
 
 A. The mechanical powers are certain contri- 
 vances, 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 de- 
 vices 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 neces- 
 sity 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 this transformation, and all 
 that implements called mechanical powers accomplish, 
 is to effect this transformation. 
 
 31. Q. Is there no power gained by the lever ? 
 A. 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 Ib. through 100 ft., as to lift 100 Ibs. 
 
THE STEAM ENGINE. 17 
 
 through one foot. A cylinder of a given cubical ca- 
 pacity 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. 
 
 32. Q. Is there no loss of power by thte use of the 
 crank ? 
 
 A. Not any. Many persons have supposed that 
 there was a loss of power by the use of the crank, be- 
 cause 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 confuse 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 ex- 
 pended, 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 di- 
 minished leverage, so that there is the same power 
 given out by the crank in each of the divisions. 
 
 33. Q. Have no plans been projected for gaining 
 power by means of a lever ? 
 
 c 
 
18 A CATECHISM OF 
 
 A. Yes, many plans, some of them displaying 
 much ingenuity, but all displaying a complete igno- 
 rance 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 : " 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 ? " Others I have heard 
 say : " By the hydraulic press you can obtain un- 
 limited power ; why not then interpose a hydraulic 
 press between the engines and the paddles ? " 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 com- 
 bination of mechanism, get increased force and in- 
 creased speed at the same time, or increased force 
 without diminished speed : and it is from the ig- 
 norance of this inexorable condition, that such myriads 
 of schemes for the realisation of perpetual motion, 
 by combinations of levers, weights, wheels, quick- 
 silver, cranks, and other mere pieces of inert matter, 
 have been propounded. Any such combination can 
 never increase power, nor diminish it either, except 
 by friction. Power is not measurable by force, but 
 by force and velocity combined. 
 34. Q. What is friction? 
 A. Friction is the resistance experienced when 
 
THE STEAM ENGINE. 19 
 
 one body is rubbed upon another body, and is the re- 
 sult of the natural attraction bodies have for one 
 another, and of the interlocking of the impalpable 
 asperities upon the surfaces of all bodies, however 
 smooth. There is also, no doubt, some electrical 
 action involved in its production, not yet recognised 
 nor understood. 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 coin- 
 cident. 
 
 35. Q. Does friction increase with the extent of 
 rubbing surface ? 
 
 A. 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 greater increase in the dura- 
 bility. When the bearings of an engine are made too 
 small, they very soon wear out. 
 
 36. Q. Does friction increase in the same ratio as 
 velocity ? 
 
 A No ; friction does not increase with the velo- 
 city at all if the friction over a given amount of sur- 
 face be considered ; but it increases as the velocity, if 
 c 2 
 
20 A CATECHISM OF 
 
 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 velo- 
 cities, the same. Of excessive velocities we have not 
 sufficient experience to enable us to state with con- 
 fidence whether the same law continues to operate 
 among them. 
 
 37. Q. Can you give any approximate statement 
 of the force expended in overcoming friction ? 
 
 A. 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 rub- 
 bing upon brass has generally been taken at about 
 one-eleventh of the pressure under the same circum- 
 stances ; but in machines in actual operation, where 
 a film of some lubricating material is interposed be- 
 tween the rubbing surfaces, it is probably not more 
 than one-third of this amount. Indeed, where un- 
 guents are interposed, the friction depends in a great 
 measure upon the nature of the unguent, the viscidity 
 of which may constitute a greater retarding force than 
 the friction : and in watchwork and other fine me- 
 chanism, it is therefore necessary to keep the bearing 
 surfaces small, as the resistance by the viscidity of the 
 
THE STEAM ENGINE. 21 
 
 unguent increases with the extent of the rubbing sur- 
 face. In some experiments upon the friction of shafts 
 by Mr. Gr. Rennie, he found that with a pressure of 
 from 1 to 5 cwt. the friction did not exceed ^th of 
 the pressure when tallow was the unguent employed ; 
 with soft soap it became ^th. The nature of the un- 
 guent, proper for different bearings, appears to depend 
 in a great measure upon the amount of the pressure 
 to which they are subjected, the hardest unguents 
 being best where the pressure is greatest. 
 
 38. Q. What do you understand by a horse power? 
 A. An amount of mechanical force that will raise 
 
 33,000 Ibs. one foot high in a minute. This standard 
 was adopted by Mr. Watt as the average force ex- 
 erted 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 em- 
 ployed, determine the size of engine that would be 
 suitable for the work. 
 
 39. Q. 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 Ibs. 
 one foot high in a minute ? 
 
 A. No, not now; such was the case in Watt'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 
 c 3 
 
22 A CATECHISM OF 
 
 power than was exerted in Watt's time, and a horse 
 power has become a' mere conventional unit for ex- 
 pressing a certain size of cylinder, without reference 
 to the power exerted. 
 
 40. Q. Then each nominal horse power of a mo- 
 dern engine may raise much more than 33,000 Ibs. one 
 foot high in a minute ? 
 
 A. Yes ; some raise 52,000 Ibs., others 60,000 Ibs. 
 and others, 66,000 Ibs., one foot high in the minute by 
 each nominal horse power ; and therefore no compari- 
 son can be made between the performances of different 
 engines, unless the power actually exerted be first dis- 
 covered. 
 
 41. Q. How is this discovery made ? 
 
 A By means of an instrument called the indicator, 
 which consists of a small cylinder, about an inch in 
 diameter, fitted with a piston, which is pressed down 
 by a spring. This piston, by the height to which it 
 rises against the spring, indicates the pressure within 
 the cylinder of the engine; and the number of pounds' 
 pressure on the square inch multiplied by the number 
 of square inches in the area of the cylinder, and by 
 the number of feet travelled through by the piston per 
 minute, gives the amount of impelling force. From 
 this a trifling deduction about a tenth in the case of 
 large engines is enough is to be made for friction, 
 &c., and the remainder is the effective moving force 
 which, divided by 33,000 Ibs., gives the actual horse 
 power. 
 
 42. Q. What quantity of steam is supposed to be 
 consumed by engines per horse power ? 
 
 A. About 33 cubic feet per minute, according to 
 
THE STEAM ENGINE. 23 
 
 Mr. Watt's rule, or a cubic foot of water raised into 
 steam per hour, which is the proportion assumed by 
 many persons, and which nearly agrees with that 
 adopted by Mr. Watt. Any such rules, however, can 
 only have a very partial application in modern engines, 
 as it is now the common practice to work engines more 
 or less expansively ; and, in such cases, less than the 
 quantity of steam formerly necessary, is used. 
 
 43. Q. What is meant by working engines expan- 
 sively ? 
 
 A. 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 com- 
 pleted by the expanding steam. 
 
 44. Q. And what is the benefit of that practice ? 
 A. 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, some power, and that power, it is 
 clear, is obtained without any expenditure of steam 
 or fuel whatever. 
 
 45. Q. Can you give any rule for ascertaining the 
 amount of benefit derivable from expansion ? 
 
 A. Divide the length of stroke through which the 
 
 c 4 
 
24 A CATECHISM OF 
 
 steam expands, by the length of stroke performed with 
 full pressure, which call 1 ; the hyperbolic logarithm 
 of the quotient is the increase of efficiency due to ex- 
 pansion. According to this rule it will be found, that 
 if a given quantity of steam, the power of which work- 
 ing at full pressure is represented by 1, be admitted 
 into a cylinder of such a size, that its ingress is con- 
 cluded 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, un- 
 less 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 resist- 
 ance of vapour in the condenser, which all become 
 relatively greater with a smaller urging force. 
 
 46. Q. What is meant by latent heat ? 
 
 A. 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 
 
THE STEAM ENGINE. 25 
 
 acceptation of the term, means sensible liquefaction or 
 vaporization ; but to produce these changes heat is as 
 necessary as to produce an expansion of the mercury 
 in a thermometer tube, and it is hard to see on what 
 ground heat can be said to be latent when its presence 
 is made manifest by a change of state. It is the tem- 
 perature only that is latent, and latent temperature 
 means sensible something else. 
 
 47. Q. But when you talk of the latent heat of 
 steam, what do you mean to express ? 
 
 A. I mean to express the heat consumed in accom- 
 plishing 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 s 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 is 
 180 degrees above the freezing point; so that it re- 
 quires 1180 times as much heat to raise a Ib. of water 
 into steam, as to raise llSOlbs. of water one degree; 
 or it requires about as much heat to raise a pound of 
 boiling water into steam as would raise 5^ Ibs. of water 
 from the freezing to the boiling point ; 5^ multiplied 
 by 180 being 990, or 1000 nearly. 
 
 48. Q. What do you understand by specific heat ? 
 A. By specific heat, 1 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 tempera- 
 
26 A CATECHISM OF 
 
 ture 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. 
 
 49. Q. What expansion does water undergo in its 
 conversion into steam ? 
 
 A. A cubic inch of water makes about a cubic foot 
 of steam. of the atmospheric pressure. 
 
 50. Q. And how much at a higher pressure? 
 
 A. That depends upon what the pressure is. The 
 higher the pressure the smaller will be the volume of 
 steam from a given quantity of water ; for high pres- 
 sure steam is just low pressure steam forced into a less 
 space. 
 
 51 . Q. If this be so, the quantity of heat in a given 
 weight of steam is the same, whether it is high or low 
 pressure steam ? 
 
 A. Yes ; the heat in steam is a constant quantity, 
 or nearly so, at all pressures, if the steam be saturated 
 with water. Steam, to which an additional quantity of 
 heat has been imparted after leaving the boiler, or as 
 it is called " surcharged steam," 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 employed for working engines, 
 and it may therefore be considered in practice that a 
 pound of steam contains the same quantity of heat at 
 all pressures. 
 
THE STEAM ENGINE. 27 
 
 52. Q. But the temperature of steam varies with 
 the pressure ? 
 
 A. Yes; the temperature rises with the pressure, 
 but the latent heat becomes less in the same propor- 
 tion. The latent heat of high pressure steam is less 
 therefore than that of low pressure steam, while the 
 sensible heat is greater, and the two taken together 
 make up the same sum at all temperatures. 
 
 53. Q. Is there any benefit arising from the use of 
 high pressure steam in steam engines ? 
 
 A. In high pressure, as contrasted with condensing 
 engines, there is always the loss of the vacuum, which 
 will generally amount to 12 or 131bs. on the square 
 inch. 
 
 54. Q. But in high pressure engines, is there any 
 benefit arising from the use of a very high pressure 
 over a pressure of a moderate account ? 
 
 A. Yes, there is an advantage; for, in all high 
 pressure engines, there is a diminution in the power 
 caused by the counteracting pressure of the atmosphere 
 on the educting side of the piston : for the force of the 
 piston in its descent would obviously be greater, if 
 there was a vacuum beneath it ; and the counteracting 
 pressure of the atmosphere is relatively less when the 
 steam used is of a very high pressure. It is clear, that 
 if you bring down the pressure of the steam, in a high 
 pressure engine to the pressure of the atmosphere, it 
 will not exert any power at all whatever quantity of 
 steam may be expended, and if the pressure be brought 
 nearly as low as that of the atmosphere, the engine 
 will exert only a very small amount of power ; whereas, 
 if a very high pressure be employed, the pressure of 
 
28 A CATECHISM OF 
 
 the atmosphere will become relatively as small in 
 counteracting the impelling pressure, as the attenuated 
 vapour in the condenser of a condensing engine is in 
 resisting the lower pressure which is there employed. 
 
 55. Q. In the case of condensing engines, is there 
 any benefit derivable from the use of steam of a high 
 pressure ? 
 
 A. Setting aside loss from friction, and supposing 
 the vacuum to be a perfect one, there would be no 
 benefit arising from the use of steam of a high pressure 
 in condensing engines, for the same weight of steam 
 used without expansion, or with the same measure of 
 expansion, would produce at every pressure the same 
 amount of mechanical power. A piston, with a square 
 foot of area, and a stroke of three feet, with a pressure 
 of one atmosphere, would obviously lift the same weight 
 through the same distance, as a cylinder with half a 
 square foot of area, and a stroke of three feet, with a 
 pressure of two atmospheres. In the one case, we have 
 three cubic feet of steam of the pressure of one atmo- 
 sphere, and in the other case 1 J cubic feet of the pres- 
 sure of two atmospheres. But there is the same weight 
 of steam, or the same quantity of heat and water in it, 
 in both cases, so that it appears a given weight of 
 steam would, under such circumstances, produce a 
 definite amount of power, without reference to the 
 pressure. In the case of ordinary engines, however, 
 these conditions do not exactly apply ; the vacuum is 
 not a perfect one, and the pressure of the resisting 
 vapour becomes relatively greater as the pressure of 
 the steam is diminished ; the friction also becomes 
 greater from the necessity of employing larger cylinders, 
 
THE STEAM ENGINE. 29 
 
 so that even in the case of condensing engines, there 
 is a benefit arising from the use of steam of a consider- 
 able pressure. Expansion cannot be carried beneficially 
 to any great extent, unless the initial pressure be con- 
 siderable ; for if steam of a low pressure were used, the 
 ultimate tension would be reduced to a point so nearly 
 approaching that of the vapour in the condenser, that 
 the difference would not suffice to overcome the friction 
 of the piston ; and a loss of power would be occasioned 
 by carrying expansion to such an extent. In some of 
 the Cornish engines, the steam is cut off at one-twelfth 
 of the stroke ; but there would be a loss arising from 
 carrying the expansion so far, instead of a gain, unless 
 the pressure of the steam were considerable. It is clear, 
 that in the case of engines which carry expansion very 
 far, a very perfect vacuum in the condenser is more 
 important than it is in other cases. Nothing can be 
 easier than to compute the ultimate pressure of ex- 
 panded steam, so as to see at what point expansion ceases 
 to be productive of benefit ; for as the pressure of ex- 
 panded steam is inversely as the space occupied, the 
 terminal pressure when the expansion is twelve times, 
 is just one-twefth of what it was at first, and so on, in 
 all other proportions. The total pressure should be 
 taken as the initial pressure not the pressure on the 
 safety valve, but that pressure plus the pressure of the 
 atmosphere. 
 
 56. Q. Then in high pressure engines working at 
 from 70 to 901bs. on the square inch, as in the case of 
 locomotives, the efficiency of a given quantity of water 
 raised into steam may be considered to be about the 
 same as in condensing engines ? 
 
30 A CATECHISM OF 
 
 A. Yes, there will not be much difference in the 
 case supposed ; if the pressure of steam in a high 
 pressure engine be 1201bs., or 105 Ibs. above the at- 
 mosphere, then the resistance occasioned by the atmo- 
 sphere will cause a loss of ^th of the power. If the 
 pressure of the steam in a low pressure engine be 
 16 Ibs. on the square inch, or 1 Ib. above the atmosphere, 
 and the tension of the vapour in the condenser be 
 equivalent to four inches of mercury, or 2 Ibs. of pres- 
 sure on the square inch, then the resistance occasioned 
 by this rare vapour will also cause a loss of ^th of the 
 power. A high pressure engine, therefore, with a 
 pressure of 105 Ibs. above the atmosphere, works with 
 only the same loss from resistance to the piston, as a 
 low pressure engine with a pressure of 1 Ib. above the 
 atmosphere, and with these proportions the power pro- 
 duced by a given weight of steam will be the same, 
 whether the engine be high pressure or condensing. 
 
 57. Q. Is there any limit to the force of steam ? 
 A. Yes ; there is a limit regulated by the modulus 
 
 of elasticity of water, which at a temperature of 60 is 
 22,100 atmospheres. The modulus of elasticity, of 
 any substance, is the measure of its elastic force, and 
 if water be enclosed in a close vessel which it exactly 
 fills, and be then subjected to heat, the expanding force, 
 it is clear, is that of compressed water for no steam 
 can be produced under such circumstances and we 
 have this proportion : as the volume of expanded water 
 is to the amount of expansion, so is the modulus of 
 elasticity of water to the elastic force of steam of the 
 same density as water. 
 
 58. Q. Have experiments been made to determine 
 the elasticity of steam at different temperatures ? 
 
THE STEAM ENGINE. 31 
 
 A. Yes ; very careful experiments. The fol- 
 lowing 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 con- 
 stant 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's 
 experiments on a larger scale : the results obtained by 
 them are not widely different, and are perhaps nearer 
 the truth, but Mr. Southern's results are generally 
 adopted by engineers, as sufficiently accurate for 
 practical purposes, and those results being identified 
 with engineering practice, it appears expedient to re- 
 tain them. 
 
 59. Q. What law is followed by surcharged steam 
 on the application of heat ? 
 
 A. The same as that followed by air, in which the 
 increments in volume are very nearly in the same pro- 
 portion as the increments in temperature. A volume 
 of air which, at the temperature of 32, occupies 100 
 cubic feet, will at 212 fill a space of 137J cubic feet. 
 
32 A CATECHISM OF 
 
 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 459 : divide the greater sum by 
 the less, and multiply the quotient by the volume at 
 the lower temperature ; the product will give the ex- 
 panded volume. 
 
 60. Q. 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 quan- 
 tity of steam expended is specified ? 
 
 A. Yes ; at the atmospheric pressure, a cubic inch 
 of water has to be supplied to the boiler for every cubic 
 foot of steam abstracted ; at other pressures, the rela- 
 tive bulk of water and steam may be determined as 
 follows : To the temperature of steam in degrees of 
 Fahrenheit,, add the constant number 459, multiply the 
 sum by 75.7, and divide the product by the elastic 
 force of the steam in inches of mercury, and the quotient 
 will give the volume required. In practice, however, 
 it is necessary 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 the accidental sub- 
 sidence of the water to a dangerously low level, which 
 it is necessary as speedily as possible to remedy. It 
 appears expedient that the feed pump should be capable 
 of raising 3^ times the water evaporated by the boiler ; 
 it is therefore made about 240th of the capacity of the 
 cylinder for low pressure engines, supposing the cylinder 
 
THE STEAM ENGINE. 33 
 
 to be double acting, and the pump single acting. In 
 high pressure engines, however, the capacity of the 
 pump should be greater, in proportion to the pressure 
 of the steam. 
 
 61. Q. How do you estimate the quantity of water 
 requisite for condensation ? 
 
 A. Mr. Watt found that the most beneficial tem- 
 perature of the hot well of his engines was 100 degrees. 
 If, therefore, the temperature of the steam be 212, and 
 the latent heat 1,000, then 1,212 may be taken to 
 represent the heat contained in the steam, or 1,112 
 if we deduct the temperature of the hot well. If the 
 temperature of the injection water be 50, then 50 de- 
 grees 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's practice was 
 to allow about a wine pint (28.9 cubic inches) of in- 
 jection water, for every cubic inch of water evaporated 
 from the boiler. The usual capacity for the cold water 
 pump is q^th of the capacity of the cylinder, which 
 allows some water to run to waste. 
 
 62. Q. Is not a good vacuum in an engine con- 
 ducive to increased power ? 
 
 A. It is. 
 
 63. Q. And is not the vacuum good in the pro- 
 
 D 
 
34 A CATECHISM OF 
 
 portion in which the temperature is low, supposing 
 there to be no air leaks ? 
 A Yes. 
 
 64. Q. Then how could Mr. Watt find a tempera- 
 ture of 100 in the water drawn from the condenser, 
 to be more beneficial than a temperature of 70 or 
 80, supposing there to be an abundant supply of cold 
 water ? 
 
 A. Because the superior vacuum due to a tempe- 
 rature of 70 or 80 involves the admission of so much 
 cold water into the condenser, which has afterwards 
 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 re- 
 duction of the temperature below 100, if such reduc- 
 tion 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 pro- 
 duced 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. 
 
 65. Q. Cannot the condensation of the steam be 
 accomplished by any other means, than by the admission 
 of cold water into the condenser ? 
 
 A. It may be accomplished by the method of ex- 
 ternal cold, as it is called, which consists in the appli- 
 cation 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 STEAM ENGINE. 35 
 
 the water used for the purpose of refrigeration. The 
 first kind of condenser employed by Mr. Watt was con- 
 structed 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 there- 
 fore reverted to the use of the jet of cold water, as being 
 upon the whole preferable. The jet entered the con- 
 denser instead of the cylinder as was the previous prac- 
 tice, and this method is now the one in common use. 
 Some few years ago, a good number of steam vessels 
 were fitted with Hall'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. 
 
 66. Q. How much water will a pound of coal raise 
 into steam ? 
 
 A. From 6 to 8 Ibs. 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 cir- 
 cumstances. Mr. Watt reckoned his boilers as capable 
 of evaporating 10.08 cubic feet of water with a bushel 
 or 84 Ibs. of coal, which is equivalent to 7-J- Ibs. of water 
 evaporated by one pound of coal, and this may be taken 
 as the performance of common land boilers at the pre- 
 sent time. In some of the Cornish boilers, however, a 
 pound of coal raises 10 Ibs. of water into steam, or a 
 cwt. of coal evaporates about 19 cubic feet of water. 
 The quantity of fuel burned on each square foot of fire 
 grate per hour, varies very much in different boilers : 
 
 D 2 
 
36 A CATECHISM OF 
 
 in waggon boilers it is from 10 to 13 Ibs. ; in Cornish 
 boilers from 3 J to 4 Ibs. ; and in locomotive boilers from 
 80 to 100 Ibs. The number of square feet of surface 
 required to evaporate a cubic foot of water per hour is 
 about 70 square feet in Cornish boilers, 9 to 1 1 square 
 feet in land and marine boilers, and about 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 waggon boilers ; about 40 square 
 feet in Cornish boilers ; and from 50 to 70 square feet 
 in locomotive boilers. 
 
 67. Q. But what is the heating surface per horse 
 power ? 
 
 A. About 9 square feet per horse power is the 
 usual proportion in waggon boilers, reckoning the total 
 surface as effective surface, if the boilers be of a consi- 
 derable size ; but in the case of small boilers, the pro- 
 portion is larger. The total heating surface of a two- 
 horse power waggon boiler is, according to Boulton and 
 Watt'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. The capacity of steam room is 8^ eftbic 
 feet per horse power, in the two-horse power boiler, 
 and 5| 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| cubic feet per horse power. The 
 content of water is 18 J cubic feet per horse power in the 
 two-horse power boiler, and 15 cubic feet per horse 
 power in the 20-horse power boiler. In marine boilers 
 
THE STEAM ENGINE. 37 
 
 about the same proportions obtain in most particulars. 
 The original boilers of the " Great Western " steamer, 
 bj Messrs. Maudslay, were proportioned with about 
 half a square foot of fire grate per horse power, and ten 
 square feet of flue and furnace surface, reckoning the 
 total amount as effective ; but in the boilers of the 
 " Retribution," by the same makers, 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 that obtains in their land boilers ; but in- 
 asmuch as in modern engines the nominal considerably 
 exceeds the actual power, they allow 11 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 not the bottoms. They have 
 been 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 are two cylinders this is 
 equivalent to 8 times the content of both cylinders, 
 which is the proportion commonly followed in land en- 
 gines,, and which agrees very nearly with the proportion 
 of between 5 and 6 cubic feet of steam room per horse 
 power. 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 
 
 D 3 
 
38 A CATECHISM OF 
 
 divided by 18.4 is rather more than 5 cubic feet per 
 horse power. There is less necessity, however, 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 ; and 
 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 
 of these modifying circumstances exist, there is no ne- 
 cessity for so large a proportion of steam room as 5 or 
 6 cubic feet per horse power, and about half that amount 
 more nearly represents the general practice. In many 
 of the marine tubular boilers, however, the steam space 
 is made too small ; in some cases only If cubic feet 
 per horse power, but the operation of boilers thus pro- 
 portioned is not satisfactory. The proportion of 11 
 square feet of heating surface per nominal horse power, 
 reckoning all the surface as effective, half a square foot 
 of fire grate, and 3 cubic feet of steam room, seems to 
 answer very well for tubular boilers, where the steam 
 chest rises above the boiler, and the engines work ex- 
 pansively through one-third or one-fourth of the stroke. 
 Boulton and Watt allow 0.64 of a square foot per 
 nominal horse power of grate bars 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 
 
 
THE STEAM ENGINE. 39 
 
 foot per horse power seems to answer very well in en- 
 gines working with some expansion, and is now very 
 widely adopted. With this allowance, there will be 
 about 22 square feet of heating surface per square foot 
 of fire grate, and if the consumption of fuel be taken 
 at 6 Ibs. per nominal horse power per hour, there will be 
 12 Ibs. 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 is impossible to fire 
 them effectually. 
 
 68. Q. Can the consumption be made as small as 
 6 Ibs. per nominal horse power per hour ? 
 
 A. It can by working expansively, and in some 
 engines the consumption per nominal horse power per 
 hour does not exceed this amount. 
 
 69. Q. Can the consumption be made as low as 
 6 Ibs. per actual horse per hour without resorting to 
 expansion ? 
 
 A. An actual horse power or 33,000 Ibs. raised one 
 foot high in the minute is represented by the evapora- 
 tion of a cubic foot of water in the hour, and if a cubic 
 foot of water has to be evaporated by 6 Ibs. of coal, 
 then 1 Ib. of coal must be capable of evaporating 10 \ Ibs. 
 of water, which is more than the usual proportion, and 
 engines, therefore, with such a rate of consumption, may 
 be set down as deriving a part of their economy from 
 expansion. 
 
 70. Q. Would it not be beneficial to introduce the 
 Cornish boilers into steam vessels, since they operate 
 with a superior economy in fuel ? 
 
 A. No ; it would not. The superior economy of 
 the Cornish boilers is not derived from any peculiarity 
 
 D 4 
 
40 A CATECHISM OF 
 
 of form or arrangement, but from the immense exten- 
 sion of heating 1 surface, which, though productive of 
 economy in fuel, is attended with an increased expense 
 of boiler, while the space occupied is such as in the 
 case of a steam vessel would be quite inadmissible. If 
 a marine boiler be made with the same quantity of 
 surface as a Cornish boiler, the marine boiler is found 
 to be the more economical of the two. 
 
 71. Q. Is not the combustion in the furnaces of 
 the Cornish boilers very slow ? 
 
 A. Yes, very slow ; and there is in consequence 
 very little smoke evolved. It is an important part of 
 smoke burning to make the combustion slow ; and the 
 chief instigator of smoke, is an insufficient size of fur- 
 nace. The coal used in Cornwall is Welsh coal, which 
 evolves but little smoke, and is therefore more favour- 
 able for the success of a smokeless furnace ; but in the 
 manufacturing districts, where the coal is more bitumi- 
 nous, it is found that smoke may be almost wholly pre- 
 vented by careful firing and a large capacity of furnace. 
 
 72. Q. What is the nature of combustion? 
 
 A. Combustion is nothing more than an energetic 
 chemical combination, or, in other words, it is the 
 mutual neutralisation 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 main- 
 tain the original temperature. 
 
 73. Q. Does air consist of oxygen ? 
 
 A. Air consists of oxygen and nitrogen mixed to- 
 gether, in the proportion of 3^ Ibs. of nitrogen to 1 Ib. 
 of oxygen. Every pound of coal requires about two 
 pounds of oxygen for its saturation, and therefore for 
 
THE STEAM ENGINE. 41 
 
 every pound of coal burned seven 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, so that from 
 12 to 14 Ibs. of air are required for every pound of 
 coal burned. 12 Ibs. of air are about 160 cubic feet, 
 and 200 cubic feet may be taken as the quantity of 
 air required for the combustion of a pound of coal in 
 practice. 
 
 74. Q. Had Mr. Watt any method of consuming 
 smoke ? 
 
 A. 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. 
 But the best arrangement for smoke burning is, it 
 appears to me, that of the revolving grate, which feeds 
 the fire at the same time by a self-acting mechanism. 
 In this plan, the fire grate is made like a round table 
 capable of turning 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 con- 
 sumed 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. 
 
42 A CATECHISM OF 
 
 75. Q Is a furnace of this kind applicable to a 
 steam vessel ? 
 
 A. I see nothing to prevent its application. The 
 arrangement of the boiler should perhaps be changed, 
 to facilitate its application, and I should prefer to 
 combine its use with the employment of vertical tubes, 
 which are found to be more efficacious in practice 
 than horizontal tubes ; but this innovation is not in- 
 dispensable. The introduction of any effectual auto- 
 matic 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 impediments, and would 
 perform with little expense the work of many men. 
 
 76. Q. 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 ? 
 
 A. 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 ; but this surface could be covered with 
 fire-brick to diminish the refrigeratory effect. 
 
 
THE STEAM ENGINE. 43 
 
 77. Q. What method of firing furnaces is the best? 
 A. 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 draft : in ordinary land or marine boilers it 
 should be thin, whereas in locomotive boilers it re- 
 quires to be much thicker. If the stratum of coal be 
 thick while the draft 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 draft 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. 
 
 78. Q. What is the method of consuming smoke 
 pursued in the manufacturing districts ? 
 
 A. In Manchester, where some stringent regula- 
 tions for the prevention of smoke have latterly been 
 . enacted, it is found that the readiest way of burning 
 the smoke is to have a very large proportion of fur- 
 nace room, whereby slow combustion may be carried 
 on, and the operation of the dead plate, prescribed by 
 Mr. Watt, may be made more effectual. In some 
 cases, too, a favourable result is arrived at by raising 
 a ridge of coal across the furnace lying against the 
 
44 A CATECHISM OF 
 
 bridge, and of the same height : this ridge speedily 
 becomes a mass of coke, which promotes the combus- 
 tion of the smoke passing over it. 
 
 79. Q. Is the method of admitting a stream of air 
 into the flues regarded favourably ? 
 
 A. 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 ap- 
 portion 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 of 10 or 12 
 per cent. 
 
 80. Q. What other plans have been contrived for 
 obviating the nuisance of smoke ? 
 
 A. They are too various for enumeration, but 
 most of them either operate upon the principle of ad- 
 mitting 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 materials. 
 Some of the plans, indeed, profess to burn the inflam- 
 mable gases as they are evolved from the coal, without 
 
THE STEAM ENGINE. 45 
 
 permitting the admixture of any of the uninflammable 
 products of combustion which enter into the composi- 
 tion of smoke ; but this object has been very imper- 
 fectly fulfilled in any of the contrivances yet, brought 
 under the notice of the public, and as the revolving 
 grate, without aspiring to a theoretic perfection, seems 
 to achieve the combustion of the smoke when the fire 
 is not urged with vehemence, and as it saves in addi- 
 tion the labour of firing, it seems to be entitled to a 
 preference in practice. Juckes' furnace, which con- 
 sists of an arrangement of the fire bars in the form of 
 an endless chain, whereby the coal is gradually carried 
 forward as it burns, and the ashes and clinkers are 
 precipitated into the ash-pit at the extremity of the 
 furnace where the chain turns down over the extreme 
 carrying roller, is also well spoken of ; but it is mere 
 expensive to construct than the revolving grate, and 
 more difficult to keep in repair. The patent-right of 
 the revolving grate expired some years ago, which 
 may, perhaps, be in some cases a further suasory to 
 its adoption. 
 
 81. Q. You have stated that an actual horse 
 power is a force capable of raising 33,000 Ibs. one foot 
 high in the minute, or a dynamical effort such as is 
 produced by an expenditure of 33 cubic feet of steam 
 per minute, or the evaporation of a cubic foot of water 
 per hour, but you have given no definition of the value 
 of a nominal horse power. How do you ascertain the 
 power of an engine in nominal horses power ? 
 
 A. The nominal power of an engine may be as- 
 certained by the following rule : multiply the square 
 of the diameter of the cylinder in inches by the velo- 
 
46 A CATECHISM OF 
 
 city of the piston in feet per minute, and divide the 
 product by 6000 ; the quotient is the number of no- 
 minal horses power. In using this rule, however, it 
 is necessary to adopt the speed of piston described by 
 Mr. Watt, which varies with the length of the stroke. 
 The speed of piston with a two feet stroke is, accord- 
 ing 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, 
 
 82. Q. By ascertaining the ratio in which the ve- 
 locity of the piston increases with the length of the 
 stroke, could not the element of velocity be cast out 
 altogether, and the nominal power be determined by a 
 reference merely to the dimensions of the cylinder ? 
 
 A. Yes, and this for most purposes is the most 
 convenient method of procedure : 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. This rule supposes a uniform effective 
 pressure upon the piston of 71bs. per square inch ; Mr. 
 Watt estimated the effective pressure upon the piston 
 of his 4-horse power engines at 6.8 Ibs. per square inch, 
 and the pressure increased slightly with the power, 
 and became 6.941bs. per square inch in engines of 
 1 00-horse power ; but it appears to be more convenient 
 to take a uniform pressure of 7 Ibs. 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. 
 
THE STEAM ENGINE. 47 
 
 83. Q. Can nominal be transformed into actual 
 horse power ? 
 
 A. No, that is not possible in the case of com- 
 mon 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, nor from anything else than the 
 dimensions of the cylinder. The actual horse power 
 is a dynamical unit, and the nominal horse power is a 
 measure of capacity of the cylinder, which are obvi- 
 ously incomparable things. 
 
 84. - Q. That is, the nominal horse power expresses 
 the size of an engine, and the actual horse power the 
 number of times 33,000 Ibs. it will lift one foot high in 
 a minute ? 
 
 A. Precisely ; and to find the number of times 
 33,000 Ibs., or 528 cubic feet of water, it will raise one 
 foot high in a minute, or, in other words, the actual 
 power, you first find the pressure in the cylinder by 
 means of the indicator, from which you deduct a pound 
 and a-half of pressure for friction, the loss of power in 
 working the air pump, &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. The same result is attained by squar- 
 ing 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 pis- 
 ton, in feet, and dividing by 42,017. The quantity 
 thus arrived at will, in the case of nearly all modern 
 engines, be very different from that obtained by mul- 
 
48 A CATECHISM OF 
 
 tiplying the square of the diameter of the cylinder by 
 the cube root of the stroke, and dividing by 47, which 
 expresses the nominal power ; and the actual and 
 nominal power must by no means be confounded, as 
 they are totally different things. 
 
 85. Q. What is meant by the duty of an engine ? 
 A. The work done in relation to the fuel con- 
 sumed. 
 
 86. Q. And how is the duty ascertained ? 
 
 A. 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 for 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 re- 
 . presents 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 941bs. of Welsh 
 coal. A bushel of Newcastle coal will only weigh 
 841bs. ; 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. 
 
 87. Q. Can you tell the duty of an engine when 
 you know its consumption of coal per horse power per 
 hour? 
 
 A. 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, 
 
 
THE STEAM ENGINE. 49 
 
 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. 
 
 88. Q. What amount of power is generated in 
 good engines of the ordinary kind by a given weight 
 of coal ? 
 
 A. 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 construc- 
 tion, lOlbs. of coal per nominal horse power per hour 
 is a common consumption, but such engines exert 
 nearly twice their nominal power, so that the con- 
 sumption per actual horse power per hour may be taken 
 at from 5 to 61bs. 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 Ibs. raised 1 ft. high by a bushel of 
 Welsh coals, which weighs 94 Ibs. This is equiva- 
 lent to a consumption of 3.1 Ibs. of coal per actual 
 horse power per hour ; but some engines reach a duty 
 of above 100,000,000, or 1.74 Ibs. of coal per actual 
 horse power per hour. Locomotives consume from 8 
 to 10 Ibs. of coke in evaporating a cubic foot of water, 
 E 
 
50 A CATECHISM OF 
 
 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. 
 Measuring the consumption of fuel by the number of 
 tons a locomotive will draw through a given distance, it 
 appears that passenger engines consume from ^ to J Ib. 
 of coke per ton per mile, and the goods engines from 
 to -J Ib. When the locomotive is worked expansively, 
 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. 
 
 89. Q. But some kinds of coal are more effective 
 than other kinds, and there will be a difference of 
 effect from this cause ? 
 
 A. Yes. In a boiler so proportioned, that a pound 
 of the best Welsh coal will evaporate 9.493 Ibs. of 
 water; a pound of anthracite will evaporate 9.014 
 Ibs. of water ; a pound of the best small Newcastle 
 8.524 Ibs. ; a pound of coke from gas works 7.908 
 Ibs. ; a pound of Welsh and Newcastle, of medium 
 quality, mixed half and half, 7.897 Ibs. ; a pound of 
 Derbyshire 6.772 Ibs. ; and a pound of Blyth Main, 
 Northumberland, 6.6 Ibs. of water. There thus ap- 
 pears to be a difference of at least one-third in the 
 efficacy of the different coals of commerce in raising 
 steam. Coal and coke may be reckoned equal to one 
 another in evaporative power. A pound of wood in 
 its ordinary state evaporates about 4.72 Ibs. of water, 
 and a pound of turf 5.45 Ibs. A pound of wood char- 
 coal, however, is said to evaporate 13.37 Ibs., and a 
 
THE STEAM ENGINE. 51 
 
 pound of turf charcoal 11.63 Ibs. The number of 
 pounds of air consumed by a pound of any combustible 
 is very nearly the same as the number of pounds of 
 water it is capable of evaporating, though twice that 
 quantity of air must pass through the fire. A pound 
 of wood in its ordinary state requires 4.47 Ibs. of air 
 for its combustion, and a pound of turf 4.6 Ibs. If one 
 pound of coal evaporate 9J Ibs. of water, then a cubic- 
 foot of water will be evaporated by 6.58 Ibs. of coal. 
 6^ Ibs. of water evaporated by a pound of coal is 
 equivalent to a cubic foot of water evaporated by 
 9.61 Ibs. of coal ; and 4^ Ibs. of water evaporated by 
 a pound is equivalent to a cubic foot of water eva- 
 porated by 13.88 Ibs. of coal. In such of the Cornish 
 boilers as evaporate 10 Ibs. of water with a pound of 
 coal, a cubic foot of water will be evaporated by 6J 
 Ibs. of coal; but the usual performance of the best 
 Cornish boilers is about 9 Ibs. of water evaporated by 
 a pound of coal of the best quality. 
 
 90. Q, By what process do you ascertain the 
 dimensions of the chimney ? 
 
 A. By a reference to the volume of air it is neces- 
 sary in a given time to supply to the burning fuel, and 
 to the velocity of motion produced by the rarefaction 
 in the chimney ; fpr the area of the chimney requires 
 to be such, that with the velocity due to that rarefac- 
 tion, the quantity of air requisite for the combustion 
 of the fuel shall pass through the furnace in the spe- 
 cified time. Thus if 200 cubic feet of air of the at- 
 mospheric density are required for the combustion of 
 a pound of coal, and 10 Ibs. of coal per horse power 
 per hour are consumed by an engine, then 2000 cubic 
 
 E 2 
 
52 A CATECHISM OF 
 
 feet of air must be supplied to the furnace per horse 
 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 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 such as will produce the 
 respective pressures ; and, therefore, when the differ- 
 ence 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 prac- 
 tice, 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. Boulton and Watt'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 com- 
 monly made about 20 in. square inside, and 80 ft. high, 
 and these dimensions are those which answer to a con- 
 sumption of 15 Ibs. of coal per horse power per hour, 
 which is a very common consumption in factory 
 engines. If 15 Ibs. of coal be consumed per horse 
 power per hour, the total consumption per hour in 
 
 
THE STEAM ENGINE. 53 
 
 a 20-horse boiler will be 300 Ibs., 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. 
 
 91. Q. Is this rule for the dimensions of the chim- 
 ney also applicable to steam vessels ? 
 
 A. In steam vessels Boulton and Watt allow 8^- 
 square inches of area of chimney per horse power, and 
 in marine flue boilers they allow 18 square inches of 
 sectional area of flue per horse power ; but this pro- 
 portion appears to be about one-third greater than 
 what is allowed by many other makers, whose boilers, 
 however, are scarcely so conspicuous for an abundant 
 supply of steam. The sectional area of the flue in 
 square inches is what is termed the calorimeter of the 
 boiler, and the calorimeter divided by the length of 
 the flue in feet is what is termed the vent. In marine 
 flue boilers of good construction the vent varies be- 
 tween the limits of 21 and 25, according to the size of 
 the boiler and other circumstances the largest boilers 
 having generally the largest vents ; and the calori- 
 meter divided by the vent will give the length of 
 the flue in feet. The collective area for the escape 
 of the smoke and flame over the furnace bridges in 
 
 E 3 
 
54 A CATECHISM OF 
 
 marine boilers is 19 square inches per horse power, 
 according to Boulton and Watt's proportion. 
 
 92. Q. Are these proportions applicable to tubular 
 and waggon boilers ? 
 
 A. No. In waggon and tubular boilers very dif- 
 ferent proportions prevail, yet the proportions of every 
 kind of boiler are determinable on the same general 
 principle. In waggon boilers the proportion of the 
 perimeter of the flue which is effective as heating sur- 
 face, 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. If then the vent be the calori- 
 meter 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 waggon boilers accordingly the 
 vent varies from 8 to 11 instead of from 21 to 25, 
 as in the case of marine flue boilers. In Boulton and 
 Watt's 45-horse waggon 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 two- 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 
 waggon boilers the consideration of facility of cleaning 
 the flues is also operative in inducing a large propor- 
 tion of sectional area. Boulton and Watt's 2-horse 
 power waggon boiler has 30 square feet of surface, 
 
THE STEAM ENGINE. 55 
 
 and the flue is 18 in. high above the level of the boiler 
 bottom, by 9 in. wide; while their 12-horse waggon 
 boiler has 118 square feet of heating surface, and the 
 dimensions of the flue similarly measured are 36 in. 
 by 13 in. The width of the smaller flue, if similarly 
 proportioned to the larger one, would be 6J in., instead 
 of 9 in., 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 inthe2-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. 
 
 93. Q. Will you extend your illustrations to the 
 case of a marine boiler ? 
 
 A. 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-horse power 
 each. The height of the flue winding within the boiler 
 is 60 in., and its mean width 16^ in., 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 twelve square inches per horse power, but 
 the engines of most of these vessels are intended to ope- 
 rate to a certain extent expansively, and the boilers are 
 less powerful in evaporating efficacy on that account. 
 
 94. Q. Then the chief difference in the proportions 
 
 E 4 
 
56 A CATECHISM OF 
 
 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 ? 
 
 A. 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 of each boiler of the 
 Dee and Sol way is 1,296 square inches ; of the Eagle, 
 1,548 square inches ; and of the Thames and Medway, 
 1,134 square inches ; and the length of flue is 57, 60, 
 and 52 ft. in the boilers respectively, which makes the 
 respective vents 221, 25, and 21 in. 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 1,548 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. 
 
 95. Q. Then the evaporating power of the boiler 
 varies as the sectional area of the flue ? 
 
 A. 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 pro- 
 portion 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 
 
THE STEAM ENGINE. 57 
 
 for each particular form. But in similar tubes the 
 length is proportional to the square root of the sec- 
 tional 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 draft 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. 
 
 96. Q. 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 ? 
 
 A. Yes ; and if the same form of flue is to be re- 
 tained 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 waggon 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 gene- 
 rating steam, may be taken ; and the effective peri- 
 meter divided by the length ought to be a constant 
 quantity in similar forms of flue, and with the same 
 velocity of draft, whatever the size of the flue may be. 
 It is clear, that with any given area of flue, to increase 
 
58 A. CATECHISM OF 
 
 the perimeter by adopting a different shape, is to 
 diminish the length of the flue ; and, if the extent of 
 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's waggon 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 
 forty-five 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's 
 proportion of sectional area for marine boilers with 
 internal flues. 
 
 97. Q. 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 ? 
 
 A. The flue of the Nile, if reduced to the cylin- 
 drical form, would be 35^ in. in diameter to have the 
 same area ; but it would then require to be made 
 47 f ft. long, to have the same amount of heating sur- 
 face. Supposing that with these proportions the heat 
 is sufficiently extracted from the smoke, then every 
 tube of a tubular boiler in which the same draft ex- 
 isted ought to have very nearly the same proportions, 
 so that a tube 3 in. in diameter ought to be about 4 ft. 
 long, supposing the conducting power of the metallic 
 
 
THE STEAM ENGINE. 59 
 
 surface through which the heat is transmitted, to be 
 in each case identical. But the metal of small tubes 
 being thinner than that of flues must conduct better, 
 and a tube 3 in. in diameter should therefore be less 
 than 4 ft. long, provided the draft remains such as is 
 due to an area of 18 square inches per horse power. 
 If the thinness of the metal attainable by the tubular 
 form be supposed to increase the efficacy of the heat- 
 ing surface in the same proportion as the increase 
 of surface due to the rectangular form, the length of 
 a tube 3 in. diameter ought to be 3 ft. 3 in., and it 
 would be of no service to extend its length beyond 
 this point, supposing the flue boiler to be properly 
 proportioned, as by the time the hot air had traversed 
 a length of 3 ft. 3 in. of tube, the heat of the air 
 would have been as thoroughly extracted as in ordi- 
 nary boilers appears to be beneficial. The tubes of 
 tubular boilers, however, are usually about 6 ft. 6 in. 
 long ; but to make this excess of length influential in 
 generating steam, the draft has to be made nearly 
 twice greater than in flue boilers having a sectional 
 area of 18 square inches per horse power, or, in other 
 words, the sectional area of tubular boilers must not 
 much exceed 9 square inches per horse power when 
 the tubes are of the length stated. The smaller the 
 tubes are, the shorter they should be made, or the less 
 the sectional area ought to be ; and with a sectional 
 area of 10 square inches per horse power there will 
 be no advantage in making the length of the tube 
 more than from 26 to 32 times its diameter, which will 
 make the tubes from 6 ft. 6 in. to 8 ft. long when the 
 diameter is three inches, and give from 7.4 to 8 square 
 
60 A CATECHISM OF 
 
 feet of heating surface of tubes per horse power. If 
 the sectional area per horse power be increased, the 
 length of tube should be diminished in the same pro- 
 portion ; for the velocity of the draft varies with the 
 sectional area of tube per horse power, and on the ve- 
 locity of draft the length of the tube ought to depend. 
 In locomotive boilers where the velocity of draft is 
 very great, long tubes are employed ; but it is prefer- 
 able to have the tubes of moderate length and a draft 
 of a moderate intensity, as in maintaining a fierce draft 
 by any process, there is a considerable expenditure of 
 power. If, however, with the view of making the 
 draft very slow, a proportion of sectional area ap- 
 proaching that of flue boilers be provided, the result 
 will not be satisfactory, as the smoke will all pass 
 through a few of the tubes, leaving the rest inopera- 
 tive ; though this defect may be in a great measure 
 corrected by partially closing up the ends of the tubes, 
 or even by partially closing the damper. The length 
 of tube multiplied by the diameter, and divided by 
 the area, is a constant quantity both in flue and tubular 
 boilers, or at least nearly so ; and when any of the 
 elements are given the rest can easily be computed by 
 the aid of this proportion, the precaution being of 
 course taken to keep within the limits which have ap- 
 proved themselves most eligible in practice. 
 
 98. Q. You stated that the capacity of the feed 
 pump was a 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 
 
 
THE STEAM ENGINE. 61 
 
 steam. Can you give any rule that will express the 
 proper capacity for the feed pump at all pressures ? 
 
 A. That will not be difficult. In low pressure en- 
 gines the pressure in the boiler may be taken at 51bs. 
 above the atmospheric pressure, or 201bs. 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 ob- 
 viously vary in the direct proportion of the pressure, 
 and if it be a 240th of the capacity of the cylinder when 
 the total pressure of the steam is 201bs. it must be a 
 120th of the capacity of the cylinder when the pressure 
 is 401bs. per square inch, or 251bs. per square inch 
 above the atmospheric pressure. This law of variation 
 is expressed by the following rule : multiply the capa- 
 city of the cylinder in cubic inches by the total pres- 
 sure of the steam in Ibs. per square inch, or the pressure 
 per square inch on the safety valve plus 15, and divide 
 the product by 4800 ; 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 act- 
 ing, the capacity of the pump must just be one-half of 
 what is given by this rule. 
 
 99. Q. How do you ascertain the power of high 
 pressure engines ? 
 
 A. 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 Ib. per square inch on the 
 surface of the pistons, and the additional fraction caused 
 
62 A CATECHISM OF 
 
 by any additional resistance is estimated at about .14 
 of that resistance ; but it will be a sufficiently near ap- 
 proximation 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 IJlbs., 
 and by the speed of the piston in feet per minute, and 
 divide by 42,017 ; the quotient is the actual horse 
 power. 
 
 100. Q. But how do you ascertain the nominal 
 horse power ? 
 
 A. 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 capa- 
 ble of performing the same work, whether high pres- 
 sure 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 pressure on 
 the piston in pounds per square inch, and by the speed 
 of the piston in feet per minute, and divide the product 
 by 120,000 ; the quotient is the power of the engine 
 
THE STEAM ENGINE. 63 
 
 in nominal horses power. If the pressure upon the 
 piston be SOlbs. per square inch, the operation may be 
 abbreviated by multiplying the square of the diameter 
 of the cylinder by the speed of the piston, arid dividing 
 by 1,500, which will give the same result. 
 
 101. Q. This rule for nominal horse power, how- 
 ever, is not representative of the dimensions of the cy- 
 linder. Cannot you give a rule for the nominal power 
 of high pressure engines which shall discard altogether 
 the element of velocity, and, as in the rule you have 
 already given for the nominal power of low pressure 
 engines, express merely the dimensions of the engine ? 
 
 A. Nothing is easier, if you maintain an unvary- 
 ing pressure of steam ; but as different pressures are 
 used in different engines, the pressure must become an 
 element in the computation. The rule for the nominal 
 power will therefore stand thus : multiply the square 
 of the diameter of the cylinder in inches by the pres- 
 sure on the piston in pounds per square inch, and by 
 the cube root of the stroke in feet, and divide the pro- 
 duct by 940 ; the quotient is the power of the engine 
 in nominal horses power, the engine working at the or- 
 dinary speed of 128 times the cube root of the stroke. 
 
 102. Q. Is 128 times the cube root of the stroke 
 in feet per minute the ordinary speed of all engines ? 
 
 A. Locomotive engines travel at a quicker speed, 
 an innovation brought about not by any process of 
 scientific deduction, but by the accidents and exigences 
 of railway transit. All other engines, however, travel 
 at about the speed of 128 times the cube root of the 
 stroke in feet ; and condensing engines, as at present 
 constructed, cannot travel much quicker, as the valves 
 
64 A CATECHISM OF 
 
 of the air pump strike very hard and wear themselves 
 quickly out if the engine is driven at a great velocity. 
 To mitigate the shock in cases in which a higher speed 
 has been desirable, as in the case of marine engines 
 employed to drive the screw propeller without inter- 
 mediate gearing, canvass air pump valves, resting on a 
 perforated metal plate, have sometimes been adopted 
 the plies of canvass being either stuck together with 
 India rubber or riveted with copper rivets, and being 
 multiplied so as to make the valve half an inch in 
 thickness; but valves of this kind, though they di- 
 minish the noise and tremor, wear rapidly away, and 
 require to be renewed very often. It is very desirable, 
 however, that this impediment should be completely 
 surmounted, not merely as a means of meeting the 
 new exigences created by the application of the screw 
 propeller to steam vessels, but because all engines will 
 then be capable of working at a greatly increased 
 speed, and with a proportionate increase of power. 
 The most feasible way of enabling condensing engines 
 to work at a high speed, appears to lie in the applica- 
 tion of a slide valve to the air pump, instead of valves 
 actuated by the pressure within the pump, and by per- 
 forming the condensation in the air pump, instead of 
 in the condenser, whereby the air pump valves will 
 operate with as little noise at any speed as the cylinder 
 valves, and the condenser may be dispensed with alto- 
 gether. 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, 
 
THE STEAM ENGINE. 65 
 
 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 21 Ibs. 
 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. 
 
 103. Q. Then, if by this modification of the air 
 pump you enable an engine to work at four times 
 the speed, you also enable it to exert four times the 
 power? 
 
 A. Yes ; always supposing it to be fully supplied 
 with steam. The nominal power of this new species 
 of engine, if condensing and if working at four times 
 the ordinary speed, may be ascertained by the follow- 
 ing rule : 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 12 ; the quotient is the 
 power of the high speed condensing engine in nominal 
 horses power. To ascertain the nominal power of a 
 high pressure high speed engine, multiply the square 
 of the diameter of the cylinder by the pressure on tho 
 piston per square inch less a pound and a-half, and by 
 the cube root of the stroke in feet, and divide thepro- 
 F 
 
66 A CATECHISM OF 
 
 duct by 235 ; the quotient is the power of the high 
 pressure high speed engine in nominal horses power. 
 
 104. Q. The high speed engine does not require 
 so heavy a fly wheel as common engines ? 
 
 A. 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 ap- 
 proach more nearly to the condition of a uniform pres- 
 sure. To find the proper quantity of cast iron for the 
 rim of a fly wheel : multiply the mean diameter of 
 the rim by the number of its revolutions per minute, 
 and square the product for a divisor ; divide the num- 
 ber of nominal horses power of the engine by the 
 number of strokes the piston makes per minute, mul- 
 tiply the quotient by the constant number 5,000,000, 
 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. 
 
 105. Q. What is the maximum speed w r ith which 
 a cast iron fly wheel may be driven without being 
 burst asunder by its centrifugal force ? 
 
 A- The velocity of the rim should not exceed 
 60 feet per second, and at that speed the bursting 
 force will amount to l,1001bs. on the square inch of 
 section, setting aside the support derived from the 
 arms. In engines for rolling iron, the fly wheel is 
 driven usually at a very great speed, and it requires 
 to be put together very firmly to resist the bursting 
 force. The best practice in such cases is to cast the rim 
 in a single piece, and to introduce malleable iron arms. 
 
 106. Q. The steam is admitted to and from the 
 cylinder by means of a slide or sluice valve ? 
 
THE STEAM ENGINE. 67 
 
 A. 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, which 
 consists of a brass box set over the two ports or open- 
 ings 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 connexion alternately be- 
 tween each cylinder port and the 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. 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. 
 107. Q. What is meant by the lead of the valve ? 
 
 F 2 
 
68 A CATECHISM OF 
 
 A. The amount of opening 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 termi- 
 nates, 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. 
 
 108. Q. And what is meant by the lap of the 
 valve? 
 
 A. : It is an elongation of the valve face to a certain 
 extent over the port or towards 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 steam 
 side 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 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 inca- 
 pable of covering both the ports at once. The com- 
 mon stroke of the valve in rotative engines is twice 
 the breadth 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 therefore given, makes the valve face 
 just so much longer. In some engines, however, the 
 
 
THE STEAM ENGINE. 69 
 
 stroke of the valve is a good deal more than twice the 
 breadth of the port ; and it is by the stroke of the 
 valve that the amount of lap is properly measurable. 
 
 109. Q. Can you tell what amount of lap will ac- 
 complish any given amount of expansion ? 
 
 A. 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 accom- 
 plished before the steam is cut off ; divide the re- 
 mainder 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 re- 
 quired. 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 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. 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 cosine is equal to the lap on the educ- 
 
 F 3 
 
70 A CATECHISM OF 
 
 tion side divided by half the stroke of the valve ; add 
 these two arcs together and subtract 90; 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. 
 
 110. Q. To what extent can expansion be carried 
 beneficially by means of lap upon the valve ? 
 
 A. 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 will 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. 
 Thus, for example, 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 ap- 
 
THE STEAM ENGINE. 71 
 
 preaches 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. The usual manner of cutting off the 
 steam, however, 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 expansive valve does not 
 appear to be required. 
 
 111. Q. What size of orifice is allowed for the 
 escape of the steam through the safety valve ? 
 
 A. About 0.8 of a circular inch per horse power 
 in condensing engines, or a circular inch per 1^-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 ; 
 
 F 4 
 
72 A CATECHISM OF 
 
 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. 
 
 112. Q. Will you state the proper dimensions of 
 the air pump and condenser and of the steam passages ? 
 
 A 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. 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 con- 
 siderable pressure of steam. In the case of ordinary 
 condensing engines, however, working with the usual 
 pressure of from 4 to 81bs. above the atmosphere, the 
 area of the steam pipe is not less than a circular inch 
 
THE STEAM ENGINE. 73 
 
 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. The area of the 
 injection orifice should be about one-fifteenth of a 
 square inch per nominal horse power ; but the area of 
 the injection pipe should be a little larger : a tenth of 
 a circular inch per horse power answers very well, or 
 the diameter of the injection pipe may be found by 
 dividing the nominal horse power by 10, and extract- 
 ing the square root of the quotient, which will be the 
 diameter in inches. 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. 
 
 113. Q. Will you explain by what process of com- 
 putation these proportions are arrived at ? 
 
 A. 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 stearn can easily be ascertained, by 
 
74 A CATECHISM OF 
 
 finding what height a column of steam must be to give 
 that velocity, and what the weight or pressure is of 
 such a column. The proper area of the injection 
 orifice per horse power can easily be told when the 
 quantity of water requisite to condense the steam is 
 known, and the pressure specified under which the 
 water enters the condenser. The vacuum in the con- 
 denser may be taken at 26 in. of mercury, which is 
 equivalent to a column of water 29.4 ft. high, arid 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 
 actual horse power per hour for the engine, or 13.905 
 cubic inches per second will be necessary, 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 inas- 
 much 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 ^d of a square inch 
 
THE STEAM ENGINE. 75 
 
 per horse power. This, it will be remarked, is the 
 area required per actual horse power ; in most of the 
 modern engines there is more than a cubic foot of 
 water evaporated per hour per nominal horse power, 
 and it is therefore found expedient to make the area 
 of the injection orifice a third larger than the area due 
 to the actual power, or -^th of a square inch per 
 nominal horse power, as already prescribed. 
 
 114. Q.If the relation you have mentioned subsist 
 between the area of the steam passages and the ve- 
 locity of the piston, then the passages must be larger 
 when the piston travels very rapidly ? 
 
 A. And they are so made. The area of the ports 
 of locomotive engines is usually so proportioned as to 
 be from y^th to th the area of the cylinder in some 
 cases even as much as ^th ; and in all high speed 
 engines the ports should be very large, and the valve 
 should have a good deal of travel. 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 no- 
 minal horse power to condensing engines working at 
 the ordinary speed ; but the excess is but small, and is 
 upon the right side. In locomotive engines the educ- 
 tion pipe passes into the chimney, and the force of the 
 issuing steam has the effect of maintaining a rapid 
 draught through the furnace. The orifice of the waste 
 steam pipe, or the blast pipe as it is termed, is much 
 
76 A CATECHISM OP 
 
 contracted in some engines with the view of producing 
 a fiercer draught ; but an area of ^d of the area of the 
 cylinder is a common proportion. 
 
 115. Q. If the area of the blast pipe be much di- 
 minished the escaping steam must so far resist the mo- 
 tion of the piston as to diminish considerably the power 
 of the engine ? 
 
 A. At a speed of 10 miles an hour the resistance 
 to the piston occasioned by the blast pipe may be taken 
 on the average at about 21bs. per square inch, and the 
 resistance increases directly as the speed of the engine. 
 In some cases, however, the blast pipe is so much con- 
 tracted, that as much as half the power of the engine 
 is spent in forcing the steam through it. The object 
 of this undue contraction is to increase the intensity 
 of the draught in the furnace, and as a consequence 
 to increase the production of steam ; but engines in 
 which such a waste of power exists from this single 
 cause, are altogether unsuitable for the work they have 
 to do, in consequence of their insufficient evaporating 
 power. The question of draught is only a question of 
 area of fire grate, and it is much preferable to enlarge 
 the fire grate than to increase the intensity of the 
 draught. The area of the chimney in locomotives is 
 usually made x^th of the area of the fire grate, and its 
 height must not exceed 14ft. above the level of the 
 rails, else it will corne in contact with the bridges 
 which cross the line. A given area of heating surface 
 in locomotive boilers is more effective than the same 
 area of heating surface in other boilers, on account of 
 the greater heat to which it is subjected. If, at a 
 speed of 20 miles an hour, a locomotive boils off a 
 
THE STEAM ENGINE. 77 
 
 cubic foot of water in the hour for every six square 
 feet of heating surface, as appears to be an average 
 performance, then 1 square foot of heating surface 
 must boil off 10.4 Ibs. of water per hour, at a speed of 
 20 miles an hour, and the rate of evaporation will vary 
 nearly as the fourth root of the speed. 
 
 116. Q. What is the amount of tractive force re- 
 quisite to draw carriages on railways ? 
 
 A. Upon well formed railways, with carriages of 
 good construction, the average tractive force required 
 for low speeds is about 7^1bs. per ton, or ^-^th of the 
 load, though in some experimental cases, where par- 
 ticular care was taken to obtain a favourable result, the 
 tractive force has been reduced as low as 5-J^th 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 fric- 
 tion is very small when the surfaces are smooth, and 
 in the case of railway carriages does not exceed yo^th 
 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 -g^th of the load. 
 
 117. Q. In reference to friction you have already 
 stated, in your answer to Question 33, 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 yytli of the pressure, but that in machines in ac- 
 tual operation, where there is a film of oil between the 
 rubbing surfaces, the friction is only about one-third 
 of this amount, or ^d of the weight. How then can 
 
78 A CATECHISM OF 
 
 the tractive resistance of locomotives at low speeds, 
 which you say is entirely made up of friction, be so 
 little as -g-J- oth of the weight ? 
 
 A. I did not state that the resistance to traction 
 was 3i7oth of the weight upon an average to which 
 condition the answer given to Question 33 must be 
 understood to apply but I stated that the average 
 traction was about g-^th of the load, which nearly 
 agrees with my former statement. If the total friction 
 be -3 J-gth of the load, and the rolling friction be ToVo tn 
 of the load, then the friction of attrition must be ^4-^th 
 of the load ; and if the diameter of the wheels be 36 in., 
 and the diameter of the axles be 3 in., which are com- 
 mon proportions, the friction of attrition must be in- 
 creased 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, ^^-ths are 
 about g^th of the load, which does not differ much 
 from the proportion of Jg-d, as previously determined. 
 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 ^th of the 
 weight ; and Mr. Wood, in some experiments upon the 
 friction of locomotive axles, found that by ample lubri- 
 cation the friction might be made as little as g^tli of 
 the weight, and the traction, with the ordinary size of 
 wheels, would, in such a case, be about ^J () th of the 
 weight. The function of lubricating substances is to 
 prevent the rubbing surfaces from coming into contact, 
 
THE STEAM ENGINE. 79 
 
 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 re- 
 ference, 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 Ibs. 
 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 sur- 
 face is too small, wears rapidly away. 
 
 118. Q. What is the amount of adhesion of the 
 wheels upon the rails ? 
 
 A. The adhesion of the wheels upon the rails is 
 about ^th 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 T 1 - or -^th of the weight or pressure upon the 
 wheels. The weight of a locomotive of modern con- 
 struction varies from 20 to 25 tons. 
 
 119. Q. And what is its cost and average perform- 
 ance? 
 
 A. The cost of a common narrow gauge locomotive 
 at the present time varies from 1,900/. to 2,200/. ; it 
 will run on an average 130 miles per day, at a cost for 
 repairs of 2\d. 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 
 
80 A CATECHISM OF 
 
 renewal of the engines when worn out, which may be 
 taken as equivalent to 10 per cent, on their original 
 cost. 
 
 120. Q. Does the expense of traction increase 
 much with an increased speed ? 
 
 A. 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, which constitutes the greatest of the 
 impediments to motion at high speeds. At a speed of 
 30 miles an hour, the atmospheric resistance amounts 
 to about 12 Ibs. 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 frontage exposed to the wind is 
 virtually 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 1 10 tons. Taking the friction of 
 the train at 7^-lbs. per ton, or 825 Ibs. operating at the 
 circumference of the driving wheel, which, with 5 ft. 
 6 in. wheels and 18 in. stroke, is equivalent to 4,757 Ibs. 
 upon the piston, and taking the resistance of the blast 
 pipe at 6 Ibs. per square inch of the pistons, and the 
 friction of the engine unloaded at 1 Ib. per square inch, 
 which, with pistons 12 in. in diameter, amount together 
 to 1,582 Ibs., and reckoning the increased friction of 
 the engine due to the load at |th of the load, as in 
 some cases it has been found experimentally to be, 
 though a much less proportion than this would proba- 
 
THE STEAM ENGINE. 81 
 
 bly be a nearer average, we have 7018.4 Ibs. for the 
 total load upon the pistons. At 30 miles an hour the 
 speed of the pistons will be at 457.8 feet per minute, 
 and 7018.4 Ibs. multiplied by 4-57.8 ft. per minute, are 
 equal to 3213023.5 Ibs. raised one 1 foot high in the 
 minute, which, divided by 33,000, gives 97.3-horses 
 power as the power which would draw 1 10 tons upon 
 a railway at a speed of 30 miles an hour, if there were 
 no atmospheric resistance. The atmospheric resistance, 
 with a load of 110 tons, is at the rate of 121 bs. a ton, 
 equal to 1,320 Ibs., moving at a speed of 30 miles an 
 hour, which, when reduced, becomes 105.8-horses 
 power, arid 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, which small excess of 
 efficiency is probably produced by a certain amount of 
 expansive action in the engine. The atmospheric resist- 
 ance is found to increase as the square of the velocity, 
 while the other resistances do not increase with the 
 velocity at all per unit of space passed over, but in- 
 crease as the velocity per unit of time during which 
 they act. It is not difficult, therefore, to approximate 
 to the power requisite for the propulsion of a train at 
 any rate of speed, when the distribution of power at 
 any one speed has been ascertained. At a speed of 
 60 miles an hour, for example, the power required to 
 overcome the friction of a train weighing 110 tons, 
 will be 97.3 x 2 = 194.6-horses power; while the 
 power requisite to overcome the atmospheric resistance 
 will be 105.8 x 4 = 423.2-horses power, if the same 
 distance be passed over at the speed of 30 miles an 
 hour ; but as twice the distance will be passed over in 
 
82 A CATECHISM OF 
 
 the hour when the speed is twice as great, the power 
 requisite to overcome the atmospheric resistance, will 
 be twice this amount, or 846.4-horses power, making 
 together a power of 1041 horses to draw a train weigh- 
 ing 1 10 tons, at a speed of 60 miles an hour. A loco- 
 motive, to perform this duty, should have 6246 square 
 feet of heating surface in the boiler, and the cylinders 
 should be sufficiently capacious to permit 320,628 cubic 
 feet of steam to pass through them in the hour, though 
 it will be preferable to make the capacity considerably 
 greater than this, and to work the steam expansively. 
 
 121. Q. How comes it, that the resistance of the 
 air to the motion of a locomotive increases as the square 
 of the velocity, instead of the velocity simply? 
 
 A. Because the height necessary to generate the 
 velocity with which the train strikes the air, or the air 
 strikes the carriage, increases as the square of the ve- 
 locity, and the resistance or the weight of a column of 
 air, or of any other fluid, varies as the height. A fall- 
 ing body, as has been already explained in the answer 
 to Question 14, 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 directly as 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 STEAM ENGINE. 83 
 
 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, how- 
 ever, the work done by a given quantity of air moving 
 at different speeds be considered, it will vary as the 
 squares of the speeds. 
 
 122. Q. But in a locomotive there is no work done 
 by the wind, and as the resistance of the air upon the 
 train varies as the square of the speed, should not the 
 power requisite to overcome that resistance vary as the 
 square of the speed ? 
 
 A. It should, if you consider the resistance over a 
 given distance, and not the resistance during a given 
 time. It will 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 will take 
 to accomplish a mile at 30 miles an hour ; but in the 
 former case there will be twice the number of miles 
 accomplished in the same time, so that when the ve- 
 locity of a train is doubled, we require an engine that 
 is capable of overcoming four times the resistance at 
 twice the speed, or, in other words, that is capable of 
 exerting eight times the power, so far as regards the 
 element of atmospheric resistance. 
 
 123. Q. When a train moves at the rate of 60 
 miles an hour, what will -be the centrifugal force of 
 the wheels ? 
 
 A. 60 miles an hour is 88 ft. per second, and if the 
 centrifugal force of a wheel travelling at this speed be 
 computed by the rule given in Answer 24, it will be 
 found to amount to 80.4 times the weight of the wheel, 
 or 4124.5 Ibs. per square inch of sectional area of the 
 
 G 2 
 
84 A CATECHISM OF 
 
 rim of the wheel, supposing any one point of the rim 
 to sustain all the centrifugal force produced by its own 
 revolution. About 4,000 Ibs. per square inch of sectional 
 area is the utmost strain to which iron should be ex- 
 posed in machinery, and even if we take the centrifugal 
 force as divided between the two sides of the rirn, rail- 
 way wheels can scarcely be considered safe at a speed 
 of 60 miles an hour, unless so constructed that the cen- 
 trifugal 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 a view of giving increased strength to 
 counteract the centrifugal force, as every increase in 
 the dimensions of the rim will increase the centrifugal 
 force in the same proportion. 
 
 124. Q. Does the law of resistance to the motion 
 of railway trains extend to the case of vessels moving 
 in water ? 
 
 A. The resistance of vessels moving in water varies 
 as the square of the velocity, and the power required to 
 overcome that resistance as the cube of the velocity ; so 
 that the resistance to ships moving in water varies in 
 the same ratio as the resistance presented by the atmo- 
 sphere to the carriages in the case of railway trains. To 
 double the velocity of a steamer it is necessary that 
 the engines should exert eight times the power ; but a 
 double velocity may be gained without any increase of 
 power by such a modification of the form of the vessel 
 as will enable it to pass through the water with greater 
 facility. It is impossible, therefore, in the case of a 
 
THE STEAM ENGINE. 85 
 
 steam vessel, to tell what velocity with a given load a 
 given power of engine will produce, unless the shape 
 of the vessel be also known ; and the shapes of vessels 
 are so various and inconsistent, that it is impossible 
 to find any one expression by which they may all be 
 represented. 
 
 125. Q. But may not the different shapes be so 
 classified that the speed answerable to a given power 
 in a specified class can be approximately predicted? 
 
 A. Yes, that may be done, and has been done, by 
 Boulton and Watt, who have ascertained, experiment- 
 ally, the speed realized by different forms of vessels 
 with different powers of engine, and have deduced 
 from thence rules which enable them to tell with great 
 precision the speed which any new vessel, of a par- 
 ticular form and power, will achieve. 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 co-efficient of performance of 
 such vessels. This co-efficient is obtained by multi- 
 plying the cube of the velocity of the vessel in miles 
 per hour by the sectional area of immersed midship- 
 section in square feet, and dividing by the nominal 
 horse power ; and its use is to enable us to determine 
 the speed of any similar vessel with any other area of 
 midship-section, and any other number of nominal 
 horses power. The better the shape of the vessel is, 
 the larger the co-efficient becomes, as appears by the 
 second set of experiments, which were made upon the 
 superior vessels Venus, Swiftsure, Dasher, Arrow 
 
 G 3 
 
86 A CATECHISM OF 
 
 Spitfire, Fury, Albion, Queen, Dart, Hawk, Margaret, 
 and Hero all vessels having flat floors and round 
 bilges, where the co-efficient became 1,160. The third 
 set of experiments was made upon the vessels Light- 
 ning, Meteor, James Watt, Cinderella, Navy Meteor, 
 Crocodile, Watersprite, Thetis, Dolphin, Wizard, Es- 
 cape, and Dragon all vessels with rising floors and 
 round bilges, and the co-efficient of performance was 
 found to be 1,430. The fourth set of experiments 
 was made in 1834, upon. the vessels Magnet, Dart, 
 Eclipse, Flamer, Firefly, Ferret, and Monarch, when 
 the co-efficient of performance was found to be 1,580. 
 The velocity of any of these vessels, with any power 
 or sectional area, may be ascertained by multiplying 
 the co-efficient of its class by the nominal horse power, 
 dividing by the sectional area in square feet, and ex- 
 tracting the cube root of the quotient, which will be 
 the velocity in miles per hour ; or the number of 
 nominal horses power requisite for the accomplishment 
 of any required speed may be ascertained by multiply- 
 ing the cube of the required velocity in miles per 
 hour, by the sectional area in' square feet, and dividing 
 by the co-efficient: the quotient is the number of 
 nominal horse power requisite to realize the speed. In 
 the whole of these experiments the pressure of steam 
 in the boiler varied between 2| Ibs. and 41bs. per square 
 inch, and the effective pressure on the piston varied 
 between 11 Ibs. and 13 Ibs. 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. Of the 
 
 
THE STEAM ENGINE. 87 
 
 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, no- 
 minal 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, nomi- 
 nal 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 co- 
 efficient appears to be about 2,550 ; but in these 
 vessels there is a still greater excess of the actual over 
 the nominal power than in the case of the vessels pre- 
 viously enumerated, and the increase in the co-efficient 
 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, 60 horses ; but 
 the actual power of the Red Rover is 147, of the 
 Herne 177, and of the City of Canterbury 153, and in 
 some vessels the excess is still greater ; so that with 
 such variations it becomes necessary to adopt a co- 
 efficient derived from the introduction of the actual 
 instead of the nominal v power. In the first class of 
 vessels experimented upon, the actual power was 
 about 1.6 times greater than the nominal power ; in 
 
 a 4 
 
88 A CATECHISM OF 
 
 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 co-efficients, we shall have 554 as the first 
 co-efficient, 694 as the second, 832 for the third, and 
 806 for the fourth, instead of 925, 1,160, 1,430, and 
 1,580 as previously specified ; while for such vessels 
 as the Red Rover, Herne, Queen, and Prince of Wales, 
 we shall have 962 instead of 2,550. These smaller co- 
 efficients then express the relative merits of the dif- 
 ferent 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 
 co-efficients 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. 
 
 126. Q. In what way is it that the shape of a ves- 
 sel influences her speed, since vessels of the same sec- 
 tional area must manifestly put in motion a column 
 of water of the same magnitude, and with the same 
 velocity ? 
 
 A. 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 
 
THE STEAM ENGINE. 89 
 
 with which the water is moved to be very small re- 
 latively 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. 
 In vessels in which a high rate of speed is intended to 
 be realized, it will generally be advantageous to put 
 the midship frame abaft the centre of the vessel ; or, in 
 other words, to made the bow end sharper than the 
 stern end, although the stern end must be sharp also, 
 else the water will be unable to fill the vacuity behind 
 the vessel with sufficient rapidity to obviate the resist- 
 ance due to a difference of level, and the vessel also 
 will steer badly. It appears expedient, in most cases, 
 to make the shape of the bow lines such, that in equal 
 times the particles of water shall occasion equal incre- 
 ments of resistance ; and it is also most important to 
 keep vessels intended to be swift as light as possible, 
 as the difference even of a few tons in the weight may 
 materially affect the speed. 
 
 127. Q. Will a vessel experience more resistance 
 in moving in salt water than in moving in fresh ? 
 
 A 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 flotation is 
 proportionably greater in the salt water the resistance 
 will be the same with the same weight carried. The 
 resistance opposed to any body moving in a fluid is 
 directly proportional to the quantity of matter moved, 
 and the height necessary to generate the velocity of 
 motion ; but the quantity of matter moved in any given 
 
90 A CATECHISM OF 
 
 distance is directly as the density or specific gravity of 
 the fluid ; so that the density multiplied by the height 
 requisite to generate the velocity, or, what is the same 
 thing, by the velocity squared, will express the resist- 
 ance universally. It has already been stated, in the 
 answer to Question 13, that the square root of the height 
 from which a body falls in feet multiplied by 8.021, will 
 give its velocity of motion in feet per second ; therefore 
 the height, multiplied by the square of 8.021, or 64^, 
 will give the square of the velocity in feet per second, 
 and the square of the velocity divided by 64^ will give 
 the height. 
 
 128. Q. Then the resistance experienced by a 
 vessel in passing through the water, will be less than 
 that of a flat board of the same area as the cross section 
 of the vessel. 
 
 A. Yes, very much less, as is illustrated by the 
 circumstance that steam vessels are propelled by a very 
 small area of paddle float in proportion to their sec- 
 tional area. When a flat board is moved through a 
 fluid with its flat side foremost, the resistance it suffers 
 is equal to the weight of a column of the fluid with 
 a base of the same area as the board, and with the 
 altitude due to the velocity of motion with which the 
 board moves ; and the resistance will be the same 
 whether the board moves through a quiescent fluid or 
 a moving fluid strikes against a stationary board. As 
 the altitude in feet due to the velocity of motion in feet 
 per second, is equal to the square of the velocity divided 
 by 64*-, and as a cubic foot of fresh water weighs 
 62 J Ibs., the pressure per square foot in Ibs. upon a 
 board moved through river water will be 62^- times 
 
THE STEAM ENGINE. 91 
 
 the square of the velocity in feet per second divided 
 by 64} ; or it will be the square of the velocity multi- 
 plied by .9715. To express the pressure or resistance 
 in actual horses power, we must multiply this quantity 
 by 60 times the velocity in feet per second, which will 
 give the velocity in feet per minute, and divide by 
 33,000 for horses power, which makes the resistance 
 per square foot in horses power equal to the cube of 
 the velocity in feet per second multiplied by '00176637 
 If the water strikes the board obliquely, the resistance 
 will follow a different law. When a body impinges 
 obliquely upon a plane, the force of impact with any 
 given velocity varies as the sine of the angle of inci- 
 dence, and therefore the force with which the particles 
 of water strike against a board will vary as the sine 
 of the angle at which they strike it becoming of 
 course less and less as the board is turned more upon 
 its edge. But the number of particles striking the 
 board will also vary as the sine of the angle of inci- 
 dence, or, in other words, as the perpendicular height 
 of the inclined board ; so that the resistance, as it 
 varies both with the force with which the particles 
 strike the board, and the number of particles which 
 strike it, must vary as the square of the sine of the 
 angle of incidence. The horizontal resistance, there- 
 fore, per square foot in horses power of a board which 
 is struck by the water obliquely, such as the float of 
 a water wheel, or which strikes the water obliquely, 
 such as the float of a paddle wheel, will be found by 
 the following rule : multiply the cube or third power 
 of the velocity in feet per second by the area of the 
 plane in feet, by the square of the sine of the angle of 
 
92 A CATECHISM OF 
 
 incidence, and by the constant co-efficient .00176637 ; 
 the result will be the resistance in actual horses power 
 of a board striking the water obliquely or obliquely 
 struck by the water. 
 
 129. Q. But in a paddle wheel the floats do not 
 move in a horizontal line ? 
 
 A. There are two kinds of paddle wheels in exten- 
 sive 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 slip 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. 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 near the centre of 
 the float; whereas, in the common radial wheel this 
 cannot be the case ; for as the outer edge of the float 
 
 
THE STEAM ENGINE. 93 
 
 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 centre of pressure ; 
 and if all the resistances were concentrated in this 
 point, they would have the same effect as before in 
 propelling the vessel. 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 resist- 
 ance 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 pres- 
 sure 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 inimerged ; but in the radial wheel, 
 the centre of pressure can never rise so high as the 
 centre of the float. 
 
 130. Q. All this relates to the action of the paddle 
 
94 A CATECHISM OP 
 
 when the vessel is at rest ; will you explain its action 
 when the vessel is in motion ? 
 
 A. 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 rolling circle, 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. With this assumption, 
 which accords sufficiently with experiment to justify its 
 
THE STEAM ENGINE. 95 
 
 acceptation, the position of the centre of pressure may 
 be found by the following rule : from the radius of 
 the wheel subtract 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 roll- 
 ing circle, and the remainder will be the distance of 
 the centre of pressure from the upper edge of the 
 paddle. The diameter of the rolling circle is very 
 easily found, for we have only to divide 5280 times 
 the number of miles per hour, by 60 times the number 
 of strokes per minute, to get an expression for the cir- 
 cumference 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 velocity of the wheel over the vessel, 
 
 which, multiplied by J, or, .9715, will give the 
 043- 
 
 resistance per square foot upon the vertical paddle. 
 
 131. Q. "Will you illustrate these rules by an ex- 
 ample. 
 
 A. 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 
 
96 A CATECHISM OF 
 
 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 f ds of the dia- 
 meter of the wheel, and this is a frequent proportion. 
 The depth of the paddle board is 2 feet, and the differ- 
 ence 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 579.74, 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; and taking the length of the floats at 10 
 feet, which makes the area of each float 20 square feet, 
 the resistance in Ibs. encountered by the vertical float 
 will be 20 multiplied by 4.997 2 , multiplied by 0.9715, 
 equal to 485.l71bs. ? which being doubled for the ver- 
 
 
THE STEAM ENGINE. 97 
 
 tical float of the other wheel, gives us 970.341bs. as 
 the pressure on the vertical floats in their motion 
 through the water. The velocity with which the floats 
 move is that of the centre of pressure, so that to find 
 the resistance in horses power, we must multiply the 
 velocity of the centre of pressure in feet per second by 
 60, to bring it to feet per minute, then by 970.34 Ibs., 
 and divide by 33,000, which will give about 36- 
 horses power as the power expended on the vertical 
 paddles. If the nominal power of the engines be 200- 
 horses, the actual horses power will be greater in 
 engines of this class in the proportion of 33,000 to 
 50,000, so that the actual power exerted by the engines 
 will be about 315-horses, and 0.114 of the power of 
 the engines will be the proportion of power expended 
 upon the vertical paddles. 
 
 132. Q. That is in the case of a common radial 
 wheel ; what will be the proportion in the feathering 
 wheel ? 
 
 A. It will be the same in the feathering wheel, if 
 the float be of the same area, and all other circum- 
 stances the same ; but in the radial wheel the vertical 
 float sustains the least resistance in propulsion, and in 
 the feathering wheel the most resistance ; and as the 
 power of the engine is a fixed quantity, which has to be 
 expended among all the floats, and as in the radial wheel 
 it is chiefly distributed among the oblique floats which 
 encounter a resistance that has to be thrown in a great 
 measure upon the vertical float in the case of the 
 feathering wheel, a larger area of float-board is 
 necessary in the feathering wheel than in the radial 
 one. To understand how the entering and emerging 
 
 H 
 
98 A CATECHISM OF 
 
 paddles of the radial wheel sustain more resistance in 
 propulsion than the vertical one, 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 resist- 
 ance 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 im- 
 mersion very great when compared with the whole 
 resistance upon the vertical float. In the feathering 
 wheel, where there is none of this oblique action, the 
 resistance will be simply 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. 
 
 133. Q. Can you give a rule for ascertaining the 
 
THE STEAM ENGINE. 99 
 
 resistance encountered by a paddle board at any part 
 of its motion ? 
 
 A. In the common radial wheel the resistance or 
 pressure upon any float may be ascertained as follows : 
 from the velocity of the centre of pressure in feet 
 per second, subtract the velocity of the rolling circle 
 multiplied by the cosine of the angle of inclination the 
 paddle-board makes with a vertical line; square the 
 remainder, and multiply it by .9715 times the area of 
 the float in feet, which will give the tangential resist- 
 ance of the float in Ibs. avoirdupois. The horizontal 
 resistance may be obtained by multiplying this quantity 
 again by the cosine of the angle of inclination the float 
 makes with a vertical line. In the feathering wheel 
 the resistance may be ascertained by multiplying the 
 velocity of the centre of pressure by the cosine of the 
 angle of inclination, subtracting from this the velocity 
 of the rolling circle, squaring the remainder, and 
 multiplying it by .9715 times the area of float in feet, 
 which will give the resistance of the float in pounds. 
 By thus calculating the resistance of the different floats 
 immersed, taking the mean of these resistances and 
 multiplying by the number of floats in the water, we 
 readily ascertain the resistance of the wheel, and by 
 finding what area of vertical paddle-board moving at 
 the velocity of the vessel would occasion the same 
 resistance as all the floats immersed, and comparing 
 this area with the sectional area of the vessel, we may 
 find the power necessary to propel a board through 
 the water of equal area with the cross section of the 
 vessel, which will show the diminution of resistance 
 consequent upon the sharpening away of the bow and 
 
100 A CATECHISM OF 
 
 stern. These relations, with many others connected 
 with the paddle wheels, have been investigated at 
 considerable length by Mr. Barlow in a paper published 
 in the Philosophical Transactions, and reprinted in the 
 Appendix to Tredgold's Treatise on the Steam Engine ; 
 but some of Mr. Barlow's deductions are erroneous, 
 and he has vitiated nearly all his conclusions by con- 
 founding the actual with the nominal horse power. 
 
 134. Q. Can you give any practical rules for pro- 
 portioning paddle wheels ? 
 
 A. 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^ 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 im- 
 mersed, and in river steamers only one or two floats. 
 There is more slip in the latter case, but there is also 
 
THE STEAM ENGINE. 101 
 
 more engine power exerted in the propulsion of the 
 ship, from the greater speed of engine thus rendered 
 possible. 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 very 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 feather- 
 ing 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 pres- 
 sure 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. 
 
 135. Q. Is the screw propeller as effectual an 
 instrument of propulsion as the radial or feathering 
 paddle ? 
 
 A. In all cases of deep immersion it appears to be 
 quite as effectual as the radial paddle ; 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. 
 
 H 3 
 
102 A CATECHISM OF 
 
 136. Q. In what way are the dimensions of the 
 screw propeller proportioned to the power of the engines 
 and area of midship-section of vessel ? 
 
 A. It has been found experimentally, that when 
 the screw is so proportioned as to make the slip about 
 Yoth of the speed of the screw, a maximum effect is 
 produced, the speed of the vessel being then T oths of 
 what it would be if the screw were working in a solid. 
 Find, by some of the rules previously given, what speed 
 is due to the form and power as if the vessel were to 
 be propelled by paddles, which speed call -nyths, and 
 adding T l oth for slip, we shall have the number of feet 
 per minute to be travelled by the screw, and this number 
 divided by the number of revolutions per minute, will 
 give the pitch of the screw in feet. The length of screw 
 that is found most beneficial is about |th of a convolu- 
 tion, and the diameter should be as large as it can be 
 got. A screw with two arms, or a portion of a double 
 threaded screw, has been found as effectual a propeller 
 as any other; but a screw with three blades, or a 
 portion of a three threaded screw, has been found to 
 act with a more equable and regular motion. The 
 stern post carries behind it a certain quantity of dead 
 water which moves with the vessel, and when the 
 screw gets into this water, which happens in the case 
 of a double threaded screw when the two arms of the 
 screw are vertical, the resistance becomes nearly equal 
 to that which would be due to the whole velocity of the 
 screw, instead of the difference of velocity of screw 
 and vessel ; and the forward thrust at that point is so 
 much increased thereby, that an uneasy motion is 
 given to the hinder part of the ship, while a waste of 
 power is at the same time occasioned. Where three 
 
THE STEAM ENGINE. 103 
 
 blades are employed, this vibratory motion is by no 
 means so conspicuous, as the impulse is equally divided 
 among the three blades; and a three-bladed screw 
 therefore appears, on the whole, to be preferable. It is 
 very important to make the run of the ship very fine, 
 so that the vessel may carry as small a quantity as 
 possible of dead water behind her. As regards the 
 form of screw, it is found that the common screw with 
 a uniform pitch is as effectual as any : screws of an 
 increasing pitch have been tried at various times, but 
 without the realisation of any appreciable advantage. 
 The water thrown backwards by the screw assumes a 
 conical form, and the obliquity and consequent loss of 
 power will be greater when the pitch of the screw is 
 coarse and the diameter small, so that it is expedient 
 to have as large a diameter as possible, a quick speed 
 and a fine pitch. 
 
 PART II. 
 
 STRENGTHS, CONSTRUCTIVE DETAILS, AND MANAGEMENT. 
 
 137. Q. In what way are the strengths of the dif- 
 ferent parts of a steam engine determined ? 
 
 A. By a reference to the cohesion of iron, or its 
 power to resist a tensile, twisting, breaking, or crushing 
 force which has been fixed by numerous experi- 
 ments, and by the computation of the amount of strain 
 to which the several parts are subjected, to the end 
 that the quantity of material may be made propor- 
 
 H 4 
 
104 A CATECHISM OF 
 
 tionate to the strain. The breaking strain of a bar of 
 malleable iron, of medium quality, one inch square, 
 when pulled in the direction of its length, is from 
 50,000 to 60,000 Ibs., and of a bar of cast-iron from 
 17,000 to 20,000 Ibs. ; but a much smaller strain than 
 this will damage the structure of the iron, and finally 
 break it, if the strain be permitted to act without in- 
 terruption. The tensile strain to which a bar of mal- 
 leable iron an inch square may be subjected, without 
 permanently deranging its structure, is 1 7,800 Ibs. ; 
 and in the case of cast iron 15,300 Ibs. : but it would 
 not be safe to apply such a strain in practice, as there 
 are so many different qualities of iron, and so many 
 irregularities of structure even in iron of* the same 
 quality, from unequal conversion, imperfect welds, and 
 other circumstances, that it would be unwarrantable 
 to reckon the maximum strength as at all times sub- 
 sisting. The greatest strain to which malleable iron 
 should be subjected in machinery is 4,000 Ibs. on the 
 square inch of section, though in locomotive boilers 
 this strain is sometimes exceeded. 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. If 
 the force acting at the end of an engine beam be taken 
 at 18 Ibs. per circular inch of the piston, then the force 
 acting at the middle will be 36 Ibs. 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 STEAM ENGINE. 105 
 
 the weight in Ibs. acting at the centre by 250, and 
 multiply the quotient by the distance between the 
 1 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 an engine beam at 
 the ends is usually made one-third of the depth at the 
 centre, which is 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 T J-sth of the length the 
 width of the edge bead being about three times the 
 thickness of the web. In low pressure engines the 
 diameter of the end studs of the engine beam are 
 usually made ^th of the diameter of the cylinder when 
 of cast iron, and y^th when of wrought iron, which 
 gives a load with low steam of about 500 Ibs. per cir- 
 cular 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. To find the 
 proper size of a cast iron gudgeon adapted to sustain 
 any given weight : multiply the weight in Ibs. 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. Experiments upon the force requisite to twist 
 off cast iron necks show that if the cube of the dia- 
 meter of neck in inches be multiplied by 880, the pro- 
 duct will be the force of torsion which will twist them 
 off when acting at 6 inches radius. To find the dia- 
 meter of a cast iron fly wheel shaft: multiply the 
 
106 A CATECHISM OF 
 
 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 diameter of the shaft in inches at 
 the smallest part, when of cast iron. To find the 
 diameter of the paddle shaft of a steam vessel when of 
 wrought iron ; multiply the square of the diameter of 
 cylinder in inches by the length of the crank in inches, 
 and extract the cube root of the product, which mul- 
 tiply by 0.242, the result is the diameter of the shaft 
 in inches at the smallest part when of malleable iron. 
 The diameter of the crank pin is usually made th of 
 the diameter of the cylinder when of cast iron, and 
 i r th of the diameter of the cylinder when of malleable 
 iron. The diameter of the piston rod is usually made 
 jLth of the diameter of the cylinder, or the sectional 
 area of the piston rod is T J ^th of the area of the cy- 
 linder. The sectional area of the main links in land 
 beam engines is Tj^th of the area of the cylinder, and 
 the length of the main links is usually half the length 
 of the stroke. 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 \th of 
 the length of the rod, the sectional area at the centre 
 2 Jgth of the area of the cylinder, and at the ends ^th 
 of the area of the cylinder : the length of the rod is 
 usually 31 times the length of the stroke. 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; mul- 
 tiply the number of actual horses power to be trans- 
 
THE STEAM ENGINE. 107 
 
 mitted 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 f ths 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 un- 
 impaired. These rules are for the most part applicable 
 only in the case of condensing engines working with 
 steam of a few pounds pressure above the atmosphere, 
 whereas in many modern engines, and especially in 
 marine engines since the introduction of tubular boilers, 
 the pressure of the steam has been so much increased 
 as to make the force urging the piston twice greater 
 than formerly. 
 
 138. Q. Cannot you give some rules of strength 
 which will be applicable whatever pressure may be 
 employed ? 
 
 A. In the rules already given, the pressure may 
 be reckoned at from 18 to 201bs. upon every square 
 inch of the piston ; 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, how- 
 ever, 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. 
 
108 A CATECHISM OF 
 
 The method of computation will then be as follows : to 
 find the dimensions of a malleable iron paddle shaft, so 
 that the strain shall not exceed jjths of the elastic 
 force, or f ths of the force iron is capable of withstand- 
 ing without permanent derangement of structure, 
 which in tensile strains is 1 7,800 Ibs. per square inch : 
 multiply 0.08264 times the pressure in Ibs. 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 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^ 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. 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 Ibs. 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 Ibs. 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 
 
THE STEAM ENGINE. 109 
 
 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 Ibs. per square 
 Inch, multiplied by the diameter of the cylinder in 
 inches ; the diameter of the crank pin may be found 
 by multiplying 0.02836 times the square root of the 
 pressure on the piston in Ibs. per square inch by the 
 diameter of the cylinder in inches. The length of the 
 pin is usually about th 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 -|rd of the elastic force. 
 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 Ibs. 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 Ibs. 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 Ibs. per square 
 inch, multiplied by the diameter of the cylinder. The 
 breadth of the web of the crank of the shaft centre 
 should be twice the thickness, and at the pin centre 1-J 
 
110 A CATECHISM OF 
 
 times the thickness of the web ; the length of the 
 large eye of the crank should 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 Ibs. per 
 square inch, multiplied by the diameter of the cylinder. 
 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 Ibs. 
 per square inch, and dividing by 50, which makes 
 the strain -Jth of the elastic force. 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 Ibs. 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 Ibs. per square inch, multiplied by the dia- 
 meter of the cylinder in inches. The diameter of the 
 cylinder side rods at the ends may be found by multi 
 plying 0.0129 times the square root of the pressure 
 on the piston in Ibs. 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 Ibs. 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 connecting rod and 
 side rods is by these rules equal to jth of the elastic 
 
THE STEAM ENGINE. Ill 
 
 force. 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 Ibs. 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 Ibs. per square inch, multi- 
 plied 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 Ibs. per square inch, multiplied by the diameter of 
 the cylinder in inches the length of the journal 
 being -|ths its diameter. The thickness of the web at 
 centre will be 0.0245 times the cube root of the pres- 
 sure on the piston in Ibs. 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 Ibs. 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 Ibs. per square inch, multiplied by the dia- 
 meter 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 Ibs. 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 2-.T2 3- times the elastic force ; the strain upon 
 the journal in ordinary working is ^.i^- times the elastic 
 
112 A CATECHISM OF 
 
 force ; and if the outer ends of the journals are the 
 only bearing points, the strain is T .T^ times the 
 elastic force, which is very little in excess of the elastic 
 force. The diameter of the main centre may be found 
 by multiplying 0.0367 times the square of the pressure 
 upon the piston in Ibs. per square inch, by the diameter 
 of the cylinder in inches, which will give the diameter 
 of the main centre journal when of malleable iron, and 
 the length of the main centre journal should be 1J 
 times its diameter ; the strain upon the main centre 
 journal in ordinary working will be about ^ the 
 elastic force. In oscillating engines the diameter of 
 the trunnions is regulated by the diameter of the 
 pipes, and the thickness of the trunnions is about the 
 same as the thickness of the cylinder. It is obvious, 
 from the varying proportions subsisting in the diiferent 
 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 large dimensions are the most in- 
 
THE STEAM ENGINE. 113 
 
 dispensable. The depth of gibs and cutters for attach- 
 ing the piston rod to the cross head, is 0.0358 times 
 the cube root of the pressure of the steam on the piston 
 in Ibs. 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 Ibs. per square inch, multiplied by the dia- 
 meter of the cylinder. The depth of the cutter through 
 the piston is 0.017 times the square root of the pressure 
 on the piston in Ibs* 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 Ibs. per 
 square inch, multiplied by the diameter of the cylinder. 
 The whole of the answers to these rules are given in 
 inches. 
 
 139. Q. How do you determine the strength of 
 boilers ? 
 
 A. The iron of boilers like the iron of machines 
 or structures is capable of withstanding a tensile strain 
 of from 50,000 to 60,0001bs. 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 Ibs. upon the square inch of sec- 
 tional area of metal; and 3, 000 Ibs. on the square inch 
 of section, is a preferable proportion. The question 
 of the strength of boilers was investigated very ela- 
 borately 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, at which point the tenacity 
 
114 A CATECHISM OF 
 
 began to diminish. At 32 the cohesive force of a 
 square inch of section was 56,000 Ibs. ; at 570 it was 
 66,500 Ibs. ; at 720, 55,000 Ibs. ; at 1,050, 32,000 Ibs.; 
 at 1240, 22,0001bs. ; and at 1,317, 9,0001bs. Cop- 
 per follows a different law, and appears to be diminished 
 in strength by every addition to the temperature. At 
 32 the cohesion of copper was found to be 32,800 Ibs. 
 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 
 favourable. The accidental overheating of a boiler 
 was found to reduce the ultimate or maximum strength 
 of the plates from 65,0001bs. to 45,0001bs. per square 
 inch of section, and riveting the plates was found to 
 occasion a diminution in their strength, to the extent 
 of one-third. In some locomotive boilers which are 
 worked with a pressure of 80 Ibs. upon the square 
 inch, the thickness of the plates is only -^gths 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 -f 5 5 ths thick to make 
 up a sectional area of one square inch, and the sepa- 
 rating force will be 39 times 3.2 multiplied by 80, 
 which makes the separating force 9,984 Ibs. sustained 
 by two square inches of sectional area, one on each 
 side; or the strain is 4,992 Ibs. per square inch of 
 
THE STEAM ENGINE. 115 
 
 sectional area, which is a greater strain than is ad- 
 visable. 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 
 rivets which certainly would not be less in amount. 
 The proper thickness for cylindrical boilers or other 
 cylindrical vessels, whether of cast or wrought iron, 
 exposed to an internal pressure, may be found by 
 the following rule: multiply 2.54 times the inter- 
 nal diameter of the cylinder in inches by the greatest 
 pressure within the cylinder per circular inch, and 
 divide by the tensile force that the metal will bear 
 without permanent derangement of structure, which 
 for malleable iron is 17, 800 Ibs., and for cast iron 
 1 5,300 Ibs. per square inch of section; the result is 
 the thickness in inches. 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 Ibs. per square 
 inch of section, as the strength of internal stays in 
 boilers is generally soon diminished by corrosion. It 
 is expedient also that 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. 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. All boilers should be 
 proved when new to three or f6ur times the pressure 
 i 2 
 
116 A CATECHISM OF 
 
 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. 
 
 140. Q. What is the cause of the rapid corrosion 
 of marine boilers ? 
 
 A. 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 cor- 
 rosion 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 embedded in mastic cement laid upon 
 a suitable platform. The greatest part of the corrosion 
 of a boiler, however, 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 engineer- 
 ing. 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's 
 condensers which supply the boiler with fresh water, 
 scarcely any increased durability of the boiler has been 
 experienced. Nevertheless, marine boilers seldom last 
 
THE STEAM ENGINE. 117 
 
 more than for 4 or o 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, effec- 
 tually 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. These facts 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 
 
 i 3 
 
118 A CATECHISM OF 
 
 that its temperature is greater than is due to its elastic 
 force ; and on this hypothesis the observed facts rela- 
 tive to corrosion become easily explicable. Felt, ap- 
 plied to the outside of a boiler, may accelerate its 
 internal corrosion by keeping the steam in a sur- 
 charged 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 can- 
 not 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 mani- 
 festly 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 forma- 
 tion of surcharged steam. Besides, the natural effect 
 of surcharged steam is 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 neces- 
 sarily very much weaker than where the iron is red 
 hot, it manifestly must have some oxidising effect, and 
 the amount of corrosion produced may be very ma- 
 terial where the action is perpetual. Boilers with 
 
 
THE STEAM ENGINE. 119 
 
 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 quan- 
 tity of the heat passes away in the smoke ; and the 
 corrosion of the boiler will be diminished if the inte- 
 rior of any flue passing through the steam be coated 
 with fire brick, so as to prevent the transmission of 
 the heat in that situation. The best practice, however, 
 appears to consist in the transmission of the smoke 
 through a suitable orifice below the water level, 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. 
 
 141. Q. Will you explain the course of procedure 
 in the construction and setting of waggon boilers ? 
 
 A. 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 waggon boiler the heads of the rivets, 
 or the ends formed before the rivets 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 plate should be 
 
 I 4 
 
120 A CATECHISM OF 
 
 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 3 or 4 Ibs. weight 
 one man holding the caulking tool while another 
 strikes. The boiler should then be filled with water 
 and caulked afresh in any leaky part ; all the joints 
 above the water should next 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. In building the brick- 
 work for the setting of the boiler the parts 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 brick work to prevent it from 
 splitting. The top of {he boiler is to be covered with 
 brick work 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 
 
THE STEAM ENGINE. 121 
 
 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 brick work to enable a 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. 
 
 142. Q. Are marine constructed in the same way 
 as land boilers ? 
 
 A. There is very little difference in the two 
 cases : the whole of the shells of marine boilers, how- 
 ever, should be double riveted with rivets ygth of an 
 inch in diameter, and 2-|th 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-eights to one inch thick : the shells should 
 be of the best Staffordshire or Thorny croft S crown 
 iron, seven-sixteenths of an inch thick. Angle iron 
 should not be used in the construction of boilers, as in 
 the manufacture it becomes reedy, and is apt to split 
 
A CATECHISM OF 
 
 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 intro- 
 ducing 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. 
 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 progres- 
 sion every stroke of the punch or shears, and ma- 
 chinery 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 instead of the 
 heavy hammer previously prescribed. In the setting 
 of marine boilers care must be taken that no copper 
 bolts or nails project above the 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 
 
THE STEAM ENGINE. 123 
 
 points of contact into holes. The platform may con- 
 sist of 3-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 sur- 
 face 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. Mastic 
 cement proper for the setting of boilers is sold in many 
 places ready made ; Hamelin's mastic is compounded 
 as follows : To any given weight of sand or pul- 
 verised earthenware add two-thirds such given weight 
 of powdered Bath, Portland,, or other similar stone, 
 and to every five hundred and sixty pounds weight of 
 the mixture add forty pounds weight of litharge, two 
 pounds of powdered glass or flint, one pound of 
 minium, and two pounds 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 six hundred and five pounds of the 
 
124 A CATECHISM OF 
 
 powder to five 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 set into a solid 
 mass. 
 
 143. Q. Will you state any other constructive 
 details in connexion with marine boilers which occur 
 to you as deserving of enumeration ? 
 
 A. It will not be possible to state them in a very 
 systematic manner by adopting this course, but per- 
 haps it may be of most importance to despatch them 
 summarily. It has already been stated that furnace 
 bars should not much exceed 6ft. in length, as it is 
 difficult to manage long furnaces, but it is a frequent 
 practice to make furnaces long and narrow, the conse- 
 quence 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 in- 
 creased 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 in- 
 clination 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 in- 
 
THE STEAM ENGINE. 125 
 
 jury 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. The furnace bridges of marine 
 boilers 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. The 
 furnaces are shallowest in boilers with a double tier 
 of furnaces one above the other ; but such boilers are 
 now little used : the steam of the lower furnace ap- 
 pears to be condensed to a certain extent in coining 
 
126 A CATECHISM OF 
 
 into contact with the iron of the superior ash-pit, and 
 it is difficult, in such shallow furnaces as the plan in- 
 volves, to give the bars a sufficient inclination to 
 enable the fuel to pass on to the after end. The flue 
 of flue boilers generally contracts in area as it ap- 
 proaches the chimney ; and it is a common 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 intro- 
 ducing 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 connexions, 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. It 
 is an advantage that there should be a division be- 
 tween the tubes pertaining to each furnace of a marine 
 tubular boiler, 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 
 
THE STEAM ENGINE. 12? 
 
 this arrangement a furnace only will be rendered in- 
 operative 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: the connection between the 
 tubes of the inactive furnace and the chimney would 
 obviously require to be closed in such a case, either by 
 a damper or otherwise. The sides of the internal fur- 
 naces 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 
 escapes 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 tem- 
 perature 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 
 
128 A CATECHISM OF 
 
 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. 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 the 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 should be zig-zagged in the horizontal 
 line, whereby a greater strength of metal will be 
 obtained around the holes in the tube plates. 
 
 144. Q. In what manner is the tubing and stay- 
 ing of boilers performed ? 
 
 A. The tubes of marine boilers are generally iron 
 tubes, 3 inches in diameter, and between 6 and 7 ft. 
 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, appears 
 to be indispensable to keep them tight ; but when the 
 tubes are of malleable iron, of the thickness of Russell's 
 boiler tubes, they may be made tight merely by driving 
 them firmly into the tube plates. The holes in the 
 
THE STEAM ENGINE. 129 
 
 tube plate next the front of the boiler are made about 
 one-sixteenth of an inch larger in diameter than the 
 holes in the other tube plate, and the holes upon the 
 outer surfaces of both tube plates are slightly counter- 
 sunk. One end of each tube is enlarged about a six- 
 teenth of an inch to fit the enlarged holes in one of the 
 plates ; both ends may then be turned slightly in the 
 lathe to make them smooth and uniform in diameter 
 and length, and the whole of the tubes are then to be 
 all 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 ac- 
 complished by means of a mandril with a collar upoii 
 it, which is driven into the tube so that the collar rests 
 upon the end of the tube to be riveted. It appears 
 expedient in all cases where ferules are not used 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. To prevent leakage through the thread 
 of the screw, if the plan of screwing some of the tubes 
 be adopted, it will be expedient to let the screwed ends 
 
130 A CATECHISM OP 
 
 project about half an inch, and to put thin nuts upon 
 them with a little white lead interposed. 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 impossible 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 com- 
 pensate 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 in- 
 jury to be attributable chiefly to imperfect fitting, 
 whereby a leakage was caused that induced oxidation, 
 and where the tubes were well fitted any injurious 
 action at the ends of the tubes was found to cease. 
 "When the pressure of steam within the boiler is con- 
 siderable, the boiler must be very securely stayed : the 
 top and bottom, and also the sides of the boiler must 
 be stayed to one another, and it will not be sufficient 
 to stay the top of the boiler to the top of the furnaces, 
 and the bottom of the boiler to the bottom of the fur- 
 naces ; for if a furnace changed its form, as it would be 
 likely to do in such circumstances, the stays connect- 
 ing it to the top and bottom of the boiler would be of 
 very little utility in preventing the boiler from burst- 
 ing. If the pressure of steam be 20 Ibs. on the square 
 inch, which is a very common pressure in tubular 
 
THE STEAM ENGINE. 131 
 
 boilers, there will be a pressure of 2,880 Ibs. on every 
 square foot of fiat surface, so tfyat if the strain upon 
 the stays is not to exceed 3,000 Ibs. on the square 
 inch of section, there must be nearly a square inch ot 
 sectional area of stay for every square foot of flat sur- 
 face 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-^ inches 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 inclina- 
 tion 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 fur- 
 nace 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 
 K 2 
 
132 A CATECHISM OF 
 
 stays for water spaces or boiler shells, are objection- 
 able ; 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. The stays where 
 the sides of the boiler are flat, and the pressure of the 
 steam is from 20 to 30 Ibs., should be pitched about a 
 foot or 1 8 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 cir- 
 cular 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. The flues of all flue boilers diminish in their 
 calorimeter as they approach the chimney : some very 
 satisfactory boilers have been made by allowing a pro- 
 
THE STEAM ENGINE. 133 
 
 portion 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 ^th of the area of fire grate, and at 
 the smallest part where it enters the chimney ^th of 
 the area of the fire grate ; but in some of the boilers 
 proportioned on this plan the maximum sectional area 
 is only -fa or -g} st according to the purposes of the 
 boiler. 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; 
 but such boilers although they may give abundance of 
 steam are generally needlessly bulky, and the method 
 of fixing the proportions does not appear so eligible as 
 that previously suggested. In sea-going steamers the 
 funnel plates are usually about 9 ft. long and -/gths 
 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 dis- 
 tance 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 pipe should be made at the bottom with 
 a faucett 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 at- 
 tachment 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 
 
 K 3 
 
134 A CATECHISM OF 
 
 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 in- 
 convenience arises from the steam occasionally passing 
 through it, if it has its termination in the engine room. 
 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. 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 
 
THE STEAM ENGINE. 135 
 
 lodgment of deposit, which will prev.ent 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 afire 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. 
 
 145. Q. Is much inconvenience experienced in 
 marine boilers from saline incrustations upon the 
 flues? 
 
 A. 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 por- 
 tion of the super-salted water to escape at short inter- 
 vals into the sea. Sea water contains about ^\ s d its 
 weight of salt, and in the open air it boils at the tem- 
 perature of 213.2; if the proportion of salt be in- 
 creased to -j%ds of the weight of the water, the boiling 
 point will rise to 214.4 ; with Ads of salt the boiling 
 
 K 4 
 
136 A CATECHISM OF 
 
 point will be 215.5; ^ds, 216.7; ^ds, 217.9; 
 
 219 ; ^ds, 220.2 ; /^ds, 221.4 ; ^ds, 222.5 ; 
 
 223.7 ;' Hds, 224.9 ; and ffla, which is the 
 point of saturation, 226. 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, its 
 temperature at a pressure of 15 Ibs. per square inch 
 will be 250, and adding to this 4.7 as the increased 
 temperature due to the saltness of the water when it 
 contains ^Vte of salt, we have 254.7 as the tempe- 
 rature of the water in the boiler, when it contains 
 3^ds of salt and the pressure of the steam is 1 5 Ibs. 
 on the square inch. 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 con- 
 tains 3^ds its weight of salt, no injurious incrustation 
 will take place, and as sea water contains only ^d of 
 its weight of salt, it is clear that it must be reduced 
 by evaporation to one-fourth of its bulk before it can 
 contain -j%ds of salt ; or, in other words, a boiler 
 must blow out into the sea one-fourth of the water it 
 receives as feed, in order to prevent the water from 
 rising above ^-ds of concentration. Taking the latent 
 heat of steam at 1,000 at the temperature of 212, 
 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 will be 962, and the 
 total heat of the steam will be 1212 in the case of 
 fresh water; but as the feed water is sent into the 
 
 
THE STEAM ENGINE. 137 
 
 boiler at the temperature of 100, the accession of 
 heat it receives from the fuel will be 1112 in the 
 case of fresh water, or 1112 increased by 3.98 in the 
 case of containing 3%ds of salt the 3.98 being the 
 4.7 increase of temperature due to the presence of 
 3%ds of salt, multiplied by 0.847, the specific heat of 
 steam. This makes the total accession of heat re- 
 ceived by the steam in the boiler equal to 1115.98, 
 or say 1116, which multiplied by 3, as 3 parts of the 
 water are raised into steam, gives us 3348 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, multiplied by 0.85, the specific heat of the 
 brine, or 130.495; and 3348 divided by 130.495 is 
 about Jgth. It appears, therefore, that by blowing 
 off the boiler to such an extent, that the saltness shall 
 not rise above what answers to ^ds of salt, about 
 g^th 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. 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 scarcely any 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 con- 
 
138 A CATECHISM OF 
 
 nexion with the small tubes for the extraction of the 
 heat from the super-salted 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. The general mode of 
 blowing off the boiler is to allow the water to rise 
 gradually for an hour or two above the lowest work- 
 ing 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 : but in every case in 
 which the super-salted water is discharged from the 
 boiler in a continuous stream, a hydrometer or salt 
 gauge of some convenient construction should be ap- 
 plied to the boiler, so that the density of the water 
 may at all times be visible. Blowing off from a point 
 near the surface of the water is more beneficial than 
 blowing off from the bottom of the boiler. Solid par- 
 ticles 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 ap- 
 pearance 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 con- 
 crete into scale, are carried in the first instance to the 
 surface of the water, so that if they be caught there, 
 
THE STEAM ENGINE. 139 
 
 and ejected from the boiler, the formation of scale will 
 be prevented. Advantage is taken of this property 
 in Lamb'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 connexion 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. In some boilers sheet iron 
 vessels called sediment collectors are employed, which 
 collect into them the impalpable matter, which in 
 Lamb'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 side conical slits are 
 cut, so as to establish a free communication between 
 the water within the conical vessel and the water out- 
 side it. The particles of stony matter, which are bal- 
 looned to the surface by the steam in every other part 
 of the boiler, subside within the cone, where no steam 
 is generated, and the water is consequently tranquil ; 
 and the deposit is discharged overboard at intervals 
 by means of the cock 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 
 
140 A CATECHISM OF 
 
 upon the surface of the water is ejected from the 
 boiler thereby removing one of the chief causes of 
 priming. As it is very desirable that boilers acting 
 on the principle of continuously blowing off a small 
 stream of the super-salted water, should be provided 
 with a salt gauge which will give immediate notice 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 dif- 
 ferential steam gauge, which shall indicate the dif- 
 ference 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. If blowing off be sufficiently 
 practised, the scale upon the flues will never be much 
 thicker than a sheet of writing paper, and no excuse 
 should be accepted from engineers for permitting a 
 boiler to be damaged by the accumulation of calca- 
 reous deposit. Flue boilers generally require to be 
 blown off once every watch, or once in the two 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. Even 
 with judicious management, however, the boilers may 
 sometimes require to be scaled, and the best method 
 of performing this operation appears to be the fol- 
 lowing: 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 STEAM ENGINE. 141 
 
 the flues, while the scale from its imperfect con- 
 ducting 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 entrusted to the 
 firemen, who in their ignorance might damage the 
 boiler by over heating the plates. It is only where 
 the incrustation upon the flues is considerable, that 
 this method of removing it need be practised; in 
 other cases the scale may be chipped off by a hatchet- 
 faced hammer, and the flues may then be washed 
 down with the hose in the manner before described. 
 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 enve- 
 loping them have actually grown together in some 
 parts so as totally to exclude the water. When a 
 boiler gets into this state the whole of the tubes must 
 be pulled out, which may be done by a Spanish wind- 
 lass 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 
 
142 A CATECHISM OF 
 
 the incrustation, but the tubes should afterwards be 
 scraped by drawing them backwards and forwards 
 between two old files, fixed in a vice, in the form of 
 the letter V. The ends of the tubes should then be 
 heated and dressed with the hammer, and plunged 
 while at a blood heat into a bed of saw dust 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 re-insertion : this result might be to a 
 considerable extent obviated, by setting the tube 
 plates at different angles, so that the several hori- 
 zontal 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 prac- 
 tice would be attended with other inconveniences. 
 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. 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 
 
THE STEAM ENGINE. 143 
 
 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. 
 
 146. Q. Will you explain the nature and cause 
 of priming ? 
 
 A. 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 with- 
 in 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. 
 The causes of priming are an insufficient amount of 
 steam room, an inadequate area of water level, an in- 
 
144 A CATECHISM OF 
 
 sufficient 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, 
 arid 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 pass- 
 ing 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 par- 
 tially opening which, any priming in that part of the 
 boiler adjacent to the steam chest is checked, and a 
 purer steam than before passes to the engine. 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 
 
THE STEAM ENGINE. 145 
 
 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 neces- 
 sary 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 insuffi- 
 cient area of water level, or an insufficient width be- 
 tween 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 cur- 
 rent of steam and water to the surface. It is desirable, 
 however, 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 towards 
 the superior part of the flues it is raised gradually 
 into steam ; and in boilers designed upon this principle, 
 there will be less need for any special provision to 
 enable currents to rise or descend. The steam pipe 
 proceeding to the engine should obviously be attached 
 to the highest point of the steam chest, in boilers of 
 every construction. 
 
 L 
 
146 A CATECHISM OF 
 
 147. Q. What is the chief cause of boiler explo- 
 sions? 
 
 A. The chief cause of boiler explosions is, un- 
 doubtedly, too great a pressure of steam, or an insuffi- 
 cient strength of boiler; but many explosions have 
 also arisen from the flues having been suffered to be- 
 come 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 some- 
 times 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 other- 
 wise, 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 con- 
 figuration 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 upwards with 
 the pressure of the steam. The flues of boilers may 
 
THE STEAM ENGINE. 147 
 
 also become red hot in some parts from the attach- 
 ment 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. It is found, however, 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, 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 pro- 
 duced so long as the high temperature is maintained ; 
 but so soon as the temperature is suffered to fall below 
 350 or 400, 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. One useful precaution against the 
 explosion of boilers from too great an internal pres- 
 sure, consists in the application of a steam gauge to 
 each boiler, which will make the existence of any un- 
 due 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 connexion 
 with the passage leading to any of the stop valves 
 
 L 2 
 
148 A CATECHISM OF 
 
 used to cut off the connexion between the boilers ; so 
 that the action of the safety valve may be made inde- 
 pendent 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 valve 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 upwards 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. 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 emer- 
 gency, and by this treatment the fires, though not 
 
THE STEAM ENGINE. 149 
 
 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. Plugs of 
 fusible metal were at one time in much repute as a 
 precaution against explosion, the metal being so com- 
 pounded 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 un- 
 able 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. All boilers in 
 actual use should be proved at least once a-year by 
 forcing water into them by the hand feed-pump until 
 the safety valve is lifted, which should be loaded with 
 at least twice the working pressure for the occasion. 
 If a boiler will not stand this test it is not safe, and 
 either its strength should be increased or the working 
 pressure should be diminished. 
 
 L 3 
 
150 A CATECHISM OF 
 
 148. Q. Will you state something of the pecu- 
 liarities of structure of locomotive boilers ? 
 
 A. Locomotive boilers consist of three portions 
 the barrel containing the tubes, the fire box, and the 
 smoke box ; of which the barrel, smoke box, and 
 external fire box are always of iron, but the in- 
 ternal 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 
 ferrules. 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. The 
 thickness of the plates composing the barrel of the 
 boiler varies generally from five-sixteenths to three- 
 eighths 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 eleven -sixteenths to three-fourths of an inch, and 
 the pitch of the rivets or distance between their cen- 
 tres should be from seventeen-eighths to 2 inches. 
 The thickness of the plates composing the external 
 fire box is in general three-eighths of an inch if the 
 fire box is circular, and from three-eighths to one-half 
 inch if the fire box is square ; and the thickness of the 
 internal fire box is in most cases seven-sixteenths if 
 copper, and from three-eighths to seven-sixteenths of 
 an inch if of iron. Circular internal fire boxes, if 
 
THE STEAM ENGINE. 151 
 
 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 intro- 
 duction of the rivets. The space between the ex- 
 ternal and internal fire boxes forms a water space, 
 which must be stayed every 4J 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. 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 pro- 
 cess of ferruling 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 ferrules are for the most part made of steel at the 
 fire box end, and of wrought iron at the smoke box 
 end, though ferrules of malleable cast-iron have in 
 some cases been used with advantage : malleable cast- 
 iron ferrules are almost as easily expanded when 
 hammered cold upon a mandril, as the common 
 wrought-iron ones are at a working heat. Spring- 
 steel, rolled with a feather-edge, to facilitate its con- 
 version into ferrules, is supplied by some of the steel 
 makers of Sheffield, and it appears expedient to make 
 use of steel thus prepared when steel ferrules are em- 
 
 L 4 
 
152 A CATECHISM OF 
 
 ployed. The roof of the internal fire box, whether 
 flat as in Stephenson's engines, or dome-shaped as in 
 Bury'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 iron ; and, with the view of facilitating the as- 
 cent of the steam, the bottom of each stay-bar should 
 be sharpened away in those parts where it does not 
 touch the boiler. 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 in. thick, and 2 in. broad ; the 
 inner fire box being dished sufficiently outwards at 
 that point, and the outer fire box sufficiently inwards, 
 to enable a circle of rivets three-fourths of an inch in 
 diameter passing through the copper ring and the two 
 thicknesses of iron to make a water-tight joint. 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 a 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 
 
THE STEAM ENGINE. 153 
 
 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 after- 
 wards to be bent into contact with the cylindrical 
 surface of the wheel is a plane. In this case the ad- 
 dition 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 dia- 
 meter, 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. 
 
 149. Q. Are locomotive boilers provided with a 
 steam chest ? 
 
 A. The upper portion of the external fire box is 
 usually formed into a steam chest, which is sometimes 
 dome-shaped, sometimes semi-circular, 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 ft. 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 Stephen- 
 son's locomotives, presents a considerable extent of 
 flat surface to the pressure of the steam, and this flat 
 
154 A CATECHISM OF 
 
 surface requires to be very strongly stayed with angle 
 irons and tension rods ; whereas the semi-globular 
 dome of the kind employed in Bury's engines requires 
 no staying whatever. The man-hole, or entrance into 
 the boiler, consists of a circular or oval aperture, of 
 about 15 in. diameter, placed in Bury's locomotive at 
 the apex of the dome, and in Stephenson'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'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 inter- 
 position of a little red lead to make them quite tight 
 when screwed together. Lead or canvass 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 re- 
 quire 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 em- 
 tying 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 
 
THE STEAM ENGINE. 155 
 
 or grit into the bearings, to their manifest injury. 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 occa- 
 sion where more steam is produced than the engine 
 can consume. The fire-bars in locomotives have al- 
 ways 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 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 work- 
 ing order, as the molten clinker, by running down be- 
 tween 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 for every species 
 of boiler malleable iron bars are to be preferred to 
 bars of cast-iron, as they are more durable, and may, 
 from their thinness, be set closer together, whereby the 
 small coal or coke is saved that would otherwise fall 
 
156 A CATECHISM OF 
 
 into the ash-pit. The ash-box of locomotives is made 
 of plate-iron a quarter thick : it should not be less 
 than 1 in. deep, and its bottom should be about 9 in. 
 above the level of the rails. The chimney of a loco- 
 motive is made of plate-iron one-eighth of an inch 
 thick : it is usually of the same diameter as the cy- 
 linder, and must not stand more than 14ft. high 
 above the level of the rails. 
 
 150. Q. What is the best diameter for the tubes 
 of locomotive boilers ? 
 
 A. Bury's locomotive with 14 in. cylinders contains 
 92 tubes of 2^th in. external diameter, and 10ft. 6 in. 
 long, whereas Stephenson's locomotive with 15 in. 
 cylinders, contains 150 tubes of If ths external diame- 
 ter, and 1 3 ft, 6 in. long. In Stephenson'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 question- 
 able whether the increased expenditure of power upon 
 the blast, in Stephenson'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 Ifths may be employed without 
 inconvenience, if the draught be of medium intensity. 
 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, is now much 
 used. There are various devices for this purpose, but 
 
THE STEAM ENGINE. 157 
 
 the best appears to be that adopted in Stephenson'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 down- 
 ward 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 di- 
 minished by the enlargement of the opening for the 
 escape of the steam thus made available. In most 
 locomotives the velocity of the draft 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, and if it were required at the same time that 
 the heat should be as thoroughly extracted. The 
 Nile steamer with engines of 1 10 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 pres- 
 sure, the evaporative efficacy of each flue may be 
 reckoned equivalent to 80 actual horses power. With 
 
158 A CATECHISM OF 
 
 this evaporative power there is a calorimeter of 990 
 square inches, or 12.3 square inches per actual horse 
 power, whereas in Stephenson's locomotive with 150 
 tubes, if the evaporative power be taken at 200 cubic 
 feet of water in the hour, which makes the engine 
 equal to 200 actual horses power, and 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, as stated in the 
 answer to Question 93, would require to be 35J in. in 
 diameter, if made of the cylindrical form, and 47 J ft. 
 long : the tubes of a locomotive if If th in. in diameter 
 would only require to be 22. 19 in. long with the same 
 velocity of draft ; but as the draft is 11.11 times faster 
 than in a flue boiler, the tubes ought to be 246.558 
 inches, or about 20^ ft. long according to this propor- 
 tion. 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 pre- 
 ferable therefore to increase the calorimeter, and di- 
 minish the intensity of the draught. 
 
 151. Q. You have mentioned the existence of the 
 steam gauge, the vacuum gauge, the salt gauge, and 
 the indicator; what other gauges or instrument are 
 
THE STEAM ENGINE. 159 
 
 there for telling the state, or regulating the power, of 
 an engine ? 
 
 A. 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. 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 revolv- 
 ing 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 quantity. 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 ob- 
 tained ; 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 screw works hang down from 
 it like a pendulum, and are kept stationary by the 
 
160 A CATECHISM OP 
 
 action of gravity. 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. 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 
 applied ; 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 dynamo- 
 meter fixed on shore, to which the floating vessel is 
 attached by a rope. By means of the glass tubes 
 affixed to the fronts of boilers the height of the water 
 within any of 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 gauge cocks are cocks pene- 
 trating 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. 
 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 in- 
 ternal 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 
 
THE STEAM ENGINE. 161 
 
 steam in the boiler, a broken tube may be replaced 
 with facility. 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 pro- 
 duced 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. The 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 connexion 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 
 M 
 
162 A CATECHISM OF 
 
 upon the boiler, and in which there is a column of 
 water sufficiently high to balance the pressure of the 
 steam. The water is sent up into the small cistern 
 by the force-pump, and any that does not gain admis- 
 sion to the boiler through the valve in the cistern, 
 runs to waste by an overflow shoot. The height of 
 the water in the stand pipe rises and falls with the 
 pressure of the steam, and a float is therefore placed 
 within it to operate upon the damper, which, when 
 the level of the water rises, from the pressure of the 
 steam becoming strong, partially closes the damper, 
 and thus moderates the intensity of the fire. The 
 cataract consists of a small pump-plunger and barrel, 
 set in a cistern of water, the barrel being furnished 
 on the one side with a valve opening inwards, through 
 which the water obtains admission to the pump cham- 
 ber from the cistern, and on the other by a cock 
 through which, if the plunger be forced down, the 
 water must pass out of the pump chamber. The en- 
 gine in the upward stroke of the piston, which is ac- 
 complished 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. If the cock of the cataract 
 be shut, it is clear that the plunger cannot descend at 
 
THE STEAM ENGINE. 163 
 
 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 neces- 
 sary 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 required 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 iden- 
 tical, and the only difference is in the detail. 
 
 152. Q. Will you explain the course of procedure 
 in the erection of a pumping engine, such as is used in 
 Cornwall. 
 
 A. 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 in- 
 cluded 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 con- 
 venient ; 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 
 M 2 
 
164 A CATECHISM OF 
 
 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. 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 in 
 the wall two parallel flat thin bars of iron equally 
 distant from each other, and from the outside and in- 
 side 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 ft. or 12 ft. 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 
 
THE STEAM ENGINE. 165 
 
 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 be also be bedded solidly, and the 
 residue of the opening must be built up in the firmest 
 manner. If there be no water in the neighbourhood 
 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 3 ft. or 4 ft. 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 ccol it, has been found detrimental ; 
 as the water is then charged with air which vitiates 
 the vacuum. To pack the piston, take 60 common- 
 sized white or untarred rope-yarns, and with them 
 plait a gasket or flat rope as close and firm as possible, 
 tapering for 18 in. 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 
 
 M 3 
 
166 A CATECHISM OP 
 
 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 5 to 
 6 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, es- 
 pecially 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. 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 
 
 
THE STEAM ENGINE. 167 
 
 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 im- 
 mediately ; and if this produces any considerable va- 
 cuum, 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, 
 arid the piston should stand high enough in the cylinder 
 when the engine is at rest, to spill over into the per- 
 pendicular steam pipe any water which may be con- 
 densed 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 
 
 M 4 
 
168 A CATECHISM OF 
 
 valve to open and remain open, otherwise a partial va- 
 cuum 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 mi- 
 nutes, and as fast k as ten strokes in one minute ; and 
 if it does not fulfil these conditions, there is some fault 
 which should be ascertained and remedied. In the 
 modern Cornish engines the steam is used very ex- 
 pansively, 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 ; and the cylinder end 
 of the main beam is generally made longer than the 
 pump end, so as to enable the cylinder to have a long- 
 stroke, and the piston to move quickly, without com- 
 municating 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. The pump now universally 
 preferred is the plunger pump, which admits of being 
 
THE STEAM ENGINE. 169 
 
 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 ren- 
 dered 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 con- 
 trived to mitigate the evil, of which the valve known 
 as Harvey and West's valve has perhaps gained the 
 widest acceptation. This valve is a compromise be- 
 tween 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 
 should first be understood. This valve consists sub- 
 stantially 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 
 
170 A CATECHISM OF 
 
 lowered without any further exertion of force than is 
 necessary to overcome the friction of the piston arid 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 em- 
 ployed, 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 out- 
 wards in the middle, so as to permit the steam to es- 
 cape 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's valves, however, the equilibrium principle 
 is only partially adopted ; the lower face is considerably 
 larger in diameter than the upper face, and the differ- 
 ence 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's valve, or any contrivance of a similar kind, 
 adds materially to the load upon the pump. In some 
 
 
THE STEAM ENGINE. 171 
 
 cases canvass valves similar to those referred to in 
 page 62, are used for pumps with the effect of ma- 
 terially mitigating the shock ; but they require frequent 
 renewal, and are of inferior eligibility in their action 
 to the slide valve, which might be applied to pumps 
 without inconvenience. The centrifugal pump, how- 
 ever, 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. Indeed, 
 it appears probable, that by working a common reci- 
 procating 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 super- 
 fluous. The best form of the centrifugal pump appears 
 to be that in which the arms diverge from the bottom, 
 like the letter V. Such pumps both draw and force ; 
 and by arranging them in a succession of lifts in the 
 shaft of the mine, the water maybe drawn without in- 
 convenience from any depth. The introduction of 
 the centrifugal pump will obviously extinguish the 
 single acting engine, as rotative engines working at a 
 high speed will be the most appropriate form of engine 
 where the centrifugal pump is employed. The single 
 acting engine, indeed, is a remnant of engineering bar- 
 barism which must now be superseded by more com- 
 pendious 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. It is a mistake to suppose that there is 
 
172 A CATECHISM OF 
 
 any peculiar virtue in the existing form of Cornish 
 engine to make it economical in fuel, or that a less le- 
 thargic 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. 
 
 153. Q. What description of rotative engine do 
 you consider the best ? 
 
 A. The oscillating engine appears to me the best 
 form of rotative engine yet introduced, and I would 
 prefer it to any other in every case where a rotatory 
 motion is required. For land purposes it is simpler 
 and more compact than the common beam engine ; for 
 steam vessels it appears to be preferable to the side 
 lever engine, as well as to any of the other forms of 
 direct action engines yet introduced ; and for locomo- 
 tives its employment seems to promise the advantage 
 of diminishing the mass of reciprocating material, 
 whereby there will be less of the sinuous or oscillating 
 motion, by which the safety of railway trains is some- 
 times endangered. The chief varieties of direct action 
 engines used for steam vessels, besides the oscillating 
 engine, are, the Gorgon engine, with the connecting 
 rod reaching from the top of the piston rod to the 
 crank situated above it ; the Steeple engine, with the 
 connecting rod above the crank ; and the Annular and 
 Siamese engines of Maudslay. The Gorgon engine 
 has the disadvantage of inconveniently raising the 
 
THE STEAM ENGINE. 173 
 
 shaft to give room for the stroke, whereby a large 
 paddle wheel becomes necessary; and with a large 
 wheel there must either be a great deal of slip, or the 
 engines must work but slowly. The Steeple engine 
 has the inconvenience of protruding a large portion of 
 the machinery above the deck ; and the Annular and 
 Siamese engines have peculiar complications, which 
 render them inferior to the oscillating engine for every 
 purpose. Against the oscillating engine itself various 
 objections have been brought at various times: 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 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 hypo- 
 thetical, and that none of them in practice have been 
 found to exist to such an extent at least as to occa- 
 sion any inconvenience ; but it is not difficult to show 
 that they are altogether unsubstantial, even without a 
 recourse to the disproofs afforded by experience. 
 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' wear it is found that the 
 amount of ellipticity is less than what 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 
 
174 A CATECHISM OF 
 
 is capable of moving a large cylinder with one hand, 
 whereas in the side-lever engine, if the parallel mo- 
 tion 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 cy- 
 linder, 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 in- 
 troduced are squeezed in a cylindrical mould. 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 communi- 
 cated by the engine, requires to adapt itself to the 
 altering forms of the vessel, as the engine and inter- 
 mediate shaft are rigidly connected, although the 
 paddle shaft requires to be capable of such an adapta- 
 tion. Even if this objection existed, however, it 
 could easily be met by making the crank pin of the 
 
THE STEAM ENGINE. 175 
 
 ball and socket fashion, which would permit the posi- 
 tion 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. 
 
 154. Q. Will you describe the structure of an 
 oscillating engine as made by Messrs. Penn ? 
 
 A. 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 in. diameter of cylinder, and 22 in. 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'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 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's 
 sides, and enters the condenser through the two mid- 
 ship 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. This valve is balanced by a weight 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 con- 
 
176 A CATECHISM OF 
 
 sists 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. The web, or base plate, of the lower frame 
 is ^ of an inch thick, and a cooming is carried 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 
 Gin. deep, and about SJin. wide, with holes at the 
 sides to take out the core ; and the thickness of the 
 metal is ||ths of an inch. Both the upper and the 
 lower frame is cast in a single piece, with the ex- 
 ception of the continuations of the upper frame, 
 which support the paddle wheels. An oval ring 
 3 in. 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 support the in- 
 termediate shaft journals. The columns are 1| in. 
 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 support- 
 ing 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 in. deep, 
 
THE STEAM ENGINE. 177 
 
 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 in. 
 deep on the lower frame, and a little more than 6 in. 
 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. The condenser, which is cast 
 upon the lower frame, consists of an oval vessel 
 221 in. w ide, by 2 ft. 4J in. long, and 1 ft. 10^ in. deep; 
 it stands 9 in. above the upper face of the bottom 
 frame, the rest projecting beneath it ; and it is en 
 larged at the sides by being carried beneath the trun- 
 nions. The air pump, which is set in the centre of 
 the condenser, is 15^ in. in diameter, and has a stroke 
 of 1 1 in. The foot valve is situated in the bottom of 
 the air pump, and consists of a disc of brass, in which 
 there is a rectangular flap valve, but rounded on one 
 side to the circle of the pump, opening upwards, and 
 so balanced as to enable the valve to open with faci- 
 lity; and the balance weight, which is formed of 
 brass cast in the same piece as the valve itself, ope- 
 rates as a stop, by coming into contact with the disc 
 which constitutes the bottom of the pump when the 
 valve has opened sufficiently. This disc is bolted 
 to the bottom 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 ; 
 and within the hot well the delivery valve, which 
 
178 A CATECHISM OF 
 
 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 connecting rod. 
 The lower frame is not set immediately below the top 
 frame, but 2Jin. behind it, and the air pump and 
 condenser are 21 in. nearer one edge of the lower 
 frame than the other. The thickness of the metal of 
 the cylinder is T 9 6 ths of an inch; the depth of the 
 belt of the cylinder is 9Jin., and its greatest pro- 
 jection from the cylinder is 2J in. The distance from 
 the lower edge of the belt to the bottom of the cylin- 
 der is 11 Jin., and from the upper edge of the belt to 
 the top flange of the cylinder is 9 in. The trunnions 
 are 7^ in. diameter in the bearings, and 3Jin. in 
 width ; and the flanges to which the glands are at- 
 tached for screwing in the trunnion packings are 
 li in. thick, and have ^ths of an inch of projection. 
 The width of the packing space round the trunnions 
 is -|ths of an inch, and the diameter of the pipe pass- 
 
THE STEAM ENGINE. 179 
 
 ing through the trunnions 4fths. which leaves 
 for the thickness of the metal of the bearing. The 
 pipe leading to the condenser, from the cylinder, is 
 made somewhat bell-mouthed where it joins the con- 
 denser, and the gland for compressing the packing is 
 made of a larger internal diameter in every part ex- 
 cept at the point 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 towards 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 at- 
 tached 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 intro- 
 duced 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 ^d of an inch of 
 
 N 2 
 
180 A CATECHISM 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 educ- 
 tion 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 inap- 
 preciable. 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 ten- 
 dency to approach one another; and as they wear 
 slightly towards midships, there would be no power of 
 re-adjustment unless the plummer-blocks were move- 
 able. 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. Above and below each trunnion a 
 feather or bracket runs from the edge of the belt be- 
 tween 3 in. and 4 in. along the cylinder, for the sake 
 of additional support ; and in large engines this feather 
 is continued through the interior of the belt, and cru- 
 ciform feathers are added for the sake of greater stiff- 
 ness. The projection of the outer face of the trunnion 
 flange from the side of the cylinder is 6jin. ; the 
 thickness of the flange round the mouth of the cy- 
 
THE STEAM ENGINE. 181 
 
 Under is f of an inch, and its projection If in. ; the 
 height of the cylinder stuffing box above the cylinder 
 cover is 4^ in., and its external diameter 4|th in. 
 the diameter of the piston rod being 2-J in. ; and the 
 thickness of the stuffing box flange is IJin. The 
 length of the valve casing is 16^ in., and its projection 
 from the cylinder is 3 J in. at the top, 4^ in. at the 
 centre, and 2^ in. 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 in., but 
 there is a portion the depth of the belt IJin. 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^ in., the thickness of the flange on the casing 
 i in., and the thickness of the flange on the cylinder 
 f ths of an inch. The valve is of the ordinary three- 
 ported description, and both cylinder and valve faces 
 are of cast iron. 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 J in., and its width externally 8f in. 
 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 re- 
 moved, permit a box-key to be introduced, to screw 
 down the piston packings. The screws in the junk 
 ring are each provided with a small ratchet, cut in a 
 fixed washer 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 
 
 N 3 
 
182 A CATECHISM OF 
 
 the engineer to know when they have all been tight- 
 ened equally. 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 T 5 ^ in. The dia- 
 meter of the crank pin is 3 in., and the length of the 
 crank pin bearing 3 J in. The thickness of the brass 
 around the crank pin bearing is 1 in , 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 bear- 
 ing has a square outline measuring 7 in. in the hori- 
 zontal direction, 3? in. from the centre of the pin to 
 the level of the top of the lugs, and 2J in. from the 
 centre of the pin to the level of the bottom of the 
 lugs. The width of the lugs is 2 in., and the bolts 
 passing through them are l^in. 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 o in., and in the centre of the cover, where 
 the lugs, continued in the form of a web, meet one 
 another, an oil cup If in. in diameter, 1-g-in. 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 IJin., and its thickness is 
 three-eighths of an inch. A similar cap attaches the 
 
THE STEAM ENGINE. 183 
 
 air pump crank to the connecting rod by which the 
 air pump rod is moved, but in this instance the dia- 
 meter of the bearing is 5 in., and the length of the 
 bearing about 3 in. The thickness of the brass en- 
 circling the bearing is three-fourths of an inch upon 
 the edge, and IJ-in. in the centre, the back being 
 slightly rounded ; the width of the lugs is If in., and 
 the depth of the lugs is 2 in. upon the upper brass, 
 and 2 in. upon the lower brass, making a total depth 
 of 4 in. The diameter of the bolts passing through 
 the lugs is 1 in., 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, the ends of which move in the 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 
 l^in. ; the external diameter of the socket encircling 
 the rod is 2-J in., and the depth of the socket 4 in. 
 from the centre of the cross head. The depth of the 
 cutter for attaching the socket to the rod is 1 in., and 
 its thickness T 5 g in. The breadth of the lugs is If in., 
 the depth 1 J in., making a total depth of 2J in. ; and 
 the diameter of the bolts seven-eighths of an inch. 
 The diameter of the cross head at the centre is 2 in., 
 the thickness of each jaw around the bearing 1 in., 
 
 N 4 
 
184 A CATECHISM OF 
 
 and the breadth of each T 9 ^ in. The diameter of the 
 intermediate shaft journal is 4y\ in., and of the paddle 
 shaft journal 4f in., the length of the journal in each 
 case is 5 in. The diameter of the large eye of the 
 crank is 7 in., and the diameter of the hole through 
 it is 4 J in. ; the diameter of the small eye of the crank 
 is 5J in., the diameter of the hole through it being 
 3 in. The depth of the large eye is 4 in., and of the 
 small eye 3 J in. ; the breadth of the web is 4 in. at 
 the shaft end, and 3 in. at the pin head, and the thick- 
 ness of the web is 2-| in. The width of the notch 
 forming the crank in the intermediate shaft for work- 
 ing the air pump is 3^ in., and the width of each of 
 the arms of this crank is 3-^jf in. ; 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 crank 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. The eccentric strap is half an inch thick, 
 and l^in. broad; and the flanges of the eccentric, 
 within which the strap works, are each three-eighths 
 of an inch thick. The eccentric is put on 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 sepa- 
 rate 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 rod 
 is attached to the eccentric hoops by means of two 
 
THE STEAM ENGINE. 185 
 
 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 pull 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. 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 accu- 
 rately fitted at first, and it appears expedient, there- 
 fore, 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. The trunnion plummer 
 blocks are formed in the same manner as the shaft 
 plummer blocks ; the nuts are kept from turning back 
 by means of a pinching screw passing through a sta- 
 tionary washer. 
 
 155. Q. Will you explain in detail the construc- 
 tion of the valve gearing, or such parts of it as are 
 peculiar to the oscillating engine ? 
 
 A. The eccentric rod is attached by a pin, 1 in. in 
 diameter, to an open curved link with a tail projecting 
 
186 A CATECHISM OF 
 
 upwards, and passing through an eye to guide the link 
 in a vertical motion. The link is formed of iron case- 
 hardened, and is 2 J in. deep at the middle, and 2-| in. 
 deep at the ends, and 1 in. broad. The opening in 
 the link, which extends nearly its entire length, is 
 l^in. broad, and into this opening a brass block 2 in. 
 long is truly fitted, there being a hole through the 
 block Jin. diameter, for the reception of the pin of 
 the valve shaft lever. The valve shaft is IJin. dia- 
 meter at the end next the link or segment, and di- 
 minishes regularly to the other end, but it assumes 
 the form of an octagon in its passage round the cylin- 
 der, measuring midway IJin. deep, by about Jin. 
 think, and the greatest depth of the finger for moving 
 the valve is about 1 in. The depth of the lever for 
 moving the valve shaft is 2 in. at the broad, and 1^ in. 
 at the narrow end. The internal breadth of the mor- 
 tice in which the valve finger moves is l^in., and 
 its external depth is IJin., 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 IJin. The valve rod is three-fourths of an 
 inch in diameter, and the mortice is connected to the 
 valve rod by a socket 1 in. long, and Ig-in. 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 semi-circular 
 brasses, 4 in. deep, passing round the columns, and 
 
THE STEAM ENGINE. 187 
 
 attached to the segment by two fin. bolts at each 
 end, passing through projecting feathers upon the 
 brasses and segment, three-eighths of an inch in thick- 
 ness. The curvature of the segment is such as to 
 correspond with the arc swept from the centre of the 
 trunnion with the distance 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 oper- 
 ation 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 en- 
 gines the hollow segment is not formed in a single 
 piece, but of two curved blades, with blocks inter- 
 posed 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. 
 
 1,56. Q. What kind of paddle wheel is supplied 
 with these oscillating engines ? 
 
 A. The wheels are of the feathering kind, 9ft. 
 8 in. in diameter, measuring to the edges of the floats ; 
 and there are 10 floats upon each wheel, measuring 
 4ft. 6 in. long each, and 18|in. 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^ in., the 
 external diameter of the pipe is 8 in., and the diameter 
 of the flanges is 20 in., and their thickness l^in. 
 The flanges are 12 in. asunder at the outer edge, and 
 they partake of the converging direction of the arms. 
 The arms are 2J in. broad, and half an inch thics ; 
 
188 A CATECHISM OF 
 
 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 ft. 6 in. from the centre, 
 and the projecting ends of the arms are bent back- 
 wards 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 each 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 in. 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 l|in. diameter in the centre, proceeding 
 to the levers, 7 in. 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 nearly in the verti- 
 cal position ; but this is of less consequence, as only 
 one float is wholly immersed. The diameter of the 
 pins upon which the float turns is If in., and between 
 the pins and the paddle ring two stud rods are set be- 
 tween 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. 
 
THE STEAM ENGINE. 189 
 
 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. 
 
 157. Q. Will you give the dimensions of some 
 other oscillating engines ? 
 
 A. In Messrs. Penn's 50-horse power oscillating 
 engine, the diameter of the cylinder is 3ft. 4 in., and 
 the length of the stroke 3 ft. The thickness of the 
 metal of the cylinder is 1 in., and the thickness of the 
 cylinder bottom is 1| in., crossed with feathers, to give 
 it additional stiffness. The diameter of the trunnion 
 bearings is 1 ft. 2 in., and the breadth of the trunnion 
 bearings 5 J in. 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 trun- 
 nion is regulated by the internal diameter of the educ- 
 tion pipe, whidi is about one-fifth 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, 
 ^d of the area of the cylinder. In the oscillating 
 engines of the Oberon, by Messrs. Rennie, the cylinder 
 is 61 in. diameter, and l^in. thick above and below 
 the belt, but in the wake of the belt it is l^in. thick, 
 which is also the thickness of metal of the belt itself. 
 The internal depth of the belt is 2ft. 6 in., and its 
 internal breadth is 4 in. The piston rod is 6| in. in 
 
190 A CATECHISM OF 
 
 diameter, and the total depth of the cylinder stuffing 
 box is 2ft. 4 in., of which 18 in. consists of a brass 
 bush ; this depth of bearing being employed to prevent 
 the stuffing box or cylinder from wearing oval. It is 
 expedient, in oscillating engines, to form the piston 
 with a projecting rim round the edge above and be- 
 low, 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. The diameter of 
 cylinders of the oscillating engines of the steamers 
 Pottinger, Ripon, and Indus, by Miller and Ravenhill, 
 is 76 in., and the length of the stroke is 7 ft. The 
 thickness of the metal of the cylinder is l^J in. ; dia- 
 meter of the piston rod 8 J in. ; total depth of cylinder 
 stuffing box 3 ft. ; depth of bush in stuffing box 4 in. ; 
 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 in. ; diameter of steam trunnion 
 journal 25 in. ; diameter of eduction trunnion journal 
 25 in. ; thickness of metal of trunnions 2J in. ; length 
 of trunnion bearings 11 in. ; projection of cylinder 
 jacket, 8 in. ; depth of packing space in trunnions 
 10 in. ; width of packing space in trunnions, or space 
 round the pipes, 1| in. ; diameter of crank pin 10^ in. ; 
 length of bearing of crank pin 15 J in. There are six 
 boilers on the tubular plan in each of these vessels ; 
 the length of each boiler is 10 ft. 6 in., and the breadth 
 8 ft., and each boiler contains 62 tubes 3 in. in dia- 
 meter, and 6ft. 6 in. long, and two furnaces 6ft. 4 in. 
 long, and 3ft. IJin. broad. In all oscillating engines 
 
THE STEAM ENGINE. 191 
 
 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. 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 impos- 
 sible to prevent the trunnion packings from leaking. 
 
 158. Q. How do you set out the trunnions of 
 oscillating engines, so that they shall be at right angles 
 with the interior of the cylinder ? 
 
 A. 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 
 
192 A CATECHISM OP 
 
 a small indentation in the middle to receive the centre 
 of a lathe, and adjusting screws to bring the centre 
 into any required position. Tin cylinder must then 
 be set in the 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 sta- 
 tionary, 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. 
 
 159. Q. Is it a beneficial practice to make cy- 
 linders with steam jackets? 
 
 A. In Cornwall, where great attention is paid to 
 
THE STEAM ENGINE. 193 
 
 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 with- 
 out one. The exterior of the cylinder, or jacket, 
 should be covered with several plies of felt, and then 
 be cased in timber, the boards, which must be very 
 narrow, 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 economization 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 ad- 
 mission 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 
 o 
 
194 A CATECHISM OF 
 
 the lateral pressure of the piston rod, and thus take 
 any strain off the packing. 
 
 160. Q. Can you give a rule for determining the 
 thickness of the cylinder and of the trunnion bearings 
 in oscillating engines ? 
 
 A. In low pressure engines, whether oscillating 
 or otherwise, the thickness of metal of the cylinder 
 should be about ^th of the diameter of the cylinder, 
 which, with a pressure of steam of 201bs. above the 
 atmosphere, will occasion a strain of only 400 Ibs. per 
 square inch of section of the metal ; the thickness of 
 the metal of the trunnion bearing should be ^d 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 -j^th its diameter, which, with a pressure of 
 steam of 80 Ibs. upon the square inch, will occasion a 
 strain of 640 Ibs. 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 
 a Vth of the diameter of the cylinder. It is very 
 doubtful whether the steam trunnions of a high pres- 
 sure 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. 
 
 161. Q. "Will you explain the various stages of 
 the manipulation connected with the preparation of 
 cylinders ? 
 
 A. In the first place the cylinder has to be cast. 
 The mould into which the metal is poured is built up 
 
THE STEAM ENGINE. 195 
 
 of bricks and loam, which is clay and sand ground to- 
 gether 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 in- 
 side 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 pro- 
 jections 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 num- 
 ber of cylinders of the same kind are required, it is ad- 
 visable to make these patterns of iron, which will not 
 be liable to warp or twist while the loam is being 
 dried. 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 compo- 
 sition 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 
 o 2 
 
196 A CATECHISM OF 
 
 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 
 appears to become greater as the specific gravity be- 
 comes 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 in 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, and the 
 expense of such a preparation would not be consider- 
 able, as, by subsequent evaporation, the salt might be 
 used over and over again for the same purpose. Be- 
 fore 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 ju- 
 
THE STEAM ENGINE. 197 
 
 diciously 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. The next stage is the boring, and in 
 boring cylinders of 74 in. diameter, the boring bar must 
 move so as to make one revolution in about 4 minutes, 
 at which speed the cutters will move at the rate of 
 about 5 ft. 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 ft. 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 J in. diameter requires the bar to make one turn in 
 about three minutes, which is also the speed proper 
 for a cylinder 60 in. in diameter. To bore a brass 
 air pump 36J in. in diameter requires a week, an iron 
 one requires 48 hours, and a copper one, 24 hours. 
 In turning a malleable iron shaft 12 Jin. in diameter 
 the shaft should make about five turns per minute, 
 which is equivalent to a speed in the tool of about 16 
 ft. per minute. 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 ordi- 
 nary wants that can occur in practice. Messrs. Penn 
 grind their cylinders after they are bored, by laying 
 them on their side, and rubbing a piece of lead smeared 
 with emery and oil, and with a cross iron handle 
 like that of a rolling stone, backwards and forwards 
 o 3 
 
193 A CATECHISM OF 
 
 the cylinder being gradually turned round so as to sub- 
 ject 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 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 impos- 
 sible to bore a large cylinder in a horizontal mill with- 
 out 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 it 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. Nor is it 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's weight. 
 
 162. Q. Have you anything further to add upon 
 the subject of cylinders ? 
 
 A. Nothing that may not be stated in a few 
 words. Locomotive 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 
 
THE STEAM ENGINE. 199 
 
 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 
 operation of priming 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 opera- 
 tion of facing, 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 re- 
 movable, 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's engines, however, with variable 
 expansion, there is but one cock provided for this pur- 
 pose, which is on the bottom of the valve chest. 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 
 
 o 4 
 
200 A CATECHISM OF 
 
 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 cy- 
 linder 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 ex- 
 ceeding that of the steam is created in the cylinder by 
 priming or otherwise, should be provided with an es- 
 cape 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 con- 
 ducted 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 fre- 
 quently 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 
 
THE STEAM ENGINE. 201 
 
 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 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 of 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 round 
 the cylinder to take the strain, and this will in all 
 cases be the preferable expedient, where, from any pe- 
 culiarities of structure, there is a difficulty in intro- 
 ducing bolts and keys. 
 
 163. Q Which is the most eligible species of pis- 
 ton? 
 
 A. For large engines, pistons with a metallic pack- 
 ing, consisting of a single ring, with the ends morticed 
 into one another, and a piece of metal let in flush over 
 
202 A CATECHISM OF 
 
 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 thick- 
 ness 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 ham- 
 mer, to expand the metal, and thus increase the elasti- 
 city. The rings are then 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 
 
THE STEAM ENGINE. 203 
 
 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 spring is used, provided they have sufficient tension. 
 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, and 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 dis- 
 
204 A CATECHISM OF 
 
 position 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. Jn a good example of an engine thus 
 provided, the piston rod is 7 in. in diameter, and the 
 screw o in., the part of the rod which fits into the cross 
 head eye is 1 ft. oj in. long, and tapers from 6^ in. to 
 6^-f 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 untaperecl, as is 
 sometimes the case, it is very difficult to detach the 
 parts from one another. 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. 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 scrap- 
 ing is now chiefly relied on. Some makers, however, 
 finish their steam surfaces by grinding them with pow- 
 dered 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 conve- 
 niently accomplished by setting the piston on a revolv- 
 ing 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 posi- 
 tion, 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. 
 Messrs. Penn's piston for oscillating engines has a single 
 
THE STEAM ENGINE. 205 
 
 packing ring, with a tongue piece, or mortice end, made 
 in the manner already prescribed. The ring is packed 
 behind with hemp packing, and the piece of metal 
 which covers the joint is a piece of thick sheet copper, 
 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. 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 
 j oint, are preferable to those which consist of many pieces. 
 In Stephenson's pistons the screws are liable to work 
 slack, and the springs to break. The piston rods of all 
 engines are now 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 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 con- 
 necting rod, while the ends of the cross heads move in 
 
206 A CATECHISM OF 
 
 guides. Between the piston rod clutch and the guide 
 blocks, the feed pump rod joins the cross head in some 
 engines. 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 brushes 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. 
 
 164. Q. Will you explain the method of fitting 
 together the valve and cylinder faces ? 
 
 A. Both faces must first be planed, then filed ac- 
 cording 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 colour upon the prominent 
 
THE STEAM ENGINE. 207 
 
 points. This operation is to be repeated frequently, 
 and as the work advances, the quantity of colouring 
 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 colouring 
 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 colouring matter in the 
 latter stages, would destroy the delicacy of the test 
 the face plate affords. 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. A flat file bent, and sharpened at the 
 end, makes an eligible scraper for the first stages ; 
 and a three-cornered file, sharpened at all the corners, 
 is the best instrument for finishing the operation. The 
 number of bearing points which it is desirable to esta- 
 blish 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. It has already been stated, that in the 
 preparation of valve faces it is necessary to take into 
 account the strain which the metal suffers from its 
 own weight ; and, it may be added, that the change 
 of figure consequent thereupon is not instantaneous, 
 but becomes greater after some continuance of the 
 
208 A CATECHISM OF 
 
 strain than it was at first, so that in gauging a cylin- 
 der 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. 
 Face plates, or planometers, as they are sometimes 
 termed, are supplied by most of the makers of engi- 
 neering 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 use of testing, from time to 
 time, the accuracy of those in use. In fitting the 
 faces of a D valve, great care must be taken that the 
 valve be not made conical ; 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. 
 Should a hole occur either in the valve, in the cylin- 
 der, 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 afterwards 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, where- 
 by 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 dove- 
 
 
THE STEAM ENGINE. 209 
 
 tailed, and the pieces thus fitted will never come out. 
 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. Much trouble is experienced with every 
 modification of valve face ; but cast-iron working upon 
 cast-iron is, perhaps, the best combination yet intro- 
 duced. 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. 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 ; 
 p 
 
210 A CATECHISM OF 
 
 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. In some engines the 
 valve rod is fitted with a parallel motion, provision 
 being made for the attachment of its standards on the 
 valve cover ; but more frequently guides are employed. 
 In those long D valves in which exhaustion is per- 
 formed from below, it is expedient to cast two pro- 
 jections on the sole plate, to prevent the valve from 
 falling down inconveniently far when the valve links 
 are taken off. In locomotive engines, the valve uni- 
 versally employed is the three-ported valve as already 
 explained. 
 
 165. Q. What is the most beneficial construction 
 of slide valve ? 
 
 A. 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 the 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 
 
THE STEAM ENGINE. 211 
 
 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. 
 
 166. Q. Will you describe the configuration and 
 mode of attachment of the eccentric by which the 
 valve is moved ? 
 
 A. In marine engines, the eccentric is 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 a-head, or in that for 
 going a-stern. 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 prefer- 
 able to round pins in this arrangement, as the pins 
 tend to wedge the jaws of the eccentric asunder. In 
 
212 A CATECHISM OF 
 
 some cases the halves of the eccentric are bolted to- 
 gether, 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 eccen- 
 tric 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. In locomotives the 
 structure and attachments of the eccentric differ some- 
 what from the foregoing. The body of the eccentric 
 here also is of cast-iron, but the eccentric hoops are 
 o-enerally of wrought-iron, as brass hoops are found 
 liable to break. In inside cylinder engines the eccen- 
 trics 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 
 
THE STEAM ENGINE. 213 
 
 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 afterwards filled by inserting a dove-tailed 
 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 sub- 
 stantial, and cases are perpetually occurring, when 
 this method of attachment is adopted, of eccentrics 
 shifting from their place. In the'Kouen engines with 
 straight axles, the four eccentrics are cast in one 
 piece. When the eccentric hoops are formed of mal- 
 leable 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 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 ad- 
 justment 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 
 
 v 3 
 
214 A CATECHISM OF 
 
 rod is determined. The forks of the eccentric rod are 
 of steel ; the length of the eccentric rod is the distance 
 between the centre of the crank axle, and the centre 
 of the valve shaft. The valve lever in locomotives is 
 usually longer than the eccentric lever, to increase the 
 travel of the valve. The pins of the eccentric lever wear 
 quickly ; Stephenson puts a ferrule of brass on these 
 pins, which being loose, and acting like a roller, faci- 
 litates the throwing in and out of gear, and when worn 
 can easily be replaced, so that there need be no ma- 
 terial derangement of the motion of the valve from 
 play in this situation. 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 seg- 
 ments 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. 
 
 167. Q. Will you explain the operation of ex- 
 pansion valves ? 
 
 A. Expansion valves have the effect of closing the 
 steam passage leading to the cylinder before the 
 stroke of the piston is completed, whereby the steam 
 shut within the cylinder is enabled to expand, and 
 the mechanical efficacy of a given bulk of steam is 
 
THE STEAM ENGINE. 215 
 
 increased by the average pressure of the expanding 
 steam, multiplied by the distance through which it 
 has urged the piston. The structure of expansion 
 valves is very various : some are slide valves, but the 
 expansion valve commonly used in marine engines is 
 of the kind used in the Cornish engines, and known 
 as the equilibrium valve ; and 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 Ings, 
 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 at- 
 tache.d to the same shaft. 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 commu- 
 nicated to the valve. The position of this projection 
 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 circum- 
 stances, 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 grade, as it is usually called, of 
 expansion. These grades all begin at the same point 
 p 4 
 
216 A CATECHISM OF 
 
 on the cam, but are of different lengths, so that they 
 would begin to move the lever at the same time, but 
 would differ in the time of returning it to its original 
 position. The change of expansion is effected by 
 moving the roller on to the desired grade ; which is 
 accomplished by slipping the lever carrying the roller 
 endways on the shaft or pin sustaining it. In loco- 
 motive engines, where the use of cams is inadmissible, 
 other expedients are employed, of which those con- 
 trived by Stephenson and by Cabrey operate on the 
 principle of accomplishing the requisite variations of 
 expansion by altering the throw of the slide valve. 
 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 ec- 
 centric 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. 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. Both Stephen- 
 son's and Cabrey's expansion gear are inferior in effi- 
 cacy to those which operate by the aid of a separate 
 valve. Gonzenbach's arrangement consist of an addi- 
 
THE STEAM ENGINE. 21 7 
 
 tional 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 deter- 
 mines the throw of the supplementary valve, and the 
 consequent degree of expansion. The other end of 
 the lever is provided with a pin, which gears into a 
 notch on the backward eccentric rod, when that rod 
 is not in gear with the steam valve. By this arrange- 
 ment, while the steam valve receives as usual the 
 motion of the forward eccentric, the expansion valve 
 receives the motion of the reversing eccentric. In 
 the expansion gear of Meyer, the steam valve is a 
 plate perforated by two ports, which are covered by 
 two blocks working upon the back of the valve, and 
 retained on a spindle which screws into both blocks, 
 but in one with a right-handed screw, and in the 
 other with a left-handed screw, so that by turning 
 the spindle the distance between the blocks may be 
 increased or diminished, and the degree of expansion 
 altered accordingly. The amount of expansion may 
 also be varied by means of a moveable plate, which, 
 by closing the port more or less, and wire-drawing 
 the steam, will accomplish the amount of expansion 
 which is desired. 
 
 168. Q. What are the details of the air pump ? 
 
 A. The air pump bucket and valves are all of 
 brass in all modern engines, and the chamber of the 
 pump is lined with copper, or made wholly of brass, 
 whereby a single boring suffices. When a copper 
 
218 A CATECHISM OF 
 
 lining is used, the pump is first bored out, and a bent 
 sheet of copper is introduced, which is made accu- 
 rately to fill the place, by hammering the copper on 
 the inside. Air pump rods of Muntz'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'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. Me- 
 tallic 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. A deep solid 
 block of metal however, without any packing, has in 
 a few instances been employed with a satisfactory 
 result. 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. The bucket-valve is generally 
 of the spindle or pot-lid kind, but butterfly valves are 
 
 
THE STEAM ENGINE. 219 
 
 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'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 pro- 
 bable that their operation would be more satisfactory 
 than that of the valves usually employed. Some de- 
 livery valve seats are bolted into the mouth of the air 
 pump, whereby access to the pump bucket is rendered 
 difficult. 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, Messrs. 
 Maudslay employ two or more concentric ring valves, 
 with a small lift. These valves have given a good 
 
220 A CATECHISM OP 
 
 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 supe- 
 rior to that of any of the other air-pump valves at pre- 
 sent in common use. 
 
 169. Q. What' are the most important details of 
 the construction of paddle wheels? 
 
 A. The structure of the feathering wheel has 
 already been described in connexion with a description 
 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 heads 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 pro- 
 jections on it, so as to be suitable for the application 
 of centres with square eyes. Messrs. Maudslay and 
 Co. bore out their paddle centres, and turn a seat for 
 them on the shaft, afterwards 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 irremoveable. 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 
 
THE STEAM ENGINE. 221 
 
 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. A 
 preferable way would be to form the paddle centre out 
 of the arms themselves, by widening them at the head 
 until they touch one another, and then applying a 
 boiler plate upon one side, and rivetting the arms 
 firmly to it. If this plan be adopted, it will be ex- 
 pedient to swell the tops of the uncovered side at the 
 part nearest the centre of the shaft. In the manu- 
 facture of this centre, the heads of the arms would 
 first be forged, then planed on the edges, and fitted 
 together on the plate. The holes would then be bored 
 for the rivets, temporary bolts fitted into them, and the 
 key-seats cut, and the ends of the arms pared in the 
 slotting machine. Finally, the arms would be welded 
 on to the heads, and the various parts of the wheel 
 riveted together. Some engineers join the paddle arms 
 to the outer ring by means of bolts ; but those bolts 
 after a time generally become slack sideways, and a 
 constant working of the parts of the wheel goes on in 
 consequence. Sometimes the part of the outer ring 
 opposite the arm is formed into a mortice, 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, 
 
222 A CATECHISM OF 
 
 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. 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 2J 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. 
 Whenthe 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. 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. 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 project- 
 ing part of the float, being unsupported, is liable to be 
 broken off. 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 arrange- 
 ment 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, we conceive, 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 
 
THE STEAM ENG1XE. 223 
 
 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'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'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. 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. 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. Paddle 
 floats, when consisting of more than one board, should 
 be bolted together edgeways, by means of bolts running 
 through their whole breadth. 
 
 170. Q. Will you describe the structure and 
 
224 A CATECHISM OF 
 
 arrangement of the pumps, pipes, and cocks of loco- 
 motive and marine engines ? 
 
 A. 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's engines they are worked 
 by rods attached to eyes on the eccentric hoops. 
 There is a ball valve 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'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 to- 
 gether 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. 
 Spindle valves have in some cases been used instead 
 
THE STEAM ENGINE. 225 
 
 t>f ball valves, but they are more subject to derange- 
 ment ; 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 easily be applied, and 
 would probably be found preferable to any of the ex- 
 pedients at present in use. It would be a material 
 improvement if the feed pumps were 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 lo- 
 comotives 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 ap- 
 pears expedient, therefore, that the pumps should be 
 far from the boiler, and should be set among the feed 
 water, so that they will only have to force. If the 
 pumps were 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 
 one pump still wrought in the usual way by the en- 
 gine, in case of derangement of the other, or in case 
 the pump in the tender might freeze. The pipes con- 
 necting the tender with the pumps should allow access 
 to the calves 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 be- 
 tween the engine and tender must be made in this 
 fashion. The feed pipe of most locomotive engines 
 enters the boiler near the bottom, and about the 
 
226 A CATECHISM OF 
 
 middle of its length. In Stephenson'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. 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 be- 
 tween 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 
 spring 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 side 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 de- 
 scending, 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 
 
THE STEAM ENGINE. 227 
 
 topmost valve, which is loaded to a pressure consider- 
 ably above the pressure of the steam, and escape into 
 the hot well. This arrangement is neater and less ex- 
 pensive than that of having a separate loaded valve on 
 the steam pipe, with an overflow through the ship's 
 side, as is the more usual practice. To enable the 
 boilers to be fed in steam vessels, there is a separate 
 pump provided distinct from the engines, and which 
 may be worked by men standing on the deck by means 
 of appropriate handles, and this pump, in addition to 
 its function of replenishing the boilers, is used to wash 
 the decks, or as a fire engine to quench accidental fire. 
 For that purpose, a double acting feed pump of the 
 plunger kind is preferable to one which operates by a 
 piston. The air vessel of the pump should be furnished 
 with an escape valve to prevent the pump from being 
 split, should it be put in connexion with the engine 
 when the cocks in the pipe leading to the boiler are 
 closed, an accident which not unfrequently happens. 
 In this species of pump, the application of a four way 
 cock enables the pump to draw from the sea, from the 
 boiler, or from the bilge, and the pump can deliver 
 either into the boiler or upon deck. In most of the 
 new vessels fitted with tubular boilers, small engines 
 have been introduced to pump water into the boiler 
 when the vessel stops under steam. Most of these 
 engines are furnished with a crank and fly wheel ; 
 but as there is no strain on the fly wheel shaft, the 
 crank is connected to the piston rod by means of a 
 horizontal slot. In some steam vessels floats have 
 been introduced to regulate the feed, but their action 
 cannot be depended on in agitated water, if applied 
 Q 2 
 
228 A CATECHISM OF 
 
 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, 
 which would otherwise impair the action of the appa- 
 ratus. The admission of feed water into the boiler is 
 sometimes regulated by cocks, and sometimes by 
 spindle valves raised and lowered by a screw. Cocks 
 appear to us 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. 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 arrange- 
 ment being to prevent the rising steam from being 
 condensed by the entering water. By being intro- 
 duced 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 tempera- 
 ture, 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 usually fed by a head of water, the feed 
 water being forced up into a small tank, from whence 
 
THE STEAM ENGINE. 229 
 
 it descends into the boiler by the force of gravity, 
 while the surplus runs to waste, as in the feeding ap- 
 paratus of land engines. 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 shut- 
 ting 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's side, 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 put 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's sides, is furnished 
 with a cock ; and in modern steam vessels Kingston'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 occa- 
 sional re-grinding, and the sea cocks cannot be re- 
 ground without putting the vessel into dock, except 
 by the use of Kingston's valves, or some equivalent 
 Q 3 
 
230 A CATECHISM OF 
 
 expedient. 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 water-ways 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 
 
 
THE STEAM ENGINE. 231 
 
 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 water-way 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. 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 ap- 
 pertaining to each boiler into a single upright tube, 
 connected suitably with the boiler, and the water 
 flowing from them could be directed downwards 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, un- 
 less 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, 
 Q 4 
 
232 A CATECHISM OF 
 
 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 them- 
 selves. 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. 
 The sea injection cocks are usually made in the same 
 fashion as the sea blow-oif cocks, and of about the 
 same size. 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. 
 The sea injection pipes should be put through the 
 ship'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'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 harbour. Where the pipes pierce 
 the ship's side, they 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 
 
THE STEAM ENGINE. 233 
 
 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 pro- 
 jecting 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 pro- 
 cedure, 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 pre- 
 vent 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'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'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 
 inwards, to 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. Marine boilers are now generally 
 supplied with stop valves, whereby one boiler may be 
 
234 A CATECHISM OF 
 
 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, connect- 
 ing 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 im- 
 possible after some time to shut them on an emer- 
 gency. These valves should always be easily acces- 
 sible from the engine-room ; and it ought not to be 
 necessary for the coal boxes to be empty to gain access 
 to them. The pipes of marine engines should always 
 be made of copper. Cast-iron blow-off pipes have in 
 some cases been employed, but they are liable to frac- 
 ture, and are dangerous. Every pipe passing through 
 the ship's side, and every pipe fixed at both ends, and 
 liable to be heated and cooled, should be furnished 
 with a faucett or expansive joint ;. and in the case of 
 cast-iron pipes, the part of the pipe fitting into the 
 faucett should be turned. In the distribution of the 
 faucetts 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 by the strain, as serious ac- 
 cidents have occurred from the neglect of this precau- 
 tion. 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 
 
THE STEAM ENGINE. 235 
 
 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 con- 
 necting links between its outer edges, or by its central 
 spindle. In some of Stephenson's engines with varia- 
 ble expansion gear, 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'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's engines a sort of conical plug is 
 used, which is withdrawn by turning the handle in 
 front of the fire box : a spiral groove of 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 
 
236 A CATECHISM OF 
 
 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. 
 
 171. Q. Will you enumerate the most interesting 
 details which occur to you in connexion with the 
 structure of locomotives ? 
 
 A. 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. A similar 
 diversity of opinion obtains at present as to the relative 
 merits of outside and inside cylinders, the outside 
 cylinders being 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. 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 setting the crank pins nearly in the 
 same line instead of at right angles, or by placing a 
 weight upon one side of the wheels, the momentum of 
 which will just balance the momentum of the piston 
 and its connexions. 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 
 
THE STEAM ENGINE. 237 
 
 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 realised by placing one 
 cylinder in the centre of the carriage, and two at the 
 sides the pistons of the side cylinders moving simul- 
 taneously : 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's 
 later engines, involves too much complication to be a 
 beneficial innovation. It is difficult, in engines in- 
 tended for the narrow gauge, to get cylinders within 
 the framing of sufficient diameter to meet the exi- 
 gencies of railway locomotion ; by casting both cy- 
 linders 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 
 
238 A CATECHISM OF 
 
 length, the frames being curved upwards 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 at 
 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. 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 spring, 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 at the ends with light 
 loads, but would be brought into contact gradually, 
 as the strain comes on : a spring would thus be ob- 
 tained that was suitable for all loads. Behind the 
 locomotive runs another carriage, called a tender, for 
 holding coke and water. A common mode of con- 
 necting the engine and tender is by means of a rigid 
 bar, with an eye at each end through which pins are 
 
THE STEAM ENGINE. 239 
 
 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. In most engines a 
 bar is strongly attached to the front of the carriage on 
 each side, and projects perpendicularly downwards to 
 \\ithin a short distance of the rail, to clear away stones 
 or other obstructions that might occasion accidents if 
 the engine ran over them. 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 up on it. The upper part of 
 the box in most engines has a reservoir of oil, which 
 is supplied to the journal by tubes with syphon 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 ia 
 the brass. Any engines constructed with outside 
 bearings have inside bearings also, which are sup- 
 ported 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. The wheels of a locomotive are always 
 made of malleable iron. The driving wheels are made 
 large 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 con- 
 structive details : sometimes they are made with cast- 
 iron naves, with the spokes and rim of wrought-iron ; 
 
240 A CATECHISM OF 
 
 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 founders' 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. 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 STEAM ENGINE. 241 
 
 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 afterwards 
 tempered. It is not indispensable that the whole tire 
 should be of steel ; but a dove-tail 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 par- 
 ticular care must be taken to attach these pieces very 
 securely to the tire by rivets, else in the rapid revo- 
 lution 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. 
 The tire is attached to the rim with rivets havin- 
 
 O 
 
 counter-sunk heads, and the wheel is then fixed on its 
 axle. 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 up- 
 right, but are slightly inclined inwards, in consequence 
 of which the wheels must be either conical or slightly 
 dished, to bear fairly upon the rails. One benefit of in- 
 clining the rails in this way, and coning the tires, is that 
 
242 CATECHISM OF 
 
 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. Much controversial ingenuity has been 
 expended upon the question of the relative merits of 
 the four and six-wheeled engines; one party main- 
 taining that four-wheeled engines are most unsafe, and 
 the other that six-wheeled engines are un-mechanical, 
 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 con- 
 nexion may be made between the tender and the en- 
 gine, 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 connexion. 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 
 
THE STEAM ENGINE. 243 
 
 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. Stephen- 
 son makes his driving wheels without flanges, to fa- 
 cilitate the passage of the engine round curves ; and 
 if six-wheeled engines be made at all, it appears ex- 
 pedient to construct them in that manner; but in- 
 stead of making enormously heavy six-wheeled en- 
 gines, it appears the preferable alternative to use four- 
 wheeled engines of a moderate weight, and to apply 
 a sufficient number of them to a train, to enable it 
 to reach the required velocity. To this arrangement 
 there is no doubt the objection, that the expense of 
 the propelling power is greater, as a small engine 
 requires a driver and stoker for itself as well as a 
 large engine ; but by making the tender double, with 
 one engine before it and another behind it, a single 
 driver and a single stoker would suffice for the two 
 engines. The starting handles of both engines might 
 be brought to the middle of the tender, so that the 
 engines might be started simultaneously, and be 
 made to act in this respect like a single engine. This 
 arrangement appears to me to be greatly preferable 
 
 R 2 
 
244 A CATECHISM OF 
 
 to that of making heavy six- wheeled engines, as the 
 rail will be preserved from the injurious effects of 
 excessive weight, and there will be less loss of power 
 in contracting the blast pipe, when the fire and flue 
 surface is increased by the addition of another engine. 
 Tenders are now made larger than heretofore to ob- 
 viate the necessity of so many coke and water stations ; 
 they should have glass windows all round them to 
 shield the engine driver, and enable him during the 
 worst winds and rains to keep a steady look out. 
 Tenders may be put on any number of wheels, so that 
 inconvenience is not likely to arise from their size and 
 weight. The cranked axle of locomotives is always 
 made of wrought-iron, with two cranks forged upon it 
 towards 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 afterwards welded together. Some- 
 times 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 
 ergines which have been in use for some time, how- 
 ever, 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 
 
THE STEAM ENGINE. 245 
 
 violent ; but this evil may be remedied by making the 
 bearings spheroidal, whereby end play becomes im- 
 possible. In every kind of locomotive it is very de- 
 sirable 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 economise steam. 
 In some engines the strap encircling the crank pin is 
 fixed immoveably to the connecting rod by dovetailed 
 keys, and a bolt passes through the keys, rod, and 
 strap, to prevent the dovetail 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 
 crosshead 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. 
 
 172. Q. Will you explain in what manner the 
 joints of an engine are made ? 
 
 A. 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 
 
 R 3 
 
246 A CATECHISM OF 
 
 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 the 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 some- 
 times occur, though Roman cement appears to be 
 nearly as effectual. 
 
 ]73. Q Will you explain the method of case- 
 hardening the parts of engines ? 
 
 A. The most common plan for case-hardening 
 consists in the insertion of the articles to be operated 
 upon among horn or leather cuttings, bone dust, or 
 animal charcoal, in an iron box provided with a tight 
 lid, which is then put into a furnace for a period an- 
 swerable to the depth of steel required. In some cases 
 the plan pursued by the gunsmith may be employed 
 
THE STEAM ENGINE. 247 
 
 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 pos- 
 sible, and kept half an hour at a uniform heat : its con- 
 tents 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 ; never- 
 theless, upon all parts not exposed to wear, a sufficient 
 coating of steel may be obtained by this process. 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 repre- 
 hended, 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 
 a 4 
 
248 A CATECHISM OF 
 
 figure. In some cases, case-hardening lias caused such 
 a twisting of the parts of an engine that they could 
 not afterwards be fitted together ; it is preferable, 
 therefore, to make such parts as are to be case-har- 
 dened to any considerable depth of Lowmoor iron, 
 which being homogeneous will absorb carbon equally, 
 and will not twist. 
 
 174. Q. What is the composition of the brass used 
 in the construction of engines ? 
 
 A. The brass bearings of an engine are composed 
 principally of copper and tin : the ordinary range of 
 good yellow brass that files and turns well, is about 
 4J to 9 oz. of zinc to the pound of copper. 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'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^ oz. to 5 oz. of tin to the pound of copper ; speculum 
 metal consists of from 7Joz. to 8* oz. of tin to the 
 pound of copper ; tough brass for engine work, 1 ^ Ib. 
 tin, IJlb. zinc, and lOlbs. copper; brass for heavy 
 bearings, 2 1 oz. tin, -1 oz. zinc, and 1 Ib. copper. There 
 is a great difference in the length of time brasses wear, 
 as made by different manufacturers ; but the difference 
 
 
THE STEAM ENGINE. 249 
 
 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 fric- 
 tion and the wear. Babbitt's patent lining metal for 
 bushes has latterly been introduced in the bushes of 
 locomotive axles and other machinery ; it is composed 
 of 1 Ib. of copper, 1 Ib. regulus of antimony, and 10 Ibs. 
 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 
 portion of tin ; charcoal being strewed over the sur- 
 face 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 
 I to fin. 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. 
 
250 A CATECHISM OF 
 
 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. 
 
 175. Q. Have you any information to offer re- 
 lative to the lubrication of engine bearings ? 
 
 A. A very useful species of oil cup is now em- 
 ployed . 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 hang- 
 ing wires touch. By this plan, however, the oil is 
 not well supplied at slow speeds, as the drops fall 
 before the wires are in the 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 
 
THE STEAM ENGINE. 251 
 
 uppermost, and delivers the oil through the bottom 
 pipe when it comes opposite to it. 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 of 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 pur- 
 sued. 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 downwards. 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. 
 
 176. Q. Will you explain the operation of erect- 
 ing engines in the workshop ? 
 
 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 raising 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 
 
252 A CATECHISM OF 
 
 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 hori- 
 zontal 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 pre- 
 viously 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 
 
THE STEAM ENGINE. 253 
 
 that have to be dealt with. It will be proper how- 
 ever to describe the method pursued in erecting oscil- 
 lating engines. The columns here are of wrought 
 iron, and in the case of small engines there is a tem- 
 plate 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 exacti- 
 tude. 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 
 
254 A CATECHISM OF 
 
 cylinder, and measuring from the cylinder flange 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 upon 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 dis- 
 tance from the centre line of the beam when level, 
 to the centre of the cross head when tjie piston is at 
 half stroke. The length of the radius rods of the 
 parallel motion is the distance from the point of attach- 
 ment 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 pa- 
 rallel motion attached to the cross head, it is the distance 
 
THE STEAM ENGINE. 255 
 
 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 to- 
 gether 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 perpen- 
 dicular 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. 
 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. 
 
 177. Q. Will you explain how the slide valve 
 of an engine is set ? 
 
 A. 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 
 
256 A CATECHISM OF 
 
 the crank shaft, on the sole plate of the engine, or on 
 the cylinder mouth if the engine be direct action ; de- 
 scribe 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 a-stern, shifting round the eccentric 
 to the opposite side of the shaft, until the rod again 
 falls into gear. In setting valves, regard must be had 
 to the kind of engine, the arrangement of the levers, 
 and the kind of valve employed. In setting the valves 
 of locomotives a similar method is adopted : place the 
 crank in the position answerable to the end of the 
 stroke of the piston, and draw a straight line, repre- 
 senting 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 to represent 
 the crank shaft, and a third circle to represent the 
 path of the crank pin. From the centre of the crank 
 
THE STEAM ENGINE. 257 
 
 shaft, draw a line perpendicular to the centre line of 
 the cylinder and crank shaft, and draw another per- 
 pendicular 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 pre- 
 cedes 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 at- 
 tachment to the valve the eccentric is set more than 
 one-fourth of a revolution in advance of the crank, 
 and with an indirect attachment the eccentric is set 
 less 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 connexion ; 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 lead, and this is effected by the 
 plan just described. In working locomotives the ec- 
 centrics sometimes shift upon the shaft, in which case 
 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 
 
258 A CATECHISM OF 
 
 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 repre- 
 senting 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 this parallel intersects 
 the circle of the eccentric are the positions of the 
 forward and backward eccentrics. Through these 
 points draw radial lines from the centre of the circle, 
 and mark the intersections 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 
 intersections and the diameter which is at right angles 
 with the crank; and the diameters being first marked 
 on the shaft itself, it will follow that by transferring 
 with the compasses the distance found in the diagram, 
 and marking the point, the position of the eccentric 
 will be fixed without difficulty. 
 
 178. Q. Will you explain the method of putting 
 engines into a steam vessel ? 
 
 A. 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 mea- 
 sure 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 STEAM ENGINE. 259 
 
 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 conve- 
 nient 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 
 s 2 
 
260 A CATECHISM OF 
 
 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 dis- 
 tance is preserved between the fore and aft line upon 
 the sole plate, and the fore and aft line upon the central 
 keelson. 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 car- 
 ried forward beyond its place by the framing shoul- 
 dering 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 squared 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 be- 
 tween 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 end, and the 
 two horizontal centres ; if not, move the end of the 
 paddle-shaft up or down, backwards or forwards, until 
 
THE STEAM ENGINE. 261 
 
 the distance between the cranks at all the four centres 
 is the same. 
 
 179. Q. In what manner are the engines of a 
 steam- vessel secured to the hull ? 
 
 A. The engines of a steamer are secured to the 
 hull by means of bolts called holding down bolts, and 
 in most steam 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 keel- 
 son, a recess being made in the floor or timbers to 
 admit of the introduction of a nut. The iron, how- 
 ever, wears rapidly away in both cases, even though 
 the bolts are tinned ; and it has been found the pre- 
 ferable method to make such of the bolts as pass 
 through the bottom, or enter the bilge, of Muntz's 
 metal, or of copper. In a side lever engine, four 
 Muntz'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 cy- 
 linder, 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 keel- 
 sons 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 
 
 s 3 
 
262 A CATECHISM OF 
 
 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. In well formed bolts, the spiral 
 groove penetrates about one-twelfth of the diameter 
 of the cylinder round which it winds, so that the dia- 
 meter 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 Ibs. on 
 the square inch, then 2, 180 Ibs. 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 expe- 
 dient very much to exceed this strength in practice, 
 on account of the elasticity of the keelsons, the lia- 
 bility to corrosion, and other causes. It is difficult 
 to fix engines effectually which have once begun to 
 work in the ship, for in time the surface of the keel- 
 sons 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's bottom, 
 there should be a large number of wood screws se- 
 curing 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 ex- 
 
THE STEAM ENGINE. 263 
 
 pedient; 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. 
 
 180. Q. What are the most important of the 
 points which suggest themselves to you, in connexion 
 with the management of marine engines ? 
 
 A. The attendants upon engines should prepare 
 themselves for any casualty that may arise, by con- 
 sidering possible cases of derangement, and deciding 
 in what way they would act should certain accidents 
 occur. The course to be pursued must have refer- 
 ence 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 every thing may depend upon his energy 
 and decision. 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 chim- 
 ney 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 
 s 4 
 
264 A CATECHISM OP 
 
 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 ori- 
 ginal 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. If the crank 
 pin breaks, the other engine must be worked with the 
 one wheel. 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 pis- 
 ton 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'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. 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 connexion 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 
 
THE STEAM ENGINE. 265 
 
 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. 
 If the shafts or cranks break, the engine may never- 
 theless be worked with moderate pressure to bring 
 the vessel into port ; but if the crank 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 dis- 
 covered in any of the main parts of the engine, whe- 
 ther 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. 
 
 181. Q. What are the chief duties of the engine 
 driver of a locomotive ? 
 
 A> The engineer of a locomotive should constantly 
 be upon the foot-board of the engine, so that the regu- 
 lator, 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 
 
266 A CATECHISM OF 
 
 the boilers with water, and the furnaces with fuel, a 
 good deal of care and some tact is necessary, as irre- 
 gularity 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 rather 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. The boiler should be well filled 
 with water on approaching a station, as there is then 
 steam to spare, and additional water cannot be con- 
 veniently 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 
 
THE STEAM ENGINE. 267 
 
 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. 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. To ascertain whether the pumps are acting 
 well, the pet-cock, which is a small cock opening into 
 the pump, 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. 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. On approaching a 
 station the regulator should be gradually closed, and it 
 
268 A CATECHISM OF 
 
 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 towards the conclusion of the journey. 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 ascer- 
 tained 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, 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 
 
THE STEAM ENGINE. 269 
 
 exist, the weight upon the driving wheels should be 
 diminished. The practice of blowing off the boiler by 
 the steam, as is always done in marine boilers, should 
 riot 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. 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 imper- 
 fection 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. 
 Should the wooden casing of the boiler catch fire, it 
 may be extinguished by throwing a few buckets of 
 water upon it, or, if the engine is at a station, it may 
 be brought under the water crane. 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 
 
270 A CATECHISM OF 
 
 heavy train the parts should be disconnected, if the 
 connexion 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. To 
 economise 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. 
 
 182. Q. Having now given a general outline of 
 the principles and details of construction involved in 
 the production of steam engines, according to the 
 existing system, can you give any suggestion of 
 material improvement? 
 
 A. For all land purposes, and for some marine 
 purposes, engines on the high speed principle (de- 
 scribed in pages 64 and 65) should be adopted ; and 
 in locomotive engines much change is necessary, as the 
 existing locomotive engine intended for high speeds 
 upon the narrow gauge is a very defective machine. 
 It is a monstrous thing that, in the present age of 
 mechanical proficiency, half the engine power should 
 be dissipated upon the blast pipe, as in high speeds 
 appears to be the case, and the first indication of im- 
 provement is to obviate this loss by enlarging the 
 grate surface and the area of the tubes. This may be 
 
THE STEAM ENGINE. 271 
 
 most conveniently accomplished by the introduction of 
 vertical tubes, inserted in short barrels, each furnished 
 with a chimney, and set upon a square fire-box ex- 
 tending the whole length of the engine ; the axle of 
 the driving wheel may be introduced above the fire- 
 box, and between two of the barrels, whereby the 
 engine will be kept so near the ground as to obviate 
 the liability of being top-heavy. If the two cylinders, 
 which may be oscillating, be set upon the top of the 
 fire-box, at the angle of 45 with each other, but in the 
 same vertical plane, and if both piston rods be coupled 
 to the same crank, the shaft of which extends to each 
 side of the carriage, where it is provided with other 
 cranks operating by means of horizontal rods upon 
 pins in the driving wheel, the highest velocities will 
 be attainable without any sinuous or rocking motion ; 
 and the whole of the machinery being above the boiler 
 will be accessible while the train is running, and will 
 not be exposed so much to ashes and dust. With such 
 a construction, indeed, it would be expedient to enclose 
 the whole of the machinery in a carriage or house with 
 glass windows round it. Every locomotive should be 
 furnished with efficient expansion gear of some kind or 
 other ; and it is very desirable that the fire should be 
 fed by some self-acting arrangement, which will make 
 it unnecessary to open the furnace door frequently. 
 The use of sediment collectors in locomotive boilers is 
 also expedient, as, if judiciously applied, they will 
 effectually prevent the formation of scale upon the 
 tubes, and will also operate as an antidote to priming 
 in many cases. The form of collector best adapted to 
 a locomotive boiler will depend in a great measure up- 
 
272 A CATECHISM OF THE STEAM ENGINE. 
 
 on the peculiar structure of the boiler ; but generally 
 any form will answer which communicates with the 
 water level, and contains water within it in a tranquil 
 state. 
 
 TABLE 1. Page 273. 
 Table of Nominal Horse Power of Low Pressure Engines. 
 
 THE table on the opposite page contains the dimensions of 
 cylinder corresponding with any given power in a low pres- 
 sure engine. The table is constructed according to the 
 rule given in page 46. 
 
 To find the nominal power of a low pressure engine, of 
 20 inches diameter of cylinder, and 2i feet stroke : find 
 the diameter in the left-hand column, and in the same hori- 
 zontal line with it, and in the vertical column headed 2*-, 
 will be found 11.55, the number of horses power of the 
 engine. 
 
 The dimensions of cylinder corresponding to a given 
 power may be found by a converse process. 
 
273 
 
 Table of Nominal Horse Power of Low Pressure Engines. 
 
 "o S S3 1 Length of Stroke in Feet. 
 
 ffl 
 
 1 
 
 1| 
 
 2 
 
 2| 
 
 3 
 
 i 
 
 4 
 
 4* 
 
 5 
 
 A 
 
 6 
 
 7 
 
 4 
 
 .34 
 
 .39 
 
 .43 
 
 .46 
 
 .49 
 
 .52 
 
 .54 
 
 .56 
 
 .58 
 
 .60 
 
 .62 
 
 .65 
 
 
 .53 
 
 .61 
 
 .67 
 
 .72 
 
 .76 
 
 .81 
 
 .84 
 
 .88 
 
 .91 
 
 .94 
 
 .96 
 
 1.02 
 
 f 
 
 .76 
 
 .87 
 
 .9(3 
 
 1.04 
 
 1.10 
 
 1.16 
 
 1.22 
 
 1.26 
 
 1.31 
 
 1.35 
 
 1.39 
 
 1.47 
 
 
 1.04 
 
 1.19 
 
 1.31 
 
 1.41 
 
 1.50 
 
 1.58 
 
 1.65 
 
 1.72 
 
 1.78 
 
 1.84 
 
 1.89 
 
 1.99 
 
 8 
 
 1.36 
 
 1.56 
 
 1.72 
 
 1.85 
 
 1.96 
 
 207 
 
 2.16 
 
 225 
 
 2.33 
 
 2 40 
 
 2.47 
 
 2.60 
 
 c 
 
 1.72 
 
 1.97 
 
 2.17 
 
 2.34 
 
 2.49 
 
 2.62 
 
 2.74 
 
 2.84 
 
 2.95 
 
 3.04 
 
 3-13 
 
 330 
 
 10 
 
 2.13 
 
 2.44 
 
 2.68 
 
 2.89 
 
 3.07 
 
 323 
 
 3.38 
 
 3.51 
 
 364 
 
 3.76 
 
 3.87 
 
 4.07 
 
 11 
 
 2.57 
 
 2.95 
 
 3.24 
 
 3.49 
 
 3.77 
 
 3.91 
 
 4.15 
 
 4.25 
 
 4.40 
 
 4.54 
 
 4.68 
 
 4.92 
 
 12 
 
 3.06 
 
 3.51 
 
 3.86 
 
 4.16 
 
 4.42 
 
 4.65 
 
 4.86 
 
 5.06! 5.24 
 
 5.41 
 
 5.57 
 
 5.86 
 
 13 
 
 3.60 
 
 4.12 
 
 4.53 
 
 4.88 
 
 5.19 
 
 5.46 
 
 5.64 
 
 5.94| 6.15 
 
 6.35 
 
 6.53 
 
 6.88 
 
 14 
 
 4.17 
 
 4.77 
 
 525 
 
 5.66 
 
 6.01 
 
 6.33 
 
 6.62 
 
 6.88 7.13 
 
 7.36 
 
 7.58 
 
 7-98 
 
 15 
 
 4.77 
 
 5.48 
 
 6.03 
 
 6.50 
 
 6.90 
 
 7.27 
 
 7.60 
 
 7.90 
 
 8.J9 
 
 8.45 
 
 8.70 
 
 9.16 
 
 16 
 
 5.45 
 
 6.23 
 
 6.861 7.39 
 
 7 86 
 
 8.27 
 
 8.65 
 
 899 
 
 9.31 
 
 9.61 
 
 9.90 
 
 10.42 
 
 17 
 
 6.15 
 
 7.04 
 
 7.75 8.35 
 
 8.86 
 
 9.34 
 
 9.76 
 
 10.15 
 
 10.52 
 
 10.85 
 
 11.17 
 
 11.76 
 
 18 
 
 6.89 
 
 7.89 
 
 8.68| 9.36 
 
 994 
 
 10.47 
 
 10.94 
 
 11.38 
 
 11.79 
 
 12.17 
 
 1253 
 
 13 19 
 
 19 
 
 7.68 
 
 8.79 
 
 968! 10.42 
 
 11.17 
 
 11.66 
 
 12.19 
 
 12.68 
 
 13.13 
 
 13.56 
 
 13.96 
 
 14.69 
 
 20 
 
 851 
 
 9.74 
 
 10.72| 11.55 
 
 1227 
 
 12.92 
 
 13.51 
 
 14.05 
 
 14.55 
 
 15.02 
 
 15.46 
 
 16.28 
 
 22 
 
 1030 
 
 11.79 
 
 12.97 13.98 
 
 14.85 
 
 15.63 
 
 16.62 
 
 17.30 
 
 17.65 
 
 18.18 
 
 18.71 
 
 19.70 
 
 24 
 
 12.26 
 
 14.03 
 
 15.44 16.63 
 
 17.67 
 
 18.61 
 
 19.45 
 
 20.23 
 
 20.95 
 
 21.63 
 
 22.27 
 
 23.44 
 
 26 
 
 14.39 
 
 16.46 
 
 18.12 19.52 
 
 20.75 
 
 21.84 
 
 22.56 
 
 23.75 
 
 24.6 
 
 2539 
 
 26.14 
 
 27.51 
 
 28 
 
 16.68 
 
 19.09 
 
 21.02 22.64 
 
 24.06 
 
 25.33 
 
 26.48 
 
 27.54 
 
 2852 
 
 29.44 
 
 30.31 
 
 31.90 
 
 30 
 
 19.15 
 
 21.92 
 
 24.13; 25.99 
 
 27.62 
 
 2907 
 
 30.40 
 
 31.61 
 
 32.74 
 
 33.80 
 
 34.80 
 
 36.63 
 
 32 
 
 21.79 
 
 24.96 
 
 27.51 29.57 
 
 31.42 
 
 33.08 
 
 34.59 
 
 35.97 
 
 37.26 
 
 3846 
 
 39.59 
 
 41.68 
 
 34 
 
 24.60 
 
 28.16 
 
 30.99 33.39 
 
 35-44 
 
 37.34 
 
 39.04 
 
 40.60 
 
 42.06 
 
 43.41 
 
 44.69 
 
 47.05 
 
 36 
 
 27.57 
 
 31.56 
 
 34.74 37.42 
 
 39.77 
 
 41.87 
 
 4377 
 
 45 52 
 
 47.15 
 
 48.67 
 
 50.11 
 
 52.75 
 
 38 
 
 30.72 
 
 35.17 
 
 38.71 41.69 
 
 44.66 
 
 46.64 
 
 48.77 
 
 50.72 
 
 52.54 
 
 54.23 
 
 55.83 
 
 58.78 
 
 40 
 
 34.04 
 
 38.97 
 
 42.891 46.20 
 
 49.10 
 
 51.69 
 
 54.04 
 
 56.20 
 
 58.21 
 
 60.09 
 
 61.86 
 
 65.12 
 
 42 
 
 37.53 
 
 42.96 
 
 47.29 50.94 
 
 54.13 
 
 56.98 
 
 59.58 
 
 61.96 
 
 64.18 
 
 66.25 
 
 68.21 
 
 71.78 
 
 44 
 
 41.19 
 
 47.15 
 
 51.90 55.91 
 
 59.38 
 
 6254 
 
 66.46 
 
 68.00 
 
 70.44 
 
 72.71 
 
 74.85 
 
 78.79 
 
 46 
 
 45.02 
 
 51.54 
 
 56.72 61.10 
 
 64.88 
 
 68.19 
 
 71.43 
 
 74.33 
 
 76.69 
 
 79.47 
 
 81.81 
 
 86.12 
 
 48 
 
 49.02 
 
 56.11 
 
 61.76 66.53 
 
 70.70 
 
 74.42 
 
 77.82 
 
 80.94 
 
 83.83 
 
 86.53 
 
 89.08 
 
 93.78 
 
 50 
 
 53.19 
 
 60.89 
 
 67.02! 72.19 
 
 76.71 
 
 80.76 
 
 84.44 
 
 87.82 
 
 90.96 
 
 93.89 
 
 96.65 
 
 01.7 
 
 52 
 
 57.55 
 
 65.86 
 
 72.48 
 
 78.08 
 
 83.00 
 
 87.35 
 
 90.25 
 
 94.98 
 
 98.40 
 
 01.55 
 
 04.5 
 
 10.0 
 
 54 
 
 62.04 
 
 71.02 
 
 78.17 
 
 84.20 
 
 89.48 
 
 94.20 
 
 98.49 
 
 102.4 
 
 106.1 
 
 109.5 
 
 12.7 
 
 18.7 
 
 56 
 
 66.72 
 
 76.38 
 
 84.07 
 
 90.55 
 
 96.23 101.30 
 
 05.9 
 
 110.1 
 
 114.1 
 
 1178 
 
 21.2 
 
 27.6 
 
 58 
 
 71.58 
 
 81.93 
 
 90.18' 97.14 
 
 03.2 108.6 
 
 13.6 
 
 18.2 
 
 122.4 
 
 126.3 
 
 29.9 
 
 36.7 
 
 60 
 62 
 
 76.60 
 81.79 
 
 87.68 
 93.62 
 
 96.50; 103-. 9 
 03.04111.0 
 
 10.4 116.3 
 17.961124.18 
 
 21.6 
 
 29.81 
 
 26.4 
 35.03 
 
 131.0 
 139.86 
 
 135.2 
 144.37 
 
 39.2 
 148.6 
 
 46.5 
 56.7 
 
 64 
 
 87.15 
 
 99.84 
 
 110.0 118.3 
 
 25.7 
 
 1323 
 
 38.3 
 
 43.9 
 
 149.0 
 
 153.82 
 
 158.4 
 
 66.7 
 
 66 
 
 92.68 
 
 06.1 
 
 116.8 
 
 125.8 
 
 33.6 
 
 140.7 
 
 47.3 
 
 53.0 
 
 158.5 
 
 163.6 
 
 168.4 
 
 77.3 
 
 68 
 70 
 72 
 
 98.40112.6 
 104.26|]19.3 
 11030126.2 
 
 123.9 
 131.3 
 139.0 
 
 133.6 
 141.5 
 149.7 
 
 41.8 
 50.4 
 59.1 
 
 149.4 
 158.3 
 1674 
 
 56.2 
 65.5 
 75.1 
 
 62.4 
 72.1 
 82.1 
 
 168.2 
 178.2 
 188.6 
 
 173.6 
 184.0 
 1947 
 
 178.8 
 189.4 
 200.4 
 
 88.2 
 99.4 
 11.0 
 
 74 H6 .5 
 
 133.4 
 
 146.8 
 
 158.1 
 
 67.9 
 
 176.7 
 
 85.4 
 
 92.4 
 
 199.2 
 
 205.7 
 
 211.6 
 
 23.4 
 
 761122.9 
 
 140.7 
 
 154.8 
 
 166.8 
 
 786 
 
 186.6 
 
 95.0 
 
 202.9 
 
 210.1 
 
 216.9 
 
 223.3 
 
 35.1 
 
 78 i 129.4 
 
 148.2 
 
 163.1 
 
 175.6 
 
 867 
 
 1965 
 
 05.4 
 
 2121 221.4 
 
 228.5 
 
 235.2 
 
 47.6 
 
 801136.2 
 
 155.8 
 
 171.6 
 
 184.8 
 
 964 
 
 206.7 
 
 16.1 
 
 224.8 232.8 
 
 240.4 
 
 247.4 
 
 60.5 
 
 82143.0 
 
 1638 
 
 180.2 
 
 194.2 
 
 06.2 217.3 
 
 26.9 
 
 237.8 ! 2 44.6 
 
 252.5 
 
 260.0 
 
 73.8 
 
 841150.1 
 
 171.8 
 
 189.1 
 
 203.8 
 
 16.5 227.9 
 
 38.3 
 
 247.8 256.7 
 
 265.0 
 
 272.8 
 
 87.1 
 
 86J 157.4 
 
 180.1 
 
 198.2 
 
 213.6 
 
 27.0 237.8 
 
 47.4 
 
 258.2 269.1 
 
 277.8 
 
 2860 
 
 01 
 
 88164.8 
 
 188.6 
 
 207.6 
 
 2'23.6 
 
 37.5 250 2 
 
 61.6 
 
 272.0 
 
 281.7 
 
 290.8 
 
 299.4 15.2 
 
 90| 172.3 
 
 197.3 
 
 217.1 
 
 233.9 
 
 248.6 261.7 
 
 73.6 
 
 284.5 
 
 294.7 
 
 304.2 
 
 313.2 329.7 
 
274 
 
 TABLE 2. Page 275. 
 Table of Nominal Horse Power of High Pressure Engines. 
 
 THE table on the opposite page contains the dimensions of 
 cylinder corresponding with any given power in a high 
 pressure engine. The table is constructed according to the 
 rule given in page 63, which is virtually the same rule as 
 that for low pressure engines, with the exception of the 
 element of pressure being taken at three times the value. 
 
 To find the nominal power of a high pressure engine of 
 20 inches diameter of cylinder, and 2 feet stroke: find 
 the diameter in the left hand column, and in the same hori- 
 zontal line with it, and in the vertical column headed 2, 
 will be found 34.65, the number of horses power of the 
 engine. 
 
 The dimensions of cylinder corresponding to a given 
 power may be found by the converse process from the 
 table. 
 
275 
 
 Table of Nominal Horse Power of High Pressure Engines, 
 
 P! 
 553 
 
 Length of Stroke in Feet. 
 
 1 
 
 ** 
 
 2 
 
 2* 
 
 3 
 
 H 
 
 4 
 
 4* 
 
 5 
 
 5* 
 
 6 
 
 7 
 
 2 
 
 .25 
 
 .29 
 
 .32 
 
 .35 
 
 .37 
 
 .38 
 
 .40 
 
 .42 
 
 .44 
 
 .4 
 
 .46 
 
 .49 
 
 2 
 
 .39 
 
 .45 
 
 .50 
 
 .54 
 
 .57 
 
 .6C 
 
 1 .63 
 
 .6 
 
 .68 
 
 .7 
 
 .72 
 
 .76 
 
 3 
 
 .57 
 
 .65 
 
 .72 .78 
 
 .83 
 
 .87 
 
 .91 
 
 .95 
 
 .98 
 
 1.0 
 
 1.04 
 
 1.10 
 
 3i 
 
 .78 
 
 .89 
 
 .98 1.06 
 
 1.13 119 
 
 1.24 
 
 1.2S 
 
 1.34 
 
 1.3 
 
 1.42 
 
 1.49 
 
 4 
 
 1.02 
 
 1.17 
 
 1.2ft 1.38 
 
 1.47 1.56 
 
 j 1.62 
 
 1.6 
 
 1.74 
 
 1.8 
 
 1.86 
 
 1.95 
 
 4s 
 
 1.29 
 
 1.48 
 
 1.63 1.75 
 
 1.86 1.96 
 
 I 2.05 
 
 2.13 
 
 2.21 
 
 2.2 
 
 2.35 
 
 247 
 
 5 
 
 1.59 
 
 1.83 
 
 2.01 
 
 2.16 
 
 2.28 2.43 
 
 1 2.52 
 
 2.64 
 
 2.73 
 
 2.8 
 
 2.88 
 
 3.06 
 
 5 
 
 1.93 
 
 2.21 
 
 2.43 2.62 
 
 2.78i 2.93 
 
 3.12 
 
 3.18 
 
 330 
 
 3.4 
 
 3.51 
 
 3.69 
 
 6 
 
 2.28 
 
 2.61 
 
 2.88 3.12 
 
 3.30 3.48 
 
 3.66 
 
 3.78 
 
 3.93 
 
 4.05 
 
 4.17 
 
 4.41 
 
 6 
 
 2.69 
 
 3.09 
 
 3.39j 3.66 
 
 3.90 4.08 
 
 4.23 
 
 4.44 
 
 4.62 
 
 4.77 
 
 4.89 
 
 5.16 
 
 7 
 
 3.12 
 
 3.57 
 
 3.93 4.23 
 
 4.50 4.74 
 
 4.95 
 
 5.16 
 
 5.34 
 
 5.52 
 
 5.67 
 
 5.97 
 
 7* 
 
 3.60 
 
 4.11 
 
 4.53 4.86 
 
 5.19 5.46 
 
 5.70 
 
 5.94 
 
 6.15 
 
 6.33 
 
 6.51 
 
 6.87 
 
 8 
 
 408 
 
 4.68 
 
 5.16 5.55 
 
 5.88| 6.21 
 
 6.48 
 
 6.75 
 
 6.99 
 
 7.20 
 
 7.41 
 
 7.80 
 
 8 
 
 4.62 
 
 5.28 
 
 5.82 6.27 
 
 663 
 
 6.99 
 
 7.32 
 
 7-62 
 
 7.89 
 
 8.13 
 
 8.37 
 
 8.82 
 
 9 
 
 5.16 
 
 5.91 
 
 6.51 
 
 7.02 
 
 7.47 
 
 7.86 
 
 8.22 
 
 8.52 
 
 8.85 
 
 9.12 
 
 9.39 
 
 9.90 
 
 9 
 
 5.76 
 
 6.60 
 
 7.26 
 
 7.80 
 
 8.37 
 
 8.76 
 
 9.15 
 
 9.51 
 
 9.84 
 
 10.17 
 
 10.47 
 
 11.01 
 
 10 
 
 6.39 
 
 7.32 
 
 8.04 
 
 8.67 
 
 2.21 
 
 9.69 
 
 10.14 
 
 10.53 
 
 10.92 
 
 11.28 
 
 11.61 
 
 12.21 
 
 10 
 
 7.05 
 
 8.04 
 
 8.88 
 
 9.54 
 
 10.14 
 
 10.68 
 
 i 11.16 
 
 11.61 
 
 12.03 
 
 12.42 
 
 12.78 
 
 13.47 
 
 11 
 
 7.71 
 
 8.85 
 
 9.72 
 
 10.47 
 
 11.31 
 
 11.73 
 
 i 12.45 
 
 12.75 
 
 13.20 1362 
 
 14.04 
 
 14.76 
 
 11| 
 
 8.43 
 
 9.66 
 
 10.62 11.46 
 
 12.15 
 
 12.78 
 
 13.80 
 
 13.92 
 
 14.61 
 
 1491 
 
 15.33 
 
 16.14 
 
 12 
 
 9.18 
 
 10.53 
 
 11.581 12.48 
 
 13.26 
 
 13.95 
 
 14.58 
 
 15.18 
 
 15.72 
 
 16.23 
 
 1671 
 
 17.58 
 
 12i 
 
 9.96 
 
 11.40 
 
 12.571 13.53 
 
 14.37 
 
 15.15 
 
 15.84 
 
 16.47 
 
 17.04 
 
 17.58 
 
 18.12 
 
 19.08 
 
 13 
 
 10.80 
 
 12.36 
 
 13.59 14.64 
 
 15.57 
 
 16.38 
 
 16.92 
 
 17.82 
 
 18.45 
 
 19.05 
 
 19.59 
 
 20.64 
 
 ISA 
 
 11.64 
 
 13.32 
 
 14.64 15.78 
 
 16.77 
 
 17.67 
 
 18.48 
 
 19.20 
 
 19.89 
 
 20.52 
 
 21.15 
 
 22.26 
 
 14 
 
 12.51 
 
 14.31 
 
 15.75 1 16.98 
 
 18.03 
 
 18.99 
 
 19.86 
 
 20.64 
 
 21.39 
 
 22.08 
 
 22.74! 23.94 
 
 14 
 
 13.41 
 
 15.56 
 
 16.921 18.21 
 
 19.35 
 
 20.37 
 
 21.30 
 
 22.14 
 
 22.951 23.70 
 
 24.39 25.62 
 
 15 
 
 14.31 
 
 16.44 
 
 18.09 19.50 
 
 20.70! 21.81 
 
 22.80 
 
 23.70 
 
 24.57 25.35 
 
 26.10 
 
 27.48 
 
 16 
 
 16.35 
 
 18.69 
 
 20.58 22.17 
 
 23.58 24 81 
 
 25.95 
 
 26.97 
 
 27.93! 28.83 
 
 29.70 
 
 31.26 
 
 17 
 
 18.45 
 
 21.12 
 
 23.25[ 25.05 
 
 26.58 28.02 
 
 29.28 
 
 30.45 
 
 31.56! 32.55 
 
 33.57 
 
 35.28 
 
 18 
 
 20.67 
 
 23.67 
 
 26.04 28.08 
 
 29.821 31.41 
 
 32.82 
 
 34.14 
 
 35 37 36.51 
 
 37.59 
 
 39.57 
 
 19 
 
 23.04 
 
 26.37 
 
 29.04 31.26 
 
 33.51 
 
 34.98 
 
 36.57 
 
 38.04 
 
 39 39| 40.68 
 
 41.88 44.07 
 
 20 
 
 25.53 
 
 29.22 
 
 32.161 34.65 
 
 36.81 
 
 38.76 
 
 40.53 
 
 42.15 
 
 43.65 45.06 
 
 46.38 48.84 
 
 22 
 
 30.90 
 
 35.37 
 
 3891 
 
 41.94 
 
 4455 
 
 46.89 
 
 49.86 
 
 51.90 
 
 52.95 54.54 
 
 56.13 
 
 59.10 
 
 24 
 
 36.78 
 
 42.09 
 
 46.32 
 
 49.89 
 
 53.01 
 
 55.83 
 
 58.35 
 
 60.69 
 
 62.85 
 
 64.89 
 
 66.81 
 
 70.32 
 
 26 
 
 43.17 
 
 49.38 
 
 54.36 58.56 
 
 62.25 65.52 
 
 67.68 
 
 71.25 
 
 738 
 
 76.17 
 
 78.42 
 
 82.53 
 
 28 
 
 50.04 
 
 57.27 
 
 6306 67.92 
 
 72.181 75.99 
 
 79.44 
 
 82.62 
 
 85.56 88.32 
 
 90.93 
 
 95.70 
 
 30 
 
 57.45 
 
 65.76 
 
 72.39| 77.97 
 
 82.861 87.21 
 
 91.20 
 
 94.83 
 
 98.22 101.40 
 
 04.4 
 
 109.9 
 
 32 
 
 6537 
 
 74.88 
 
 82.531 88 71 
 
 94.26! 99.24 
 
 103.7 
 
 07.9 
 
 11.8 
 
 115.4 
 
 18.7 
 
 125.0 
 
 34 
 
 73.80 
 
 84.48 
 
 9297100.22 06.3 
 
 112.0 
 
 117.1 
 
 21.8 
 
 26.2 
 
 1302 
 
 34.0 
 
 141.1 
 
 36 
 
 82.71 94.68 
 
 04.2 112.2 
 
 1193 
 
 125.6 
 
 131.3 
 
 36.5 
 
 41.4 146.0 
 
 50.3 
 
 158.2 
 
 38 
 
 92.16105.5 
 
 16.1 1125-0 
 
 134.0 1369 
 
 1463 
 
 521 
 
 57.6 162.7 
 
 67.5 
 
 176.3 
 
 40 
 
 102.1 
 
 116.9 
 
 29.6 1128.6 
 
 147.3 155.1 
 
 162.1 
 
 68.6 
 
 746 180.2 
 
 85.6 
 
 195.3 
 
 42 
 
 112.6 
 
 128.9 
 
 41.8 152.8 
 
 162.4 
 
 170.9 
 
 178.7 
 
 85.9 
 
 92.5 
 
 198.7 
 
 04.6 
 
 215.3 
 
 44 
 
 123.5 
 
 141.4 
 
 55.7 
 
 167.7 
 
 178.1 
 
 187.6 
 
 199.4 
 
 204.0 
 
 11.3 
 
 218.1 
 
 245 
 
 236.3 
 
 46 
 
 35.0 
 
 154.6 
 
 70.1 
 
 183.3 
 
 194 6 204.6 
 
 214.3 
 
 223.0 
 
 30.0 
 
 238.4 
 
 45.4 
 
 258.3 
 
 48 
 
 147.0 
 
 1683 
 
 85.3 
 
 199.6 
 
 212.1 223.2 
 
 233.4 
 
 242.8 
 
 51.5 
 
 259.6 
 
 67.2 
 
 281.3 
 
 50 
 
 159.6 
 
 182.6 
 
 201.0 216.5 
 
 230.1 242.3 
 
 253.3 
 
 263.4 
 
 72.9 
 
 281.6 
 
 89.9 
 
 505.1 
 
 52 
 
 172.6 
 
 197.6 
 
 217.4 234.2 
 
 249.0 1262.0 i 
 
 270.7 
 
 284.9 
 
 95.2 304.6 
 
 13.5 330.0 
 
 54 
 
 186.1 
 
 213.0 
 
 234.5 
 
 252.6 
 
 268.4 
 
 282.6 
 
 295.4 
 
 07.2 
 
 18.3 (328.5 
 
 38.1 356.1 
 
 56 
 
 200.1 J229.1 
 
 252.2 
 
 271.6 288.7 
 
 303.9 
 
 317.7 
 
 30.3 
 
 42.3 353.4 63 6 . 
 
 $82. 8 
 
 58 
 
 214.7 '245.8 
 
 270.5 
 
 291.4 309.6 325.8 
 
 340.8 
 
 54.6 
 
 67.2 378.9 
 
 389.7 ' 
 
 110.1 
 
 60 
 
 229.8 263.0 
 
 289.5 311.7 331.2 348.9 
 
 364.8 
 
 79.2 
 
 93.0 
 
 105.6 
 
 117.6 439.5 
 
 x 2 
 
276 
 
 TABLE 3. Page 277. 
 
 Expanded Steam. Mean Pressure at different Densities 
 and Rates of Expansion. 
 
 THE tables pn the opposite page are intended to facilitate 
 the computation of the power of an engine working expan- 
 sively. The first column in each table contains the initial 
 pressure of the steam in pounds, and the remaining columns 
 contain the mean pressure of steam throughout the stroke, 
 with the different degrees of expansion indicated at the top 
 of the columns, and which express the portion of the stroke 
 during which the steam acts expansively. Thus, for ex- 
 ample, if steam be admitted to the cylinder at a pressure of 
 3 pounds per square inch, and be cut off within th of the 
 end of the stroke, the mean pressure during the whole 
 stroke will be 2.96 pounds per square inch. In like manner 
 if steam at the pressure of 3 pounds per square inch were 
 cut off after the piston had gone through |th of the stroke, 
 leaving the steam to expand through the remaining |th, the 
 mean pressure during the whole stroke would be 1.154 
 pounds per square inch. Steam, however, of as little as 
 3 Ibs. per square inch, is never used, in working an engine ; 
 for this would be steam of 12 Ibs. below the atmospheric 
 pressure ; and if steam of 3 Ibs. above the atmospheric pres- 
 sure be taken, this will be steam of 18 Ibs. pressure upon 
 the square inch, the mean pressure of which throughout 
 the stroke, if cut off at the time the piston has gone through 
 ith of the stroke, or has |ths of the stroke still to perform, 
 is 6.927 Ibs. per square inch, being nearly 8 Ibs. below the 
 atmospheric pressure. 
 
277 
 
 3 
 
 l 
 
 1^ 
 t^ 
 
 ?! 
 
 p 
 
 >t-00 CJ O 
 
 jSS 06 S 
 
 io -oiNfii 
 
 L-. oot~<D5Oift'^<Tt>:(5rN<Neooi ocF-f~^SiX-q<X-oo 
 JO o ; =7 o cr. i-. Ci ci OCjaoc;. oococacocooSooi^i^piS 
 
 M "* "^ ,_rt ^ M 2 J2 n rt 2 2 S 5i 5 
 
 O I ' 
 
 
278 
 
 TABLE 4. Page 279. 
 
 TABLE 4 contains four small tables ; the first gives the tempera- 
 ture and elastic force of steam, as experimentally determined by 
 Dulong and Arago; the second gives the expansion of air by heat ; 
 the remaining tables have reference to the use of steam expan- 
 sively by means oflap on the valve. 
 
 The larger of these tables is intended to show the amount of 
 cover required on the steam side of the valve to cut off the steam 
 at different parts of the stroke. The first column contains differ- 
 ent lengths of the stroke of the valve in inches, and the remain- 
 ing columns are headed by fractions, indicating the degree of 
 expansion. To cut off the steam at gth from the end of the 
 stroke, the stroke of the valve being 17 inches: in the column 
 headed ^, and in a line with 17, will be found 3.47, which is the 
 required cover in inches, the valve being without lead. To give it 
 | inch of lead, subtract one half the lead from the cover, and the 
 remainder, 3.345 inches, is the cover for the required expansion 
 and lead. Subtract the cover from one half the length of the 
 valve stroke, and the remainder, 5.155 inches, is the greatest 
 breadth of port with that stroke. 
 
 The remaining table is to show at what parts of the stroke, 
 under any given arrangement of slide valve, the exhausting ports 
 close and open. The columns headed A, contain the amount of 
 cover on the exhausting side of the valve in parts of its stroke ; 
 in the column B, the figures represent the distance of the piston, 
 in terms of the length of its stroke, from the end of its stroke 
 when the exhausting port before it is shut ; and C, shows simi- 
 larly at what part of the stroke the exhausting port behind the 
 piston is opened the steam in both cases being cut off at |d from 
 the end of the stroke. In like manner in D E the steam is cut off 
 at |jths from the end of the stroke ; in F G at jth ; in H K at 5 5 -,ths ; 
 in LM at Jth; in NO at |th; in PQ at T ' 2 th; in RS at ^th: in 
 each case the left hand single column of each double column, re- 
 presents the distance of the piston from the end of its stroke 
 when the exhausting port before it is shut ; and the right hand 
 single column when the exhausting port behind it is opened. 
 
 Let the stroke of the piston be 6 feet, and the slide valve cut 
 off the steam at *d from the end of the stroke, and the cover on 
 the exhausting side of the valve be gth of the valve stroke. In a 
 line with ^th, and under the columns B C will be found .178 and 
 .033, which multiplied respectively by 72 inches will give 12.8 
 inches for the distance of the piston from the end of its stroke, 
 when the exhausting port before it is shut, and 2.38 inches, when 
 the exhausting port behind it is opened. 
 
279 
 
 the Val 
 Parts o 
 
 of Cover required on the 
 e Steam olf at any of th 
 
 HS 
 
 i c4 o5 c^ c 
 
 ^* o"o si c. 
 
 > in ra ^"TJ" co*co 
 
 Ir ^ 
 
 Illi 
 
 sis! 
 
 CO O C t^. 
 
 isi 
 
 OOOOOOOOOOOOOOOO 
 
 a SS2S 
 
 O. O O O O O O 
 
 O O "^^O *^" 
 
 C^^OCOlOlCCCO^ 
 
 O O O O O O 
 
280 
 
 Screw Steam Vessels. 
 
 TABLE showing the principal Dimensions and the Performance 
 per Experiments of the Screw Steam Vessels, " Free Trade," 
 " Eider," " Thames," and " Elbe," constructed by Boulton, 
 "Watt, & Co., 1847. 
 
 
 " Free 
 Trade." 
 
 " Eider." 
 
 " Thames."i 
 
 "Elbe." 
 
 Length between perpendiculars 
 Breadth - - - - - 
 
 140.0ft. 
 25 ft. 8 in. 
 
 140.0 ft. 
 25 ft. 8 in. 
 
 130.0 ft 
 24 ft. 2 in. 
 
 130.0 ft. 
 24 ft. 2 in. 
 
 
 14 ft 6 in 
 
 14 ft. 6 in. 
 
 13ft. 6 in. 
 
 13 ft. Gin. 
 
 Tonnage - 
 
 42411 
 
 
 355 
 
 355 
 
 Immersed sectional area - 
 
 166 sq. ft. 
 
 179 sq. ft. 
 
 136 sq.ft. 
 
 133 sq.ft. 
 
 Draft of water - 
 
 8ft. 4 in. 
 
 8 ft. 10 in. 
 
 7ft. 4$ in. 
 
 7ft. 2 in. 
 
 Speed in knots - 
 
 766 
 
 7.31 
 
 7 
 
 - 
 
 ,, miles - 
 
 8.9 
 
 8.32 
 
 8.209 
 
 7.544 
 
 Diameter of screw - 
 
 7.9 ft. 
 
 8.3ft. 
 
 7.3ft. 
 
 7.3ft. 
 
 Slip of the screw in miles - 
 Pitch of screw - 
 
 1.33 
 9.9 ft. 
 
 103ft. 
 
 80ft" 
 
 9.3ft." 
 
 Length of screw - 
 
 1.3ft. 
 
 1.8ft. 
 
 1.4ft. 
 
 1.4ft. 
 
 Number of blades of screw 
 
 Three. 
 
 Two. 
 
 Two. 
 
 Two. 
 
 Number of revolutions of screw 
 
 
 
 
 
 per minute - 
 
 94$ 
 
 90 
 
 108 
 
 93 
 
 Diameter of cylinder - 
 Length of stroke - 
 
 31$ in. 
 3. ft 
 
 31$ in. 
 3ft. 
 
 27 in. 
 2.6ft. 
 
 27 in. 
 2.6ft. 
 
 Number of cylinders - 
 
 Two. 
 
 Two. 
 
 Two. 
 
 Two. 
 
 Number of strokes per minute - 
 Vacuum by the barometer - 
 Nominal power - 
 
 31$ 
 27 in. 
 60 horses. 
 
 30 
 26 in. 
 60 horses. 
 146 horses 
 
 36 
 
 24$ in. 
 40 horses. 
 102 horses 
 
 31 
 
 26 in. 
 40 horses. 
 100 horses 
 
 Pressure of steam in boiler 
 
 13 Ibs.' ' 
 
 13 Ibs. 
 
 12 Ibs. 
 
 11 Ibs. ' 
 
 Average effective pressure on 
 
 
 
 
 
 piston - 
 
 15.75 Ibs. 
 
 17. 30 Ibs. 
 
 16.975 Ibs. 
 
 19 Ibs. 
 
 Steam cut off at of stroke 
 
 
 
 A 
 
 i 
 
 Cubic feet of water evaporated 
 
 
 
 
 
 
 105 ft. 
 
 105 ft. 
 
 70ft. 
 
 70ft. 
 
 Square feet of surface of boiler 
 
 
 
 
 
 to evaporate a cubic foot - 
 
 9.5 ft. 
 
 9.5ft. 
 
 9.585 ft. 
 
 9.585 ft. 
 
 Square feet of fire bars to evapo- 
 rate a cubic foot - 
 
 0.433 ft. 
 
 0.433ft. 
 
 0.4928ft. 
 
 0.4928ft. 
 
 Actual horse-power produced by 
 the evaporation of a cubic foot 
 
 1.257 h.p. 
 
 1.39 h.p. 
 
 1.457 h.p. 
 
 1.428 h.p. 
 
 Sectional area of tubes per cubic 
 
 
 
 
 
 foot evaporated - 
 Multiple of the wheels 
 
 8.51 sq. in. 
 1 to 3 
 
 851 sq. in. 
 1 to 3 
 
 lOsq.in. 
 Ito3 
 
 lOsq.in.j 
 1 to 3 
 
 Diameter of wheel - 
 
 9ft. 4$ in. 
 
 9ft. 4$ in. 
 
 8ft. 6 in. 
 
 8 ft. 6 in. 
 
 ,, pinion - 
 
 3ft. l$in. 
 
 3ft. l$in. 
 
 2ft. 10 in. 
 
 2ft. 10 in. 
 
 Pitch 
 
 3 927 in. 
 
 3 927 in 
 
 3.141 in. 
 
 3.141 in. 
 
 Breadth - j; 
 
 2 teeth, 
 each 6 in. 
 
 2 teeth, 
 each 6 in. 
 
 2 teeth, 
 each 4$ in. 
 
 2 teeth, 
 each 4$ in. 
 
 
 Wheel 
 
 Wheel 
 
 Wheel 
 
 Wheel 
 
 
 geared 
 
 geared 
 
 geared 
 
 geared 
 
 Whether teeth of wood - 
 
 with horn- 
 beam. 
 
 with horn- 
 beam. 
 
 with horn- 
 beam. 
 
 with horn- 
 beam. 
 
 
 The 
 
 The 
 
 The 
 
 The 
 
 
 pinion of 
 
 pinion of 
 
 pinion of 
 
 pinion of 
 
 
 iron. 
 
 iron. 
 
 iron. 
 
 iron. 
 
281 
 
 INDEX. 
 
 Actual and nominal horse pow- 
 er, 4548. 
 
 Air-pump, details of, 217 220. 
 
 Air-pump, proportions of, 72. 
 
 Air-pump for high speeds, 64, 
 65. 
 
 Atmospheric resistance to lo- 
 comotives, 80 83. 
 
 Beams, strength of, 104, 
 
 Blowing off boilers, 136140. 
 
 Boilers, waggon, construction 
 and setting of, 119 121. 
 
 Boiler explosions, 146 149. 
 
 Boilers, incrustation of, 135 
 142. 
 
 Boilers, locomotive, 150 158. 
 
 Boiler, locomotive, steam chest 
 of, 153. 
 
 Boilers, locomotive, tubes of, 
 156, 157. 
 
 Boilers, marine, construction 
 of, 121128. 
 
 Boilers, marine, corrosion of, 
 116119. 
 
 Boilers, scaling of, 140. 
 
 Boilers, strength of, how deter- 
 mined, 113 116. 
 
 Boilers, tubing and staying of, 
 128132. 
 
 Brass for engine work, 248 
 250. 
 
 Calorimeter, 53. 
 
 Case hardening, 246, 247. 
 
 Cataract, 162, 163. 
 
 Centre of gravity, 9. 
 
 Centre of gyration, 9. 
 
 Centre of oscillation, 10. 
 
 Centre of pressure, 93. 
 
 Centrifugal force, 9. 11. 15. 
 
 Centrifugal pump, 171. 
 
 Centripetal force, 9. 15. 
 
 Chimney, proportions of, 51 
 53. 
 
 Chimney, temporary, for steam- 
 ers, 263, 264. 
 
 Coal, consumption of, per horse 
 power, 39. 
 
 Coal, evaporating efficacy of, 
 49, 50. 
 
 Cocks, pumps, and pipes, 224 
 236. 
 
 Combustion, 40. 
 
 Condensation of steam, 33, 34. 
 
 Condenser, proportions of, 72. 
 
 Condensing engines, varieties 
 of, 4, 5. 
 
 Condensing engines, high speed, 
 6466. 
 
 Connecting rod, proportions of, 
 106110. 
 
 Cornish boilers, 35, 36. 39, 40. 
 
 Cornish pumping engine, erec- 
 tion of, 163172. 
 
 Corrosion of marine boilers, 
 cause of, 116 119. 
 
 Counter, 159. 
 
 Crank pin, diameter of, 106 
 109. 
 
282 
 
 INDEX. 
 
 Cylinder faces, 206 209. 
 Cylinders, manipulation of, 194 
 
 198. 
 Cylinder passages, dimensions 
 
 of, 7275. 
 Cylinders, steam jackets, benefit 
 
 of, 192, 193. 
 
 Cylinder, thickness in oscil- 
 lating engines, 1 94. 
 Direct acting engines, varieties 
 
 of, 172. 
 
 Double acting engines, 5, 6. 
 Duty of an engine, 48 50. 
 Dynamometer, 160. 
 Eccentric pulley, 211 213. 
 Engine bearings, lubrication of, 
 
 250, 251. 
 
 Engines, erection of, in work- 
 shops, 251255. 
 Engines, erection of, in steam 
 
 vessels, 258263. 
 Expansion of gases, 279. 
 Expansion of steam in cylinder, 
 
 23,24. 6871. 277. 279. 
 Expansion valves, operation of, 
 
 214217. 
 Explosion of boilers, cause of, 
 
 146149. 
 Feathering paddle wheel, 92. 
 
 187, 188. 
 Feed pump, capacity of, 32. 60, 
 
 61. 
 
 Fire bars of locomotives, 155. 
 Fly wheel, 66. 
 Fly wheel shaft, diameter of, 
 
 105. 
 Flues, dimensions of, 53 60. 
 
 132, 133. 
 
 Flues, incrustation of, 135 142. 
 Friction, nature of, 18 20. 
 Friction, amount of, 77 79. 
 Fuel, comparative evaporative 
 
 power, 50. 
 Funnel, 133. 263. 
 
 Furnace bars, 124, 125. 
 Furnace bridges, 125, 126. 
 Furnaces, firing of, 41 43. 
 Gauge cocks, 4. 160. 
 Gauge, steam, 3. 
 Gauge, vacuum, 3. 
 Glass gauges, 160, 161. 
 Governor, 13 15. 
 Gravity, centre of, 9. 
 Gudgeons, strength of, 105. 
 Gyration, centre of, 9. 
 Harvey and West's valve, 169, 
 
 170. 
 
 Heat, latent, 24, 25. 
 Heat, specific, 25, 26. 
 Heating surface, 36 39. 
 High pressure steam engines, 
 
 power of, 61 63. 
 High speed condensing engines, 
 
 64, 65. 
 
 High speed engines, power of, 
 
 65, 66. 
 
 Horse power, actual and nomi- 
 nal, 21. 22. 4547. 273. 275. 
 
 Hydrometer, 138. 140. 
 
 Incrustation of marine boilers, 
 135 142. 
 
 Indicator, 22. 
 
 Iron, strength of, 104. 
 
 Joints of engines, 245, 246. 
 
 Jucke's fire grate, 45. 
 
 Lamb's scale preventer, 139. 
 
 Lap of the valve, 68 71. 279. 
 
 Latent heat, 24, 25. 
 
 Lead of the valve, 67. 279. 
 
 Locomotive boilers, 150 158. 
 
 Locomotive boilers, fire bars, 
 155. 
 
 Locomotive boilers, steam chest 
 of, 153. 
 
 Locomotive boilers, tubes of, 
 156, 157. 
 
 Locomotives, cocks, pumps, and 
 pipes, 224 236. 
 
INDEX. 
 
 283 
 
 Locomotives, cost and perform- 
 ance of, 79 84. 
 Locomotives, details of, 234 
 
 246. 
 Locomotives, duties of engine 
 
 driver, 265 270. 
 Locomotives, wheels of, 239 
 
 242. 
 Lubrication of engine bearings, 
 
 250, 251. 
 
 Marine boilers, cause of corro- 
 sion, 116119. 
 Marine boilers, construction of, 
 
 121128. 
 Marine boilers, incrustation of, 
 
 135142. 
 Marine engine, pumps, pipes, 
 
 and cocks, 224236. 
 Marine engine, management of, 
 
 263265. 
 
 Mechanical powers, 16 18. 
 Momentum, 8. 
 Muntz's metal, 248. 
 Nominal horse power, 45 47. 
 
 273275. 
 
 Oscillation, centre of, 10. 
 Oscillating engine, objections 
 
 to, 173, 174. 
 Oscillating engine by Penn, 
 
 description of, 175 188. 
 Oscillating engines, dimensions 
 
 of, 189191. 
 Oscillating engines, thickness 
 
 of cylinder, 194. 
 Oscillating engines, trunnions, 
 
 191, 192. 
 Oscillating engines, trunnion 
 
 bearings, 194. 
 
 Oscillating engine, valve gear- 
 ing, &c., 185 187. 
 Paddle wheels, details of, 220 
 
 223. 
 Paddle wheels, feathering, 97. 
 
 187189. 
 
 Paddle wheel shaft, 106108. 
 Paddle wheels, theory of, 91 
 
 101. 
 Pendulous bodies, vibration of, 
 
 1014. 
 Piston, construction of, 201 
 
 206. 
 Piston rod, diameter of, 106 
 
 1 10. 
 Power of engines, actual and 
 
 nominal, 4547. 273275. 
 Power of engines, measure of, 
 
 21, 22. 
 Power of high pressure engines, 
 
 how ascertained, 61 65. 
 Pressure, centre of, 93. 
 Priming, nature and causes of, 
 
 143145. 
 
 Pump, centrifugal, 171. 
 Pumping engine, Cornish, erec- 
 tion of, 163172. 
 Pumps, pipes, and cocks of en- 
 gines, 224236. 
 Pump valves, 169 171. 
 Rails, adhesion of wheels to, 79. 
 Rotatory engines, 4, 5. 
 Safety valve, area of, 71. 
 Salt gauge, 138140. 
 Scale Preventer, Lamb's, 139. 
 Scaling of boilers, 140, 141. 
 Screw propeller, 101 103. 
 Screw steam vessels, 280. 
 Sediment Collectors, 139. 
 Single acting engines, 5, 6. 
 Shaft-paddle, diameter of, 106, 
 
 108. 
 
 Slide valve, 66, 67. 
 Slide valve, best construction of, 
 
 210, 211. 
 
 Slide valve, expansion by, 279. 
 Slide valve, setting of, 255 
 
 258. 
 Smoke, consumption of, 41 
 
 45. 
 
284 
 
 INDEX. 
 
 Specific heat, 25, 26. 
 
 Speed of engines, 63, 64. 
 
 Staying of boilers, 130 132. 
 
 Steam, properties of, 26 36. 
 
 Steam chest of locomotive boil- 
 ers, 153. 
 
 Steam, consumption per horse 
 power, 22, 23. 
 
 Steam, elasticity of, 30, 31. 279. 
 
 Steam engine, suggestions for 
 improvement of, 270 272. 
 
 Steam gauge, 3. 
 
 Steam, high pressure, benefit 
 of, 27 30/ 
 
 Steam jackets, benefit of, 192, 
 193. 
 
 Steam passages, dimensions of, 
 7276. 
 
 Steam pipe, area of, 72. 
 
 Steam vessel, method of putting 
 engines into, 258 261. 
 
 Steam vessels, securing of en- 
 gines to hull, 261 263. 
 
 Strength of boilers, how deter- 
 mined, 113116. 
 
 Strength of parts of steam en- 
 gine, 103 113. 
 
 Surcharged steam, 26. 31. 117. 
 
 Teeth of wheels, proportions of, 
 106, 107. 
 
 Tractive force on railways, 77. 
 
 Trunnions of oscillating en- 
 gines, 191, 192. 
 
 Trunnion bearings of oscillating 
 engines, 194. 
 
 Tubes, incrustation of, 141, 142. 
 
 Tubes of locomotive boilers, 
 156, 157. 
 
 Tubing of boilers, 128 130. 
 
 Unguents, 20, 21. 
 
 Vacuum, nature and properties 
 of, 13. 6, 7. 
 
 Vacuum gauge, 3. 
 
 Valve and cylinder faces, me- 
 thod of fitting, 206 209. 
 
 Valves, expansion, operation of, 
 214217. 
 
 Valve gearing of oscillating en- 
 gines, 185. 187. 
 
 Valve, Harvey and West's, 169 
 171. 
 
 Valve, lap of, 68 71. 279. 
 
 Valve, lead of, 67. 
 
 Valve, pump, 169 171. 
 
 Valve, safety, area of, 71. 
 
 Valve, slide or sluice, 66, 67. 
 
 Valve, slide, setting of, 255. 
 258. 
 
 Velocity of falling bodies, 6 8. 
 
 Vent of boilers, 53. 
 
 Vessels, resistance of water to, 
 84 90. 
 
 Waggon boilers, construction 
 and setting of, 119 121. 
 
 Water, quantity requisite for 
 boiler, 32. 
 
 Water, quantity requisite for 
 condensation, 33, 34. 
 
 Water, resistance of, 84 90. 
 
 Waste steam pipe, 1 33. 
 
 Waste water pipe, 134. 
 
 Wheels, adhesion on rails, 79. 
 
 Wheels of locomotives, 239 
 242. 
 
 Wheels, strength of teeth, 106, 
 107. 
 
 THE END. 
 
 LONDON: 
 
 SPOTTISWOODES and SHAW, 
 New-street-Square. 
 
AN ALPHABETICAL CATALOGUE 
 
 OF 
 
 NEW WORKS 
 
 IN GENERAL AND MISCELLANEOUS LITERATURE, 
 
 PUBLISHED BY 
 
 MESSRS. LONGMAN, BROWN, GREEN, AND LONGMANS, 
 PATERNOSTER ROW, LONDON. 
 
 CLASSIFIED INDEX. 
 Agriculture and Rural 
 Affairs. 
 
 Pages 
 
 Bayldon on ValuingRents, etc. 5 
 
 Crocker's Land Surveying - 8 
 
 Johnson's Farmer's Encyclopaedia . - 16 
 
 Loudon's Encyclopaedia of Agriculture - 18 
 
 , , Self-Instruction for Farmers, etc. 17 
 
 ,, (Mrs.) Lady 'sCountry Companion 17 
 
 Low's Elements of Agriculture - - 18 
 
 ,, On Landed Property - - 18 
 
 Arts, Manufactures, and 
 Architecture. 
 
 Bourne's Catechism of the Steam Engine 6 
 
 Brande's Dictionary of Science, etc. - 6 
 
 Budge's Miner's Guide - - 6 
 
 Cresy's Encycl. of Civil Engineering - 8 
 
 D'Agincourt's History of Art - - - 23 
 
 Dresden Gallery - - - 9 
 
 Eastlake on Oil Painting . 10 
 
 Evans's Sugar Planter's Manual - - 10 
 
 Gwilt's Encyclopaedia of Architecture 11 
 
 Humphreys' Illuminated Books - . 15 
 
 Jameson's Sacred and Legendary Art - 15 
 
 London's Rural Architecture - - - 18 
 
 Moseley's Engineering and Architecture 22 
 
 Scoffern on Sugar Manufacture - - 26 
 
 Steam Engine [The) , by the Artisan Club 5 
 
 Tate on Strength of Materials - - 29 
 
 Twining on Painting - - - - 31 
 
 Ure's Dictionary of Arts, etc. - - 31 
 
 Biography. 
 
 Foss's Judges of England - 10 
 
 Grant (Mrs.) Memoir and Correspondence 11 
 
 Head's Memoirs of Cardinal Pacca - 13 
 
 Hnmphreys's Black Prince ... 14 
 
 Kindersley's De Bayard .... 16 
 
 Maunder'sBiographicalTreasury - . 21 
 
 Southey's Life of Wesley .... 29 
 
 ,, Life and Correspondence - 28 
 
 Stephen's Ecclesiastical Biography - 29 
 
 Taylor's Loyola ..... 30 
 
 Townsend's Twelve eminent Judges - 31 
 
 Waterton's Autobiography and Essays - 31 
 
 Books of General Utility. 
 
 Acton's (Eliza) Cookery Book 
 k's Treatise on Brewing - 
 
 Cabinet Lawyer (The) - 
 Foster's Hand-bo 
 
 5 
 
 - - 6 
 
 ok of Literature - - 11 
 
 Hints on Etiquette "13 
 
 Hudson's Executor's Guide 14 
 
 On Making Wills ... 14 
 London's Self Instruction ... 17 
 , , (Mrs.) Amateur Gardener - 17 
 Maunder's Treasury of Knowledge - . 20 
 , , ScientificandLiteraiyTreasury 20 
 ,, Treasury of History > - 20 
 , , Biographical Treasury . - 21 
 
 Natural History - ' - -20 
 Pocket and the Stud .... 12 
 Pycroft's Course ol English Reading - 24 
 Reece's Medical Guide . ... 25 
 Rich's Companion to the Latin Dictionary 25 
 Riddle's Latin Dictionaries and Lexicon 25 
 Rowton's Debater - - - 26 
 
 Short Whist 26 
 
 Stud (The) for Practical Purposes - 12 
 
 Thomas's Interest Tables - . -30 
 Thomson's Management of Sick Room - 30 
 Interest Tabl 
 
 . 
 
 Webster's Encycl. of Domestic Economy Z2 
 
 Botany and Gardening. 
 
 Callcott's Scripture Herbal ... 7 
 
 Conversations on Botany ... 7 
 
 Evans's Sugar Planter's Manual - . 10 
 
 Hoare On the Grape Vine oil Open Walls 13 
 
 Hooker's British Flora - - . - 13 
 
 ,, Guide to Kew Gardens - - 13 
 Lindley's Introduction to Botany 
 
 _ _ __ jy 
 
 London's Hortus BritannicuV""' - ^18 
 
 ,, Encyclopaedia of Trees & Shrubs IS 
 
 M Gardening - 18 
 
 Encyclopaedia of Plants - - 18 
 
 ,, Self-Instruction for Gardeuers 17 
 
 ,, (Mrs.) Amateur Gardener - 17 
 
 Rivers's Rose Amateur's Guide - - 2S 
 
 Schleiden's Botany, by Lankester - - 26 
 
 Chronology. 
 
 Allen ou the Rise of tbe Royal Prero- 
 
 Blair's Chronological Tables - 6 
 
 Bunsen's Ancient Egypt ... 7 
 
 Haydn's Book of Dignities - 12 
 
 Commerce and Mercantile 
 Affairs. 
 
 Banfield and Weld's Statistics - - 5 
 
 Gilbart's Treatise on Banking - - 11 
 
 Gray's Tables of Life Contingencies . 11 
 
 Lorimer's Letters to a Master Mariner - 17 
 
 London : Printed by M MASON, Ivy Lane, Paternoster Bow. 
 
2 CLASSIFIED INDEX 
 
 Pages 
 M'Culloch's Dictionary of Commerce 19 
 Steel's Shipmaster's Assistant - 2 
 Symons' Merchant Seamen's Law - 29 
 Thomas's Interest Tables - - 31 
 Thomson's Tables of Interest - oO 
 
 Criticism, History, and 
 Memoirs. 
 
 Blair's Chron. and Historical Tables - 6 
 Bunsen's Ancient Egypt - 7 
 Coad's Memorandum - " . " 
 Conybeare and Howson's St. Paul - S 
 Dandolo's Italian Volunteers - 
 Dennistoun's Dukes of Urbiuo 
 Dunlop's History of Fiction 
 Eastlake's History of Oil Painting - 
 Foss's Judges of England - - JO 
 Foster's European Literature - - J] 
 Gibbon's Roman Empire - 
 Grant (Mrs.) Memoir andCorespoudence 11 
 Hamilton's (Sir William) Essays - - 12 
 Harrison On the English Language - 12 
 Head's Memoirs of Cardinal Pacca - - 13 
 Holland's (Lord) Foreign Remmis- 
 
 PHges 
 Laneton Parsonage - - 27 
 Mrs. Marcel's Conversations 19,20 
 Margaret Percival - - - 27 
 Marryat's Masterman Ready - 20 
 ,, Privateer's-Man - 20 
 
 Mission; or, Scenes in Africa 20 
 Pycroft's Course of Ehglish Reading - 24 
 Twelve Years Ago: a Tale - 31 
 
 Medicine* 
 
 Bull's Hints to Mothers - - 6 
 Management of Children - 7 
 Copland's Dictionary of Medicine - 8 
 Latham On Diseases of the Heart 17 
 Moore On Health, Disease, and Remedy S 
 Pereira On Food and Diet - - 24 
 Reece's Medical Guide - - 2a 
 
 Miscellaneous 
 and General Literature. 
 
 Allen on Royal Prerogative - - - 5 
 Coad's Memorandum 7 
 
 Humphreys's Black Prince - - - 14 
 Jeffrey's (Lord) Contributions - - 1 
 Kemble's Anglo-Saxons in England - 16 
 Macaulay's Essays - - - * 1 
 History of England - - 19 
 Mackintosh's Miscellaneous Works - 19 
 M'Culloch's Dictionary, Historical, Geo- 
 graphical, and Statistical - - - 19 
 Maunder's Treasury of History - - 20 
 Merivale's History of Rome - - - 21 
 Mosheim's Ecclesiastical History - - 22 
 Mure's Ancient Greece . - - 22 
 Rich's Companion to the Latin Dictionary 25 
 Riddle's Latin Dictionaries - - 25 
 Rogers's Essays from the Edinburgh Rev. 25 
 Schmitz's History of Greece - 3C 
 Smith's (S.J_ Lectureson Moral Philosophy 27 
 Southey's The Doctor etc. - - - 28 
 Stephen's Essays * 
 Sydney Smith's Works - 27 
 Taylor's Loyola - - - - 31 
 Thirlwall's History of Greece ... 30 
 Tooke's Histories of Prices - 31 
 Townsend's State Trials 31 
 Twining's Philosophy of Painting - - 31 
 Twiss on the Pope's Letters - - 31 
 Zumpt's Latin Grammar - - - 32 
 
 Geography and Atlases. 
 
 Butler's Ancient and Modern Geography 7 
 ,, Atlas of General Geography - 7 
 Erman's Travels through Siberia - - 10 
 Hall's Large Library Atlas - -12 
 Railway Map of England - - 12 
 Johnston's General Gazetteer - - 16 
 M'Culloch's Geographical Dictionary - 19 
 Murray's Encyclopaedia of Geography - 22 
 Sharp's British Gazetteer - 26 
 
 Juvenile Books. 
 
 Amy Herbert ----- 27 
 Corner's Children's Sunday Book - 8 
 Earl's Daughter (The) - 27 
 Gertrude ------ 27 
 
 Dunlop's History of Fiction - 9 
 Gower's Scientific Phenomena - - 11 
 Graham's English - - 11 
 Grant's Letters from the Mountains - 1 1 
 Haydn's Beatsou's Index - - 12 
 Hooker's Kew Guide . - - - 13 
 Howitt's Rural Life of England - - 14 
 ,, Visits to Remarkable Places - 14 
 Jardine's Treatise of Equivocation - .15 
 Jeffrey's (Lord) Contributions - - 16 
 Kav on Education, etc. in Europe - - 16 
 Loudon's (Mrs.) Lady's Country Companion 17 
 Macaulay's Critical and Historical Essays IS 
 Mackintosh's (Sir J .) Miscellaneous Works 19 
 Maitland's Church in the Catacombs - 19 
 Pascal's Works, bv Pearce - 24 
 Pycroft's Course of English Reading - 24 
 Rich's Companion to the Latin Dictionary 25 
 Riddle's Latin Dictionaries and Lexicon 25 
 
 Seaward ' Narrative of his Shipwreck - 26 
 Sir Roger De Coverley - - 27 
 Southey's Common-Place Books - 28 
 The Doctor etc. - - - 28 
 Stow's Training System - 29 
 Sydney Smith's Works - - - 27 
 Townsend's State Trials - 31 
 Willoughby's (Lady) Diary - - - 32 
 Zumpt's Latin Grammar - - - - 32 
 
 Natural History in 
 General. 
 
 Callow's Popular Conchology 7 
 Doubleday's Butterflies and Moths - 9 
 Ephemera and Young on the Salmon - 10 
 Gosse's Natural History of Jamaica 11 
 Gray and Mitchell's Ornithology - - 11 
 Kirby and Spence's Entomology - - 16 
 
 Elements of Natural History - - 17 
 Maunder's Treasury of Natural History 20 
 Tnrton'sShellsoftheBrilishlslands - 31 
 Waterton's Essay son Natural History - 32 
 
 Gower's Scientific Phenomena - 11 
 Howitt's Boy's Country Book - - 14 
 Children's Year - - 14 
 
 Youatt's The Dog 32 
 
 
TO MESSRS. LONGMAN AND Co.'s CATALOGUE. 
 
 Novels and Works of 
 Fiction. 
 
 Pages 
 
 - 9 
 
 - 12 
 
 - 32 
 
 - 19 
 
 Dunlop's History of Fiction 
 
 Head's Metamorphoses of Apuleius 
 
 Ladv Willoughby's Diary 
 
 Mac'donald's Villa Verocchio - 
 
 Marryat's Masterman Ready 
 
 Privateer's-Maii - - 20 
 
 ,, Settlers in Canada - 
 
 ,, Mission; or, Scenes in Af ica - 
 
 Mount St. Lawrence 
 
 Sir Roger de CoTerley 
 
 Southey's The Doctor etc. 
 
 Twelve Vears Ago : a Tale 
 
 One Vol. Encyclopaedias 
 and Dictionaries. 
 
 Blsine's, of Rural Sporti .... 
 Brande's, of Science, Literature, and Art 
 Copland's, of Medicine - 
 Cresy's, of Civil Engineering - 
 Gwilt's, of Architecture .... 
 Johnson's Farmer ..... 
 Johnston's Geographical Dictionary - 
 Loudon's, of Treesand Shrubs 
 
 ,, of Gardening .... 
 j, of Agriculture .... 
 
 of Plants 
 
 ,, of Rural Architecture 
 M'Culloch's Geographical Dictionary - 
 
 , , Dictionary of Commerce 
 Murray'sEncyclopzcdiaof Geography 
 Ure's Arts, Manufactures, and Mines - 
 Webster's Domestic Economy 
 
 Poetry and the Drama* 
 
 Aikin's (Dr.) British Poets . - 
 Baillie's (Joanna) Poetical Works - 
 Flowers and their Kindred Thoughts 
 Fruits from the Garden and Field - 
 Goldsmith's Poems, illustrated 
 Gray's Elegy, illuminated ... 
 Key's Moral of Flowers .... 
 
 Sylvan Musings .... 
 L.E.L.'s Poetical Works - . . 
 Linwood's Anthologia Oioniensis . 
 Macaulay's Lays of Ancient Rome - 
 Montgomery's Poetical Works 
 Moore's Irish Melodies - ... 
 ,, LallaRookh .... 
 ,, Poetical Works .... 
 Songs and Ballads ... 
 Shakspeare, by Bowdler - ... 
 
 ,. 's Sentiments and Similes 
 Southey's Poetical Works . - - 
 British Poets .... 
 Swain's English Melodies ... 
 Taylor's Virgin Widow .... 
 Thomson's Seasons, illustrated - . 
 
 with Notes, by Dr. A.T.Thomson- 30 
 Watts's Lyrics of the Heart ... 33 
 Winged Thoughts ..... 22 
 
 Political Economy and 
 Statistics. 
 
 Banfield and Weld's Statistics - 5 
 
 Gilbart's Treatise on Banking - - - 11 
 Gray's Tables of Life Contingencies - 11 
 
 Page 
 
 Kay on the Social Condition, etc.of Europe 16 
 Laiug's Notes of a Traveller ... 17 
 M'Culloch's Geographical, Statistical.aud 
 Historical Dictionary ... 
 
 M'Culloch's Dictionary of Commerce - 
 On Taxation and Funding 
 ,, Statistics of the British Empire 
 Marcel's Conversations on Polit. Economy 
 Tooke's Histories of Prices ... 
 
 Religious and Moral 
 Works, etc. 
 
 Amy Herbert ...... 
 
 Bloomfield's Greek Testament 
 
 ,, Annotations on ditto - 
 
 ,, College and School ditto - 
 
 Lexicon to Greek Testament 
 
 Book of Ruth (illuminated) ... 
 
 Callcott's Scripture Herbal - 
 
 Conybeare and Howson's St. Paul - 
 
 Cook's Edition of the Acts - 
 
 Cooper's Sermons - 
 
 Corner's Sunday Book 
 
 Dale's Domestic Liturgy . - . 
 
 Discipline ...... 
 
 Earl's Daughter (The) - 
 Ecclesiastes (illuminated) - 
 Elmes's Thought Book - - 
 
 Englishman's Hebrew Concordance 
 Greek Concordance 
 
 Gertrude - - 
 
 Hook's (Dr.) Lectures on Passion Week 
 Home's 1 ntroduction to the Scriptures - 
 Compendium of ditto 
 
 Howson's Sunday Evening - - - 14 
 Jameson's Sacred and Legendary Art - 15 
 Monastic Legends - * 15 
 
 ,, Legends of the Madonna - 15 
 Jeremy Taylor's Works - - - - 16 
 Laneton Parsonage ----- 27 
 Letters to my Unknown Friends - "17 
 ,, on Happiness - - - - )7 
 Maitland's Church in the Catacombs - 19 
 Margaret Percival ... - 37 
 
 Marriage Service (illuminated) - - 23 
 Maxims, etc. of the Saviour * - - 15 
 Miracles of Our Saviour - - - 15 
 
 Moore on the Power of the Soul - - 21 
 ,, on the Use of the Body - - 21 
 ,, on Man and his Motives - - 21 
 Morell's Philosophy of Religion - - 22 
 Mosheim's Ecclesiastical History - . 22 
 Mount St. Lawrence ... - 22 
 Neale's Closing Scene - 22 
 
 Resting Places of the Just- - 22 
 Newman's (J. H.) Discourses - -22 
 Paley's Evidences, etc., by Potts - -22 
 Parables of Our Lord - 15 
 
 Pascal's Works, by Pearce - - - 24 
 Readings for Lent ----- 16 
 Robinson's Lexicon of the Greek Testa- 
 ment .-----.25 
 Sermon on the Mount (The) - - -23 
 Sinclair's Journey of Life - - - 27 
 ,, Business of Life - 27 
 
 Sketches (The) ..... g7 
 Smith's (G.) PerilousTimes - 28 
 
 ,, Religion of Ancient Britain * 28 
 
 Sacred Annals - - - 27 
 
 ,, Doctrine of the Cherubim - 27 
 
 (J.) St. Paul's Shipwreck - - 28 
 (S.) Lectures on Moral Philosophy 27 
 Solomon's Song (illuminated) - . - 03 
 Southey's Life of Wesley - - . 29 
 Stephen's (Sir J.) Essays ... 29 
 
4 CLASSIFIED INDEX. 
 
 Pages 
 
 Pages 
 
 Sydney Smith's Sermons - 27 
 Tayler's (Rev. C. B.) Margaret - - 29 
 ' V ., Lady Mary - - 29 
 
 Herschel's Outlines of Astronomy - - 13 
 Humboldt's Aspects of Nature - - 14 
 Cosmos .... 14 
 
 Taylor's (J.) Thumb Bible ... 30 
 ., (Isaac) Loyola ... 30 
 Tomline's Introduction to the Bible - 30 
 Turner's Sacred History ... 31 
 
 Hunt's Researches on Light - 15 
 Marcel's Conversations - 19, 20 
 Memoirs of the Geological Survey - - 21 
 Moseley's Practical Mechanics - - 22 
 Engineering and Architecture 22 
 Owen's Comparative Anatomy - - - 23 
 Peschel's Physics - - - 24 
 
 Twis s on the Pope's Letters - - - 31 
 
 Wi'llou'ghby's (Lady) Uiarv - - 32 
 Wisdom of Johnson's Rambler, etc. 16 
 
 Phillips'sPalieozoicFossilsof Cornwall, etc.24 
 Mineralogy, by Miller & Brooke 24 
 Portlock's Geology of Londonderry - 24 
 
 
 Schleiden's Scientific Botany- - - 26 
 
 Rural Sports* 
 
 Smee's Electro-Metallurgy - - 27 
 Steam Engine (Ure), by the Artisan Club 5 
 
 
 Tate on Strength of Materials - - 29 
 
 Blaine'sDictionaryof Sports - - 6 
 
 Thomson's School Chemistry - - 30 
 
 Ephemera on Angling 10 
 's Book of the Salmon - 10 
 Hawker's Instructions to Sportsmen - 12 
 
 Veterinary Medicine. 
 
 The Hunting Field - 12 
 Loudon's(Mrs.) Lady'sCountryCompanion 17 
 Pocket and the Stud - - - - 12 
 Practical Horsemanship - - - - 12 
 Pulman's Fly-Fishing .... 24 
 Ronalds's Fly-Fisher .... 25 
 Stable Talk and Table Talk - 12 
 
 rri_ t IT* iJ 10 
 
 The Pocket and the Stud - - - 12 
 Practical Horsemanship - 12 
 Stable Talk and Table Talk - 12 
 The Stud for Practical Purposes - - 12 
 
 The Horse - - - . 32 
 
 The Stud, for Practical Men ... 12 
 
 
 Wheatley's Rod and Line - 32 
 
 
 
 Voyages and Travels. 
 
 The Sciences in General 
 and Mathematics. 
 
 Chesney's Euphrates and Tigris - - 7 
 Erman's Travels through Siberia - - 10 
 Forbes's Datromey - - 10 
 
 Bourne's Catechism of the Steam Engine 6 
 Brande's Dictionary of Science, etc. - 6 
 Conversations on Mineralogy 7 
 DelaBecheontheGeology ol Cornwall, etc. 9 
 
 Forester and Bid dulph'a Norway . 10 
 Head's Tour in Rome - - 13 
 Humboldt's Aspects of Nature . 14 
 Laing's Notes of a Traveller - - 17 
 Power's New Zealand Sketches . 24 
 
 's Geological Observer - 8 
 De la Rive's Electricity .... 9 
 
 Richardson's Overland Journey . - 25 
 Rovings in the Pacific - - . . 25 
 
 Dizon's Fossils of Subsex ... 9 
 Gower's Scientific Phenomena - .11 
 
 Seaward's Narrative of his Shipwreck - 26 
 Snow's Arctic Voyage - ... 28 
 
 
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 HARRISON. ON THE RISE, PROGRESS, AND PRESENT 
 
 STRUCTURE OF THE ENGLISH LANGUAGE. By the Rev. M. Harrison, M.A., late 
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 HARRY HIEOVER. THE HUNTING-FIELD. 
 
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 HARRY HIEOVER. PRACTICAL HORSEMANSHIP. 
 
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 HARRY HIEOVER. THE STUD, FOR PRACTICAL PUR- 
 
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 HAWKER. INSTRUCTIONS TO YOUNG SPORTSMEN 
 
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 HAYDN. THE BOOK OF DIGNITIES; 
 
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 HEAD. THE METAMORPHOSES OF APULEIUS: 
 
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PUBLISHED BY MESSRS. LONGMAN AND Co. 13 
 
 HEAD. HISTORICAL MEMOIRS OF CARDINAL PACCA, 
 
 Prime Minister to Pope Pius VII. Written by Himself. Translated from the Italian, by Sir 
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 SIR JOHN HERSCHEL. OUTLINES OF ASTRONOMY. 
 
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 MRS. HEY. THE MORAL OF FLOWERS* 
 
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 HINTS ON ETIQUETTE AND THE USAGES OF SOCIETY: 
 
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 HOARK A PRACTICAL TREATISE ON THE CULTIVA- 
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 HOOK (DR. W. F.) THE LAST DAYS OF OUR LORD'S 
 
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 HORNE (THE REV. T. H.) AN INTRODUCTION TO THE 
 
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 HORNE (THE REV. T. H.) A COMPENDIOUS INTRODUC- 
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=% 
 14 NEW WORKS AND NEW EDITIONS 
 
 HOWITT THE CHILDREN'S YEAR. 
 
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 HOWITT. THE BOY'S COUNTRY BOOK; 
 
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 HOWSON SUNDAY EVENING: 
 
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 HOWSON AND CONYBEARE. THE LIFE AND EPISTLES 
 
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 HUDSON THE EXECUTOR'S GUIDE. 
 
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 HUDSON. PLAIN DIRECTIONS FOR MAKING WILLS 
 
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 HUMBOLDT ASPECTS OF NATURE, 
 
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 BARON HUMBOLDT'S COSMOS; 
 
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PUBLISHED BY MESSRS. LONGMAN AND Co. 15 
 
 HUMPHREYS. THE BOOK OF RUTH. 
 
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 HUMPHREYS.-MAXIMS A!\ T D PRECEPTS OF THE SAVIOUR: 
 
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 HUMPHREYS. THE MIRACLES OF OUR SAVIOUR. 
 
 HUMPHREYS. PARABLES OF OUR LORD. 
 
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 HUNT. RESEARCHES ON LIGHT: 
 
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 MRS. JAMESON'S LEGENDS OF THE MONASTIC ORDERS 
 
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 JARDINE. A TREATISE OF EQUIVOCATION. 
 
 Wherein is largely discussed the question Whether a Catholicke or any other Person before 
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 (notwithstanding his perfect knowledge to the contrary) without Perjury, and securely in 
 conscience, answer No : with this secret meaning reserved in his mynde - That he was not 
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16 NEW WORKS AND NEW EDITIONS 
 
 JEFFREY (LORD). CONTRIBUTIONS TO THE EDINBURGH 
 
 RB VIEW. By Francis Jeffrey, late One of the Judges in the Court of Session in Scotland. 
 Second Edition. Svols.Svo. 42. cloth. 
 
 BISHOP JEREMY TAYLOR'S ENTIRE WORKS: 
 
 With the Life by Bishop Heber. Revised and corrected by the Rev. Charles Page Eden, 
 Fellow of Oriel College, Oxford. Vols. II. III. IV. V. VI. VII .and VIII. 8vo.lO.6rf. each, 
 cloth. 
 
 In course of publication In 10 vol. price half-a-guinea each. Vol. I. (the last in order 
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 [Pol. IX. it in the press. 
 
 READINGS FOR EVERY DAY IN LENT. 
 
 Compiled from the Writings of Bishop Jeremy Taylor. By the Author of "Amy Herbert," 
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 JOHNSON. THE WISDOM OF THE RAMBLER, ADVEN- 
 
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 JOHNSON. THE FARMER'S ENCYCLOPEDIA, 
 
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 KINDERSLEY. THE VERY JOYOUS, PLEASANT AND 
 
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 KIRBY AND SPENCE. AN INTRODUCTION TO ENTO- 
 
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 L E. L. THE POETICAL WORKS OF LETITIA ELIZABETH 
 
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PUBLISHED BY MESSRS. LONGMAN AND Co. 17 
 
 LAING. OBSERVATIONS ON THE SOCIAL AND POLI- 
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 LATHAM. ON DISEASES OF THE HEART. 
 
 Lectures on Subjects connected with Clinical Medicine ; comprising 1 Diseases of the Heart. 
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 LEE. TAXIDERMY. 
 
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 LEE. ELEMENTS OF NATURAL HISTQRY; OR, FIRST 
 
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 LETTERS ON HAPPINESS, ADDRESSED TO A FRIEND. 
 
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 LETTERS TO MY UNKNOWN FRIENDS. 
 
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 LINDLEY. AN INTRODUCTION TO BOTANY. 
 
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 Additions. 2 vols. Svo.with Six Plates and numerous Woodcuts, 24j. cloth. 
 
 LINWOOD (W.) ANTHOLOGIA OXONIENSIS; 
 
 Sive, Florilegium e lusibus poeticis diversorumOxoniensium Grjecis et Latinisdecerptum. 
 
 Curante Gulielmo Linwood, M.A. .Sdis Christi Alummo. Svo. 14*. cloth. 
 " Were the prize of song- to be awarded by our arbitration between the competing Minstrels 
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 more of airiness and variety, the Anthologin is not inferior in poetical spirit ; while in 
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 LORIMER. LETTERS TO A YOUNG MASTER MARINER 
 
 On some Subjects connected with his Calling. By the late Charles Lorimer. A New Edi- 
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 LOUDON. THE AMATEUR GARDENER'S CALENDAR: 
 
 Being a Monthly Guide, as to what should be avoided as well as what should be done in a 
 Garden in each Mouth : with plain Rules how to do what is requisite ; Directions for laying 
 out and planting Kitchen and Flower Gardens, Pleasure Grounds, and Shrubberies: and a 
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 LOUDON THE LADY'S COUNTRY COMPANION; 
 
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 LOUDON'S SELF-INSTRUCTION FOR YOUNG GARDENERS, 
 
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 With a Portrait of Mr. Loudon, and a Memoir by Mrs. Loudon. Svo.with Wood Engravings, 
 7s. 6d. cloth. 
 
18 
 
 NEW WORKS AND NEW EDITIONS 
 
 LOUDON'S ENCYCLOPAEDIA OF TREES AND SHRUBS: 
 
 Being ;the Arboretum et Fruticetum Britannicum abridged: containing the Hardy Trees 
 and Shrubs of Great Britain, Native and Foreign, scientifically and popularly described : 
 with their Propagation, Culture, and Uses in the Arts. 8vo. with upwards of 2,OOOEngravings 
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 LOUDON'S ENCYCLOPAEDIA OF GARDENING: 
 
 Comprising the Theory and Practice of Horticulture, Floriculture, Arboriculture, and 
 Landscape Gardening : including all the latest Improvements ; a General History of Garden- 
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 Future Progress in the British Isles. By J. C. Loudon, F.L.S. H.S., etc. ' Illustrated with 
 nisiny hundred Engravings on Wood by Branston. An entirely New Edition (1850), cor- 
 rected throughout and considerably improved by Mrs. Loudou. In One large Volume, 8vo. 
 
 LOUDON'S ENCYCLOPAEDIA OF AGRICULTURE: 
 
 Comprising the Theory.and Practice of the Valuation, Transfer, Laying-out, Improvement, 
 and Management of Landed Property, and of the cultivation and economy of the Animal and 
 Vegetable Productions of Agriculture, including all the latest improvements. Fifth 
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 LOUDON'S ENCYCLOPEDIA OF PLANTS: 
 
 Including all the Plants which are now foundin, or have been introduced into, Great Britain | 
 giving their Natural History, accompanied by such Descriptions, Engraved Figures, and 
 Elementary Details, as may enable a beginner, who is a mere English reader, to discover the 
 name of every Plant which he may find in flower, anil acquire all the information respecting 
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 LOUDON'S ENCYCLOPAEDIA OF COTTAGE, FARM, AND 
 
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 requisite Fittings-up, Fixtures, and Furniture, and appropriate Offices, Gardens, and Garden 
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 Wood, 63*. cloth. 
 
 LOUDON'S HORTUS BRITANNICUS; 
 
 Or, Catalogue of all the Plants indigenous to, cultivated in, or introduced into Britain. An 
 entirely New Edition (1850), corrected throughout: with a Supplement, including all the 
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