ItKtllV LIBRAR uwivfMiTY CMIfORNIA THE STEAM-ENGINE. THE STEAM-ENGINE; BEING A POPULAR DESCRIPTION OF THI CONSTRUCTION AND ACTION OF THAT ENGINE ; A SKETCH OF ITS HISTORY, AND OF THE LAWS OF HEAT AND PNEUMATICS. ILLUSTRATED BY A NUMBER OF WOOD ENGRAVINGS. BY HUGO REID, LECTURER ON CHEMISTRY, ETC. SECOND EDITION, REVISED AND ENLARGED. EDINBURGH: WILLIAM TAIT, PRINCE S STREET ; J. M'LEOD, GLASGOW; SIMPKIN, MARSHALL, & Co., LONDON; AND JOHN CUMMING, DUBLIN. MDCCCXL. GLASGOW: W. Lowe and Co., Printers, 7, Queen Street. T PREFACE. THE Steam-engine is so interesting a subject from the extent and variety of its applications, the great power with which it has armed mankind, the varied forms in which it meets us at every turn, the singular ingenuity of its construction, the beautiful mechanical contrivances which it presents, and the many great laws of nature which it illustrates that there are few who do not desire some knowledge of its structure and mode of action. The present work is designed to furnish to the gen- eral reader such an account of this great machine as may be easily understood by those who are previously unacquainted with the subject. The general laws of HEAT and PNEUMATICS, on which the action of the engine depends, are fully detailed ; its construction and mode of action are minutely explained, so that, with the aid of the figures, it may be readily under- stood, even by those who have never seen an engine ; and the different forms into which the engine is thrown, to fit it for its various applications, are sepa- rately described. A sketch of its origin and progress is given, as every one must be desirous to know some- 180 VI PREFACE. thing of the history of an invention, second only to that of Printing in the magnitude of the results which have flowed from it, and far surpassing that operation in the genius displayed in its conception, and the points of interest it offers to the intelligent observer. It is hoped that this little work may furnish the general reader with all that he requires on the subject of the Steam-Engine, and enable him, when he meets one, to observe its motions with that interest and en- joyment which a knowledge of its structure is calcu- lated to impart. The author trusts, also, that it may be useful, as an introduction or guide, to smooth the path for those who intend to prosecute the study more fully. In page 224 will be found a list of books on the Steam-Engine, which may be studied or con- sulted by those who wish to go farther than this work can carry them. The full scope of Steam, in its varied applications, is yet but dimly seen. Even now, it may be deemed an eighth wonder of the world, from the changes it has wrought in the Arts and Manufactures. But its powers of increasing the swiftness, multiplying the means, and reducing the expense of locomotion, are only beginning to be developed. The wonders it is to work in this respect cannot be properly estimated until the time, which is fast approaching, when the great wilderness of the ocean shall present a stirring scene like what meets us near some crowded port. The ocean will be alive with steam. The paddle wheel PREFACE. Vll will be heard, and the dark wreath will be seen where nought but the howl of the tempest or foam of the breaker has before disturbed the solitude of the deep. The shipwrecked mariner, tossed in his open boat, or drifted in his shattered bark, with scarcely a hope to cheer him, will not then wait long for a rescue. Stir- ring, hurried, exciting, as the world is at present, it is calmness and lethargy to what a century will bring forth. What a busy, bustling, buzzing world it will be, when the people of the most remote climes will be whisking past each other on the waters, in every direction ; when India, - North and South America, the myriads of fruitful and sunny isles in the Indian and Pacific oceans, and the continent of Australia, will be connected by regular and frequent steam-com- munication ; when the resources of these hitherto desert countries will be developed, capital introduced, the arts and comforts of civilised life established, a busy, active and intelligent population created, when every little nook over the wide surface of the earth shall have its ships and railroads its ports and marts, its spot where " merchants most do congregate ;" and every port shall be crowded with these active messen- gers, arriving in rapid succession, with news, and tra- vellers, and treasure, from all quarters of the globe. Then will the power of steam be felt ; and those joint sovereigns, the Printing Press and Steam-Engine, will receive the homage of all the nations of the earth, and be acknowledged as the master-spirits who have created a new world. Vlll PREFACE. Since the remarks in the body of the work on the invention of the Steam- Engine were printed,* I have perused the life of Watt by Arago, in which there are some observations on that subject. Where there are so many, who have each contributed a little to an in- vention, it is not possible to fix on one as the inventor; and M. Arago properly remarks, " By seeking to discover a single inventor where it was necessary to recognise many, we have been in ' endless mazes lost.' " This remark is particularly just when applied to the invention of the Steam-Engine. As elsewhere remarked (par. 185,) no one, except Watt, can be singled out pre-eminently. But, on reading M. Arago' s remarks, it does not appear that he has adhered to the rule he has himself laid down. Two Frenchmen, DE CAUS, and PAPIN, are particularly held forth, as the grand originators of ideas, which others have only extended; and peculiar honour is awarded to them, to the dis- paragement of PORTA, SAVERY, and NEWCOMEN ; all of w T hom, according to my own view, and the two latter acording to the generally received opinions, have claims fully equal, if not superior, to those of M. Arago's favourites. In one point, I certainly concur heartily with the distinguished author of the Eloge on Watt ; namely, with respect to the claims of the Marquess of WOR- CESTER. I cannot consider that there are any sufficient grounds for assigning to that nobleman, a place among the inventors of the Steam-Engine. See par. 183. With regard to DE CAUS, M. Arago observes, " I cannot allow that that individual accomplished nothing which was useful, who, pondering upon the enormous pow T er of steam, raised to a high temperature, was the first to perceive that it might serve to elevate great * These are not altered from the first edition of this work. PREFACE. IX masses of water to all imaginable heights. I cannot admit that no gratitude is due to that engineer who was the first also to describe a machine which was capable of realising such effects." There is a mixture of truth and exaggeration in the above quotation, which would be very apt to mislead one who is not precisely aware of what DE CAUS had effected, and what had been done previously by others. It is true that DE CAUS was the first to propose the application of steam to raise water on the large scale. It is true that DE CAUS described a thing which he called a machine, by which water put into the machine might be raised above it, But DE CAUS did not perceive this useful application of steam by " pondering," as if he was the original discoverer of this power of steam; for, 10 years previously, in a work with which there is good rea- son to believe that DE CAUS was acquainted, BAP- TIST A PORT A had shewn that imprisoned steam would raise water, and given a drawing of a small machine, far more effectual than that of DE CAUS ; though he did not propose it as a machine for the purpose of raising large quantities of water for use. And, the machine which DE CAUS described " ca- pable of realising such effects" was no more capable of realising any useful end than PORT A' s. It was only fit for a toy, or for an experimental illustration of a phi- losophical truth. We are not to consider it as a useful machine because DE CAUS loosely described it as such. In truth, PORT A' s drawing was a far better hint for a useful machine, than that of DE CAUS.* * Porta formed the steam in a vessel separate from that con- taining the water to be raised. Mr. ROBEUT STUART, in his very instructive and entertaining work " Historical and Descrip- tive anecdotes of Steam-Engines," remarks of Porta, " The author, it is admitted, made no application of his apparatus as a mode of raising water, directly by the force of steam, from rivers X PREFACE. PORTA, then, pointed out the principle, and metho d of applying it. DE CAUS proclaimed this may be made useful. We can place no value whatever on his drawing of a machine : it was useless. The sug- gestion of the application on the large scale is all we owe to DE CAUS, and that was certainly an important step. But PORT A ought not to be forgotten : DE CAUS is not entitled to be considered as the inventor of a machine, capable of giving effect to his suggestion, thereby exaggerating his merits, and detracting from those of SAVERY, who followed him, and worked out the idea into a practicable form. PORTA, DE CAUS, and SAVERY, were on the same track, raising w T ater by steam directly applied, and must be associated together. SAVERY was the first to construct a truly serviceable engine, to go beyond the bare idea ; and he did so by combining ingeniously together a number of beautiful contrivances and ad- justments, many of them entirely new. See par. 191. " It is to PAPIN," says M. Arago, " that France owes the honourable rank she may claim in the his- tory of the Steam-Engine." PAPIN is certainly en- titled to more credit than is generally allowed him, and I trust full justice has been done to him in this work : See par. 185, &c. But taking the highest estimate of the value of his invention, and of the genius it displayed, it is surely too much to associate and fountains ; but his diagram and description are so complete, that its application to this purpose by another, could not be con- sidered even as a variation of his idea." M. Arago rejects PORTA altogether from the catalogue of contributors to the invention of the Steam-Engine, because he did not propose a machine for use on the large scale " did not speak, either direct- ly or indirectly, of any machine.' 1 '' Surely this is treating lightly the value of the principle, and of the clear hint how to apply it, which PORTA'S apparatus gave, and which formed the leading and distinguishing features of the new power. DE CAUS could have been better spared than POKTA. PREFACE. XI him with WATT in the following manner : " "When the immense services already rendered by the Steam- Engine shall be added to all the marvels it holds out to promise, a grateful population will then familiarly talk of the ages of Papin and Watt." Why, in this enumeration of the landmarks of an era, is NEWCOMEN forgotten, who developed the capa- bilities of the scheme of PAPIN, on which his claims rest, but which he never was able to work out, and left in a perfectly useless condition. NEWCOMEN, by a great number of beautiful contrivances, brought this crude project into practice (par. 216, 235, and 236,) at the very time when it was abandoned by its parent, so completely abandoned, that, though he was still en- deavouring to work out the application of steam, he proceeded on a totally different principle. See par. 208, 209. Why is PAPIN placed on a level with WATT, who not only suggested a new and beautiful principle, (se- parate condensation), fully equal in novelty and in- genuity to PAPIN'S ; but gave practical effect to that principle, and extended immensely its range of appli- cation, by a number of the most ingenious, beautiful, and novel mechanical contrivances; who shewed such 1 fertility of resources, in meeting the difficulties which the extended applications and more complex structure of the engine offered to him ; who brought his machine into such a state not only inventing the principle, but extending and adding so much to it, that seventy years' experience has suggested few material improve- ments on it? WATT did far more for the Steam-Engine than PAPIN and NEWCOMEN combined. The separate condensation was but a small part of what WATT did. If, however, M. Arago's estimate of the other parts of WATT'S labours, as will be naturally drawn from the following passage, be correct, there are good Xll PREFACE. grounds for placing WATT and PAPIN side by side, or even placing PAPIN above WATT; though it is usually considered that WATT'S merits lay very much in those identical contrivances spoken so lightly of : " It was to the production of an economical moving power, capable of effecting the unceasing and power- ful strokes of the piston of a large cylinder, that PAPIN consecrated his life. The procuring afterwards from the strokes of the piston, the power requisite to turn the stones of a flour mill, the rolls of a flatting mill, the paddles of a steam-boat, the spindles of a cotton mill ; or to uplift the massy hammer, which with oft- repeated stroke, thunders upon the enormous masses of redhot iron just taken from the blast-furnace ; to cut with great shears thick metal bars, as easily as you divide a ribband with your scissors ; these, I repeat, are problems of a very secondary order, and which would not embarrass the most ordinary en- gineer." Surely there is some mistake. One would consider the above an extract from an Eloge on PAPIN, not on WATT. These problems, which " would not embarrass the most ordinary engineer," involve WATT'S happiest efforts the invention of the parallel motion, double acting engine, expansively acting engine, and the application and adjustment of the crank, governor, fly-wheel, &c. They were a stumbling-block to SMEATON, long after PAPIN' s idea had received all the perfection of which it was capable. Having, both in the former and present editions of this work, given a more favourable view of the share of the French (Ds CAUS and PAPIN) in this great in- vention ; and a less favourable estimate of the claims of Lord WORCESTER, than most British authors; I trust I will not be accused of a national leaning in the pre- ceding remarks. Suum cuique tribuito has been my guide ; how far I may have adhered to it, others must PREFACE. Xlll judge. I have given what appears to me, on 6!ata accessible to every one, the true state of the case. Let me add, in justice to the distinguished man on whose views I have ventured to remark, and to my- self, that it is impossible to assign a positive numeri- cal value to the services of each inventor, and that the estimate of the comparative value of each step will therefore vary with the intellectual constitution of the individual who judges of it. There must be a positive in this as in every thing else ; but the degrees are too small, the distinctions too subtle, to enable us to de- tect and define it. ERRATUM. Page 2U9, loth line from bottom, /or 520 read 420. CONTENTS. INTRODUCTION PART I. Attraction and Repulsion, and their Application as Moving Powers 5 Sect. I. ATTRACTION ....... Chap. I. Attraction of Cohesion . Attraction of Cohesion as a Moving Power II. Attraction of Gravitation, or Gravity 9 A. Power from the Descent of Heavy Bodies B. Pressure of the Atmosphere . Power from the Atmospheric Pressure Sect. II. REPULSTOW ... 20 Chap. I. Manner in which Heat spreads . II. Effects of Heat . III. Expansion The Thermometer Rate of Expansion in Bodies IV. Elasticity of Gaseous Bodies Gaseous Elasticity as a Moving Power The Air- Pump ... 44 V. Vaporisation ... 45 - A. Vaporisation as a Moving Power 46 B. Return of Vapours to the Liquid State 48 C. Influence of Pressure on Vaporisation 49 D. Force of Steam .... 51 VI. Latent Heat ...... 58 PART II. Chemical Relations of Water, Coal, and Iron PART III. History and Description of the Steam-Engine in its various forms Sect. I. ^Eolipile, B. C. 130 Organ of Gerbert, 12th century Steamboat of Garay, 1543 . Baptista Porta, 1606 .... De Caus, . 1615 Branca, 1629 Worcester, . 1663 Morland, . 1683 Papin, 1690 II. SAVERY, . . 1698 HI. PAPIN and DESAGUUERS Papin, . . 1707 Desaguliers, . 1?18 -First, The machinery which comes into immediate contact with the substance to effect some change upon which is the ultimate object of the operation ; second, The engine, or machine, which sets that machinery in motion. The latter is called the first mover, first moving poicer, or prime mover. 3. In a common turning lathe, or in the case of the 2 INTRODUCTION. hand-ptfmp for raising water ; in the windmill ; or the water-wheel for moving a grindstone the MAN who, by his muscular power, sets the turning lathe in motion, or works the handle of the pump ; the VANES OF THE WINDMILL ; and the WATER- WHEEL are the first movers. It is in them that the motion com- mences their object being simply the production of moving power, which has to be transmitted from them to the machinery which comes into immediate contact with the wood to be turned, the water to be raised, or the corn to be ground. The steam-engine is a FIRST, or PRIME MOVER. 4. In every case of the production of motion by machinery, the first mover is simply an engine, or machine, so constructed as to take advantage of some natural properties of bodies which are capable of giving rise to motion. In describing the steam-engine, then, there are two things to be considered : First, Those natural powers resident in bodies from which we pro- cure a force, or moving power ; Second, The machine, or engine, by which those powers are made effective for the general production of motion. We shall first direct our attention to the former the source and mode of action of the natural forces, which, in the steam-engine, give rise to the motion. 5. Infinitely various as the different kinds of power may, at first sight appear, and however complex the machinery by which they are applied so as to produce motion, upon analyzing them, it will be found that there are only three sources from which we can obtain a force, or moving power ANIMAL STRENGTH, AT- TRACTION, and REPULSION. 6. Of these, the first and most obvious, and the only one within reach of man in an uncultivated condition, is the MUSCULAR POWER OF ANIMALS, or, as it is fre- quently called, ANIMAL STRENGTH. This source of INTRODUCTION. power resides in the muscles long, fleshy bodies, of a fibrous structure, fixed at each extremity, and pos- sessed of the property of contracting, (diminishing in length,) in obedience to the will of the animal. By this concractile power, the more movable of the points to which the extremities of the muscle are attached, is made to approach the other. These muscles are possessed of great strength, being capable, as has some- times happened, of breaking the bone to which they are attached. The muscles of the thumb are believed to exert a force nearly equal to a weight of 4000 pounds. We have familiar examples of the applica- tion of this power, in the plough, carts, and carriages, canal-boats, horse and cattle mills, all set in motion, and continued in that state by the contractile power of the muscles of animals. This power is not made use of in the steam-engine ; but the power of an engine is generally estimated by the number of horses that would be required to do the same work the first steam-engines having been used chiefly as substitutes for horse labour. 7. The other two sources of moving power are First, THE ATTRACTION WHICH EXISTS BETWEEN BODIES, and tends to make them approach each other ; and, Second, THE REPULSIVE POWER, which exists, more or less, in all bodies, and tends to drive their par- ticles asunder. These influences are universally diffused through bodies, and are antagonists i. e., opposed to each other in their action. To the operation of these fundamental properties of matter, all the phenomena of inanimate nature can be traced ; and animate beings, though endowed with the independent principle of life, are in no small degree subject to their control while living, and when dead, are solely obedient to the laws of these great powers. They act with great energy, and both have been 4 INTRODUCTION. used as sources of power in the steam-engine. The first is applied in some kinds of engines only (now called atmospheric engines) ; the latter, either applied directly as a moving power, or used to prepare for the action of the attractive force, has been a leading ele- ment in the operation of every sort of steam-engine ; and, as steam is the medium through which the repul- sive power is introduced, all are called steam-engines, although the steam may not be the direct cause of the motion. At first they were termed fire-engines, the steam being formed by the action of fire upon water. 8. The attractive force was taken advantage of by man as a moving power as in the water-wheel, the windmill, the common pump long before the repulsive principle was applied, or even thought of, as a source of motion. Now, however, this great power, so long overlooked, has almost entirely superseded the other ; acting in the form of steam, it is seen everywhere, and is the prime mover chiefly employed by civilized nations of modern times. For ages a hidden treasure, it has at last been brought to light ; and has placed within the reach of mankind a force so enormous, that it is limited only by the strength of the materials which must be employed to give it effect ; a power unremit- ting in its labours and universal in its applications ; so versatile, that it may be transferred from place to place, worked at any time, and suspended or set in action again at a moment's warning ; and withal, so steady and regular, so manageable, so completely under our control, and possessed of a self-regulating property to such an extraordinary extent, that it almost realises the fable of Prometheus, and may fitly be compared to an intelligent being devoted to our service. PART I. OF THE PHENOMENA OF ATTRACTION AND REPULSION, AND THEIR APPLICATION AS MOVING POWERS. 9. EXCLUDING the vital energy, then, which give rise to muscular motion and all the phenomena of life, there are two great powers which are (one or other, or both) concerned in producing all the motions and changes which we see going on around us. These are ATTRACTION and REPULSION : they are universally dif- fused through bodies ; and they are antagonists i. e., opposed to each other in their action. 10. As the latter, Repulsion, is called into action in an unusual degree in bodies which are heated, while its power seems to diminish in proportion as they are cooled, it has generally been regarded as identical with the influence which gives rise to the phenomena of heat. THE STEAM-ENGINE. SECTION I. ATTRACTION. 11. THE universal influence, Attraction, which ope- rates in drawing bodies and the particles of bodies together, and retaining them in contact, is of several kinds,* of which two chiefly must be attended to in the consideration of force, or motion : First, That which forms bodies into coherent masses, acting be- tween their minute particles only when in contact, (at insensible distances,) called the attraction of cohesion, attraction of aggregation, or simply cohesion; illus- trated by the firmness with which the particles of a piece of iron or marble adhere to each other: and, second, That which brings and retains bodies near to each other, acting at sensible or apparent (indeed at all possible) distances, called the attraction of gravita- tion, or simply gravitation, illustrated by a stone falling to the ground when left in the air unsupported. 12. Probably the phenomena of every kind which consist in a drawing together or holding together of * We here omit chemical attraction or affinity, electric attrac- tion, and magnetic attraction. The first, acting between the particles of different bodies, unites them together, gives rise to new varieties of bodies, and to the phenomena of combination and decomposition; but is not a source of visible motion. The two latter give rise to distinct motion ; but the moving power exerted has hitherto been considered unfit for use as a mechani- cal force, working through too short a distance, and not being easily procured. Attempts have lately been made, however, to render magnetism efficient for this purpose. THE STEAM-ENGINE. bodies, arc the result of one fundamental power. But it is convenient to subdivide them, and to make dis- tinctions between the different effects produced. CHAPTER I. ATTRACTION OF COHESION. 13. When we attempt to break a piece of wood, stone, glass, ice, or any other solid, we find that its particles are firmly bound to each other, and that the exertion of a considerable force is necessary before we can effect a separation. The force which binds the particles so firmly together, and which must be over- come by some superior force before we can break the solid, is spoken of as the ATTRACTION OF AGGREGATION, Or ATTRACTION OF COHESION. 14. It is particularly to this form of attraction that the repulsive influence is opposed, as we see in water, which, when cooled, (see note to paragraph 114,) be- comes ice, in which cohesion predominates, and the particles are firmly bound to each other, so as to form a solid; while the ice, when heated, again becomes water, in which the cohesive attraction is neutralized or overcome, and the particles are loosened, so as to be movable upon each other. Application of Attraction of Cohesion as a Moving Power. 15. This force has never been used as a source of motion, except, perhaps, in the following remarkable instance, in which it was happily applied for that pur- pose : The walls of a building in Paris had declined from the perpendicular, and v ere in danger of falling 8 THE STEAM-ENGINE. outwards, from the pressure of a heavy roof. By the following plan, suggested by M. Molard, -they were restored to the upright position. A number of iron bars were stretched across the upper part of the build- ing, passing freely through the walls. The bars were heated, in consequence of which they increased in length (57), and parts of the bars, at first within the walls, were now exterior to them. In this state, the bars vferejfiased to the walls. They were then allowed to cool ; when cooled, they returned to their former size, and, being firmly fixed to the walls, necessarily pulled them inwards, (towards each other;) the con- traction of the bars taking place gradually, but with great force. By repeating this process several times, the walls were restored to the perpendicular. Here the repulsive influence, repelling the particles of the bar, made it longer. When the bar had cooled, some power drew the particles back to their former dis- tances. This force is considered the same as that which binds the particles of a solid so firmly together the attraction of cohesion. 16. The same means were used to save from destruc- tion Armagh Cathedral, in Ireland, by restoring to the perpendicular the pillars, which were considerably in- clined, and on the stability of which the whole struc- ture depended. These are two very interesting and striking illustrations of the application of scientific knowledge to practical purposes, and of the truth of the fine saying knowledge is power. 17. Though this force is not, in ordinary cases, made use of as a moving power by giving materials rigidity, and strength, and firmness, so" as to bear pulls, strains, thrusts, and pressure of every kind without yielding, it is an essential element in giving effect to other moving powers. Cast-iron pillars, chain piers, iron cables, steam-engines, suspension bridges, are striking TIIE STEAM-ENGINE. 9 instances of the power of the cohesive attraction. See an interesting account, in The Penny Magazine for 1836, of the suspension bridge at Fribourg. The great force of the cohesive attraction is well illustrated by the following table, shewing the loads required to break (i. e. overcome the cohesion of) a prism, or cylinder, of one square inch transverse section, of the following bodies, if suspended from them. Pounds Avoirdupois. Rope, or hempen fibres .... 6,400 Memelfir 9,540 Beech 12,225 Ash 14,130 Copper 19,072 Cast-iron 19,096 English malleable iron .... 55,872 Swedish do. do 72,064 Cast-steel 134,256 The cohesive attraction, and. friction (arising from the roughness of the surfaces of bodies), are the sources of that resistance, without which we could not have any control over motion, or power of regulating it. CHAPTER II. ATTRACTION OF GRAVITATION, OR GRAVITY. 18. The peculiar feature of those cases of attraction which are classed under " gravity," is, that the sub- stances drawn towards each other are at distances ap- parent to our senses ; or, if in contact, yet not so near as to be within the sphere of action of the cohesive attraction. A stone falling to the ground is an example of the attraction of gravitation. It is retained there with a certain force, and cannot be lifted without JO THE STEAM-EiNGINE. applying force : the attraction between the earth and the stone, is the force which retains it there. But it does not stick to the ground in the same way in which its particles adhere to eacli other ; therefore, although, to our sense of vision, apparently in close contact with the ground, it is not so near as to be within reach of the cohesive attraction ; not so close as the particles of the stone are to each other. 19. When a heavy body is suspended by a wire, its GRAVITY pulls it towards the ground ; causes it to hang perpendicularly, giving it that property of downward force which we call weight. The cohesive attraction, binding the particles of wire firmly to' each other, enables it to support the weight. 20. This attractive force is found to operate between all bodies, at whatever distances ; and it acts with a force directly proportional to the mass of matter, and in inverse proportion to the square of the distance. Thus, if the distance be 1, and the attractive force 1, (the mass remaining the same,) the following propor- tions will hold : Distance. Force. 1 1 21. The earth being of a globular form, and so enormous a mass (7912 miles in diameter) compared with any of the bodies on its surface in regard to them^ the earth, though continually in motion, may be looked upon as a fixed body, drawing towards its centre, with a prodigious force, everything which rests on its surface. 22. Formerly, this was the great source of motion for all sorts of machinery ; and it was procured from THE STEAM-ENGINE. 11 the falling of water, which was made to strike upon a board, or fall into a bucket, fixed to one side of a wheel. Its weight and force in falling, pressed the board or bucket downwards ; and, by having a series of these around the wheel, a continuous circular motion was procured. The motion in the vanes of a wind- mill is also an example of powder from the force of gravity. These methods have now been almost en- tirely superseded by the steam-engine. When Watt's steam-engines first came into use, some of them, in- stead of being applied directly, as now, to work machinery, were used to raise water to turn a water- wheel, by w r hich the machinery was impelled; and Papin's engine was proposed by him to be applied in a similar manner. 23. This source of power is not applied in the modern steam-engine ; but, in the first forms the engine assumed as in the engines of Newcomen, Savery, Leopold ; and even in Watt's first engine (single acting) it was a leading element. There were two ways in which it was taken advantage of : First, In causing the descent of heavy bodies, as in New- comen' s, Leopold's, and Watt's first engine; second, In producing that constant force, acting on all bodies at the earth's surface, which we call atmospheric pressure. A. Power from the Descent of Heavy Bodies. 24. In Newcomen' s, Leopold's, and Watt's first en- gine, this power performed the important, though secondary office, of restoring the parts to the proper situation for the exertion of the other or direct mov- ing power. Indeed the descent of a heavy body can hardly be called a source of power (except in the case of a natural fall of water) ; for, as much force is 12 THE STEAM-ENGINE. expended in raising the heavy body to the necessary height as is procured by its fall ; so that there can be no gain of moving power. B. The Pressure of the Atmosphere. 25. That thin, light, attenuated, and invisible body, which surrounds the earth on every side, and which we call the air, or atmosphere, possesses the same pro- perty as other material bodies that of gravity or weight. Hence it exerts a downward force or pres- sure on every substance at the surface of the earth ; and though a light body, this force is considerable, as the air extends upwards to a height of about forty-five or fifty miles. The amount of this force has been F & h estimated with great precision. Take a stout glass tube, closed at one ex- tremity, and about thirty-three or thirty-four inches long, and fill it with quicksilver ; then, having the open extremity closed by the thumb, a cork, or any flat plate, so as to prevent the quicksilver escaping invert it, and place the open end under the surface of the quicksilver in 'a vessel contain- ing a quantity of this liquid. Now, withdraw the substance closing the lower end of the tube ; immediately, the quicksilver will descend a little in the tube, leaving a vacant space at the top, and will soon become settled at a point (#) about thirty inches above the surface of the quicksilver in the lower vessel. The accompanying figure will illustrate this experiment. THE STEAM-ENGINE. 13 26. Here, the quicksilver in the tube, contrary to the usual action of gravitation, which causes fluids communicating freely to come to the same level, re- mains considerably elevated above that in the lower vessel. There must be some force supporting it in that elevated situation. This power is the pressure of the air. The air is pressing with great force on the sur- face of the quicksilver in the lower vessel, and thereby tending to push the quicksilver up into the tube. There is nothing in the upper part of the tube pressing the quicksilver down ; but the column of quicksilver, by its weight or force of gravity, is pressing downwards upon the quicksilver in the lower vessel, resisting the atmospheric pressure, and tending to descend in the tube, and come to a level with the quicksilver below. As these powers the atmospheric pressure and gravity of the quicksilver are the only forces acting, they must be equally balanced (in equilibrium) w T hen the quicksilver has become stationary in the tube. This takes place when the column is about thirty inches high. In Figure 1, the arrows outside of the tube represent the force and direction of the atmospheric pressure, which, from the movability of liquid particles, communicates its pressure to the liquid at the mouth of the tube, as shewn by the curved arrows, evidently tending to push the liquid upwards into the tube, and resist its descent. The arrows within the tube repre- sent the gravity of the quicksilver, acting in an oppo- site direction. 27. It may perhaps be remarked, that the pressure of the quicksilver in the tube is that of a narrow column only, while the air's pressure acts upon the whole of the exposed surface of the mercury below ; and it may be asked, how much of the air's pressure on the liquid in the lower vessel acts against tJie column in the tube ? The weight of air which presses on the 14 THE STEAM-ENGINE. surface of the liquid in the vessel is, evidently, that of a column of air equal in transverse section to the sur- face of the liquid, and reaching from it to the extreme limits of the atmosphere ; and of this, the portion which acts against the column of quicksilver in the tube, is, that, of a column of air equal in transverse section to the orifice of the tube. The two forces meet at that point, and may be said to be equal to columns of air and of quicksilver of the respective heights of each fluid, and equal in horizontal section, to that of the orifice of the tube. 28. We thus ascertain that a column of air, reaching from the surface of the earth to the extreme limits of the atmosphere, exerts the same downwards force as (is equal in weight to) a column of quicksilver thirty inches high. And if we suppose the horizontal section of the tube to be equal to a square inch, the column of quicksilver would weigh 14.7 avoirdupois pounds.* The pressure of the air which balances the quicksilver, must be the same in amount ; and, as the pressure which is transmitted to the orifice of the tube is that of a column of air the same in section, a column of air a square inch in section must weigh 14.7 pounds ; and the atmosphere must press with that force on every square inch of surface. Or, every square inch is as much pressed by the air as if, supposing there were no air, a weight of 14.7 pounds rested upon it. 29. The degree of pressure to which any surface is exposed from a gaseous body, is always spoken of by * The specific gravity of mercury being reckoned 13.58. But the mean pressure of the air in this country is less than 30 inches of mercury about 29.8 inches. If this estimate were taken, it would reduce the pressure on the square inch to 14.6 Ibs. Few scientific works, however, have reduced it even to 14.7 Ibs. ; the rougher estimate of 15 Ibs. to the square inch is more usually adopted. THE STEAM-ENGINE. 15 stating the amount of pressure on the square inch. A force double that of the air is 29.4 pounds per square inch ; half that of the air, 7-35 pounds per square inch. The term "atmosphere" is sometimes employed, to denote degrees of pressure as, a pressure of " two atmospheres," meaning a pressure double that of the air three atmospheres, ten atmospheres, an atmosphere and a half, and so on. To know the total amount of pressure exerted by a gas on any body, find the number of square inches in the surface on which the gas acts, and multiply this number by the pressure on each square inch. To find the number of square inches in a circular area, multiply the square of the inches in its diameter by .7854 ; or, multiply half the circumference by half the diameter. The area of a circle is a little more than three-fourths, and a little less than four- fifths of the square of the diameter. 30. The instrument which has just been described, (25,) is the common barometer, which is used to indi- cate variations in the pressure of the air ; for, from some causes at present not well understood, its pres- sure varies. These variations, however, are within small limits, the mercury in this country seldom rising higher than 30.8 inches, or falling lower than 28.1 inches. Its mean height, at the level of the sea, is 29.82 inches. The barometer is a useful instrument for measuring the force of confined gases or vapours, as will be seen afterwards. 31. The space between the upper surface of the mercury (a) and the top of the tube, Fig. 1, is called a vacuum or void ; meaning thereby an empty space, a space containing nothing, or, at least, none of the material bodies with which we are at present ac- quainted. A vacuum procured in this manner, is called the Torricellian vacuum (36.) It is the only perfect vacuum; that of the air-pump and steam- engine not being quite free from elastic fluid. 16 THE STEAM-ENGINE. 32. As water is a much lighter fluid than quick- silver, it is supported in a tube much higher than the latter fluid. A column of water 33.87 feet high is required to counterbalance the pressure of the air. Accordingly, the surface of the globe is as much pressed by the air as if, in place of air, it were encircled with mercury to the height of 30 inches, or water to the height of 33.87 feet, above the level of the sea. $3. If, in the tubes described, filled with water to the height of 33.87 feet, or mercury for 30 inches, an opening be made at the top, so that the air is admitted to press on the upper surface of the liquid, as the pressure of the air communicated from outside the tube, and which supported the liquid in that elevated posi- tion, is now balancedby the atmospheric pressure acting directly upon the liquid in the tube, and pressing it in an opposite direction, the liquid will obey the law of gravitation, and descend till it come to the same level without and within the tube. 34. A good example of the action of atmospheric pressure is seen in the pneumatic trough of the chemist, in which, by taking advantage of this power, water is supported in jars far above the level of the water in the trough. The action of the sucker, or moistened leather with string, with which boys raise stones for amusement, depends on atmospheric pressure, which presses the leather to the stone with a force of 14.7 pounds on every square inch. When the nozzle and valve-hole of a pair of bellows are shut, it requires very great force to separate the sides, as the atmo- sphere presses them together with great force (102.) 35. As air is composed of very fine particles, and exposed to great pressure at the surface of the earth, there is no situation in which it is not to be found, insinuating itself into all crevices, however minute, and rushing in on all sides, and filling up the vacant space when any body is moved. Or, if it be not itself THE STEAM-ENGINE. 17 adjoining to the vacant space, it presses the adjacent bodies into it hence the effects of suction, the syringe, the common pump for raising water, &c. There are few operations going on at the earth's surface which are not, more or less, influenced by atmospheric pressure. 36. The pressure of the atmosphere was discovered in 1643 by TORRICELLI, who also invented the baro- meter. The air-pump a machine for withdrawing air from a vessel containing that substance was invented by OTTO GUERICKE, a magistrate of Magdeburg, about the year 1650. It will be explained afterwards. Application of the Atmospheric Pressure to produce Motion. 37. As every space above the surface of the earth is filled with air, or some substance which resists and balances its pressure, it cannot be taken advantage of as a moving power until we have procured a vacuum, or empty space into this the air will press with great force. 38. If we introduce under quicksilver the extremity of a tube closed at both ends, containing no air* or other substance, and open the end under the quick- silver, the fluid will be pushed up in the tube to that height at which the gravity of the mercury will balance the pressure of the air thirty inches ; or water (had that liquid been used) to the height of thirty-three feet. If we place a thin plate of glass, or piece of bladder, air-tight, on the top of a glass cylinder open at both ends, and set the cylinder on the plate of an air-pump, with the closed end uppermost, the air, though pressing the glass plate downwards with a force of 14.7 pounds on every square inch of its surface, will nevertheless cause no motion or change, as the air * The method of extracting the air from a vessel is described in par. 104. i THE STEAM-ENGINE. in the interior resists and balances this pressure by its elasticity (102). But, if, by working the air-pump, the air be withdrawn from the interior of the cylinder, the exterior air will then crush the glass plate, and rush with great force into the interior of the cylinder. Or, had there been, in place of the flat piece of glass, a piston fitting air-tight to the sides of the cylinder, the atmospheric pressure would have forced it gradually down, as the air was withdrawn from the interior. 39. Here is a source of motion ; but how is the air to be removed from the interior of the tube or cylinder ? this being essential before the atmospheric pressure can be applied as a moving power. The process of extracting the air by the air-pump requires force, and there would therefore be no gain of power by removing the air in that way. 40. Take a glass flask with a long neck, and, having put a little spirit of wine in it, make the liquid boil, by holding it for a short time over a fire or spirit lamp. When the liquid is boiling briskly, having the hand protected by a thick glove, take the flask and invert it quickly, dipping the mouth under cold water. Imme- diately the water will be forced up with great violence into the flask ; and it may even be forced out of the hand if the experiment be performed smartly, and the flask be not held very firm. In this experiment, the vapour arising from the boiling liquid gradually ex- pelled the air from the flask, the vapour resisting the pressure of the air at the mouth of the flask. But when the flask was removed from the heat, and the vapour brought into contact with the cold water, it was rapidly condensed (returned to the liquid state). A sort of vacuum was thus formed in the flask, little resistance was offered to the entrance of any substance, and the atmospheric pressure forced the liquid up into the bodv of the flask. THE STEAM-ENGINE. 19 41. Here is a gain of moving power from the atmo- spheric pressure ; and this experiment is an exact re- presentation of one part of Savery's steam-engine. Indeed, it is said that this experiment, performed by Savery with a little wine in a flask accidentally sug- gested to him, from having thrown the flask on a fire, and seen the vapour issuing from its mouth led him to the construction of his steam-engine. The same prin- ciple formed a leading feature in Newcomen's, or the atmospheric engine ; the air was expelled by steam from a cylinder having a piston working in it, and the vapour being then condensed, the piston was pressed down by the atmospheric pressure on its upper sur- face. The latter contrivance was first suggested by Papin. 42. It is this power (atmospheric pressure) that turns the vanes of the windmill; that has been proposed to be applied to the purpose of locomotion in the " pneumatic railway ;" and that raises the water in the common pump. Wind the source of the moving power in the windmill is produced by air rushing into spaces where the resistance of the air previously occu- pying these spaces has been diminished by the effects of heat (101). In the common pump, the air is withdrawn from a tube dipping into the water to be raised, when the atmospheric pressure on the water exteriorly pushes it up into the tube, from which it is lifted by a piston working air-tight in the tube ; and, as it ascends, fresh quantities of water rise. In the lately-proposed pneumatic railway, the air is with- drawn from a tube on one side of a piston, while the atmospheric air is freely admitted to press on the other side thus motion is produced in the piston, to which the carriage is attached. 20 THE STEAM-ENGIKE. SECTION II. BEPULSION. 43. ALL substances contain, or have the power of producing a peculiar principle, which, applied to our bodies, excites the sensation called heat or warmth. The term " Heat " is used to express the sensation, and also the influence or substance (if it be a sub- stance) which causes the sensation, the context shew- ing in which sense it is applied. To express the latter solely the something which, coming from a fire to a person near it, causes the feeling of warmth the term CALORIC is sometimes used. 44. Caloric has the power of producing certain effects on bodies. When any substance has this power in a freat degree (as a red-hot iron), it is said to be at a igh temperature ; at a low temperature, when in the reverse state (as a piece of ice) ; and the terms, rise and fall of temperature, are used in a corresponding sense. 45. Caloric has the power of moving about among bodies, and always tends to an equilibrium. Bodies at different temperatures, placed in contact or near each other, soon come to the same temperature, the warmer bodies losing heat which the colder ones gain. The particles of heat are highly repulsive of each other, so that they fly off with rapidity from any body in which they are accumulated in considerable quantity ; but they have a great attraction for the particles of all other bodies, and enter rapidly into any body deficient in heat. This is w T ell seen, when a hot iron, or vessel THE STEAM-ENGINE. 21 of hot water, is placed near several other bodies at lower temperatures. 46. COLDNESS in any body does not arise from the total absence of heat, nor from the presence of a pecu- liar principle of an opposite nature, but simply from its containing comparatively little heat, so that it ab- stracts heat rapidly from other bodies. A cold sub- stance applied to the skin takes away heat a warm one communicates heat. 47. Equality of temperature would soon be esta- blished over the globe, from this tendency of heat to an equilibrium, but for three causes : First, The sources of heat whether natural, as the sun's rays and subterraneous heat, or artificial, as combustion are unequally distributed and applied ; second, While the passage of heat through bodies is not instantaneous, but requires time, they differ in the rate at which they transmit heat through them ; and, third, Bodies differ in their powers of absorbing heat, and also in the de- gree in which their temperatures are affected by it. CHAPTER 1. MANNER IN WHICH HEAT SPREADS. Heat passes among bodies in two ways ; by radia- tion and by conduction. 48. All bodies throw out (radiate) heat from their surfaces in straight lines, like radii from the centre of a circle. This mode of transmission of heat is called RADIATION. The radiated heat moves in straight lines, till it strikes on some other body, when, according to the surface on which it strikes, it is absorbed and warms the body, or bounds off (is reflected) like a ball thrown 22 THE STEAM-ENGINE. upon a wall obeying the same laws of reflection as light and sound. In some cases, part is transmitted, that is, passes directly through the substance, without affecting its temperature. 49. Those bodies radiate most heat, and, of course, (other things being equal,) cool soonest, whose surfaces are dark, and of a rough and porous texture. Those surfaces which are bright, of alight colour, resplendent, and highly polished as tin-plate, polished gold, brass, or silver radiate little heat, and hence retain their heat long. Again, those surfaces which radiate most heat, absorb the greatest quantities of radiated heat ; those which radiate least, throw off (reflect) the greater part of the radiated heat which falls upon them. The following table shews the comparative powers of vari- ous surfaces in radiating and reflecting heat. Radiating PC Lamp-black . Water . Writing paper Kosin . Sealing Wax Crown Glass Ice Plumbago Tarnished Lead Mercury Clean Lead Iron, polished Tin Plate . Gold, Silver, Copp wers. er 100 100 98 96 95 90 85 75 45 20 19 15 12 12 Reflecting Powers. Brass .... Silver .... Tin -Foil Block Tin . 100 90 85 80 Lead .... Tin Foil, softened by Mercury . Glass .... Glass, coated with wax or oil ... 60 10 10 5 A polished surface of silver, if the metal were warm, would lose little heat by radiation, and would throw off the greater part of any radiant heat which might fall upon it. If covered with a coating of lamp-black, (by smoking it with the soot from an oil lamp or candle,) the metal would lose a great deal of its heat by radiation, and would absorb the greater part of the THE STEAM-ENGINE. 23 radiant heat which fell upon it. The application of these principles to preserve bodies warm or cool, and to the economizing of heat, is obvious. The cylinder of a steam-engine should be brightly polished, that it may lose little heat by radiation. Tubes containing steam, water, or heated air, for heating apartments, should be rough, dark, and porous in the apartment where it is intended that they should give out their heat ; but bright and polished before they reach that place. 50. Second, Heat also passes from bodies by another mode. When a poker is put in the fire, the end out of the fire soon becomes warm; this is by the transmission of heat through its substance from particle to particle. In the same way in which heat travels along the par- ticles of one body, it can pass between two bodies in contact. The transmission of heat in this way is called CONDUCTION. 51. Bodies vary much in their power of conducting heat some transmitting it with great celerity, while others give it a very slow passage through them. Place a rod of wood and one of iron in a fire. The end of the iron rod not in the fire will be very hot long be- fore the similar end of the w r ooden rod feels sensibly warm. The following table shews the comparative conducting powers of several bodies. Gold Silver Copper Platinum Iron Zinc 1000 973 898 381 374 363 Tin . Lead . Marble Porcelain . Brick earth 303 179 23 12 11 The powers of bodies in conducting heat, appear nearly in proportion to their densities. Loose, spongy substances as fur, straw, cotton, silk, wool, are ex- tremely slow conductors. Bad conductors take a 24 THE STEAM-ENGINE. long time to get heated, but lose their heat slowly, and hence are useful for confining heat, or excluding heat. Good conductors get quickly heated, and cool quickly. There are many interesting applications of our knowledge of these differences in the relative con- ducting powers of bodies, as clothing, lining for fur- naces, ice-houses, &c. 52. Liquids and gases, whose particles are loose, and move freely on each other, transmit heat through their substance in the same manner as solids but with ex- treme slowness, if the heat be applied at the upper part of the fluid. But they have another and very rapid way of conveying heat, if the heat be applied be- low. The heated particles rise, cold particles from above descending and pushing them upwards ; these in their turn become heated and ascend, colder par- ticles descending; and thus a set of cold descending and warm ascending currents is established, which continue till the whole fluid comes to one temperature. Heat, entering into a fluid, causes it to become larger, and, of course, lighter ; and the cold and heavier particles above, necessarily descend and push the warm particles upwards. Thus the whole of the fluid is quickly heated not by the transmission of heat from particle to particle, as in solids but by the successive appli- cation of every part of it directly to the source of the heat. Whenever a fluid is heated currents ensue. Hence the wind (42) ; hence the removal of the warm and foul air expired from the lungs of animals, and the supply of fresh air to support their respiration ; hence the removal of the noxious air formed by burning bodies, and the supply of pure air to keep up the com- bustion ; hence ventilation the most perfect method of which yet devised (that introduced into the House of Commons by Dr. D. B. Reid) consists simply in ensuring a current by a strong fire in a tall chimney, THE STEAM-ENGINE. 25 the room to be ventilated being in the course of the current of fresh air which rushes to the fire in the chimney. CHAPTER II. EFFECTS OF HEAT. 53. When heat enters a body, it makes it larger.* It penetrates through its entire substance, and, re- pelling its particles from each other, their distances are increased, and the body is enlarged in bulk. This effect is termed EXPANSION. When heat leaves any body, its particles approach to each other, and its bulk is diminished an effect termed CONTRACTION. When solids are sufficiently heated, they melt, or become liquid- a change termed LIQUEFACTION ; and when liquids are heated to a great degree, they become gaseous, like steam or the air to which change the term VAPORIZATION is applied. It is, simply, a very great degree of expansion, but attended by a change in form. Liquids become solid again (congeal,) and vapours turn liquid (condense,) when they are cooled sufficiently. Heat also appears to be the cause of the ELASTIC POWER which aerial bodies possess at all tem- peratures, however low. * There is no real exception to this general rule. Some bodies as ice, iron, antimony, zinc, bismuth diminish in bulk when they melt, from losing their crystalline form. 26 THE STEAM-ENGINE. CHAPTER III. EXPANSION. 54. This may be illustrated by a very simple experiment. Take a common glass flask, about half full of water, which may be coloured to be better seen, and invert it in a vessel of water, the open mouth of the flask being a little under the sur- face of the water, as seen in the ad- joining cut. Then pour hot water on the flask. The heat from the water will enter the cold glass, and from it will pass to the air occupy- ing the upper part of the flask. The air thus heated will acquire in- creased elastic force, and expand (increase in bulk). Pressing on the water, it will cause it to descend in the neck of the flask. If the heat be great, and the quantity of water in the flask small, the liquid will be forced entirely out of the flask, and perhaps also some bubbles of the air may be ex- pelled. Or if, when the air has been expanded to any bulk, its temperature be then kept stationary, it will remain at that bulk as long as it continues of the same temperature. The same is true of liquids and solids. 55. Here is a force or moving power procured by heating a gaseous body. This is the source of motion in an engine lately invented by Mr. Ericsson, which he has called the Caloric Engine heated air pressing a piston in a cylinder, as in the steam-engine. This THE STEAM-ENGINE. 27 is also taken advantage of in Howard's vapour engine to increase the elastic force of the steam before it is applied to effect the motion. After leaving the boiler, it is heated by contact with the flue containing the heated air from the furnace, by which a further degree of expansive force is imparted to it. 56. Take a glass tube, closed and expanded into a bulb at one end, the other being open ; fill the bulb and part of the tube with spirit of wine, which may be coloured with cudbear, that the experiment may be well seen ; plunge the bulb in hot water ; the heat, expanding the liquid in the bulb, will cause it to press up the liquid in the stem, in which it will be seen gra- dually rising. 57. Take an iron rod (as in Fig. 3) of such length that, when cold, it will just enter between two projections at the ends of an iron bar, and of such j- diameter as to enter close- ly a circular hole in the |~o~L_ bar. Heat the iron rod Tf~ to a red heat ; it will now (j have increased in length, so that it cannot be made to enter between the two projections ; and its diameter will be enlarged, so that it is too thick to pass through the hole. 58. Had the iron rod been immovably fixed at one end, and a movable body placed in contact with the other extremity, the rod, when heated, would have pushed the movable body aside, to a distance corre- sponding to its own increase in length, a moving power being thus obtained. The force with which this ex- pansion takes place, is very great, equal to the force with which it would contract on cooling (15). Had 28 THE STEAM-ENGINE. the rod been immovably fixed at both ends, it would have become bent, to adapt itself to its expanded con- dition. These effects are often seen in structures where metals are used, and particularly in iron work about fire-places, where allowances have not been made for alterations of temperature, in the bending of the bars or disjointing of the stone or brick work to which they are fixed. In laying railway bars, allowances must be made for expansion and contraction attending altera- tions of temperature. 59.' This enlarged condition of bodies remains while the caloric which caused it remains ; when this leaves them, they return to their former size, the cohesive attraction taking greater effect in proportion as the repulsive influence is withdrawn. Plunge into cold water the heated rod, or the bulb with the liquid in its expanded state ; both will return to their former di- mensions the liquid will sink in the tube, and the rod will now pass through the hole and enter between the ends of the bar. Place the bulb of the tube, when at the ordinary temperature of the atmosphere, in a freezing mixture, which will withdraw much heat from the liquid ; a contraction will ensue, as will be indica- ted by the sinking of the liquid in the stem. 60. In these cases, we see the opposing action of the cohesive and repulsive powers. The former was over- come to a certain extent by the heat when the bodies were expanded, but resumed its influence, and drew the particles back to their former distances, when they were deprived of the heat which caused the expansion. 61. The heated gas also (54), when cooled, returns to its former volume, and the liquid ascends in the flask. It is more correct to say, that, as the heat leaves the gas, the liquid, forced up by the atmo- spheric pressure, ascends and compresses the gas to its previous dimensions. Gases are considered to have THE STEAM-ENGINE. 29 no cohesive attraction, their particles being at such dis- tances as to be without the sphere of this influence ; and they do not diminish in volume except from the action of some external force upon them. This will be better understood after the perusal of Chapter IY. of this section, on the elasticity of gaseous bodies. The Thermometer. 62. As expansion is the invariable effect of heating bodies, and a proportionate contraction ensues when they are cooled, the bulk of a body at any time is in proportion to its temperature at that time ; and we may estimate its temperature by measuring its bulk. And, as two bodies always come to the same tempera- ture by being for a short time in contact, or near each other (45), we may use one body as an instru- ment for taking temperatures ; having the means of measuring the bulk of this body, we know its tempera- ture, and the temperature of any substance to which it is for a short time applied. Hence the THERMOMETER. 63. This instrument consists of a glass tube similar to that mentioned in par. 56, but closed at the upper extremity, and having the bulb and a part of the stem filled with quicksilver or coloured spirit of wine the substance the expansion or contraction of which is to be noted. There is a graduated scale attached to the tube, by which the height (and thereby the bulk) of the liquid is indicated. 64. The bulb is applied to the body of which the temperature is required. If it be warmer than the thermometer, heat will pass to the latter, and cause expansion in the liquid ; and when they come to the same temperature, the liquid will become stationary. The bulk now occupied by the liquid, indicates its temperature, that indicating the temperature of the 30 THE STEAM-ENGINE. body to which it was applied. If the body be colder than the thermometer, heat passes from it to the latter, when the liquid contracts, and sinks in the stem till they come to the same temperature. The diminished bulk of the liquid indicates its temperature, and that of the body which caused the contraction. Thus this useful instrument shews the comparative temperatures of bodies. 65. It is necessary, in speaking of different tem- peratures, that there be some fixed points or standards of reference, by which different degrees of temperature may be compared : so that, when any particular tem- perature is spoken of, it may be known precisely what is meant. Very convenient fixed points for this pur- pose are found in the temperature at which water freezes (or, which is the same, that of melting snow or ice,) and that at which it boils. 66. If a thermometer be placed in a vessel contain- ing a quantity of snow and water, or in the water flowing from melting snow or ice, and the height of the liquid marked, it will be found to stand at that point as long as any snow remains unmelted (if kept near the snow ;) and at whatever time or place the experiment be made, the liquid in that thermometer will always stand at the same point. 67- If the same thermometer be placed in boiling water, the liquid will rise in the stem until it reaches a certain point. There it will remain as long as the thermometer is kept in the boiling water; and at whatever time or place the same experiment be per- formed with the same thermometer, the liquid will stand at the same point as before.* If the same ex- periments be performed with any other thermometer, * Not strictly true. The cause and extent of the variation, which is slight under ordinary circumstances, will be ex- plained afterwards. THE STEAM-ENGINE. 31 the same uniformity of temperature will be found in these two operations the melting of ice or snow, and boiling of water. As the thermometer, when placed in water freezing, stands at the same point as in ice or snow melting, this point is called the freezing point ; the other is termed the boiling point. 68. Here, then, are two constant degrees of temper- ature, two fixed points, easily ascertained, and to which reference can be made for comparing different temperatures. These are now universally adopted for thermometers ; and the scale of degrees is numbered in the following manner : 69. On the scale at the side of the thermometer tube, the freezing and boiling points are marked. The space between them is then divided into a certain number of equal parts, called " degrees." In the thermometer in general use in this country, (Fahren- heit's) this space is divided into 180 degrees. To indicate higher and lower temperatures, the scale above and below these points is divided into degrees similar to those between the two fixed points. Fahrenheit imagined that the most intense cold which could be produced was when the liquid in the thermometer stood 32 degrees below the freezing point ; accordingly, he numbered the degrees from the supposed point of greatest cold, calling it Zero. Thus, the number 32 is opposite to the freezing point, and 212 (180 + 32) opposite to the boiling point. 32 is familiarly known as the freezing point ; 212 as the boiling point. For the numbers below zero, the sign (minus) is used. Thus, 10 (minus 10) signifies 10 below zero, or 42 below the freezing point. 70. In the Centigrade thermometer, much used on the Continent, a better division is adopted. The degrees are numbered from the freezing point, and the space between it and the boiling point is divided into 32 THE STEAM-ENGINE. 100 degrees ; the boiling point being thus 100. One degree in the Centigrade thermometer is equivalent to 1.8 or 1^ of a degree in Fahrenheit's thermometer. In Reaumur's, used in some parts of the Continent, the distance between the freezing and boiling points is divided into 80 degrees, and the scale commences at the freezing point. 71. As the degrees are equal to each other, and an equal increase of temperature causes an equal expan- sion, it will cause the liquid to ascend through an equal number of degrees ; and different thermometers will give the same indications with the same temper- ature, however different the distances between the two fixed points and size of the degrees ; for that dis- tance is divided into the same number of degrees in all ; so that, in all, the proportion of the degree to the bulk of the liquid and to the distance between the fixed points, is the same. The greater, however, the mass of matter in the thermometer to be heated or cooled, the longer time it requires to take up the temperature of the body to which it is applied. 72. The spirit-of-wine thermometer is used for low temperatures, as this liquid has never been frozen. It cannot be used for temperatures above 174, as it boils at that temperature. The mercurial thermome- ter is used for considerably elevated temperatures, as quicksilver does not boil till 662. It cannot be used for temperatures below 39, as it freezes at that point, then contracting at a different rate. Kate of Expansion in Bodies. 73. The following table exhibits the amount of ex- pansion in different bodies, when heated from the freezing point of water (32) to the boiling point (212). TIIE STEAM-ENGINE. 33 Elongation of Bars, Rods, or Wires. Lead l-351st. Silver 1 -524th. Copper ...... 1 -581st. Brass 1 -532nd. Gold 1 -602nd. Iron wire 1-81 2th. Bar iron l-819th. Hard steel l-927th. Platinum l-ll67th. Flint glass 1-1 248th. 74. A bar of lead 351 inches long at 32, becomes 352 inches at 212. Besides this increase in length, it increases in breadth and thickness. To find the total expansion, place 3 as the numerator of the above fractions, or, retaining the same numerator, divide the denominator by 3. 75. The expansion of the following liquids, heated through the same range, (32 to 212) is seen below. The expansion in bulk, or total expansion, is stated. The two first are taken from different points ; as spirit of wine boils at 174, and oil freezes about 36. Spirit of wine (8 to 174) Whale oil (60 to 212) . ' . . . -9th. -llth. -14th Water -22nd. -55th. 76. All gases and vapours expand equally through the same range of temperature. Their expansion is very great. 1000 volumes of any gas at 32, be- come 1375 volumes at 212 expanding 3-8ths; or 1 -480th for every rise in temperature of one degree of Fahrenheit. 77- Thus, in expanding bodies, heat produces the least effect upon solids, a greater effect on liquids, ani has a still greater expansive power in gases. Also, while all gases undergo the same expansion from an 34 THE STEAM-ENGINE. equal increase of temperature, it is very different with solids and liquids ; the same rise in temperature causes different degrees of expansion in different solids and liquids. 78. The reasons for these peculiarities, are, the differences in the strength of the cohesive attraction in solids and in liquids, and the absence of it in gases. In expanding solids, heat is resisted by the cohesive force, which is strong in them hence it produces a small effect. The particles of liquids are less firmly bound by cohesion, and the same increase of heat, having less cohesion to overcome, produces a greater expanding effect than in solids. The cohesive force appears to be entirely suspended in gases ; heat is not resisted in its expanding power, and a great increase in bulk is produced by a small rise in temperature. The cohesive force being different in solids, and also among liquids, each opposes a different degree of force to the efforts of heat to expand them. Hence the unequal expansion of solids and of liquids through the same range of temperature. In gases, where this force is absent, the same increase of heat produces the same expansion in all. TITE STEAM-ENGINE. 35 CHAPTER IV. OF THE ELASTICITY OF GASEOUS BODIES. 79. We have seen that the expansion of gases, when heated, is a source of moving power. But gases in their ordinary state, at all times, exert a force or pres- sure on the surrounding bodies. Every gas or vapour contains within itself a source of expansion, and hence of moving power, which is prevented from acting and producing motion, only by some other force which compresses the gas, and thus resists its action. It is similar in its nature to a compressed or wound-up spring. Its particles are constantly pressing outwards on each other, and upon the bodies around them, and the gas is continually endeavouring to swell out in all directions, and occupy a larger space. This power of gaseous bodies is termed their elasticity, elastic power, or elastic force. 80. This remarkable property of gases, which is peculiar to them liquids and solids not possessing any such power most probably arises from the distances of their particles, which are thus without the sphere of the cohesive attraction, so that no resistance is offered to the repulsive power of the great quantity of heat they contain, which is constantly exerting upon them its usual action that of repelling their particles asun- der. Hence, the consideration of this elastic power of gases has been placed beside the other phenomena of heat 81. Place a rather flaccid bladder in the receiver of an air-pump, and withdraw the air from the interior of the receiver ; the air in the bladder will expand in proportion as the pressure upon it (from the surround- 36 THE STEAM-ENGINE. Fig. 4. ing air in the receiver) is diminished by the withdraw- ing of the air ; the bladder will swell, become full and distended, and even be burst by the expansion of the contained air, if the vacuum be very complete, or the bladder have been nearly full of air. 82. In the adjoining figure, (Fig. 4,) shewing the section of a cylinder, with a piston moving freely but air-tight, if the space a in the cylinder below the piston were filled with lead, or iron, or a any other solid, and the piston were raised, the solid would re- main in exactly the same situa- tion as before, being retained by the force of gravity and the cohe- sion of its particles ; and the space between the solid and the piston would be a vacuum. "With a liquid in the place of the solid, the same would take place ; the liquid would remain if the piston were raised.* 83. But if the space below the piston had been occu- pied by any gas or vapour, then, on elevating the pis- ton, the gaseous body would follow it ; there would be no vacuum ; the gas would expand and be equally diffused through the whole space between the lower surface of the n and the bottom of the cylinder. 84. This elastic force of gaseous bodies is resisted by the pressure to which they are exposed ; and, there- fore, these forces must be equal to each other in any gas which is in a quiescent state. Thus, in an appara- tus such as Fig. 4 represents, if the piston be at rest at some distance from the bottom, it is clear that the * A little vapour would rise from volatile liquids, as ether, spirit of wine, water, and be diffused through the space between the piston and the surface of the liquid ; but the mass of the liquid would remain in its previous situation. THE STEAM-ENGINE. 37 gas confined below the piston is pressing it upwards (the resistance from friction being disregarded) with a force exactly equal to that with which the piston tends downwards from its own weight, and that of any bodies resting upon it. In Fig. 4, if the piston be at rest in the situation a 2, and the force with which it tends to descend be equal to a weight of ten pounds, then the force with which the gas below presses upwards on the piston, is also equal to a weight of ten pounds. Hence, then, the elastic force of a gas is exactly equal to the force l>y which it is confined. 85. If the piston have now additional weights equal to ten pounds laid upon it, it will descend till the gas occupies only half the space through which it was at first extended; then (at a 1) it will remain at rest. Here, while the same quantity of gas is diminished in bulk to one-half, the force with which it presses the piston upwards is doubled, for it now supports a weight of twenty pounds. But when a given quantity of a gas is diminished in bulk, its density or specific gravity is increased. In this case, the density has been doubled, at the same time that it supports a double [force. Hence, then, the elastic force of a gas is in direct pro- portion to its density, and inverse proportion to its bulk that is, its elastic force increases in the same propor- tion in which its density is increased, or its bulk diminished. 86. This important general proposition might also be illustrated in the following ways. 87- If five pounds had been taken off the piston while at rest in the situation a 2, it would be forced up by the elasticity of the gas to the situation a 4. Here, while the volume of the gas is doubled, its den- sity and elastic force are diminished to one-half, for it is now diffused through twice the space, and supports only half the weight. 38 THE STEAM-ENGINE. 88. If one half of the gas had been withdrawn while the piston was in the position a 2 and its weight equal to ten pounds ; thedensity of the gas being thereby reduced one-half, its elastic force would be reduced in the same proportion, and the piston would descend to a 1. In this situation, the density of the gas is now the same as before any was withdrawn, and the force it now exerts against the piston is also the same. 89. If, instead of withdrawing gas, a quantity were forced in equal to what was there before, the piston (still loaded to the amount of ten pounds) would be forced up to the situation a 4. Twice the quantity of gas being diffused through twice the space, its density remains the same, and therefore its elastic force is also the same, or equal to a force of ten pounds pressing the piston upwards. 90. If, when this additional quantity of gas was forced in, the piston were loaded with an additional weight of ten pounds, it would have remained at a 2. The density of the gas being double, its elastic force is double, and it resists a double compressing force. 91. In all these cases, we have supposed the pres- sure downwards on the piston to be entirely within our control, and disregarded the atmospheric pressure, which would constantly press the piston downwards, with a force equal to a weight of 14.7 pounds on every square inch of its surface. For performing the experi- ment, the friction and atmospheric pressure might be neutralized by a counterpoise, attached to the piston by a cord passing over a pulley. 92. The following table will illustrate this general law of the constitution of gaseous bodies. Let the volume and elastic force of any given quantity of a gaseous body be represented each by the number 1, while the density is 1. "With alterations of the den- THE STEAM-ENGINE. 39 sity, the following will be the corresponding altera- tions of the volume and elastic force. Density. 1 . . . Volume. . . 1 . . Elastic Force. ... 1 2 . i 2 3 . . , k . . . 3 10 i 10 i . , . . 2 . . I i . , 4 , i This relation between the density and elasticity of aerial bodies, is known by the name of " the law of Marriotte," that philosopher having pointed it out. Till lately, it was supposed not to apply in high pres- sures ; but, from the experiments of Oersted, it was found to hold with pressures so great as 110 atmos- pheres, and is probably universal. 93. It is to be understood as a condition in the pre- ceding experiments, that the temperature is the same in all. Any increase in temperature increases the elastic force (54,) while this is diminished in a cor- responding degree by a reduction of temperature. In any gaseous body, temperature and density remaining the same, the elastic force is also the same ; and any change in either determines a cot-responding change in the elastic force. 94. As gaseous bodies are thus capable of being drawn out by relieving them from pressure, and com- pressed by increasing the pressure, they are frequently termed elastic fluids, in opposition to liquids, which possess this property in a very slight degree. Water was for a long time supposed to be quite incompressi- ble it is almost so ; its diminution in volume being only 51.3 millionths (about l-20,000th) for every atmosphere of pressure, as determined by the experi- ments of Oersted and others. 95. It must be observed that this elastic force of a 40 THE STEAM-ENGINE. gas is totally different from its weight or gravity, and in effect much greater. A hundred cubic inches of air weigh only 31.0117 grains i a column of atmosphere of one square inch transverse section, has only a weight (downwards force) of 14.7 pounds. The pressure from its weight is thus small ; but its elasticity is compara- tively very great, as may be easily illustrated. The at- mospheric pressure would force 14.7 pounds of mercury (30 cubic inches) into a tube of one square inch trans- verse section from which the air had been previously exhausted, on opening it under mercury (38). But if the tube were full of air, and the open end then plunged under the surface of the mercury, not a particle would enter, if the tube were held quite perpendicular. Now, supposing the tube to be about 30 inches high, about 10 grains weight of air would fill it, completely resist this atmospheric pressure, and prevent the mer- cury from entering. It cannot be the weight of this small quantity of air which resists a force of 14.7 pounds, about 10,000 times its own weight it must be some other power, so that, here, the elastic force of this trifling quantity of air balances the force pro- duced by the weight of a whole column of atmosphere of the same area. 96. In like manner, any quantity of air, however minute, introduced into the space above the mercury in the barometer tube, would, by its elasticity, exert a certain influence in resisting the atmospheric pres- sure, and depress the liquid in the tube. Hence an important application of the barometer. If the space above the mercury in a barometer tube communicate with a vessel containing any gaseous body, we can ascertain the elastic force of that body. It will depress the mercury in the tube, and, by noting the difference between the height of the mercury in this tube, and its height in another having no gaseous fluid above the THE STEAM-ENGINE. 41 mercury (the common barometer,) this difference will express the elastic power of the gas pressing on the upper surface of the mercury. For every inch of difference, we may allow 0.49 pounds (3,430 grains) of pressure on the square inch to the gas which de- presses the quicksilver. Thus, if the difference be four inches, the elastic force of the gas is 1.96 pounds on the square inch. In this manner, the barometer is used in the common air-pump, and in the condenser of the steam-engine. 97. On the other hand, if the gas be of an elastic force greater than the atmospheric pressure, the baro- meter is made in the form of a U, (see Fig. 15,) one end communicating with the gas, the elasticity of which is to be measured, the other being open, and of course exposed to the atmospheric pressure. When the elastic force of the gas is exactly equal to the atmospheric pressure, the mercury will be at the same height in both limbs of the tube ; and when the elasti- city of the gas exceeds the atmospheric pressure, the mercury will be depressed in the limb communicating with the gas and raised in the other. The difference in level of the mercury in the two limbs, will express the excess of the elastic power of the gas over the atmos- pheric pressure. 98. As the air at the surface bears the compression of a force of 14.7 pounds on every square inch, its elas- tic force must be exactly equal to the compressing power, 14.7 avoirdupois pounds on every square inch of surface ; on every side, above, and below, as this elastic power knows no distinction of up and down. This pressure is frequently in round numbers, termed 15 pounds. For small quantities, the difference is not important ; but it makes a considerable difference on high pressures. The true number is 14.6 pounds: see note, p. 14. 42 THE STEAM-ENGINE. Gaseous Elasticity as a Moving Power. 99. Let us suppose a cylinder with a movable par- tition in the middle, and filled with air or any other gaseous fluid. Let this partition be light, fitting closely to the sides, so that no gas can pass from one side of the partition to the other, and at the same time capa- ble of free motion within the cylinder. Now, if there be equal quantities of the same gas on each side of the partition, and the different portions be at the same temperature, the partition, being equally pressed on each side, will remain exactly in the middle. If, in this state of things, some of the gas be withdrawn from one cavity, the density of the gas remaining in that cavity being thereby reduced, its elastic force will be less; and the gas on the other side, now being less resisted, its particles will obey the impulse of their elasticity, motion will take place, and the partition will be pressed towards that side from which the gas. was withdrawn. ] 00. Here is a moving power gained by withdrawing some of a gas pressing on one side of a body, while there is a quantity of confined gas on the other side. Power procured in this manner, is used in those of Watt's engines, called " expansion engines," with the view of economizing the steam. 101. The same effect would take place, were the gas in one cavity reduced in temperature, or the tempera- ture of the other portion raised. Thus, a confined gas may be made a source of moving power in two ways : First, by increasing its temperature; second, by remov- ing some of the pressure by which it is confined. And the latter may be done in two ways when the pressure arises from a gaseous body : First, Reducing its tem- perature; second, Withdrawing some of the gas, When the gaseous body to be withdrawn is a vapour, THE STEAM-ENGINE. 43 this may be done in the way described in paragraph 40, called condensation, which will shortly be explained more fully. 102. Knowing that the air possesses elasticity as well as weight^ we can understand many phenomena other- wise inexplicable. Hollow vessels containing air (38) support the enormous pressure of the external air, by the elasticity of the air within. Were not air, or some other elastic fluid, within, their sides would be crushed together ; and we shall see that, in the boiler of the steam-engine, it is necessary to have a particular con- trivance to prevent this occurring. When we attempt to separate or press together the boards of the bel- lows (34,) the nozzle and valve hole being shut, the elasticity of the air within, tending to separate the boards, and the pressure of the exterior air, tending to force them together, are equal at first ; but, when we press them together or separate them, the elasticity of the air within the bellows is increased in the first case, diminished in the second, and force is required to keep them in either state. In the case of the sucker with which boys raise great weights (34,) if the moistened leather be properly applied, there is no air between the leather and the stone, so that the atmospheric pressure is not resisted in its pressure on the leather. 103. The elastic power of air is taken advantage of in many machines as Hero's fountain, the hydraulic ram, the air-vessel for producing a continuous stream in the force pump and bellows for blast furnaces, the air-gun, common lifting pump, condensing syringe, and air-pump. The latter, an important part of Watt's steam-engine, we shall now shortly describe. 44 THE STEAM-ENGINE. The Air Pump. Fig. 5. 104. The air pump is a machine for extracting the air from a vessel, a more difficult operation than might at first be supposed. Its action depends on the elastic property of the air to be removed. It will be understood from the annexed Fig. (5,) and de- scription. Let d be the vessel to be exhausted of air. Let it be connected with a cylinder having a valve c open- ing upwards, and a piston a b with with one valve (or two) also opening upwards. Let the vessel d and the cylinder contain air of the usual elas- ticity, and the piston be near the top of the cylinder. Now press down the piston the air in the cylinder being thus condensed, will press and keep shut the lower valve c, and, when it has sufficient elastic force, will press open the valve in the piston and escape. Let the piston be pushed to the bottom of the cylinder all the air it contained will thus be expelled. Now raise the piston to the top of the cylinder : in the figure, the piston is represented ascending. Whenever the piston is raised, there will be a vacuum between it and the valve c, and, therefore, no pressure on the upper sur- face of the valve c ; the air in d will therefore force it open and rush into the cylinder, and when the piston is at the top, the air formerly in d will be diffused through d and the cylinder. Thus a quantity of air has been removed from d, and, from the construction of the valve c, it cannot return. Also, no air can THE STEAM-ENGINE. 45 enter the cylinder from without, as the piston valve is kept shut by the atmospheric pressure, a much greater force than that of the now rarified air pressing on the lower surface of the piston valve. Push down and raise the piston as before, and repeat this often. The air in the cylinder will be expelled as before, and the remaining air in d will divide itself between d and the cylinder, and so on no air ever returning into d., as the valve c opens outwards. This may be continued until the air in d is of such weak elasticity as to be unable to push up the valve c. Hence, in some air- pumps, there are contrivances for lifting the valves by the power that works the pump ; and in others the air is withdrawn without the aid of valves. The above, however, is the plan adopted in the steam-engine. CHAPTER V. VAPORIZATION. 105. It is an invariable effect of heat, then, to enlarge the dimensions of any body into which it enters. But this enlargement, in ordinary cases, is not great ; gases, which expand most, must be heated through a range of about 480 Fahrenheit before their bulk be doubled. 106. There is one case, however, in which heat does produce a very great increase of bulk when it causes a liquid to pass to the gaseous or aerial state ; as when water boils (becomes steam). Here there is not only expansion, far greater in amount than in the former cases there is also a change in the form or condition 46 THE STEAM-ENGINE. of the body; it is now an elastic fluid (94,) light, eluding the sense of touch, and, in most cases invisible. This change is called VAPORIZATION, and the elastic fluid into which the liquid is converted is called a VAPOUR. A. Vaporization as a Moving Power. 107- Take a flask, such as that represented in Fig. 2, and pour coloured water into it till it is almost full, leaving room for a tea-spoon full of ether, which is then to be added; then, closing the mouth of the flask, invert it, make the mouth dip under water, remove the substance closing the mouth, and get it properly supported in that position. The ether, being a light liquid, and not mixing with water, will ascend to the upper end of the flask, resting on the surface of the water. Now, pour boiling water on the flask: almost instantaneously, the ether will expand enor- mously, become a gaseous body, transparent and co- lourless, press down the water, and occupy a large part of the flask. 108. Here is a force or moving power obtained by the conversion of a small bulk of liquid into a vapour occupying a far greater space. This experiment illus- trates the methods which De Cans and Lord "Worces- ter proposed as a means of raising water, and the power used in modern steam-engines ; and it is an ex- act representation of one part of Savery's engine. 109. Most gaseous bodies are invisible. Chlorine has a pale yellowish-green colour, and the vapour of iodine is of a fine violet hue. That the vapour of water is invisible may be seen by boiling a little water in a glass flask. The vapour between the surface of the liquid and mouth of the flask, is clear, transparent, and colourless : it is only after it is fairly out of the THE STEAM-ENGINE. 47 flask, and is cooled and partly condensed by the cold air, that it assumes an opaque and white or grey ap- pearance, like a cloud. 110. This phenomenon takes place with almost all liquids, when they are sufficiently heated ; but at dif- ferent temperatures, each having a boiling point pecu- liar to itself. Also, they expand differently wh'en va- porized. The following table shows the boiling points of several liquids; the bulk of the vapour into which they expand ; and the specific gravities of these va- pours that of air at 212 being 1. Boiling Bulk of Specific Gra- Point. Vapour. vity air, at 212? = 1. Water 212 1696* 0.623 Spirit of Wine 174 493 1.603 Sulphuric ether 96 212 2.586 Oil of Turpentine . 316o 192 5.013 The expansion of water is very nearly one cubic inch into one cubic foot (1728 times its former bulk.) 111. Vapour rises from most liquids at all ordinary temperatures, even at temperatures far below their usual boiling points; but it comes from the surface only, when the temperature is below the boiling point of the liquid. 112. The temperature of the vapour is the same as that of the liquid from which it arises, as may be easily seen, by holding a thermometer in boiling water and then in the steam arising from it. 113. Yapour is raised, and sustained in that state, solely by the influence of heat, not at all by the * The estimate of the increase in tulk is calculated from the greatest density of water, which is at 39.39 Fahrenheit. 48 THE STEAM-ENGINE. traction of the air, as was at one time supposed ; and the quantity of vapour which can exist in any given space bears a certain proportion to the temperature (129, &c.) B. Return of Vapours to the Liquid State. 114. Vapours, when the heat which caused them to be in that state is withdrawn, return to their former bulk (the bulk of the liquid from which they were raised), and to the liquid condition. This phenomenon is called condensation. It is seen when steam, issuing from a boiler, strikes on any cold surface. The steam is condensed, and returns to the state of water, ap- pearing in small globules. The heat being withdrawn by the cold body, the cohesive attraction resumes its influence, draws and retains the particles in contact, so as to form water.* 115. The colourless nature of steam, its formation, and condensation, are well shewn by a beautiful appa- ratus, devised by Dr. Wollaston. The annexed figure illustrates it. A glass tube is formed into a bulb at * Thus, there are two great antagonist powers operating between the particles of matter : the influence of heat, or repul- sion, tending to separate them and make bodies occupy a large space ; the attraction of cohesion, tending to draw the particles of bodies closer and closer to each other, and to reduce them in bulk. When there is little of the repulsive principle present, as in ice, the attractive principle operates powerfully, and the par- ticles are firmly bound together in the form of a solid. When the ice is heated, the heat, to a certain extent, overcomes the cohesive attraction, and the particles are loosened and become movable on each other, as in water ; and, when a large addi- tional quantity of heat is infused, the cohesive principle is over- come, and, the repulsive principle being predominant, the par- ticles are driven far asunder, in the form of steam. Reverse these operations, and we have the steam successively passing to the state of water and ice. THE STEAM-ENGINE. 49 one end, and has a piston within, which, with its rod, is perforated. There is a screw at the top of the piston rod, by which the aperture in the Fig - G - piston-rod may be opened or shut at pleasure- A little water being intro- duced into the bulb, it is made to boil, and, when the air has been expelled, CZ^r^f the opening in the piston is shut. Then, if the heat be continued, and more steam formed, it will raise the piston ; on al- lowing the tube to cool, the steam will be condensed, and the piston will be depressed by the atmospheric pressure. It will be seen that the steam, unmixed with air, is perfectly clear, transparent, and colourless. 116. The prodigious expansion of water when vaporized (a cubic inch to a cubic foot), the great reduction in bulk when condensed (a cubic foot to a cubic inch), and the ease with which steam is con- densed, are the properties which render water so valuable as a means of procuring force or moving power. C. Influence of Pressure on Vaporization. 117. We have seen that pressure resists the endea- vours of gases to expand (84, &c.) ; in like manner, pressure upon the surface of any liquid opposes the expansion of its particles into the gaseous state, and, in proportion as the pressure is great, a higher tem- perature is required to overcome it, and cause part of the liquid to expand into vapour. 118. When a quantity of a liquid is exposed to heat in a confined space, from which the vapour that rises cannot escape, this vapour, by its elastic power 50 THE STEAM-ENGINE. (79), will press upon the surface of the liquid, and oppose the further vaporization of the liquid. If tho heat be increased, this force will be overcome and an additional quantity of vapour will be added to that already pressing upon the surface of the liquid. The density of the vapour being thus increased, as well as its temperature (93, 101), its elastic force is further increased, and it now resists with still greater force the passage of any of the liquid into the aeriform con- dition. There is thus a struggle between the heat, which tends to repel the particles of the liquid asunder, in the form of vapour, and the pressure, which tends to confine these particles in a small space. When the vapour that rises is not confined, the temperature remains at the usual boiling point, as the steam that rises carries off the heat as fast as it is infused into the liquid but when the vapour is not permitted to escape, the heat added remains in the liquid and in the vapour above it, and raises their temperature. 119. Thus, by exposing liquids to heat, in confined vessels, we may procure vapours of any density, and, hence, of any degree of elastic force^ compatible with the strength and power of sustaining heat of the ves- sel, on the interior of which it thus exerts what is called a BURSTING PRESSURE. 120. Hence, liquids vary in their boiling points with the pressure to which they are exposed. In elevated situations, (as the tops of high mountains, the cities of Quito and Mexico, where the pressure of the atmo- sphere is less less by the amount of atmosphere be- neath the elevation,) water boils at lower temperatures than on low plains, where subjected to the pressure of the whole atmosphere. A change of one degree of Fahrenheit in the boiling point of water, indicates a change in elevation of 530 feet; or, a variation of 1.76 Fahrenheit, in the boiling point of water, takes THE STEAM-ENGINE. 51 place with a change of one inch in the height of the barometer, between the limits of 26 and 31 inches. In the vacuum of an air-pump, liquids boil at about 140 Fahrenheit lower than when exposed to the ordinary atmospheric pressure. 121. At Quito, 9542 feet above the level of the sea, water boils at 194 Fahrenheit. At Geneva, about 1200 feet above the level of the sea, water boils at 209.4 Fahrenheit. 122. In the Digester, on the other hand, which is merely a stout metallic vessel (copper,) like a boiler, with a fixed lid and a stopcock attached to the tube for emitting the steam, by confining the vapour, we may retard the boiling of water, and raise it to any temperature compatible with the capacity of the ves- sel to bear pressure, and the action of the high tem- perature necessary to produce steam of such elastic power. In this manner, substances can be exposed to higher temperatures than can be procured by boiling water in an open vessel. In elevated situations such as Quito or Geneva the same temperatures cannot be procured by boiling water or other liquids in open vessels, as in lower situations. D Of the Force qf Steam. 123. In considering the elastic force of steam, it must be recollected that, the temperature remaining the same, the density and elastic force of a gaseous body are in direct proportion ; and that an increase of either temperature or density increases the elastic force. (93, 101.) 124. The elastic force of a vapour rising from a loll- ing liquid is always exactly equal to the pressure which resists (117) its passage to the gaseous state, or, as it is usually expressed, equal to the pressure under which 52 THE STEAM-ENGINE. it is raised. In fact, a liquid does not boil until it has sufficient elastic force to balance and overcome this pressure. 125. There is a constant force the atmospheric pressure resisting the expansion of liquids into vapours ; hence the elastic force of any vapour pro- duced from a liquid boiling in an open vessel while the barometer is at thirty inches, is 14.7 pounds to the square inch, and varies with the height of the baro- meter (the index to variations in atmospheric pres- sure), the boiling point varying also, as the following table illustrates square inch. 28 208.43 13.72 29 210.19 14.21 30 212 14.7 31 213.76 15.19 126. The following more extended table will illus- trate better the condition of watery vapour at different temperatures, the proportion between the temperature And density, and the correspondence between these two and the elastic force or pressure. The manner in which the elastic force of a vapour is ascertained may be judged of by referring to paragraphs 96 and 97. THE STEAM-ENGINE. 53 Temperature, Fahrenheit. Specific Grav- ity, air at GO" being 1.* Weight in Grains of a Cubic Foot.* Pressure in inches of a co- lumn of Mer- cury. Pressure, in pounds on the square inch. Deqreex. 60.00 0.0115 6.10 0.55 0.2695 77.00 0.0202 10.70 1.00 0.49 98.70 0.0388 20.50 2.00 0.98 123.00 0.0744 39.00 4.00 1.96 147.60 0.134 71.00 7.50 3.675 178-00 0.255 135.00 15.00 7.35 197-40 0.371 196. 22.50 11.025 212-00 0.484 254.7 30.00 14.7 220-00 0.553 292.0 35.00 17-15 233.80 0.687 363.0 45.00 22.05 242.50 0.81 427.0 52.50 25.725 250.20 0.915 483.0 60.00 29.4 274.70 1.33 700.0 90.00 44.1 320.60 2.5 1317.0 180.00 88.2 350.00 3.61 1910.0 270.00 132.3 450.00 10.75 5670.0 900.00 441.0 The following table is the result of an inquiry insti- tuted by the Academy of Sciences at Paris, in which Arago and Dulong were engaged. Up to the pressure of twenty-five atmospheres, the table gives the results of actual experiments. The temperatures and corre- sponding pressures above that were obtained by calcu- lation. The first column shews the force of the steam, expressed in atmospheres ; and, in the second column, the figures express the corresponding temperature in degrees of Fahrenheit. Thus, steam formed at 263.84 has an elastic force of 2^ atmospheres ; or, a pressure on the square inch of 36.75 pounds = 14.7 Ibs. X 2^. * The weight of a cubic foot of air at 60 F., 30 Barom., is. 535.8821 grains; JOO cubic inches weigh 31.0117 grains. A cubic foot of air at 212 F., 30 Barom., weighs 413.6832 grains ; and, if the specific gravity of air at 212 be termed 1.000, that of steam formed at 212 is 0.624. 54 THE STEAM-ENGINE. at fij i .9 I & g il l = rt Si* *G So 4 s "c5 M I i! 1 11 p. 11 P. g WJ H H^ H S^ H 1 212. 74 336.86 20 418.46 14 233.96 8 341.96 22 427.28 2 250.52 9 350.78 24 435.56 24 263.84 10 358.88 25 439.34 3 275.18 11 366.85 26 443.16 34 285.08 12 374.00 28 450.38 4 293.72 13 380.66 30 457.16 44 300.28 14 386.94 32 463.64 5 307.5 15 392.86 34 469.78 54 314.24 16 398.48 36 475.64 6 320.36 17 403.82 38 481.24 64 326.26 18 408.92 40 486.59 7 331.70 19 413.78 45 499.14 50 510.60 127. From these tables, it appears that, if a quan- tity of water were heated to 320 Fahrenheit by con- fining the vapour, a cubic foot of the vapour at that temperature would weigh 1317 grains (about three ounces avoirdupois ;) its specific gravity, compared to air at 60 as 1, would be 2.5, weighing, therefore, two and a half times as much as an equal bulk of air ; if communicating with a closed tube, like a TJ, contain- ing mercury, would support a column of that fluid metal 180 inches (fifteen feet) high ; or 150 inches if the tube were open, the atmospheric pressure being equivalent to thirty inches of the column ; and would exert on every square inch of surface of the vessel containing it, a pressure equal to that of a weight of 88.2 pounds avoirdupois i.e., a pressure of six atmo- spheres. 128. This table might be continued downwards THE STEAM-ENGINE. 55 as, at lower temperatures still, vapour can be sus- tained ; of diminished density and elastic force, but never losing elastic power while it retains the form of vapour. At 32 Fahrenheit, according to Dalton, watery vapour will have an elastic force equal to 0.2 inch of mercury (.098 nearly one-tenth of a pound of pressure on the square inch) ; and a cubic foot of such vapour weighs 2.3701 grains. At fifty degrees Fahrenheit, the force of vapour, according to the same author, is 0.375 inches of mercury (.183 of a pound pressure on the square inch) ; and a cubic foot of such vapour weighs 4.2819 grains. J 29. Any given space, then, can contain only a cer- tain quantity of vapour at a certain temperature ; the vapour is sustained in that state solely by the influence of heat ; and its quantity bears a constant proportion (which has been determined by experiment) to the temperature. 130. Hence, if a quantity of vapour, in a confined space, be reduced in temperature, the space having contained as much vapour as it could at the previous temperature (being saturated with vapour), a certain quantity of vapour will now return to the liquid state, and the remainder will expand and be spread through the whole of the space much reduced, however, in den- sity and elastic force ; tables such as that in paragraph 126 shew how much. For example, if a cubic foot of steam, at 212 Fahrenheit, and of elastic force of 14.7 pounds to the square inch, being of the specific gra- vity 0.484 i.e., 254.7 grains of steam (all that can be sustained in vapour at that temperature in such a space) be reduced in temperature to 60 Fahrenheit ; 248.6 grains will return to the liquid state, and 6.1 grains will remain in the state of vapour, diffused through the entire cubic foot, having a specific gravity 56 THE STEAM-ENGINE. of 0.0115, and an elastic force of 0.2695 pounds (about a quarter of a pound) on the square inch. 131. Thus, the condensation of vapour by cold can never produce an absolute vacuum some vapour will remain, though of greatly diminished elasticity. This vapour will be rare, and of weak elastic force, just in proportion to the intensity of the cold employed to reduce the rest to the liquid state. This must be kept, in mind in studying the steam-engine, and also for understanding the history of its progress from the first rude attempts to its present more perfect form. 132. From these tables, then, it will be seen that vapour rises from water at all temperatures ; that its density increases with the temperature, and its elastic force with the density. 133. Steam of the same elastic force as the atmo- spheric pressure is called low-pressure steam, no pres- sure above that of the atmosphere being required to produce it. To produce steam of greater elastic force than that of the air, a close vessel must be used, the lid being kept down by weights proportioned to the strength of steam required. To procure steam having twice the elastic pressure of the air, we must confine it by twice the force, or 29.4 pounds to the square inch. The atmospheric pressure furnishes 14.7 pounds of pressure (a pressure of one atmosphere, as it is termed ;) and, to provide the other atmosphere of pressure, we must lay such weights on the lid of the vessel, that there are 14.7 pounds for every square inch of the opening which admits the lid. In this manner, we procure steam of any required pressure greater than the atmospheric pressure, and it is called high-pressure steam. Steam of only a few pounds' (five or six) pres- sure higher than that of the atmosphere is still usually termed low-pressure steam. THE STEAM-ENGINE. 57 134. In the preceding paragraphs, we have spoken of steam when in contact with its water of generation. In this condition, it obeys a different rate of decrease or increase in elastic force from that of steam cut off from communication with water. In the first case, when the vessel is heated, the elastic force of the steam is increased by two causes : First, By the increase of heat ; second, by the increase in density from the addition of more steam, and vice versa, when the tem- perature is diminished. But, when not in contact with any water to generate more steam, addition of heat increases its elastic force from the increased tempera- ture only, no increase of density taking place. 135. Thus, the conditions, liquid and gaseous, do not seem to be absolute and essential to the constitu- tion of any body, but relative to and depending on the temperature ; so that it is likely that all liquids might be vaporized, even liquid metals, could we procure temperatures sufficiently high ; and that all aerial bodies might be condensed, by simply abstracting heat from them, could we procure temperatures consider- ably lower than we can at present command. 136. There are some bodies which are known to exist only in the gaseous state ; such are oxygen, hy- drogen, nitrogen, and a few others. These, which can- not be reduced to the liquid state by a reduction of temperature, are called gases ; while the aerial bodies which are formed by the influence of heat upon liquids, and which return to the liquid state when they are cooled, are exclusively called vapours. 137. Some aerial bodies, which cannot be rendered liquid by the mere abstraction of heat, have yet been reduced to the liquid state by pressure. As pressure retards the passage of a liquid to the aerial state, so it tends to reduce an aerial body to the liquid condi- 58 THE STEAM-ENGINE. tion. The particles are thus approximated, and brought within the sphere of action of the cohesive attraction. The following gases have been liquefied by the pressure stated after each, as determined by Dr Faraday. Sulphurous acid Suphurettted hydrogen Carbonic acid Chlorine Nitrous oxide Cyanogen Ammonia Muriatic acid 2 atmospheres, at 45 F. 17 . 50 36 . 32 4 . 60 50 . 45 3.6 45 6.5 50 40 . 50 CHAPTER VI. LATENT HEAT. 138. When water is made to boil in an open vessel, if a thermometer be placed in the liquid, it will be found, as would be expected, that the temperature of the water will gradually rise until it reaches the boil- ing point (212.) After this, however strong be the heat applied to the water, however long the water be kept boiling, no further rise in temperature will take place; the thermometer will remain at 212 as long as the water continues to boil. Also, it will be found that, after the water has begun to boil, and as long as it is boiling, the steam arising from it will be at the temperature of 212. 139. Here is a striking circumstance. The water THE STEAM-ENGINE. 59 must continue to receive heat after it has begun to boil, as well as before, but nevertheless the temperature of the water and the steam remains stationary. What has become of the heat which entered the water after it began to boil ? It has entered into the steam in a CONCEALED or LATENT state, and has been removed by the steam flying away as fast as it is formed. That this is the case, may be inferred from so much heat having disappeared, and may be proved by recovering it from the steam. 140. Let a tube be adapted to a flask or other vessel in which water is made to boil, and convey the steam arising from the boiling water into cold water. Let a known weight of water, in the form, of steam, pass into the cold water, which must also be of an ascer- tained quantity and temperature. Note the tem- perature to which the water has been raised by trans- mitting the .steam into it. Now, add to a like quan- tity of water at the same temperature, a quantity of loiling water equal to that which had been passed in the form of steam into the first portion of cold water, and observe the temperature of the mixture. It will be found that the water to which the steam was added will be at a far higher temperature than that to which the boiling water was added that is, the steam has given out more heat than the boiling water. But the steam and boiling water were equal in quantity and temperature therefore, the steam must have con- tained more heat. We now see what has become of the heat which entered the water after it began to boil. It entered the steam ; and, being in some peculiar relation to the water, becomes hid, or not discoverable by the thermometer, the usual test of the presence of heat. When the steam returns to the state of water, it restores this heat which it had absorbed into the concealed state ; and, giving out the heat which it had 60 THE STEAM-ENGINE. as boiling water, and the additional heat which it had absorbed on becoming steam, must produce a much greater heating effect than the same weight of water at the same temperature. 141. Heat which thus eludes the thermometer is called LATENT HEAT. Heat which is discoverable by the thermometer, is termed FREE or SENSIBLE HEAT, or HEAT OF TEMPERATURE. 142. The quantity (or rather proportion) of heat which becomes latent when water passes into the state of vapour, has been ascertained with considerable pre- cision. This may be done in two ways : 143. First, By estimating how long water requires to be heated (i.e., how much heat must be added) after it has been brought to the boiling point, to dissipate it entirely in vapour, and comparing this with the time required to raise it to 212 from any given point. To convert a given quantity of water at 212 into vapour, heat must be applied about 5f times as long as to raise the same quantity of water from 32 to 2i2(i.e., 5 times the quantity of heat must be added to the water.) From 32 to 212 is 180 ; 180 multiplied by 5f gives 1000 as the heat of conversion of water into steam.* 144. Secondly, the same may be estimated by trans- mitting a known quantity of steam into a quantity of water of a known weight and temperature, and observ- ing how much the temperature of the latter is raised. In this way, it is found that the heat absorbed by a given quantity of water at 212 in becoming steam, will raise 5| times the quantity of water at 32 to 212. * Any one may easily satisfy himself of this by experiment. Expose a quantity of water to a steady source of heat; note how soon the temperature of the water rises to 2 1 2 how long be- fore it is entirely vaporized. THE STEAM-ENGINE. 61 , multiplied by 5f , gives 1000 Fahrenheit, as the proportion of latent heat contained in steam. 145. The same takes place during the melting of solids and their congelation, or return to the solid condition* In melting, they absorb heat which does not raise their temperature ; in congealing, they give out this heat into the free or sensible state. The latent heat of water is 140 Fahrenheit. 146. It thus appears that that heat which is en- gaged in effecting a change in the condition of a solid or liquid, is combined with it in such a way as not to affect its temperature. These general laws of caloric may be expressed in a few words. "When solids become liquid, and when liquids become gaseous, they absorb a quantity of caloric, which does not raise their temper- ature. They evolve this caloric into the free or sen- sible state, when they return to their former condition* These laws of heat were developed by the celebrated Dr Joseph Black. 147. Though of high interest and importance in other applications of heat, and in relation to precise calculations as to the quantity of heat required to pro- duce a certain effect, they are not essential to an un- derstanding of the principle of the steam-engine, nor was it by a knowledge of them that Watt effected his grand improvements, as has been erroneously supposed. " These improvements," says Watt, " proceeded upon the old-established fact, that steam was condensed by the contact of cold bodies, and the later-known one, that water boiled in vacuo at heats below 100." It will be seen, as we go along, that Watt's improve- ments have no connection with the laws of latent heat, and would as readily have occurred to him though these laws had never been known. 148. When water boils at temperatures lower or higher than 212, it appears that still the same 62 THE STEAM-ENGINE. quantity of heat is always required to vaporize the same quantity of water ; the latent heat being as much greater as the sensible heat is less, when the water is made to boil at low pressures ; and as much less as the sensible heat is greater, when water is boiled at high pressures : the sum of the free and latent heat of steam at all pressures, being 1180 that is, at 212 1000 of latent, and 180 (reckoning from the freezing point) of sensible caloric. Hence, there would not be any economy of heat in raising steam at low temperatures, as was at one time supposed. 149. It appears that equal weights of different bodies require different quantities of heat to raise them to the same temperature, a fact generally expressed by say- ing that the specific heats of bodies are different. A body which requires much heat to raise its tempera- ture, is said to have a high specific heat, or a great capacity for heat and vice versa. Now, the specific heat of an aerial body is greater as its volume in- creases, continuing the same in quantity or weight ; increasing with the bulk, decreasing as the density and elasticity increase. Hence, when aerial bodies are rarified, to satisfy their increased specific heat, they absorb heat into the latent state. When condensed having now a less specific heat they give out heat into the sensible condition. Thus, rarefaction of a gaseous body causes cold ; compression causes heat. Hence the cold in the upper regions of the atmo- sphere, where the air is rare, and, therefore, requires more heat to raise its temperature than the dense, lower strata of air. Hence a thermometer sinks in temperature when placed in the receiver of an air- pump, from which the air is quickly withdrawn. Hence the syringe for procuring a light, which is simply a cylinder in which a piston works ; the latter being suddenly forced down, compresses the air, and THE STEAM-ENGINE. 63 the heat thus evolved kindles some tinder in the cylinder. 150. Several of the phenomena of heat are well illustrated by a beautiful instrument, devised by Dr. Wollaston, called the Cyrophorus, or Frostbearer. It Fig. 7- A" consists of a glass tube, expanded into a glass bulb at each extremity, and containing only pure water and watery vapour. Before it is closed, the water is divided between the two bulbs, and made to boil in each the vapour escaping by the aperture in the middle of the tube, so that the vessel cannot contain any air. While the liquid is boiling briskly, the aperture is suddenly closed by directing the flame of a blowpipe across it. 151. With this instrument, the following striking experiment may be performed : Collect all the water in one bulb, and place the other in a freezing mixture. In a short time, the water will be frozen ; illustrating three points in the phenomena of heat: First, That water evaporates rapidly as the pressure on its surface is diminished ; second, That it evaporates at very low temperatures ; and, third, That, during evaporation, an immense quantity of heat is absorbed into the latent state, the adjoining liquid being robbed of sen- sible heat to supply this demand. 152. The vapour in the bulb being condensed by the freezing mixture, the vapour in the tube and upper 64 THE STEAM-ENGINE. part of the other bulb expands and rushes into the bulb in the freezing mixture. The pressure upon the surface of the liquid being thus reduced, and the space above it containing less vapour than its temperature can support, evaporation takes place from the surface. But any vapour which rushes into the other bulb is immediately condensed : hence, evaporation from the surface goes on with great rapidity, and the tempera- ture of the liquid is so much reduced by the vapour absorbing heat into the latent state, that it actually freezes. If the bulb in the freezing mixture be exa- mined, it will be found to contain some water or ice, though there was nothing but vapour in it at first. PART II. CHEMICAL RELATIONS OF WATER, COAL, AND IRON. CHAPTER I. WATER. 153. Water, in its purest state, consists solely of two elementary bodies, OXYGEN and HYDROGEN. These two substances are met with in the aerial state when uncombincd with other bodies, or each other ; they are clear, colourless, and transparent; and are incapable of being reduced to the liquid or solid form by cold or pressure, or both combined. The following tables will illustrate the composition of water. COMPOSITION OF WATER. Name of Gas. Weight. Bulk. Oxygen 8 0.5 Hydrogen 1 1.0 Steam at 212 9 1.0 66 THE STEAM-ENGINE. Proportions necessary for forming water in 100 parts of the gases. By weight. By measure. Oxygen . 88.9, or 8 33.34, or 1 Hydrogen . 11.1, or 1 66.66, or 2 Mixed . 100.0 9 100.00 3 Combined . 100.0 9 66.66 2 154. When the gases combine, a condensation en- sues. They are reduced l-3rd in bulk. The steam formed occupies only the bulk of the hydrogen. Thus, when steam is decomposed (its elements separate), there must be an increase in bulk of one-half. Also, the gases into which it is formed are not condensible by cold, as steam is. Thus, while steam is easily con- densed, and made the means of procuring a vacuum, its uncombined elements are totally unfit for such a purpose. 155. Some of the metals, as iron and zinc, possess the property of decomposing water when they meet at a high temperature. The metal abstracts the oxygen, with which it unites and forms a solid crust of metallic oxide at its surface. The hydrogen thus eliminated, assumes that form which is proper to it when uncom- bined, and becomes a clear, colourless, incondensible gas, equal in bulk to the steam from which it was formed. The hydrogen is inflammable; and, if it meet with the necessary quantity of free oxygen (as in air) and a sufficiently high temperature, will burn, uniting with the oxygen, and forming vapour of water. When hydrogen and oxygen unite, great heat is evolved, and the gases are thereby enormously expanded for a moment, some have said so much as to occupy fifteen times their former bulk. At all events, they expand with very great force, causing a loud report when the experiment is performed with the proper proportions of the gases in a stout glass jar. THE STEAM-ENGINE. 67 156. But water such as we have been just speaking of is nowhere met with in nature. It is pure distilled water, found only in the laboratory of the chemist. Common water contains in solution small quantities of air, and of any soluble earthy matters it may have been in contact with, as sulphate of lime, &c. The water of the Clyde contains, in an imperial pint (34^ cubic inches, or about 8750 grains), 1.14 grains of earthy matters, and about l-35th of its bulk of gases. The earthy matters consist chiefly of muriate of mag- nesia, sulphate of soda, common salt, silica or flinty earth. Of the gaseous matters, l-20th is carbonic acid, and the remaining 19-20ths are common air. The proportions of these ingredients vary in different streams; but all contain some earthy matters and gases in solution ; besides what may be present, me- chanically suspended in the liquid. 157. Sea- water contains a much larger proportion of earthy matters. The water of the Atlantic, as ana- lyzed by Dr. Marcet, consists, in 1000 parts, of Pure matter of Water .... 956.84 Common Salt (chloride of Sodium) . . 26.6 Sulphate of Soda ..... 4.66 Muriate of Lime 1.99 Muriate of Magnesia . . . . 9.91 1000.00 This gives, as nearly as possible, l-23rd of saline and earthy matter, and 22-23rds of pure matter of water ; or about forty-three parts in the thousand are saline and earthy matter. The water of the Frith of Forth, examined by Dr. Murray, contained, in 1000 parts Pure matter of Water .... 969.691 Common Salt 22.001 Sulphate of Soda . . . . 3316 Muriate of Lime 0.784 Muriate of Magnesia .... 4.208 ToobTiP 68 THE STEAM-ENGINE. This analysis gives about thirty parts in the thou- sand as saline and earthy matter ; or, nearly l-33rd the proportion of saline matters being less, as might be expected, near the shore and mouths of rivers, than out in the ocean. 158. "When water containing any gases and earthy matters is boiled, the gases rise in the gaseous form with the first portions of vapour that are expelled; so that the steam of common water always contains a small portion of air. When the steam condenses into water, this air does not entirely condense along with it : a great part retains the gaseous form, as water cannot absorb much air when warm, and the water formed by the condensed steam is very warm at first. Th earthy matters remain in the vessel in which the water is boiled; and, when there is not sufficient water left in the vessel to retain them in solution, fall down in the solid form. If the same vessel be used for boiling successive portions of water, and be not frequently cleaned out, a crust of these earthy matters will form at the bottom, which will gradually thicken, and may lead to injurious consequences, as the earthy crust is a slow conductor of heat that is, takes heat slowly from bodies, and gives off heat slowly in short, gives heat a very slow passage through it. This will be explained more particularly in the chapter on iron. THE STEAM-ENGINE. CHAPTER IT. FUEL. 159. The fuel used for the production of heat to va- porize water for steam-engines, is CHARCOAL, COKE, COAL, ANTHRACITE, TAR, or REFUSE WOODY MATTER, such as saw-dust^ tanner's spent bark, peat^ &c. Of all these the chief combustible ingredient is carbon. It forms the principal part of charcoal, coke, and anthra- cite the latter (called also blind-coal, glance-coal, stone-coal) contains a considerable proportion of earthy matters, silica, &c., which remain as ashes after com- bustion. It is the mineral chiefly used as fuel in the States of North America. Coal contains, besides car- bon, hydrogen, a combustible ingredient, and also oxygen and nitrogen. Tar and wood also contain hydrogen. Where the fuel contains hydrogen, it burns with a yellow flame, and then with a steady red light, like cinder. Where there is no hydrogen, the fuel burns more steadily, and a more uniform heat is sus- tained. Such a fuel is found in charcoal and coke. The former is prepared by heating wood in close vessels; the latter from coal, by a similar process. Anthracite contains no hydrogen. A new composition called " prepared fuel" has lately been introduced. It is composed of screened coal (coal otherwise too small for use), river mud, and tar, formed into blocks of the same size and shape as a common brick ; and is said to present the advantage, so important in steam navi- gation, of concentrating a great quantity of combus- tible matter in a small compass. 70 THE STEAM-ENGINE. 160. The following tables of the composition of the different kinds of coal, and quantity of coke and ashes they yield, are from analyses by Dr. Thomson. Carbon . . Hydrogen . . Nitrogen . . Oxygen . . Caking Coal. Splint Coal. Cherry Coal. Cannel Coal. 75.28 4.18 15.96 4.58 75.00 6.25 6.25 12.50 74.45 12.40 10.22 2.93 64.72 21.56 13.72 0.00 100. 100. 100. 100. 1000 parts of "] Caking Coal 1 Splint Coal . Vgive Cherry Coal . Cannel Coal J Volatile Products. Weight of Coke. Incombus- tible Ash. 226 352 477 600 774 647 522 400 15 95 100 110 In the last table, the volatile products, and coke, make up the 1000 parts. These kinds of coal differ considerably in composition in different places, whic h accounts for the discrepancies in the analyses given by various chemists. 161. In the combustion of fuel, a chemical action goes on, in which the carbon and hydrogen unite with oxygen, furnished by the air; so that a free and ample supply of air is essential. It has been estimated that a pound of coal requires about two-and-a-half pounds of oxygen for combustion. This is about twenty-nine cubic feet of oxygen. This quantity of oxygen will be contained in 145 cubic feet of air. About a third of the air which enters the furnace, passes through without aiding in the combustion ; so that, to furnish the necessary quantity of oxygen, about 217 cubic feet of air are required for the complete combustion of every pound of coal. THE STEAM-ENGINE. 71 CHAPTER III. IRON. 162. Iron is the material used for all large steam- boilers, interposed between the heat and the water to be boiled. Malleable iron is generally ' employed. It will bear a considerable heat without injury ; but, if too strongly heated, it will oxidate, or rust a crust of brittle oxide forming upon its surface, whether exposed to air or to water. It is not improbable that malleable iron much in contact with the carbonaceous matter of fuel, and at a high temperature, may combine with some carbon, and thereby become impaired in its tenac- ity, acquiring the properties of cast iron. Iron is a good conductor of heat, and, when employed as a boiler, is in no danger of rusting, (or burning, as it is some- times termed,) if there be plenty of water in contact with it, to carry off the heat in the form of vapour, and the vapour have free exit. If the vapour be confined, however, from any cause, its temperature will rise, and the heat, not being carried off, will tend to accu- mulate both in the vapour and the boiler, and thence to corrode the boiler. If the water be entirely dissi- pated, then also, the heat, not being carried away in the latent state by vapour, will accumulate and burn the boiler that is, enable it to combine with the oxygen of the air, which it does not do at a moderate temperature. Or, if there be an earthy crust lining the boiler, this (a slow conductor) will transmit the heat so slowly through it, and give it off so slowly to the water, that the boiler will be apt to be destroyed from the action of the fire. "Where, from any of these causes, the boiler is at a very high temperature, 72 THE STEAM-ENGINE. it has been conjectured (though never proved to have taken place) that the iron may decompose the steam in the interior, and replace it by the incondensible gas hydrogen, retaining the oxygen, in the crust of oxide formed. Many seem disposed to consider this a common cause of the explosion of steam-boilers. The difficulty here is to account for the supply of oxygen to form an explosive mixture with the hydrogen. Hydrogen is not separated from steam by a hot metal, except the oxygen of the steam be abstracted by the metal, in which case the oxygen is fixed down in the form of a solid crust of oxide. If explosions ever take place from this cause, the necessary quantity of oxygen must be derived from a leak in the boiler admitting atmospheric air, which can hardly be supposed to be the source of the oxygen for an explosion, so that we may regard it as next to impossible that the decomposition of the steam can ever lead to the formation of an explosive mixture in a steam-boiler. Besides the above consid- erations, it is to be borne in mind, that, even supposing the necessary quantity of oxygen to be present, there would be no explosion from two causes 1. The want of a sufficiently high temperature ; 2. The presence of the steam in large quantity in the gaseous mixture. The American Committee gave it as their opinion, from experiments instituted, that this is not a cause of ex- plosions in steam-boilers. Danger may also arise from a deficiency of water, when the sides of the boiler may become red-hot, and, if water then come suddenly in contact with them, an explosion may ensue. This, there is reason to believe, is a frequent cause of the explosion of steam-boilers. PART III. HISTORY AND DESCRIPTION OP THE STEAM-ENGINE. 163. IT is very interesting to trace the progress of a great invention, from the first rude attempts, till it attains a somewhat perfect form to mark the succes- sive changes it undergoes, and observe how often men have been on the very brink of the discovery, and yet allowed it to escape them ; and there is perhaps, no better or easier way to understand the later and more complex forms it assumes, than tracing it from the first simple conception, and at each stage contrasting it with its previous condition. "We shall, therefore, prefix, to the description of the modern engine, a brief sketch of the progress of the invention from the earliest records. SECTION I. jEOLIPILE OF HERO ORGAN OF GERBERT GARAY'S STEAM BOAT FOUNTAIN OF PORTA AND KIRCHER ENGINES OF DE CAUS, BRANCA, WORCESTER, AND MORLAND AND PAPIN'S FIRST ENGINE. 130 B.C. TO 1690. JEOLIPILE. B.C. 130. 164. The first instance on record of the force of steam being applied to produce motion, is that of the 74 THE STEAM-ENGINE. Fi s- 8 - jEolipile, a philosophical toy, described in the writings of Hero of Alexandria, who flourished during the reign of Ptolemy Philadelphia, about 130 years before the birth of Christ. This writer was distinguished for his mechanical knowledge. Besides the JEolipile, described in the next paragraph, he also was ac- quainted with the forcing-pump for raising water, (the invention of Ctesibius ;) the beautiful contrivance for an artificial fountain, still called Hero's fountain ; a machine for producing a rotatory motion by a jet of heated air ; and many other curious mechanical inven- tions. The following cut will explain the action of the .ZEolipile. 165. This consists of a globular metallic vessel, a, revolving on two pivots, the pointed extremities of the tubes, &, c, and having two tubes, . " We enclose copies of certificates from engineers, showing that the boiler has not suffered in the least degree from the use of the patent." When the boiler was worked without the patent, 1 lb. of coal evaporated 6.66 Ibs. of water. THE STEAM-ENGINE. 133 III Statement by Mr Bell, EVAPORATION OF WATER BY IVISON'S PATENT. " The following table shows the result of twenty-three several experiments detailed below, and certified respectively by Professors Forbes and Traill, Dr. Fyffj, Messrs Slight, Hamilton, and Dougall, engineers, the editor of the Mining Journal, and Mr Casey, The experiments were performed with common Scotch coals. In the table the results are also stated in English caking coal, (on the ordinary propor- tion of four of Scotch to three of English caking coal,) in order to contrast them with the best results on record which were performed wish English coal, and these last are also converted into Scotch in the first column; but even irrespec- tive of the difference in the strength of the coal, the average given in the last line gives 4*62 Ib. of Scotch coal, while the best by the ordinary method, gives 5*32 Ibs. of English coal to the cubic foot of water, or the horse power of engines per hour. co rj* .b- CO 00 CO C^ O Oi -^ T* 1-- CO CO co" J^- 06 GO i i i~-l co* -^ irj tN r- Ir-tr-H- ICNCNCOCOCOCO CO CO ^H J^ O^ OiOi* Oi -t^ ifj (N i i i-H-^iftC^CO lOGit^OiOiTfOiCNt ^ iOcoJt^l>*>od'-HCoeoTjIeo S3 - g ? s CO O rz3 ^" '4-< .^-, ert R- ~ ,? be ^ g .g ^ P CC "Ti K oa 5 V < o z H S -r, W 8 -.S k=i 1 I I I s. i II T1IE STEAM-ENGINE. 135 268. In a work in Wales, where a large engine is used, smoke from the chimney is almost entirely pre- vented by placing a pot of water at the back of the furnace, and interposing a horizontal flue between the pot and the bottom of the chimney. The steam from the water mixes with the smoke, moistens the solid matter it contains, which is deposited in the horizontal flue, and the gaseous matters pass up the chimney and emerge nearly free from smoke. 269. We here conclude the description of the boiler, and shall now proceed to explain the engine, begging the reader to bear in mind that there are two points of connection between the boiler and the engine : First, the steam-tube (o 0, Fig. 15), which conveys steam from the loiler to the engine ; and, second, The hot- water pipe (r r, Fig. 15,) which conveys hot water from the engine to the boiler. THE ENGINE. 270. In describing the engine, it may be naturally divided into two parts : First, That which is directly connected with the steam, embracing the cylinder, condenser, air-pump, and hot-well ; and, Second, That part which is engag-cd in trasmitting and regulating the motion, embracing the beam, crank, fly-wheel, governor, &c. In Figures 19, 20, the piston, belong- ing to part first, is represented detached from the boiler and other parts of the engine. In Fig. 21, the condenser and apparatus connected with it are shewn. The point of union between these two figures is the tube, the extremities of which are marked m u in each. 271. In the steam-engine which is now to be de- scribed, the double-acting engine, the steam causes 136 THE STEAM-ENGINE. THE STEAM-ENGINE. 137 both the ascending and descending motions of the pis- ton. For this purpose, it must be admitted alternately above and below the piston ; and the vacuum, to give effect to its pressure, must be made alternately on each side of the piston. This is brought about by the fol- lowing very ingenious method, illustrated by Figures 19 and 20. The steam is conveyed to the cylinder from the boiler by the large steam-pipe, t S. The Suantity of steam admitted is regulated according to le demand, by the throttle-valve , which, as will be easily understood, admits more steam in proportion as it is more inclined. The action of this valve will be explained under the head GOVERNOR. It is supposed to quit this pipe at the point S, and is then directed upwards to the top of the cylinder, or in an opposite course to the bottom of the cylinder, according to the position of the valve. C y is the cylinder, having two apertures, one above and one below, by each of which steam may be admitted to the cylinder from the steam- pipe, or withdrawn from it to the condenser. P is the piston, to be moved alternately up and down ; e i o u is a box at the side of the cylinder, in which the valve works, and into which the steam enters first ; and a l> c d is the valve, which is a tube, capable of being mov- ed up and down from the position in Fig. 19, to that shewn in Fig. 20. These two figures are alike in all respects, except the position of the movable bodies the valve and piston. Tho valve is moved by the engine itself, in the manner that w T ill be explained afterwards : it is by the rod v v that it is worked. There are many kinds of valves. That shewn in these figures is one of those called slide-valves, and is now very generally em- ployed. By the tube m n, at the lower part of the valve-box e i o u, the steam passes to the condenser, after it has performed its office in the cylinder. The condenser, &c., is shewn in Fig. 21, page 139, but had better be disregarded at present, confining our attcn- 138 THE STEAM-ENGINE. tion to. what passes on in the valve and cylinder, and simply bearing in mind that there is a constant vacuum in the condenser, and, consequently ', in that part of the cylinder which communicates with it. 272. Let us suppose, then, that the steam has just pushed the piston up to the top of the cylinder ; the object now is to remove the steam which fills the cylinder, cause a vacuum in the cylinder, and admit steam above the piston, which steam not being resisted by any force below the piston, will easily press that body to the bottom of the cylinder. For this purpose, the valve is raised to the position shewn in Fig. 19. In this position of the valve, the communication be- tween the lower part of the cylinder and the condenser (by the tube m n) is free, and the steam rushes to the condenser, as shewn by the course of the arrows; thus the vacuum is formed in the cylinder below the piston; at the same time, it will be seen that, from the con- struction of the valve, the passage from S to the cylin- der, by its upper aperture, is now open, so that steam enters the cylinder above, and, exerting its elastic force on the upper surface of the piston, while there is a vacuum below it, presses it down to the bottom of the cylinder. Thus, the downwards motion is produced ; steam being the moving power, and steam, by its con- densation, the means of forming a vacuum to give effect to this moving power. 273. The manner in which the upwards motion is effected, will be easily understood, with the aid of Fig. 20. The piston is there represented as it would be, after being acted on by the steam with the valve in the position shewn in Fig 19. To raise the piston, let the valve be brought down to the position given in Fig. 20. Then, the steam in the cylinder above the piston will rush to the condenser, passing out by the upper opening in the cylinder, and through the tube of the valve, which communicates freely with the con- THE STEAM-ENGINE. 139 denser, following the course shewn by the arrows in the figure. Thus, a vacuum is formed in the cylinder above the piston. This new position of the valve, at the same time admits steam from S to the lower open- ing of the cylinder; it enters, and presses up the piston to the top of the cylinder. 274. Thus, by the movements of the valve, steam is admitted alternately on each side of the piston ; while the steam on the other side is removed by a communi- cation being at the same time opened with the con- denser; and, by this beautiful adjustment, a steady alternate rectilinear motion is produced. We cannot help remarking here how perfectly the action of the steam, in producing motions of the same body alter- nately, in two directly opposite directions, illustrates Worcester's graphic description of the powers of this versatile agent, (page 82.)- The connection of the piston-rod, the medium by which the motion is trans- mitted from the cylinder, with the other parts of the engine, will be explained afterwards. We shall now trace the course of the steam after it leaves the cylinder. 275. Fig. 21 represents the condenser and appara- tus connected with it. Cd is the condenser : above, Fig. 21. 1 40 THE STEAM-ENGINE. it communicates with the cylinder by the pipe n m, and, at its lower part, with the air-pump A, by the valve between them. This valve, as will be seen in the figure, is of such a construction as to permit the passage of fluids from the condenser to the air-pump ; but not from the air-pump to the condenser. The condenser and air-pump are surrounded with cold water, a jet of which is continually playing into the interior of the condenser. The piston (p) of the air- pump, is alternately raised and depressed by the beam of the engine, to which its rod is attached, and thus draws the fluids out of the condenser ; the air-pump piston and cylinder piston moving simultaneously in the same direction. At the right of the air-pump, is the hot-well (wh), into which the piston of the air-pump throws the liquids which it draws from the condenser. To the extreme right of the figure, is the pump (worked by the engine) which draws cold water to sur- round and supply the condenser. At the left of the figure is a tube leading from the condenser, with a plug (s) permitting the exit of any fluids; but not the entrance. This is the snifting valve. 276. Let us now suppose that the engine is to be started, (set a-going). All the valves are opened, and steam driven through the engine to expel the air, which is driven out at the snifting valve s, Fig. 21. The injection-cock i, Fig. 21, is then adjusted so as to pour in the necessary quantity of water into the condenser. The steam, after acting on the piston, rushes to the condenser, where it is instantly reduced to the liquid state. The condenser would soon be filled with the injection water, condensed steam, and air which entered along with the steam ; but the air- pump removes these. The valves in the air-pump piston open upwards only. Accordingly, when the piston is raised, as nothing can pass through the piston THE STEAM-ENGINE. 141 from above downwards, there is a vacuum below the piston. The valve at the bottom of the condenser being pressed by the fluids in the condenser, and open- ing towards the air-pump ; and that pressure not being resisted in the air-pump, the valve is forced open, and the fluids rush from the condenser to the air-pump. When the piston of the air-pump descends, it tends to press the fluids back into the condenser; but, from the construction of the valve, they cannot return. Being pressed, then, by the descending piston, they force open its valves ; and pass through it to the upper side of the piston, where they accumulate. When the piston ascends again, they are lifted by it and trans- ferred to the hot- well (w h.} By this series of actions, regularly continued while the engine is at work, the fluids in the condenser are withdrawn from it, and thrown out into the hot-well. The water removed from the condenser being warm, (having received much of the heat of the condensed steam,) is not altogether thrown away ; but part is returned to the boiler, being- conveyed, by a pump dipping into the hot- well, to the cistern at the top of the feed-pipe. Thus, a part of the heat which the steam carried from the boiler is returned to it. This pump is worked by a rod from the beam of the engine. The cold water is supplied, and the whole apparatus kept cool, by water pumped by the engine, also by a rod from its beam. This is the cold-water pump, at the right of the figure, page 139. Connected with this part of the engine, there are four contrivances the Indicator, the Condenser Guaye, the Eccentric Rod, and the Governor, which will be most conveniently described at present. 277. THE INDICATOR. This extremely useful piece of apparatus is attached to the cylinder, and points out the state of the steam in the cylinder, showing the difference between the strength of the steam in the 142 THE STEAM-ENGINE. boiler and that in the cylinder between the vacuum in the condenser, and that in the cylinder. The indicator consists of a brass cylinder attached by a tube to the grease cock of the steam-cylinder. There is a stopcock on this tube, by opening which and the grease cock, the indicator cylinder is open to the steam-cylinder. The indicator cylinder contains a pis- ton which works in it, and the motion of which is resisted by a spring, which yields a tenth of an inch for every pound of pressure applied to the indicator piston. An index is attached to the piston rod, which, shewing the situation of the piston, indicates at the same time, the degree in which the spring is com- pressed. By means of a pencil attached to the indi- cator's piston rod, and a cylinder with a card or piece of drawing paper round it, which is connected with the indicator cylinder, the motions and successive situations of the indicator piston are represented by lines drawn on the card l)y this pencil. The cylinder with the paper has a connection with some moving part of the engine (as a radius bar) which causes it (the paper cylinder) to revolve once during one stroke of the steam piston. When the steam is above the piston, it forces up the indicator piston, and the line drawn on the paper shews the height of that piston, and consequently the strength of the steam at different parts of the stroke. When the steam is below, and the vacuum above the piston, the pressure of the air on the indicator piston depresses it, in proportion to the degree of exhaustion in the cylinder, and thus indicates the extent of the vacuum there. It is found by the indicator that the steam attains its maximum effect almost immediately on entering the cylinder; while the condensation does not reach its greatest extent, until some little time after the commu- THE STEAM-ENGINE. 143 nication has been opened between the cylinder and condenser. Hence, the eduction pipes require to be much larger and more capacious than the induction or steam pipes. 278. CONDENSER GAUGE. The object of the con- denser gauge is to shew the elastic force of any vapour that may remain in the condenser to judge of the extent of the condensation there. As water retains the state of vapour at very low temperatures, some vapour will exist in the condenser, however cool ; and its elastic force may be judged of in the usual manner, by communication with a bent tube containing mer- cury, open to the air at one end and to the condenser at the other. If the vacuum were perfect, there would be a difference of 29.8 or thirty inches in height be- tween the mercury in the tube open to the air, and that in the other extremity open to the condenser, the mercury in the latter being pressed up by the atmo- spheric pressure on the surface of the liquid in the other limb of the tube. But the vapour in the condenser resisting the atmospheric pressure, depresses this co- lumn a little, reducing it to about 26 to 28 inches in general. The temperature of the vapour in the con- denser is generally about 100 Fahrenheit, at which it has an elastic force of about two inches of mercury. 279. ECCENTRIC ROD. The object of this rod is to work the valve to communicate an alternate recti- linear motion to the rod v v, so that the valve may bo made to assume alternately the positions shewn in Fi- gures 19 and 20. This is done in the following manner. The axis on which the fly-wheel (the large wheel in Fig, 28) turns, has a continued circular motion. By means of the eccentric rod, and one or two bent levers interposed between this axis and the rod of the slide- valve, the latter is moved as required. The construe- 144 THE STEAM-ENGINE tion of the eccentric rod and its motions will be under- stood from the following figures (22, 23.) Let C in both figures be the rod or axis which by its revolution gives motion to the eccentric rod (e r u 0.) C, although revolving, always remains in the same point. This is shewn in the two positions of the ec- centric rod in the figures, by C being in the same per- pendicular line. To C is fixed a disk or plate (a b d), which revolves along with C, with its centre c at some distance from the point C on which it turns. Hence the name eccentric (ex, out of, the centre.) Fitting close to this plate, there is a ring (e o u\ within which the plate has free motion, but fitting closely to each other. The rods e r, r u, fixed to the ring, are attached to the free end of one limb of the bent lever r P q : to the extremity (^) of the other limb, the rod of the valve v v is attached. P is the fixed point, (or rather rod, for the two arms of the lever are attached to different points of one rod, necessarily represented as one in the figure) on which the lever turns. That it is fixed, is shewn by P in both figures being in one perpendi- cular line the dotted line. It is clear that, when THE STEAM-ENGINE. ] 45 the plate a I d makes a half revolution from the posi- tion shewn in Fig. 22, it will carry the eccentric rod and levers into the position shewn in Fig. 23. This raises the end of the lever ( nearly double what it was previously. 411. Explosions of steam-boilers are of two kinds EX- PLOSION OUTWARDS, or EXPLOSION, properly so called, when, from the elastic force of gaseous matter within the boiler being greater than it can support, it is burst, and its sides forced outwards and COLLAPSE, when the sides of the boiler are forced inwards by the atmospheric pressure, from want of support, arising from diminution of the resistance within. When the flues pass through the boiler, explosion of the latter is at the same time collapse of the flue, which must be distinguished from the true collapse just mentioned. It is a collapse as regards the flue, an explosion as regards the boiler. 412. Although the causes of explosions are stated sepa- rately, according to their nature, it is not meant to be implied that explosions often or usually arise from the action of any one of these causes alone : several may be concerned, and in general there are more than one of the following causes in action. But to obtain a clear view of them, it is best to con- sider them individually. The large letters at the end of each line refer to a subse- quent note, where any necessary explanation or commentary on that subject is given. There is not room, consistent with the plan of the present work for the full discussion of each that would require a volume. 232 EXPLOSION OF CAUSES OF STEAM BOILER EXPLOSIONS. EXPLOSION OUTWARDS arises from I. Too HIGH PRESSURE OF STEAM, caused by 1. Inefficiency of the Safety Valve, from being (1.) Overloaded, A (2.) Fastened by oil drying, (3.) Corroded, (oxidated, rusted), J (4.) Gagged, Q a. From expansion of plug, J)t 6. From cohesion. c. From action of blast from aperture, E (5.) Being too small. 2. The sudden formation of more steam than can escape in time by the safety valve, caused by "Water brought suddenly in contact with too hot metal. BOILER TOO HOT FROM (1.) Water falling too low, J\ from a. Fire increased, evaporation increased, and supply the same. b. Supply stopped, (j a.a. From engine not being started. b.b. From engine stopping. c.c. From feed-pipe out of order. d.d. From supply cut off by engine-man. (2.) Water driven out of narrow water spaces. (3.) Fire suddenly increased. (4.) Sediment in boiler. WATER COME SUDDENLY ON BOILER, from (1.) Supply pump set on. (2.) Lurch in a steam- vessel. (3. ) Inertia of liquid, when steam-vessel starts. (4.) Foaming (water boiling up on sides) from a. Water low, and valve suddenly opened. 7 b. Water low, and engine started, J "" (5.) Crack in sediment. 3. By the boiler being at too high a temperature. STEAM-BOILERS 233 II. WEAKNESS OF THE BOILER, from 1. Boiler too weak at first, J^ 2. Boiler of a bad form. 3. Boiler yitld at the seams, 4. Form of boiler altered by unequal heating. 5. Tenacity diminished from being too hot, ]. 6. Metal rendered brittle. (1.) From action of heat upon it. (2. ) By sudden application of cold water when highly expanded by heat. (3.) Carbonised? (4.) Sulphuretted-? (5.) Cells of air in cast iron. 7. Metal corroded, (oxidated, j (1.) By fire outside. (2.) By the sediment. (3.) By water inside (when red-hot) . . ? 8. Pressure of high column of water in certain Boilers, J^. 413. A. Safety-valve overloaded. This is a frequent cause of the explosion of steam-boilers, particularly those of marine and locomotive engines. The Parliamentary Committee which reported on this subject in 1816, gave it as their opinion that the overloading of the safety-valve was one cause of the explosion which had led to the inquiry (at Norwich), and from the evidence led as to the causes of explosions, and the opinions of many engineers and engine-makers who were examined, they recommended, " That every boiler should be provided with two sufficient safety-valves, one of which should be inaccessible to the engine- man) and the other accessible both to him and to the persons on board the packet." This is quoted to shew that it was the opinion of the committee, and of many of the witnesses, that the valve is frequently overloaded by the engineman, as it is imagined by some that the valve is so constructed, and such weights applied, that the engineer has only a safe and limited control over it. 414. It is well known that when there is much competi- tion among the steamers on any line, it is very customary, in the haste on calling at any port, not to relieve the valve 234 EXPLOSION OF trusting not to be detained a moment to permit the steam to accummulate to get a good start accidents cause a longer delay than was anticipated, and explosion ensues. 415. Mr. David Napier, in his evidence before the jury at the inquest on the last explosion of the VICTORIA, admits that there were extra weights on the safety valve. He says, " The engineer ought to have removed the extra weight on the lever at Black wall, going and coming, and the accident could not have happened." 416. In the evidence at the inquest after the explosion of the PATENTEE locomotive engine last autumn, it came out that the " Engineers were in the practice of weighting the valve, or keeping it shut by holding down a lever by the hand" when ascending an inclined plane, or wishing a strong power of steam, and thus raising the elastic power of the steam far above the pressure allowed by the directors. 417. Another cause why the safety-valve is sometimes inefficient is, that while it is too heavily weighted to relieve itself, it is of a form not adapted for being easily opened, or in a situation where the erigineman has not ready access to it. 418. In many of the smaller boats the weights consist of flat pieces of metal with a hole in the middle which are slipped down a rod, and require a considerable time to be taken off. In some boats, where this is the manner of load- ing the valve, there is a lever, by which, if necessary, the whole can be raised in an instant. But in other boats, this cheap, simple, and effectual device is wanting ; and the valve when over-weighted can only be relieved by the tedious process of removing the weights, raising them one by one to the top of the rod. 419. With regard to the situation, in few of the small boats is the valve at hand for the engineer who is regulating the engine. On one occasion I noticed the engineman of a steam-vessel calling hastily and impatiently for some one to raise the weights off the valve ; no one answered for a little : he could not leave the engine ; at last a boy appeared, who had some difficulty in reaching the uppermost weights to take them off. And others have assured me that they have often observed similar occurrences in steam-boats. 420. In every steam-boat there is an engineer stationed at one particular spot, to regulate the motions of the engine. STEAM-BOILERS. 235 It is singular that the very simple contrivance of a lever within his reach, by which he could control 1 the valve has not been universally adopted so essential where there is only one valve, and that one in the practice of being overloaded. At the inquest on the second explosion of the VICTORIA, the jury gave it in their verdict that, " The engineer having no immediate control over the safety-valve, in the engine-room, is highly reprehensible." 421. From these and similar circumstances, there can be very little doubt that overloading the safety valve is a common, practice with the engineers in marine and locomotive engines, and that they are kept overloaded at a time when the safety valve is most likely to be required. No one can foresee those sudden emergencies at which the action of the safety valve is essential to give vent to an accumulation of steam ; and it cannot be looked upon as a security at all, unless it be always in such a state as to rise instantaneously whenever the steam tends to acquire undue force. 422. ]3, Safety-valve failing, from the surfaces being cor- roded. This is not a frequent cause of inefficiency of the valve, but it has happened, and the valve should be frequently inspected to ascertain that the opposed surfaces of metal are not in any degree rusted or corroded. Corrosion may either cause the plug of the valve to adhere altogether to its seat, or produce such a degree of friction as to interfere seriously with the easy motion of the valve, and add a resistance, equal to a weight of many pounds per square inch, to the exit of the steam. 423. 0. Safety-valve gagged. It seems to be pretty well ascertained that the safety-valve sometimes fails, in cases where it could not be attributed to overloading, nor to cor- rosion. 424. I). Safety-valve gagged from Expansion of the Plug. The plug is usually made of brass, while the ring, or cylinder, or cone in which it works, is of iron. The latter is less expanded by heat than brass, so that if the plug be made to tit close at ordinary temperatures, it will, when they are both expanded by heat, be rather too large for the 236 . EXPLOSION OP tube in which it works. Hence, if this tube be cylindrical unless it be of a conical form with a large angle at the apex the effect of this expansion will be to tighten the plug in its seat, fix it there with great force, and thus completely counteract the object of the safety-valve. This is a possible a probable, cause of adhesion of the safety-valve but I am not aware that it has yet been ascertained. It was sug- gested to me by Mr. Edington of the Phoariix Foundry, Glasgow, who, 1 believe, intends to investigate the subject, experimentally. 425. J]. Safety valve gagged from action of blast from aperture It is well known that in certain circumstances, a blast from an aperture has the effect of drawing the lid or disc of the aperture towards it instead of driving it away. It has been shown that this is determined in a great measure by the proportion between the aperture and the disc covering it. Seethe recommendation of the American committee, page 243. 426. J\ Water falling too low in the boiler This is the most frequent cause of the over-heating of the sides of the boiler. When a part exposed to the action of the fire, how- ever fierce, is covered interiorly by water, the liquid removes the heat from the metal as fast as it is supplied to it, and it can never become very hot, if the steam formed has free exit. But if the water have fallen low in the boiler, and a part exposed to the action of the fire be bare internally, the heat will accumulate in the part left uncovered by water, and it will become red hot (as has often happened) if it be long in this state, or the fire be very strong. 42 ? G. Water falling low in the boiler from the supply being stopped. The supply of water by the feed-pipe being altogether cut off, while the action of the fire is still conti- nued, is a common cause of the water sinking too low. The feed-pipe is supplied by a pump worked by the engine, so that the supply ceases when the engine stops : and, before the engine is started, or whenever its action is suspended, there is no fresh water supplied, and if the fire be continued long, the water must necessarily fall low. Hence it happens, that most explosions, both in stationary and in marine STEAM-BOILERS. 237 engines have occurred, either when the engine is just about to be started, immediately after it has been started, or when it stops, as in steam-vessels when calling at a port in the course of the voyage. The Americans are well aware of the danger of cutting off the supply when a steam-boat stops. See p. 192, 428. JJ. Foaming of the water in a boiler. When the sup- ply pipe is stopped, and perhaps the steam not escaping freely, so that there is considerable pressure, and the water, there- fore, not boiling freely ; and the water has sunk low so that the sides are hot ; any cause that diminishes suddenly the pressure of the steam, will enable the liquid to boil more vigorously, so that it will be thrown up upon the hot sides, and suddenly a large volume of steam be produced. 429. Now, the engine starting and consuming the steam or the safety-valve being opened, will, either of them, relieve the pent up steam in the interior of its force, diminish the pressure on the surface of the water, and cause the water to boil up .briskly upon the sides just as the well known ex- periment devised by Bishop Watson, in which, by pouring cold water on a flask containing only tepid water and watery vapour, the water enters into very brisk ebullition. 430. J.. Boiler too weak at first. The strength of a boiler is tested by a gradually applied pressure, whereas, in explo- sions, the power is applied suddenly ; and a boiler may bear a very great strain, gradually increased up to a certain point, which it could not stand if thrown upon it rapidly. Is this con- sidered in the estimation of the strength and testing of boilers? 431. J. Tenacity of boiler diminished from being loo hot. This is a very important consideration. Malleable iron reaches its maximum strength at a temperature a little above that at which condensing engines are commonly worked. Above this, the decrease in tenacity is rapid, su as to be, at a red- heat, only about one-sixth of its tenacity at ordinary tem- peratures. 432. Hence another cause of danger, when the boiler is permitted to become too hot, a. most reprehensible practice in every point of view. 433. L Boiler weakened by pressure of high column of water EXPLOSION OP in certain boilers. In the Victoria, which'exploded twice, and in which the boilers were very large and deep, it was calcu- culated that the water exerted a pressure upon the bottom, equal to 3 Ibs. on the square inch. 434. In considering the means that may be adopted to prevent or lessen the chances of steam-boilers exploding, the same plan will be followed as in describing the causes. First, a tabular view will be presented, and this will be fol- lowed by such observations as seem requisite on each point. On these we can only remark very briefly, referring to the proper sources for detailed plans. MEANS OF PREVENTING THE EXPLOSION OF STEAM-BOILERS I. HAVE THE SAFETY-VALVE EFFICIENT. 1. Additional safety-valve, not under the control of the engine-man. j^J 2. Working valve so that it cannot be loaded above a certain point. 3. "Working valve stamped, so as to shew the pressure at any time. "^ 4. "Working valve within reach of the usual place of the engineman. Q 5. Working valve so that it can be completely relieved in a moment. Q 6. Safety-valve in motion, constantly, or at short intervals. P 7. Disc valve to be used the diameter of disc not to be more than 1 that of the valve-seat. Q 8. Lever of valve to be bent up at the end, so as to relieve it of part of its weight in rising. J^ 9. Valve to be large, g 10. Plug samu metal as valve seat. STEAM-BOILERS. 239 II. KNOW THE HEIGHT OF THE WATER IN THE BOILER. 1. Gauge cocks. See plate II., Parliamentary Report ; and p. 102, ditto*. 2. Glass-tube gauge. III. KEEP THE BOILER ALWAYS SUPPLIED WITH WATER. 1. Throw paddles out of gear and keep engine going in marine engines. 2. Evan's Plan, Parliamentary report, p. 177. 3. Kussel's, do., p. 55. see p. 245 of this work. IV. Know THE FORCE OP THE STEAM. 1. Mercurial Gauge. 2. Gauge by bulk of confined air. 3. Thermometer immersed in Steam. V. KNOW TEMPERATURE OF "WATER AND OF BOILER. 1 . Thermometer in water and in metal at side of boiler. 2. Fusible plug. See Plan of Professor Bache, Report of American Committee ; also, Plan of M. Cazalat, Parliamentary Report on Steam-vessels, 1839, p. 198. VJ. PREVENT SEDIMENT. 1. Hall's Patent Condenser. 2. Blowing out. VII. PRECAUTIONS IN MANAGING THE ENGINE. 1. Boilers examined at short regular intervals. 2. Boiler supplied with water by hand when Engine stopped. 3. Safety-valve quite or nearly open when Engine stopped. 4. Fires lowered when boiler too hot. 5. Water introduced slowly (or not at all) when boiler too hot. 6. The safety-valve opened very slowly, or steam let into engine very slowly, when water low and boiler hot, to prevent boiling up. 435. ]\| There is a very obvious remedy for overloading of the safety valve namely, to have two safety valves one to be used by the engineer for working the engine the other to*be inaccessible to him, and, therefore, to act as a check Upon him. 436. This was recommended by most of the witnesses (17 out of 23) who were examined by the Parliamentary commit- tee, which investigated and reported on this subject. It was recommended by the committee themselves ; and also by the American committee, which has been already referred 240 EXPLOSION OF to and has been adopted in locomotive engines : and in some steam-vessels. 437. As this has been almost universally recommended and adopted, and is in constant use in many vessels, there does not appear to be any feasible objection to it, while it presents other advantages to which I shall presently allude, besides being a check upon the engineer. I cannot help thinking it strange that it has not been generally adopted. 438. There is in every boiler, a limit beyond which it is confessedly not safe to strain its powers. Ignorance, care* lessness, recklessness, accident may occasion the working safety valve, the only means of safety to be overloaded at some critical period. Why should there not be another means of outlet for the steam a safe and sure one, not liable to be interfered with or deranged by carelessness, ignorance, or accident ? Why should there not be a valve always loaded to the same extent and that load adjusted so as to confine the steam for all necessary purposes, and only permit it an outlet by yielding when the steam is acquiring what is al- lowed to be an unsafe pressure. 439. The words of the report of the Parliamentary com- mittee are : t( That every such boiler should be provided with two sufficient safety valves, one of which should be inaccessi- ble to the engineman, and the other accessible both to him and to the persons on board the packet." The American committee recommend " That every boiler be provided with two safety valves, each of which shall be competent to discharge the steam, made in the ordinary working of the engine." " The second valve to have a weight immovably fixed upon it, the pressure of which upon the seat, together with that of the atmosphere upon the valve, is equal to the working pressure of the engine. This valve should be so arranged as to admit of raising, but not of placing additional weight upon it. To this end it should be enclosed." " The rise allow- ed by the enclosure should rather exceed half the radius of the valve seat." STEAM-BOILERS. 241 440. Besides acting as a check on the engineer, the ad- ditional safety valve would present other advantages. 1. The valve is apt to go out of order or get gagged. There would be a very small chance of both failing at the same moment. 2. In case of the sudden formation of a large volume of steam, where one valve is insufficient to give it quick escape, an additional one might make up the defficiency and prevent an explosion. 441. N A S ever y valve is apt occasionally to fail, the lock-up valve should not be entirely trusted to. The free valve also should be arranged in such a manner that it cannot be loaded beyond a certain extent. The American commit- tee recommend that the free valve " Should be graduated by the maker of the engine, and have stamped upon the lever by which it is weighted, the bursting pressure at which it will open, by calculation, when the movable weight is placed at the several notches. The pressure corresponding to the last notch to be equal to the bursting pressure, under which the engine is to work." 442. Whether the free or working valve should be open to passengers, so that they may at any time know the pres- sure of the steam, and how far it is from the extreme pressure allowed, may admit of some question. It might be certainly attended by some inconveniences, interference with and annoyance of the engineer in the discharge of his duty. Some, however, consider this necessary, as a still farther check on the engineer. I should almost be disposed to con- sider, however, that the state of the lock-up valve being always open to the inspection of passengers (it being stamped so that they can easily know its condition) would be a suf- ficient check, and that it would not be necessary that they should at all times have the power of knowing how much pressure the engineer is applying. 443. But it is absolutely essential that he himself should know exactly what he is about ; what weight he is laying on the valve under his control ; to what pressure he is bring- ing up the steam. It is evident that unless the engineer knows this accurately, he is working in the dark ; in a random 242 EXPLOSION OP sort of way, that may be very apt to lead to dangerous con- sequences. We, therefore, consider that it is essential that, whatever be the form of the valve, it should be graduated, stamped, or, in short, be of such a construction, that, in all his operations with it, he may know, and see clearly and easily, what will be the precise effect of each step on the force of the steam in the boiler. 444. That the engineer may have complete control over the valve, two other things are required, which can be so easily arranged, and are so obviously necessary, that it will be quite enough here, simply to mention them. The first is, that the SAFETY VALVE be within reach of the engineman when in the usual place for working the engine, the valve either being placed there, or brought within his reach by a lever. Second, that the SAFETY VALVE be of such a construction that it can be completely eased in a moment; that a lever be connected to it, which, by one simple motion, will at once raise all the weights. These precautions I have seen adopted in some boats, but there are many in which the S. V. is not at hand for the engineman, and where it can only be eased completely by lifting off successive weights, an operation which requires considerable time. It is at once obvious that the engineman should have the safety valve at hand, and not need to send for or wait for others to ease it, and that it should be capable of being com- pletely relieved at once, by one simple action. In short, THAT THE MAN WHO GUIDES THE ENGINE BE ABLE TO EASE THE VALVE COMPLETELY IN A MOMENT. ' 445. P To guard against the safety valve failing from oil-drying, rusting, or cohesion, it might be made to keep itself in order, or be preserved in proper working condition by the action of the engine. In short, self-preserving. 446. This might be attained by giving the plug of the safety valve a motion along with the engine, so as to keep it constantly in action ; and thus provide the best possible se- curity against adhesion, from whatever cause ; and render the STEAM-BOILERS. 243 efficacy of the great security against explosion, quite inde- pendent of any care or attention on the part of the individuals in charge of the engine, whom a thousand causes may interfere to prevent being always on the alert. The details of mechanism requisite to bring about the motion of the valve plug, would not offer any material diffi- culty to those who are familiar with practical mechanics. The plug might be kept constantly in motion, or it might be made to rise at regular intervals, and let offa little steam, thereby notifying that it is in good working condition. There are many ways in which this might be done so as to secure the constant or frequent assurance that the valve is in effi- cient condition. It might also be so arranged that when the engine stops, it should always be open to a certain height, leaving it low enough to permit the accumulation of sufficient steam to start with. 447. As long as the present safety valve is in use, the safety valve in which two smooth surfaces are kept in close contact, there appears no way so effectual for providing against failure from friction arising from oil-drying, rusting, or even accidental particles slipping in, as keeping it constantly, or, at least, very frequently in motion, so as either to prevent these adhesions altogether, or give notice, by the stoppage of the motion, when the action of the valve is^n any way deranged. 448. Q As there is a less surface of metal in contact in the disc valve than in the conical valve, were the former to be adopted there would be less danger from cohesion, or ad- hering particles, from its construction ; while, as to the ten- dency of discs to approach an aperture from which an aerial body is issuing forcibly, this seems to be very much modi- fied by the proportion between the area of the disc and that of the aperture. 449. The American committee recommend the Disc VALVE, which they consider very safe, when the diam. of the disc is made not more than one and a half times that of the valve seat. They state that a less ratio than 1^ to 1 will leave suf- 244 EXPLOSION OP ficient margin, and any sensible tendency to close from the effect of the issuing current, will be certainly avoided." 450. J{, There is another recommendation of the Ameri- can committee with regard to the safety valve which appears to be of value, namely, that there be some method of reliev- ing the valve of part of the weight in rising. This has been proposed to be effected by having the weight on the lever to roll towards the fulcrum when the valve opens. But the committee, on the grounds that this construction might lose its power of action by disuse, preferred the plan of having the lever bent at the end ; the weight being fixed there, and rising when the valve is pressed upon, would diminish further the power exerted by the weight, and thus aid in giving freer exit to the steam. 451. S The last circumstance requiring attention with regard to the valve is its SIZE. This is evidently a matter of very great importance. If the steam always accumulated very slowly and gradually, a small'aperture would be sufficient for the safety valve, but as it is so apt to be suddenly formed in large quantities, the safety valve, to meet such cases, should have an aperture of a considerable size ; as large as is conve- nient, or would not permit the escape of too much steam when it is open under ordinary circumstances. 452. There is reason to believe that many safety-valves, though sufficient for the case in which the steam acquires its increased strength slowly, are far too small to meet the other emergency. They might easily be made larger, and would, if the probability of the rapid vaporization of a large quantity of water were kept in mind. Some engineers consider that they should have at least one square inch area, for every two and a half horse power ; others, for each horse power. 453. From what has been shewn, it will be pretty clear that with the present form of safety-valve, it is essential that all, or at least some, of the above-mentioned measures should be adopted. Many of them have the authority of the British and American committees who examined the subject and these at least are entitled to some consideration, as founded either on the opinion of the most experienced engineers in either continent, or on the experiments instituted by th.e STEAM-BOILERS. 245 transatlantic committee. When steam navigation is liable to such dreadful occurrences as have lately taken place in this country, the owners and makers of marine engines are not altogether justified in neglecting to provide precautions easily adopted recommended by the authority of bodies whose opinions carry such weight and evidently doing some- thing towards providing security, and diminishing the proba- bility of explosions occurring. 454. After what has happened lately, however, we think most persons will feel that, to ensure adequate security, there must be a vigilant control by some public body. There is a Dean of Guild to inspect building in towns, and enforce proper repairs, or even cause houses to be pulled down, if regarded as unsafe. There is need of a Dean of Guild for the waters, moie especially when so dangerous an element as steam is to be guarded against. 455. A few years ago, shortly after the explosion of the EARL GREY at Greenock, the Town Council of Glasgow offered a premium for the best plans for preventing these fatal occurrences. A number of plans were given in, but no report on the subject has yet appeared from the Council. As a number of very excellent schemes, there is reason to believe, were given in, the public are deprived of valuable hints by these plans being locked up, which might perhaps have prevented some of the fatal explosions which have occurred since ; and the individuals who suggested them are deprived of the benefit of their ingenuity and labours. Surely that body will not long delay fulfilling the pledge which they gave to both the public and the competitors. The remaining parts of the Appendix, Nos. III. to XII. inclusive, are extracted from the Keport of Messrs. PARKES and PRINGLE, on Accidents on Steam-boats, published last summer. They exhibit the opinions of eminent engineers on the subject of explosions ; and some interesting tables regarding accidents to steam-boats, and the number and size, &c., of Steamers in Great Britain. 246 EXPLOSION OF III. Mr J. SCOTT RUSSEL'S plan for supplying boilers with water during the stoppage of the Engine. " A safety reservoir It has already been stated, that the great Hull accident arose from want of water in the boilers before starting. This is a very common cause of danger, and arises from the circumstance that it is the motion of the engine which usually feeds the boiler with water ; so that if by any accident there shall be too little water in the boiler when the fires are lighted, or the fire shall burn more briskly than was expected, or some unforeseen delay shall arise, there will re- main no remedy, unless, indeed, the crew shall be set to work the force-pump, which is tedious and laborious, and is not only an unwilling task to them, but exposes the improvidence or neglect of the engineer, which he is of course desirous to conceal. Having experienced the advantage which would occur from such an arrangement as should afford such a supply of water to the boiler, I constructed for a steam-boat of sixty horse power the following safety reservoir, by which the boiler can always be filled, even when the steam is strong, without manual labour or the motion of the engine. It is on the principle adopted by Savary in his engine, and is so simple that it has, in all probability, been applied to a similar purpose. " A. reservoir of a few cubic feet in capacity is placed on the top of the boiler, connected by pipes (furnished with cocks or valves), firstly, with the steam-chest; secondly, with the lower part of the body of water in the boiler ; and thirdly, with the external water in which the vessel floats. When the engineer wishes to supply his boiler with water, he opens the first cock, and the reservoir is filled with steam ; he shuts it, and the steam is condensed. A vacuum is form- ed; the water rises on opening the second cock and fills the reservoir. The second cock is then closed, and the two others being opened, a free communication is established be- tween the steam-chest, the reservoir and the water contents of the boiler. The water from the reservoir then passes into the boiler by its pressure from greater height. This may be repeated until the whole supply is obtained. The whole appa- ratus might be rendered self-acting, but is simpler without it." Report) p. 59. STEAM-BOILERS. 247 IV. Statement by Messrs. TOD and MACGREGOR, Engineers } Glasgow. ft The sea-going steamers in general on our coast are kept in good repair, both in machinery and hull ; but small river boats are often run till they are unsafe. " We know of little improvement, either in the safety valves, feed or blow-off cocks, but being well manufactured and well attended to. We always put two safety-valves, one of which is inaccessible to the engineer ; we also always put in water-guages, and should further recommend the general use of mercurial guages." Report, p. 79. V. Statement (>y Messrs. MAUDSLAY, SONS, and FIELD, Engineers, London. * The safety-valves should be large enough to admit of the escape of the whole of the steam, when the engine is sudden- ly stopped, without its rising more than half a pound on the jnch beyond the usual pressure. Two valves, having an area of one square inch for every horse-power, are sufficient for this purpose. Those valves should be so constructed that no increase of weight can possibly be put on, even by the engi- neer ; and there should be provided an apparatus by which they may be conveniently lifted from the engine-room, when it is requisite to ease off the steam. In many ports, especially in the North of England, the safety-valves are too small to relieve the pressure fast enough, and require a portion of the weight to be taken off whenever the engine is stopped. Many such valves have an indefinite number of weights, which the attendants put on at pleasure, and being on the deck, they are open to the chance of being overloaded, either by accident or design. This practice is highly dangerous, arid has, no doubt, been the cause of many accidents. Its never having prevailed in the passenger vessels of the river Thames, may account for so few accidents having happened among them. The feed-pumps should be in duplicate, each of ample size for the supply of the boiler, well constructed, with valves, so contrived that they may be taken out, examined, cleaned or repaired while the vessel is on her voyage, the other pumps supplying the boiler the while ; and besides this, the hand- pump should be capable of forcing water into the boiler." Report, p. 118. 248 EXPLOSION OP VI. Messrs. John Seaward and Co., Engineers, London. " 1. Of the very numerous accidents occasioning direct loss of life or personal injury, which within the last few years have oc- curred in steam vessels, and to he ascribed to the machinery, ninety-nine cases out of a hundred have been occasioned by some imperfection of the boiler, either by a collapse, or by bursting, or rending ; the casualties which have occurred through imper- fection of other parts of the machinery have been so few and in- considerable as hardly to be of any importance. We do not include the loss of life occasioned by wreck arising from the ma- chinery being incapable of continuing to work, as this class of accident comes under the head of general unseaworthiness. " 2. That of the many accidents so occurring in steam-vessels through imperfection of the boilers, it will, we believe, invaria- bly be found that they have happened in vessels where steam of high pressure has been used, and in no instance with steam of low pressure. By the term low-pressure steam, we mean steam of a pressure not exceeding 6 Ibs. to the square inch. In the vessels fitted by Messrs. Boulton and Watt and the London en- gineers, the pressure is generally under four or four arid a half pounds per square inch. if 3. Of the numerous accidents so occurring to steam-boat boilers employing high pressure steam, or steam of a dangerous pressure, it will be found that a large proportion, probably half, have occurred through the collapsing of large internal cylindri- cal chambers or flues employed in such boilers ; the remaining accidents being occasioned through the bursting or rending of the external casings of boilers. " 4. Of the various causes which have been suggested by differ- ent persons to account for the explosions of steam boat boilers, such as the sticking of the safety valves, the igniting of explosive gases, the loss of feed and heating of the metal plates, the sudden immission of a large quantity of feed and consequent generating of an unusual volume of steam, and other pretended causes of similar character, not one, in our opinion, is deserving the smallest attention ; they should be all scouted as merely calcu- lated to mislead the inquirer from the only true cause of these accidents, which is simply, that the materials of the boiler are not sufficiently strong to withstand the force of the steam. It is however true, that a boiler may lose its water so far as to allow some of the internal parts to become red hot, and thereby assist in producing a collapse when high pressure steam, or steam of a dangerous pressure, is used ; but the circumstance of some internal part of a boiler becoming red hot, ought not to be con- STEAM-BOILERS. 249 sidered as the true immediate cause of the accident, because the losing of feed in a boiler, and the consequent heating of a flue red hot, is a mishap of very frequent occurrence in low pressure boilers ; but no accident has ever occurred on such occasions calculated to occasion loss of life or personal injury : the fact is, that the parts of a boiler liable to become red hot should even in that state be sufficiently strong to resist the force of the steam, so that no dangerous collapse shall take place ; and all good low pressure boilers are so made." Report, p. 125. No. VII Extract from Report by Messrs, PARKER and PRINGLE, Parliamentary Commissioners on Accidents in Steam-boats. " That the surveyor shall ascertain that the safety-valves be sufficient to pass all the steam which the hollers can generate in their ordinary state of work, at the pressure determined by the weight on the valves ; the maximum of which pressure shall be fixed by the maker of the engines, or boilers, and the valves be loaded accordingly. " That, after an assigned period, no passenger license be granted to any vessel having safety-valves whose spindles or levers are exposed on deck, or capable of being loaded exter- nally, unless satisfactorily protected. Penalty on engineers,, masters, or others, for loading valves beyond the weight ascertained by the surveyor, and regulated as above. i .> 15 ditto in rectangular boilers. ,, 1 ditto, the " Eagle" form of boiler not ascertained. TOTAL 23 19 Explosions happened whilst the vessels were stopping, or on the instant of setting the engines in motion. Ditto, whilst steaming. Ditto, the ' ' Antelope, 1 ' not ascertained 23 Report, p. 10. I m ^'V tk-T3 g bcj | iif||h M - CM c CO O T* CO ^D CO CM " CM CM CM "* CO O O rj rfi 00 id C CO CO O O CO "9S*"" 1 .5 . .5 .5 10 o co QO Cl ' O 30 iOODT^ 10 3 i 8 ~ ^ o 2 .5 .5 .5 "* 00 C > o rQ ^ c T O cS _2 ^ O * = ? ft W a f o 2 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN OEPT. c: o o =^ rrs - 1 to CO IM E^SF - ^ Q V> ^Jk o CD f 3. 5 CO - CO M 3D TO ^ s GO CO CO cz < S 3- s m I err: 9 SE2 c-a ' rn o ^ M c C in I !H li i " s tl g~ ' __ A C ^ fe ^ ro CO CD I c r s 09 i> * e g- > M J* m 1 CD O* < o" y I" ft 1 Ln hO CO 3? \l fi DEC 131986 LD 21-100m-6,'56 (B9311slO)476 General Library University of California Berkeley r VA089I9