THE STEAM-ENGINE—continued.
Fig, 391.
The first steam-boat, the Comet, built by Henry Bell, in 1811, who brought steam navigation into practice in Europe.
"So shalt thou instant reach the realm assign'd
In wondrous ships, self-mov'd, instinct with mind.
Though clouds and darkness veil the encumbered sky.
Fearless, through darkness and through clouds they fly,
Tho' tempests rage,—tho' rolls the swelling main,
The seas may roll, the tempests swell in vain;
E'en the stern god that o'er the waves presides,
Safe as they pass, and safe repass the tides,
With fury burns; while careless they convey,
Promiscuous, ev'ry guest to ev'ry bay."
These lines, from Pope's translation of the "Odyssey," were very aptly quoted twenty-five years ago by Mr. M. A. Alderson, in his treatise on the steam-engine, for which he received from Dr. Birkbeck, the originator of Mechanics' Institutions, the prize of 20l., being the gift of the London Mechanics' Institution, and these lines seem to indicate some sort of rude anticipation by the ancients of that free passage of the ocean by the agency of steam which has rendered ships almost independent of wind and weather.
Homer's description, as above, of the Phœnician fleet of King Alcinous, in the eighth book of the "Odyssey," is certainly an ancient record of an idea, but nothing more. In a work written by Hero of Alexandria, about a hundred years b.c., and entitled "Spiritalia seu Pneumatica," a number of contrivances are mentioned for raising liquids and producing motion by means of air and steam, so that the first steam-engine is usually ascribed to Hero; and the annexed cut displays the apparatus. (Fig. 392.)
Fig. 392.
Hero's steam-engine. a. The boiler in which steam is produced, and then passes through the hollow support b, from which there is no outlet but through the two apertures, c c. The reaction of the air on the issuing steam produces a rotatory motion in the jets, c c, attached to a centre but hollow axle.
It is a remarkable circumstance that Sir Isaac Newton applied the same principle in a little ball, mounted on wheels, containing boiling water, and provided with a small orifice; and in his description he says: "And if the ball be opened, the vapours will rush out violently one way, and the wheels and the ball at the same time will be carried the contrary way." From the time of Hero, there does not appear to be any record or mention made of steam apparatus till the year 1002, when, in a work called "Malmesbury's History," mention is made of an organ in which the sounds were produced by the escape of air (query, steam) by means of heated water. It is strange that, in these days of steam application, the Calliope, or steam organ, should be an important feature at the present moment at the Crystal Palace; and it only shows how the same ideas are reproduced as novelties in the ever-recurring cycles of years.
On the revival of classical learning throughout Gothic Europe, the work of Hero began to attract attention, and it was translated and printed in black letter, and most likely first from the Arabic character, as in the year 1543 the first fruits appeared in Spain, where Blasco de Garay, a sea captain, propelled a ship of 200 tons burden, at the rate of three miles per hour, before certain commissioners appointed by the Emperor Charles the Fifth. Alas for inquisitorial Spain! had she looked deeper into the matter, and performed her auto-da-fées on the boilers of steam engines instead of the bodies of poor human beings, what lasting glories would have been her reward. The invention made its début in Spain, the commissioners reported, the worthy inventor was rewarded, but the mighty giant invoked was put to sleep again for at least 150 years. The steam giant was disturbed with dreams; one Mathias, in 1563, gave him a nightmare; Solomon de Caus, in 1624, nearly woke him up; Giovanni Bianca, in 1629, did more; and the Marquis of Worcester, in the middle of the seventeenth century, as the evil genius of Spain, carried off the giant bodily and made him the slave of England; at least, he experimented, and wrote such wondrous tales of his new motive power, that in 1653 we read of steam being fairly tethered to its work, and set to draw water out of the Thames at Vauxhall; and Cosmo de Medici, a foreigner who inspected the apparatus in 1653, says, "It raises water more than forty geometrical feet by the power of one man only, and in a very short space of time will draw up full vessels of water through a tube or channel not more than a span in width, on which account it is considered to be of greater service to the public than the other machine near Somerset House, which last one was driven by two horses."
What would the Marquis of Worcester and Cosmo de Medici have thought of Blasco de Garay on the ocean, and ruling 12,000 steam horses? Write the name of the brave and prudent Captain Harrison, in the good ship Great Eastern, date 1859, instead of that of the gallant Spaniard, and our brief history is finished.
The first really useful steam-engine was made, not by a plain Mr., but again by a captain—namely, Captain Savery, who appears to have been the first inventor who thoroughly understood and applied the vacuum principle. (Fig. 393.)
Fig. 393.
Savery's engine.
a a. The furnaces which contain the boiler. b 1 and b 2. The two fireplaces. c. The funnel or chimney, which is common to both furnaces. In these two furnaces are placed two vessels of copper, which I (Savery) call boilers—the one large as at l, the other small as d. d. The small boiler contained in the furnace, which is heated by the fire at b 2. e. The pipe and cock to admit cold water into the small boiler to fill it. f. The screw that covers and confines the cock e to the top of the small boiler. g. A small gauge cock at the top of a pipe, going within eight inches of the bottom of the small boiler. h. A large pipe which goes the same depth into the small boiler. i. A clack or valve at the top of the pipe h (opening upwards). k. A pipe going from the box above the said clack or valve in the great boiler, and passing about one inch into it. l l. The great boiler contained in the other furnace, which is heated by fire at b 1. m. The screw with the regulator, which is moved by the handle z, and opens or shuts the apertures at which the steam passes out of the great boiler at the steam-pipes o o. n. A small gauge cock at the top of a pipe, which goes half way down into the great boiler. o 1, o 2. Steam pipes, one end of each screwed to the regulator; the other ends to the receivers p p, to convey the steam from the great boiler into those receivers. p 1, p 2. Copper vessels called receivers, which are to receive the water which is to be raised. q. Screw joints by which the branches of the water-pipes are connected with the lower parts of the receivers. r 1, 2, 3, and 4. Valves or clacks of brass in the water-pipes, two above the branches q and two below them; they allow the water to pass upwards through the pipes, but prevent its descent; there are screw-plugs to take out on occasions to get at the valves r. s. The forcing-pump which conveys the water upwards to its place of delivery, when it is forced out from the receivers by the impelled steam. t. The sucking-pipe, which conveys the water up from the bottom of the pit to fill the receivers by suction. v. A square frame of wood, or a box, with holes round its bottom in the water, to enclose the lower end of the sucking-pipe to keep away dirt and obstructions. x is a cistern with a bung cock coming from the force-pipe, so as it shall always be kept filled with cold water. y y. A cock and pipe coming from the bottom of the said cistern, with a spout to let the cold run down on the outside of either of the receivers, p p. z. The handle of the regulator to move it by, either open or shut, so as to let the steam out of the great boiler into either of the receivers.
This is Savery's own description (taken from the "Miner's Friend," printed in 1702), of his water-engine, which differs from that suggested by the Marquis of Worcester, in the fact that he made the pressure of the air carry the water up the first stage. Savery's patent was "for raising water and occasioning motion to all sorts of mill-work by the impellant force of fire;" and the patent was granted in the reign of King William the Third of glorious memory.
Thus Savery overcame, as he remarks, the "oddest and almost insuperable difficulties," and introduced a steam apparatus or engine, a good many of which were constructed, and employed for raising water. The mechanical skill required to construct the boiler, the very heart (as it were) of the iron engine, had not been acquired in the time of Captain Savery, and hence the weakness of the boilers, and the danger of working them. As the pressure required was very considerable to overcome the resistance of a lofty column of water, these engines were gradually relinquished for those of another clever mechanician—viz., for those of Thomas Newcomen, an ironmonger of Dartmouth, who, about the year 1705, constructed and introduced the cylinder, from which the transition was gradually made to the mode of condensing by a jet of cold water, the use of self-acting valves, and the construction of self-acting engines by Smeaton, Hornblower, and finally by the illustrious Watt, whose portrait heads the first chapter on Heat in this book.
Newcomen was assisted in his work by one Cawley, a glazier; and their persevering labours were crowned with a successful result of the most memorable importance in the history of the steam-engine.
In the engine by Savery, the operation of the steam was twofold—namely, by the direct pressure from its elasticity, and by the indirect consequence of its condensation, which affords a vacuum. This last may be said to be the only principle used by Newcomen, who employed a boiler for the generation of steam, and conveyed it by a pipe to the bottom of a hollow cylinder, open at the top, but provided with a solid piston, that moved up and down in it, and was rendered tight by a stuffing of hemp, like the piston of a boy's common squirt. It can readily be understood, that if the jet of the latter was connected with a tight little boiler, and steam blown into it, that the piston of the squirt would rise to the top of the barrel in which it works, being thrust up by the pressure or force of the steam; but unless the steam was cut off, and cold water applied to the interior of the barrel, the piston could not descend again. As soon, therefore, as Newcomen had thrust up the piston by the action of steam, he introduced a jet of cold water, supplied from an elevated cistern beneath the piston, when the steam was condensed into water, and a vacuum or void space obtained. The piston being free to move either up or down, was now forced in the latter direction by the pressure of the air, which is a constant force equal to fifteen pounds on the square inch; and thus the piston in Newcomen's engine was raised by heat—viz., by steam, and thrust down by cold—i.e., by the condensation of the steam producing a vacuum. The void obtained in this manner was very considerable, because one cubic foot of steam at 212° condenses into one cubic inch of water. The production of a vacuum with the aid of steam is quickly effected by boiling some water in a clean camphine can, and when the steam is issuing freely from the mouth of the latter it is then corked, and cold water thrown over the exterior. Directly the temperature is lowered, the steam inside the tin vessel is condensed suddenly into water, and a void space being suddenly obtained, the whole pressure of a column of air of a breadth equal to the area of the vessel, and of a height of forty miles, is brought suddenly down like a sledge-hammer upon the sides of the tin vessel, and as they are not sufficiently strong to offer a proper resistance, they are crushed in like an egg-shell by the giant weight which falls upon them.
The barometer, or measurer of the weight of the air, consists of a glass tube about thirty-three inches in length, hermetically sealed at one end, and containing mercury that has been carefully boiled within it, and being perfectly filled the tube is inserted in a cistern of clean mercury, when it gravitates to a height equal to the pressure of the air, leaving a space at the top called the torricellian vacuum. As the atmospheric air decreases in density by admixture with invisible steam or vapour, any given volume becomes specifically lighter: hence the column of mercury falls to a height of about twenty-eight inches; whilst if the aqueous vapour diminishes, the weight of the air becomes greater, and the barometer may rise to a height of about thirty-one inches.
Having thus secured a "reciprocating motion," Newcomen applied it to the working of a force-pump by the intervention of a great beam or lever suspended on gudgeons (an iron pin on which a wheel or shaft of a machine turns) at the middle, and suspended like the beam of a pair of scales; and, in fact, he invented that method of supporting the beam which is in use to the present day. Supposing we compare Newcomen's beam to a scale beam, he attached to the extremities (instead of scale pans) a water pump and his steam cylinder—the latter being at one end, and the former at the other. The beam played at "see-saw:" by the primary action of the steam on the bottom of the piston in the cylinder it was pushed up at this end, and of course suffered an equal fall at the other, to which the pump piston was attached; and when the motion was reversed by the condensation of the steam, down went the piston again by the pressure of the air, whilst that of the water pump was again raised, and being provided with proper valves, the water was pumped slowly out of the mine, although the steam power used was very moderate, and only just sufficient to counterpoise the weight of the atmosphere. Newcomen made the end attached to the water pump purposely heavier than the steam piston of the other end of the beam, and by this means the work of the steam, by its elasticity, was very moderate, whilst the actual lift of the water from the mine was performed by the pressure of the air, equal (as already stated) to fifteen pounds on every square inch of the surface of the steam piston. This engine is called the atmospheric engine, and in the next cut we have a picture taken from a photograph by the "Watt Club" of the actual model of the Newcomen engine in the Hunterian Museum of the University of Glasgow; the dimensions being—length, 27 in.; breadth, 12 in.; height, 50½ in.; from which, "in 1765, James Watt, in seeking to repair this model, belonging to the Natural Philosophy Class in the University of Glasgow, made the discovery of a separate condenser, which has identified his name with that of the steam-engine." (Fig. 394.)
Fig. 394.
Model of the Newcomen engine, in which the furnace and boiler, the steam cylinder, beam, water-pump, and elevated cistern of water, are apparent.
In Newcomen's engine, the opening and shutting of the cocks required the vigilant care of a man or boy, and it is stated on good authority that a boy who preferred (like nearly all other boys) play to work, contrived, by means of strings, a brick, and one or two catches on the working beam, to make the engine self-acting.
This poor boy's ingenious contrivance paved the way for the improved methods of opening and shutting the valves, which were brought to a great state of perfection by Beighton, of Newcastle, about 1718. Between that time and the year 1763, we find honourable mention made of Smeaton in connexion with the steam-engine, but the name of the great James Watt at this time began to be appreciated, and by a series of wonderfully simple mechanisms, he at last perfected the machine whose origin could be traced back not only to the time of Blasco de Garay, in 1543, but even to the days of the ancient mechanicians, such as Hero, who lived 130 b.c.
In 1763, James Watt was a maker of mathematical instruments in Glasgow, and his attention was drawn to the subject of the steam-engine by his undertaking to repair a working model of Newcomen's steam-engine, which was used by Professor Anderson, who then filled the Chair of Natural Philosophy, and subsequently founded the Andersonian Institution. The repairs required for this model induced Watt to make another, and by watching its operation, he discovered that a vast quantity of heat, and therefore fuel, was wasted in the constant and successive heating and cooling of the steam cylinder. About two years after, when Watt was twenty-nine years of age, he had made so many experiments, that he was enabled to put into a mechanical shape his original ideas, which are embodied in his patent of 1769, as follows:—
"My method of lessening the consumption of steam, and consequently fuel, in fire-engines, consists of the following principles:
"First: That vessel in which the powers of steam are to be employed to work the engine, which is called the cylinder in common fire-engines, and which I call the steam-vessel, must, during the whole time the engine is at work, be kept as hot as the steam that enters it—first, by enclosing it in a case of wood or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor any other substance colder than steam to enter or touch it during that time.
"Secondly: In engines that are to be worked wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessels or cylinders, although occasionally communicating with them; these vessels I call condensers; and whilst the engines are working, these condensers ought at least to be kept as cold as the air in the neighbourhood of the engine, by application of water or other cold bodies.
"Thirdly: Whatever air or other elastic vapour is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps wrought by the engines themselves, or otherwise.
"Fourthly: I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the open air after it has done its office.
"Lastly: Instead of using water to render the piston or other parts of the engines air and steam-tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state.
"And the said James Watt, by a memorandum added to the said specification, declared that he did not intend that anything in the fourth article should be understood to extend to any engine when the water to be raised enters the steam-vessel itself, or any vessel having an open communication with it."
"About the time he obtained his patent, Watt commenced the construction of his first real engine, the cylinder of which was eighteen inches in diameter, and after many impediments in the details of the work he succeeded in bringing it to considerable perfection. The bad boring of the cylinder, and the difficulty of obtaining a substance that would keep the piston tight without enormous friction, and at the same time resist the action of steam, gave him the most trouble, and the employment of a piston rod moving through a stuffing-box was a new feature in steam-engines at that time, and required great nicety of workmanship to make it effectual. While Watt was contending with these difficulties, Roebuck's finances became disarranged, and in 1773 he disposed of his interest in the patent to Mr. Boulton, of Soho. As, however, a considerable part of the term of fourteen years, for which the patent was granted, had already passed away, and as several years more would probably elapse before the improved engines could be brought into operation, it was judged expedient to apply to Parliament for a prolongation of the term, and an Act was passed in 1775 granting an extension of twenty-five years from that date, in consideration of the great merit of the invention." (Bourne's "Treatise on the Steam-engine.")
In Fig. 395, [page 427], we give an illustration of a low-pressure condensing engine and boiler of eight-horse power, constructed on the principle of Boulton and Watt, as the latter had fortunately united his skill, learning, originality, and experience with Mr. Boulton, of Soho, near Birmingham, whose metal manufactory was already the most celebrated in England.
During the explanation of this eight horse-power engine, the opportunity may be taken to discuss occasionally the special improvements effected by Watt. The steam-pipe a conveys the steam generated in the boiler b to the slide-valve c, which is kept close to the surface, against which it works by the pressure of the steam.
Here we notice some of the valuable improvements of Watt in the admission of steam above as well as below the piston, by which he increased the power of his engine, and no longer confined it to the force of the atmospheric pressure. It is also necessary to remark the beautifully simple mechanism of the slide-valve, by which steam is admitted alternately above and below the piston. Want of space prevents us tracing out the gradual improvements effected by Watt, and therefore we take his invention as it stood in the year 1780, and refer our readers to Bourne's "Treatise on the Steam-engine" for the full and minute particulars of the improvements to that date.
Fig. 395.
An eight-horse power condensing steam-engine, after the principle of Boulton and Watt, and explained in pages 426 to 432.
At that time it occurred to Watt that the condensation of the steam from the cylinder after it had done its work, might be made more perfect if a perpetual vacuum was maintained beneath the piston, while an alternate steam-pressure and vacuum were produced above it. (Fig. 396.)
Fig. 396.
"e e is the cylinder. j. The piston, a. The steam-pipe. b. The regulating or throttle valve, e. The eduction and equilibrium single valve, performing the functions of both. c. The upper, and f the under, portholes, by which passages only the steam can enter and pass away. d, j, g. The eduction-pipe by which the steam passes from above the piston during every returning stroke to the condenser, a perpetual exhaustion being maintained beneath it."—From Bourne on the Steam-engine.
Instead of obtaining a specific advantage the contrary occurred, and Watt was obliged in this case to return to the ponderous Newcomen counterweight to balance the difference in the vacuum above and below the piston, consequently this form of the cylinder and valves was abandoned. The juvenile reader will perceive in the above drawing that the superior arrangement of Watt's cylinder to that of Newcomen arises from the steam operating above and below the piston, and that the piston rod works air-tight in a stuffing box at the top of the cylinder. A most important improvement in the employment of steam as a motive power has been discovered in the mode of using it "expansively," by which the steam, at a pressure say of sixty pounds on the square inch, is admitted below the piston, and then cut off and allowed to expand and drive up the latter without the expenditure of any more fuel, and leaving, after lifting the piston to a height say of three feet, an average or mean power of thirty pounds on the square inch.
Returning to the eight-horse condensing engine, d is the steam cylinder surrounded by a case to prevent the steam cooling and to maintain in the cylinder the same, or nearly the same, temperature as that of the steam in the boiler, according to the condition of Art. I. of Watt's Patent, quoted at p. 425 of this book. The same outer case is apparent around the cylinder in Fig. 396; e, the piston, which, by stuffing with hemp or other proper material, fits the interior of the cylinder in the most accurate manner, and prevents the escape of steam by its sides: e is the piston rod attached to the parallel motion. This clockwork-like piece of mechanism has often been quoted as one of the masterpieces of Watt, and in its greatest perfection is called the complete parallel motion, and may be found in all the best land beam steam-engines. The object of the parallel motion is to cause the piston and pump rods to move always in straight lines, never deviating to either side. (Fig. 397.)
Fig. 397.
a b is half the beam, a being the main centre, b e. The main links connecting the piston-rod f with the end of the beam. g d. The air-pump links, from the centre of which the air-pump rod is suspended. c d and e d produce the parallelism, because c d is moveable only round the fixed centre c, whilst e d is not only moveable round the centre d, but the centre itself in the arc described by c d, and by this action e d corrects the distorting influence of its own radius. The dotted lines and letters above enable the observer to see the effect of the movement of the beam on the parallel motion.
In the eight horse-power engine shown in page picture, e is also attached to the piston e, which moves the beam f, and the other end of this beam, by the connecting rod g, gives motion to the heavy fly wheel g, by means of the crank h.
h is an eccentric circle on the axle of the fly wheel g, it gives motion to the slide valve, which admits the steam alternately above and below the piston. The slide valve and its seat are contained within an oblong box or case, large enough to permit the easy motion of the valve within it, and usually forming an enlargement in the course of a pipe.
The valve rod by means of which the valve is opened and shut, passes out through a stuffing box; or, instead of such a rod, a valve of moderate size often has a nut fixed to it, within which works a screw on the end of an axle which passes out through a bush, and has shoulders within and without to prevent it from moving longitudinally, and a square on the outer end on which the key fits that is used in turning it. i is the throttle valve inside the steam pipe and lever connected with a governor for regulating the admission of steam into the cylinder.
Here, again, we pause in the description of our eight horse-power engine to illustrate more particularly this admirable contrivance of Watt, which remains to the present day without any material alteration even in the best steam-engines. (Fig. 398.)
Fig. 398.
a. The seat of the throttle valve, z. The valve itself turning on a spindle, which passes through its centre. a is the steam pipe. w. The throttle valve lever on which the rod h, proceeding from the governor, acts. d d. The spindle of the governor revolving by a belt acting on the pulley d. e e. The balls hung on the ends of the arms, which cross each other at e like a pair of scissors. When d d is set in motion, the balls fly out by centrifugal motion, and in doing so draw down the collar into which the lever f works by means of the links f h. When f is depressed, of course h rises, and the valve z is partly closed, and the supply of steam reduced.
In the eight-horse engine already partly explained, k is the cylinder of an air-pump to remove any air, and the water which condenses the steam, from the condenser l. There is also the eduction pipe, which conducts the steam from the cylinder to the condenser l. o is the pump that supplies cold water to the cistern s, in which the condenser and air-pump stand, p is a rod connected with the injection cock for admitting a jet of water into the condenser from the cistern, and which is continually flowing during the working of the engine, q q, cast-iron columns, four of which support the principal parts of the engine.
We now come to the boiler of the steam-engine, which is of course of almost equal importance with the engine itself; and the one in our page-picture is a good type of one of the favourite boilers used by Messrs. Boulton and Watt, and is called the "Wagon boiler." The boiler is made of wrought-iron plates rivetted together, and properly strengthened where necessary; and the steam-pipe a conveys the steam to the engine. It may be remarked here that the cylindrical boiler—consisting of two cylinders, one within the other, of which the former contains the fire, whilst the furnace-draught circulates outside the latter, and the space between the two cylinders being filled with water—is the form of boiler which is most highly approved of, and is employed in the famous economical steam-engines of the Cornish mines.
As the water evaporates in the form of steam, the boiler must be continually supplied with fresh water, which comes (as will be noticed by inspecting the page picture) from the hot well s, by means of the hot-water pump r, attached to the beam f. The water is pumped to the top of a column rising above but connected with the boiler. There is a cylindrical float, inside the column of water, connected with the boiler, suspended ever a pulley by a chain passing to the damper of the furnace. The damper and float balance each other, and when the water in the boiler rises to too high a temperature, it causes the float to rise in the column of water, which lowering the damper or shutter that stops the draught of the chimney of the furnace t, diminishes the intensity of the heat, and reduces the formation of steam. On the other hand, as the temperature diminishes, the float descends and the damper rises, and permitting more air to rush to the burning fuel in the fire, a greater quantity of steam is generated.
There is likewise a stone float inside the boiler, for regulating the supply of water by the feed pipe, or column of water, which latter must always be sufficiently lofty to press with greater force than the steam produced in the boiler, or else the power of the steam might, under certain circumstances, eject or blow out the water from the top of the column. The stone is suspended by a brass wire which works through a stuffing box, and is connected with a lever, to which is attached a heavy counterpoise, so adjusted that when the stone is immersed to a certain depth in water (according to the principle of a solid body losing weight in a fluid, explained in the article on specific gravity, page 48), it shall exactly balance the latter, but when the water sinks in the boiler, and the stone is no longer surrounded with water, it becomes heavier, and sinking down opens a conical plug, ground so as to fit water-tight into a hole in the bottom of the column of water or feed pipe, and directly the plug opens, water rushes into the boiler; being cut off again as the stone rises when immersed or surrounded with the proper height of water. Unless our juvenile readers refer to the article on specific gravity, they will not understand the otherwise seeming anomaly of a stone float.
A large hole, called the man-hole, covered with an iron plate and securely fastened with screws, is provided for the purpose of allowing the engineer to enter the boiler, when cold, for the purpose of clearing out the incrustation and dirt arising from the water. To prevent the incrustation of lime and other earthy matters, it is sometimes usual, on the principle "that prevention is better than cure" to put a large log of "logwood" inside the boiler, as it is found that the colouring matter curiously prevents the earthy matter, so well known as the "fur" in iron "tea-kettles," sticking to the sides of the boiler. Sal ammoniac and other salts also have the same property, but neither are much used, the mechanical labour of chipping out the boiler and stopping its work for a day or so, being preferred to the prevention plan already described.
There is also a valve opening inwards to prevent the consequences of a sudden condensation in the boiler, and also a safety valve and lever with weights opening outwards, and allowing the steam to escape when it reaches a dangerous excess, and in order to look as it were at the state of the pressure inside the iron boiler, a proper steam gauge is provided, also two cocks—viz., a water and steam cock, to enable the engineer to ascertain if the water is up to, and does not exceed, the proper height, because when turned, supposing that all is going on properly, the former, No. 7, should eject water, the latter, No. 8, steam.
It is truly wonderful, considering the number of safeguards and warnings provided, that accidents ever happen to boilers, but the statistics of deaths and annual destruction of property show that science is powerless, nay, absolutely dangerous, when handled by ignorant and careless persons. The great fly-wheel, which is usually such an awe-inspiring and marvellous exhibition of strength in an engine of any great power, is employed for the purpose of storing up force, so that if any parts of the engine work indifferently (they all work with resistance), it shall equalize the wants of the whole, and by its inertia it will continue to move until its motion is stopped by a resistance equal to its momentum.
In starting an engine, the engineer may sometimes be observed labouring to move the "fly-wheel," and when once he succeeds in getting it to move, the resistance of the other parts of the machinery is soon overcome. Mr. Alderson, in his prize essay, remarks that "it is in the property which the steam-engine possesses of regulating itself, and providing for all its wants, that the great beauty of the invention consists. It has been said that nothing made by the hand of man approaches so near to animal life. Heat is the principle of its movement; there is in its tubes circulation, like that of the blood in the veins of animals, having valves which open and shut in proper periods; it feeds itself, evacuates such portions of its food as are useless, and draws from its own labours all that is necessary to its own subsistance. To this may be added, that they are now regulated so as not to exceed the assigned speed, and thus do animals in a state of nature. That the safety valves, like the pores of perspiration, open to permit the escape of superfluous heat in the form of steam. The steam gauge, as a pulse to the boiler, indicates the heat and pressure of the steam within; and the motion of the piston represents the action and the power of which it is capable. The motion of the fluids in the boiler represents the expanding and collapsing of the heart; the fluid that goes to it by one channel is drawn off by another, in part to be returned when condensed by the cold, similar to the operation of veins and arteries. Animals require long and frequent periods of relaxation from fatigue, and any great accumulation of their power is not obtained without great expense and inconvenience. The wind is uncertain; and water, the constancy of which is in few places equal to the wants of the machinist, can seldom be obtained on the spot where other circumstances require machines to be erected. To relieve us from all these difficulties, the last century has given us the steam-engine for a resource, the power of which may be increased to infinitude: it requires but little room; it may be erected in all places, and its mighty services are always at our command, whether in winter or summer, by day or by night, on land or water; it knows no intermission but what our wishes dictate."
The high-pressure steam-engine appears to have been first brought into general use by Trevethic and Vivian, although the primary notion of such a modification of the Newcomen or water-engines did not originate with them. As the name implies, the steam is brought to a much higher temperature and pressure than is required in the condensing engines of Boulton and Watt. It consisted, in the first place, of a cylinder open at the top, and provided with a piston. To save heat the cylinder was fixed inside the boiler, and was provided with a two-way cock worked by a crank, for the purpose of supplying and cutting off the steam. The downward stroke was produced by the atmosphere, and the steam having done its work, was simply blown away and wasted in the air.
The engine was provided with a fly-wheel, to which the piston-rod was at once attached, producing a continuous rotatory movement without the assistance of the heavier parallel motion, or hot and cold water pumps.
This form of engine was soon adopted for pumping work—such as that of draining fens; and in 1804 Mr. Richard Trevethic used it for propelling the first carriage on the Merthyr Tydvil rail or tram way, and it was then speedily adopted in all the coal districts where the levels were moderate. Stephenson the elder, succeeded by the late lamented Robert Stephenson, followed with inventions and improvements of the locomotive steam-engine; and we are told in "Once a Week" that,
"One of those best qualified to speak to the latter's contributions to the development of the locomotive engine, states that from about five years from his return from America, Robert Stephenson's attention was chiefly directed to its improvement. 'None but those who accompanied him during the period in his incessant experiments can form an idea of the amazing metamorphosis which the machine underwent in it. The most elementary principles of the application of heat, of the mode of calculating the strength of cylindrical and other boilers, of the strength of rivetting and of staying flat portions of the boilers, were then far from being understood, and each step in the improvement of the engine had to be confirmed by the most careful experiments before the brilliant results of the Rocket and Planet engines (the latter being the type of the existing modern locomotive) could be arrived at.'
"Stephenson's time was not, however, so fully taken up during the above interval as to preclude attention to his other civil engineering business, and he executed within it the Leicester and Swannington, Whitby and Pickering, Canterbury and Whitstable, and Newton and Warrington Railways; while he also erected an extensive manufactory for locomotives at Newton, in Lancashire, in partnership with the Messrs. Tayleur. About the middle of the above period, also, the first surveys and estimates for the London and Birmingham Railway were framed, leading eventually to the obtaining of the Act. Then followed the execution of that line, and here Robert Stephenson had an opportunity of showing his great talent for the management of works on a large scale. This was the first railway of any magnitude executed under the contract system; perfect sets of plans and specifications (which have since served as a type for nearly all the subsequent lines) were prepared—no small matter for a series of works extending over 112 miles, involving tunnels and other works of a then unprecedented magnitude.
"Many other railways in England and abroad were executed by him in rapid succession; the Midland, Blackwall, Northern and Eastern, Norfolk, Chester and Holyhead, together with numerous branch lines, were executed in this country by him; and among railways abroad may be enumerated as works either executed by him or recommended in his capacity of a consulting engineer, the system of lines in Belgium, Italy, Norway, and Egypt, and in France, Holland, Denmark, India, Canada, and New Zealand.
"Robert Stephenson first saw the light in the village of Willington, at a cottage which his father occupied after his marriage with Miss Fanny Henderson—a marriage contracted on the strength of his first appointment as "breaksman" to the engine employed for lifting the ballast brought by the return collier ships to Newcastle. Here Robert was born on the 17th of November, 1803. As the cottage looked out upon a tramway, the eyes of the child were naturally familiarized from infancy with sights and scenes most nearly connected with his future profession."
In locomotive steam-engine boilers, the principal object is to generate steam with the greatest rapidity; hence the boiler consists of two parts—viz., a square box containing the fire, and around which a thin stratum of water circulates, whilst the draught for the fire rushes through a number of copper tubes placed in the second or cylindrical part of the boiler. By the use of these tubes an immense surface of water is exposed to the action of the fire, and the steam is not only generated with amazing rapidity, but is also maintained at a very high pressure.
Within the last few years "superheated steam" has been favourably mentioned, and employed economically for driving certain engines. The principle consists in first generating steam, and then passing it through coils of strong wrought-iron pipe, by which it acquires additional heat, and we have therefore combined in steam the ordinary principle of evaporation of water with the heated-air principle of Stirling, described at [page 367]. We give a drawing of Scott's patent generator and superheated steam engine. (Fig. 399.)
The apparatus is used as follows:—A fire is made in the furnace, and so soon as a pyrometer connected with that indicates about 800 degrees, a little water is pumped into the coils by hand, which is immediately converted into steam. The donkey engine is then started, which maintains the necessary feed of air and water. The generator produces a copious supply of elastic mixed gaseous vapour, at a pressure of 250 pounds on the square inch; and it is stated that this engine works satisfactorily, and is started in the incredibly short time of from three to five minutes, so that for marine engines in war vessels, expecting to to be ordered out suddenly, no fuel need be burnt till the moment required.
Fig. 399.
Scott's patent generator, or new versus old steam.
Experiments with superheated steam have already been tried most successfully on board the Peninsular and Oriental Company's ship the Valetta, whereby it is stated that a saving of thirty per cent. in fuel is obtained. The engine to which the superheated steam was adapted was constructed by Penn and Sons, and the vessel attained a speed of nearly sixteen knots per hour, and under the most adverse circumstances had an abundance of steam to spare.
"A most important experimental improvement in steam machinery was on Thursday last tried for the first time down the river, on board the Peninsular and Oriental Company's ship, the Valetta. The actual nature of the improvement may be described in a few words as consisting of a simple apparatus for working marine engines by means of superheated steam; but it is not too much to say that in the success or failure of this experiment are involved results so important as to affect materially all ocean-going steamers, and, indeed, steam machinery of all kinds. To be able to work machinery with superheated steam, means to command increased power with a thirty per cent. reduction in the consumption of fuel. A principle which can effect such important changes in the universal application of steam has not remained undiscovered to the present day. The want of superheated steam has long been felt, and the enormous comparative advantages of working engines on such a plan have long been known. A simple and effective working of the principle, however, has been an engineering difficulty which various expedients—all, however, sufficiently successful to show the value of the improvement—have failed to obviate entirely. This obstacle has now, we believe, been effectually overcome by Mr. Penn, and the value of the improvement so clearly demonstrated, that the general application of the principle to steam machinery of every kind may now be regarded as certain.
"The idea of working engines by superheated steam, and the immense saving of fuel and increase of power it would effect, was, we believe, first started many years ago by Mr. Howard, and subsequently by Dr. Haycraft. The difficulties, however, in the way of its adoption at that time, and the undue estimate of the importance of the principle, prevented those gentlemen from realizing very great practical results. At a later period the matter was again taken up by an American engineer—Mr. Weatherhead—who, however, only superheated a portion of the steam and mixed it with common steam in its way to the cylinders. The success which attended even this partial application of the process again revived the idea, and encouraged other engineers to turn their attention to the subject. The result of these renewed efforts is that several methods of securing the great economy to be effected by superheating the steam are now under trial, and there is no doubt that a most important step in the progress of steam, especially as applied to ocean navigation, is now at last on the point of being successfully accomplished.
"The value of the improvement on the score of economy in working may be best illustrated by a single fact—namely, that the Peninsular and Oriental Company's bill for coal annually amounts to the enormous sum of 700,000l., and that by working their vessels with superheated steam properly applied, it is become almost certain that, without any detriment to the machinery, from 28 to 30 per cent. of this gigantic outlay can be saved. As to the various proposed methods of superheating steam, it may be briefly explained, that the conditions required to be fulfilled are perfect simplicity of arrangement with ready control over the apparatus; that it should be so placed as not to be liable to accidental injury in the engine-room; and that the heat employed for superheating the steam should be waste heat which has already done its duty in the boilers and is passing away.
"All these conditions have been most satisfactorily fulfilled by Mr. Penn in the new engines on board the Valetta, which were tried down the Thames for the first time on Thursday. The Valetta, as our readers may remember, was for many years the mail-boat between Marseilles, Malta, and Constantinople. While thus employed, she had Penn's engines of 400 horse-power, and to work these up to an average speed of 15 miles an hour required a consumption of fuel of from 70 to 75 tons of coal per day. At no time was it less than from 45 to 55 tons. These engines have now been removed to a vessel nearly double the tonnage of the Valetta, and the latter fitted with engines by Mr. Penn on the superheating principle. We may mention that, besides this alteration, the Valetta has been considerably improved. A poop and forecastle have been added, increased accommodation given to passengers, and the whole vessel fitted up in the richest style. The saloon is one of the simplest and handsomest things of the kind we have seen, sufficiently lofty and capacious, and above all, admirably ventilated on the system which is now being adopted on all sea-going steamers, and the merit of devising which belongs to Mr. Robinson, of the Peninsular and Oriental Company.
"To return, however, to the engines. Mr. Penn, at the repeated request of Mr. Allen, the Managing Director of the Peninsular and Oriental Company, undertook to apply to them the principle of superheating, to which his attention had many years before been seriously directed by Dr. Haycraft. His method of doing this is to place in the smoke-box of the boiler, through which the hot air from the furnace first passes, as large a number of small pipes as is consistent with allowing a free draught from the furnaces. Through these all the steam from the boilers passes in its way to the cylinders. By this plan an immense heating surface in the pipes is secured, the steam is in a subdivided form, so as to be readily acted on, and the waste heat from the furnace is utilized at the point where its intensity is greatest, and where the greatest conveniences exist for applying the apparatus. By means of three ordinary stop-valves, the whole contrivance can be shut in or off from the engines at pleasure. In ordinary engines steam leaves the boilers at about 250°, but declines from this temperature in its way to the engines to 230°, undergoing from condensation a still greater and more serious diminution of heat in the cylinders. From these causes, and also from the immense quantity of waste heat which escapes through the smoke-box and up the funnels, there has always been a theoretical loss of steam power amounting to forty per cent., as compared with the coal consumed. It is this loss of power and waste of heat which the superheating process is intended to prevent, and which will, of course, allow a reduction of from twenty-eight to thirty per cent. on the fuel now consumed. By the superheating process the steam is raised in passing along the pipes in the smoke-box (where the heat is about 650°) from a temperature of 250° to 350°, and so enters the cylinders at 100° in excess of the temperature due to its pressure. This extra heat is, of course, rapidly communicated to the metals, and prevents the condensation in the cylinders or other parts of the engines, which would otherwise, of course, take place. Singularly enough, a smaller amount of cold water is required to condense the steam at this high temperature of 350° than when at the ordinary heat of common steam.
"The trial trip of the Valetta on Thursday was most satisfactory, not only as regards the engines, but still more so as to the application for the superheating process. At the measured mile at the Lower Hope, near the Nore, the result of repeated runs gave an average speed of nearly 14½ knots per hour, thus realizing with engines of 260 horse-power, and a small consumption of fuel, the same rate of speed as had been gained with her previous engines of 400 horse-power, and a consumption of seventy-five tons of coals per day. The superheating apparatus evidently effected a most important saving in fuel, but until an average of many days' working can be obtained, it would be difficult to estimate the exact amount economized. There seems, however, every reason to believe that an average of fourteen knots an hour can be obtained with a consumption of only from twenty-four to twenty-six tons per diem. The thermometer during the trial indicated in the steam pipes an addition to the ordinary temperature of 100°, which Mr. Penn believes to be enough for all practical purposes of superheating. Even when making from thirty-three to thirty-four revolutions per minute, and driving the vessel against a strong head wind and tide, it was impossible to consume all the steam generated, which was blowing off from both boilers all the trip. The engines are remarkable for the extraordinary beauty and simplicity of their proportions, qualities well known in all engines from Penn and Sons, and which, combined with the strength of the materials and perfection of the workmanship, make this firm the foremost in the world for machinery of this description. Both cylinders are oscillating, of sixty-two inches diameter, and with a stroke of four feet six inches. The paddles are on the feathering principle, and the boilers of Lamb and Co.'s patent. During the whole course of the trials, and when going at one time nearly sixteen knots, there was no perceptible vibration, even at the end of the saloon nearest to the engines. When it is remembered that the superheating process which can effect such important results is capable, as we have said, of application to steam machinery of every kind, including even locomotives, it cannot be doubted that the trial of Thursday and its great success is one of the most important events for the progress of steam which we have had to chronicle for many years." (The Times, April 23rd. 1859.)
Whilst speaking of the application of this somewhat novel condition of steam, it may be observed that many inventors, who have paid little or no attention to first principles, have proposed to apply the vapours of alcohol, ether, or turpentine, instead of that of water; and they have founded their notions on the idea that in consequence of the less latent and sensible heat of alcohol, ether, and turpentine vapour, and of the small quantity of fuel required to boil them, that they would compete advantageously with steam. This view of the case, however, is soon proved to be a very shortsighted one, because the amount of expansion has been quite overlooked; and if it was desirable, by way of comparison, to produce a cubic foot of steam, alcohol, ether, or turpentine, the steam would stand first for cheapness, and would require the least quantity of fuel to produce it, so that if the more expensive of combustible liquids could be obtained for nothing, it would still be cheaper to employ water.
| Latent heat, or equivalent for fuel. | |
| A cubic foot of water yields 1700 cubic feet of steam | = 1000° |
| A cubic foot of alcohol produces 493 cubic feet =457°. Then, by rule of proportion, 493 cubic inches : 457 :: 1700 : | 1575° |
| A cubic foot of ether yields only 212 cubic feet of vapour = 312°, and 212 : 312° :: 1700 : | 2500° |
| A cubic foot of the oil of turpentine affords 192 cubic feet of vapour = 183°, and 192 : 183 :: 1700 : | 1620° |
It will therefore be seen that water, when converted into steam, expands eight times as much as sulphuric ether, and nearly three times and a half as much as alcohol.
The application of steam for the purpose of propelling vessels has already been mentioned in connexion with the Spanish inventor, Blasco de Garay, in the year 1543. The first patent in this kingdom granted for that purpose was that of Mr. Jonathan Hull in 1773. In 1787, Mr. Miller tried a number of important experiments in the propulsion of vessels by steam-engines, and it would appear that Lord Cullen advocated his ideas, and endeavoured to secure the co-operation of the great firm of Boulton and Watt, who, occupied with their land engines, could not pay attention to it; and twenty years elapsed after the reply of Watt to Lord Cullen's application, before the real novelty appeared of a first successful experiment with a steam-boat in "the open sea," by Henry Bell, in 1811. A picture of this boat, called the Comet, which was afterwards wrecked, is shown at p. 418. Henry Bell's novelty was success, and he is fairly entitled to the merit of first introducing steam navigation into Europe.
In 1811, the public stared with mingled astonishment and satisfaction at the realization of that which was called a fable. Only forty-seven years afterwards another generation spontaneously exhibits the liveliest interest in the gigantic private speculation of the Great Eastern. Henry Bell's vessel of 1811 was 40 feet keel, 10 feet 6 inches beam, and 25 tons burthen! The Great Eastern of 1859 is 692 feet long, 83 feet wide, 60 feet deep, and 24,000 tons burthen!! The whole nation with one voice wish her God speed in her projected voyage across the Atlantic, as the embodiment of that great goodwill which every generous-hearted Englishman feels towards the enlightened free-born people of the United States.
Should the author's little vessel, with its humble freight of science, meet with the approbation of his good friends, the boys and their advisers, another and another, if health permits, shall be launched for their benefit. Vale.
THE END.
Transcriber's Notes.
Chapter XV. Experiment one is not indicated by a title heading.
Page 99. "the pulse is raised forty or fifty beats per second" changed to "the pulse is raised forty or fifty beats per minute"
Page 148. "it is allowed to dry spontaneously, and being coated with amber varnish (a solution of amber in chloroform) is now ready to print from. (Fig. 123.) It is, perhaps, hardly necessary to add, that the sensitizing and developing processes must be performed in a dark room." Fig. 123. is irrelevant to this section. The reference has been deleted.
Page 365. "an air thermometer has been employed by Sir John Leslie, under the name of the "Differential Thermometer," in his refined and delicate experiments with heat. (Fig. 401.)" Ref. to (Fig. 401.) removed. Fig. 401. not in original hard copy version.