From similar experiments Dr. Black deduced the important truth, "that in all cases of liquefaction a quant.i.ty of heat _not indicated by, or sensible to_, the thermometer, is _absorbed_ or disappears, and that this heat is _withdrawn_ from the _surrounding bodies_, leaving them _comparatively cold_." At p. 79 it is shown how the sudden solution or liquefaction of certain salts produces cold, and hence numerous freezing mixtures have been devised. In olden times, when officials in authority did what they pleased, without being troubled with disagreeable returns, and colonels clothed their men, and were merchant tailors on the grand scale, gun cartridges were not confined to practice on the enemy, but they did duty frequently in the absence of ice as refrigerators of the officers" wine, in consequence of the gunpowder containing nitre or saltpetre; as a mere solution of this salt finely powdered will lower the temperature of water from 50 Fah. to 35; whilst a mixture of four ounces of carbonate of soda and four ounces of nitrate of ammonia dissolved in four ounces of water at 60, will in three hours freeze ten ounces of water in a metallic vessel immersed in the mixture during the liquefaction or solution of the salts.
Fahrenheit imagined he had attained the lowest possible temperature by mixing ice and salt together, and it is by this means that confectioners usually freeze their ices, or ice puddings; the materials are first incorporated, and being placed in metallic vessels or moulds, and surrounded with ice and salt placed in alternate layers, and then well stirred with a stick, they soon solidify into the forms which are so agreeable, and so frequently presented at the tables of the opulent. The temperature obtained is Fahrenheit"s _zero_--viz., thirty-two degrees _below_ the freezing point of water. According to the very wise police regulation observed in London, all householders are required to sweep or remove the snow from the pavement in front of their houses, and this is frequently done with salt; should an unfortunate shoeless beggar, tramp past whilst the sudden liquefaction is in progress, the effect on the soles of his feet is evidently very disagreeable, and the rapidity with which he retires from the _zero_ affords a thermometric ill.u.s.tration of the most lively description.
_Heat the Cause of Vapour._
Every liquid, when of the same degree of chemical purity, and under equal circ.u.mstances of atmospheric pressure, has one peculiar point of temperature at which it invariably boils. Thus, ether boils at 96 Fahr., and if some of this highly inflammable liquid is placed carefully in a [Page 414] flask, by pouring it in with a funnel, and flame applied within one inch of the orifice, no vapour escapes that will take fire; but if the flame of a spirit lamp is applied, the ether soon boils, and if the lighted taper is again brought near the mouth of the flask, the vapour takes fire, and produces a flame of about two feet in length. This fire only continues as long as the flame of the spirit-lamp is retained at the bottom of the flask, and on removing it the vessel rapidly cools. The length of the flame is reduced, and is gradually extinguished for the want of that essence of its vitality, as it were--viz., heat. (Fig. 387.) If a thermometer is introduced into the flask, however rapid may be the ebullition or boiling of the ether, it is found to be invariably at 96. The heat carried off by evaporation is most elegantly displayed by placing a little water in a watch gla.s.s, and surrounded by charcoal saturated with sulphuric acid, in the vacuum of an air-pump. The rapid evaporation and condensation of the water by its affinity for the sulphuric quickly produces ice; and the pumps and other apparatus of Knight and Co., Foster-lane, City, are greatly to be recommended for this and other ill.u.s.trations.
[Ill.u.s.tration: Fig. 387. Heat the cause of vapour.]
The ill.u.s.tration of the determination of the fixed and invariable boiling point belonging to every liquid is further carried out by introducing some water into a second flask standing above a lighted spirit-lamp, with a small thermometer, graduated, of course, properly to degrees above the boiling point of water; when the water boils, it will be found to remain steadily at a temperature of 212. And however rapidly the water may be boiled, provided there is ample room for the steam to escape, the heat indicated by the thermometer is like the law of the Medes and Persians, which altereth not, and it remains standing at the number 212. The only exception (if it may be so termed) to this law is brought about by the shape and nature of the containing vessel; under a mean pressure the boiling point of water in a metallic vessel is generally 212; in a gla.s.s vessel it may rise as high as 214 or 216, but if some metallic filings are dropped in, the escape of steam is increased, and the temperature may then drop immediately to 212.
When a thermometer is inserted in a flask containing water in a state [Page 415] of ebullition or boiling, so that the bulb does not touch the fluid, but is wholly surrounded with steam, it will be found that the temperature of the latter is exactly the same as that of the former; and if the liquid boils at 96, the vapour will be 96, if at 212, the steam is 212. Steam has therefore exactly the same temperature as the boiling water that produces it. (Fig. 388.)
[Ill.u.s.tration: Fig. 388. Thermometer in the steam escaping from boiling water.]
Whilst performing the last experiment, it may be noticed that the steam inside the neck of the flask is invisible, and that it only becomes apparent in that kind of intermediate condition between the vaporous and liquid state called _vesicular vapour_--a state corresponding with the "earth fog," and called by Howard the _stratus_. When a flask containing boiling water is placed under the receiver of an air pump (as soon after the ebullition has ceased as may be possible), and the air pumped out, it will be noticed that the water again begins boiling as the vacuum is obtained, showing that the boiling point of the same fluid varies under different degrees of atmospheric pressure, and according to the height of the barometer.
Height of Boiling point barometer. of water.
26 204.91 26.5 205.79 27 206.67 27.5 207.55 28 208.43 28.5 209.31 29 210.19 29.5 211.07 30 212 30.5 212.88 31 213.76
Alcohol and ether confined under an exhausted receiver boil violently at the ordinary temperature of the atmosphere, and in general liquids boil with 124 less of heat than are required under a mean pressure of the air; water, therefore, in a vacuum must boil at 88 and alcohol at 49.
On ascending considerable heights, as to the tops of mountains, the boiling point of water gradually falls in the scale of the thermometer.
Thus, on the summit of Mont Blanc water was found by Saussure to boil at 187 Fahr. In Mr. Albert Smith"s delightful narrative of his ascent of Mont Blanc, he mentions the violent commotion and escape of the whole of the champagne in froth directly the bottle was opened at the summit of this king of mountains.
Dr. Wollaston"s instrument for measuring the heights of mountains by [Page 416] the variations of the boiling point of water has long been known and used for this purpose.
If a Florence flask is first fitted with a nice soft cork, and this latter removed, and the former half filled with water, which is then boiled over a gas or spirit flame, the same fact already mentioned and ill.u.s.trated in the preceding table may be rendered apparent when the flask is corked and removed from the heat. If it is now inverted, and cold water poured over it, an ebullition immediately commences, because the cold water condenses the steam in the s.p.a.ce above the hot water in the flask, and producing a vacuum, the water boils as readily as it would do under an exhausted receiver on an air-pump plate. (Fig. 389.)
[Ill.u.s.tration: Fig. 389. The paradoxical experiment of water boiling by the application of _cold_ water.]
Water may be heated considerably higher than 212, if it is enclosed in a strong boiler, and shut off from communication with the air; by this means steam of great pressure is obtained.
Dr. Marcet has invented a very instructive form of a miniature boiler, supplied with a thermometer and barometric pressure gauge, which can be purchased at any of the instrument makers, and is figured and described in nearly every work on chemistry.
The reason water boiled in an open vessel does not rise to a higher temperature than 212 is because all the excess of heat is carried off by the steam, and is said to be rendered latent in the vapour. The fixation of caloric in water by its conversion into steam may be shown by the following experiment. Let a pound of water at 212 and eight pounds of iron filings at 300 be suddenly mixed together. A large quant.i.ty of steam is instantly generated, but the temperature of the water and escaping steam are still only 212; hence the steam must therefore contain all the degrees of heat between 212 and 300, or eight times 88. When the water is heated in the hydro-electric machine or other boiler, to 322.7, it very quickly drops to 212 when the steam is allowed to blow off; yet if the latter is collected, it represents but a very small quant.i.ty of water which const.i.tuted the steam, and it has carried off and rendered latent the excess of heat in the boiler--viz., the difference between 212 and 322.7, or 110.7
If steam can carry off heat, of course it may be compelled, as it were, [Page 417] to surrender it again; and this important elementary truth is shown by adapting a tube, bent at right angles, and a cork, to a flask containing a few ounces of water, and when it boils, the steam issuing from the end of the pipe may now be directed into and below the surface of some water contained in a beaker gla.s.s; in a very short time the water in the latter will be raised to the boiling point by the condensation of the steam and the latent heat arising from it. (Fig.
390.) The amount of latent heat is enormous, when it is remembered that water by conversion into steam has its bulk prodigiously enlarged--viz., 1698 times, so that _a cubic inch_ of water converted into steam of a temperature of 212, with the barometer at thirty inches, occupies a s.p.a.ce of _one cubic foot_, and its latent heat amounts, according to Hall, to 950; Southeron, 945; Dr. Ure, 967. When we come to the consideration of the steam-engine, it will be noticed that the question of the latent heat of steam is one of the greatest importance.
[Ill.u.s.tration: Fig. 390. A. Flask for generating steam. B. Gla.s.s pipe bent at right angles to convey the steam into the fluid containing some cold water.]
Temperature of Elasticity in inches Latent Heat.
Steam. of Mercury.
229 40 942 270 80 942 295 120 950
The same weight of steam contains, whatever may be its density, the same quant.i.ty of caloric, its latent heat being increased in proportion as its sensible heat is diminished; and the reverse. In consequence of the enormous amount of latent heat contained in steam, it is advantageously employed for the purpose of imparting warmth either for heating rooms or drying goods in certain manufacturing processes. The wet rag-pulp pressed and shaken into form on a wire-gauze frame or _deckle_, pa.s.ses gradually to cylinders containing steam, and is thoroughly dried before the guillotine knife descends at the end of the paper machine, and cuts it into lengths. In calico stiffening and glazing, also in calico printing, steam-heated cylinders are of great value, because they impart heat without the chance of setting the goods on fire. The elementary principles already described with reference to heat, will prepare the youthful reader for the application of the expansion of water into steam, as the most valuable _motive power_ ever employed to a.s.sist the labour of man.
[Page 418]
CHAPTER XXIX.
THE STEAM-ENGINE--_continued_.
[Ill.u.s.tration: 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 a.s.sign"d In wondrous ships, _self-mov"d_, instinct with mind.
Though clouds and darkness veil the enc.u.mbered 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 G.o.d that o"er the waves presides, Safe as they pa.s.s, and safe repa.s.s 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 [Page 419] originator of Mechanics" Inst.i.tutions, the prize of 20_l._, being the gift of the London Mechanics" Inst.i.tution, and these lines seem to indicate some sort of rude antic.i.p.ation by the ancients of that free pa.s.sage 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 Phoenician 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 ent.i.tled "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.)
[Ill.u.s.tration: Fig. 392. Hero"s steam-engine. A. The boiler in which steam is produced, and then pa.s.ses 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 circ.u.mstance 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 cla.s.sical 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-fees_ on the boilers of [Page 420] steam engines instead of the bodies of poor human beings, what lasting glories would have been her reward. The invention made its _debut_ 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 s.p.a.ce 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.)
[Page 421]
[Ill.u.s.tration: 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 c.o.c.k to admit cold water into the small boiler to fill it.
F. The screw that covers and confines the c.o.c.k E to the top of the small boiler. G. A small gauge c.o.c.k 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 pa.s.sing 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 pa.s.ses out of the great boiler at the steam-pipes O O. N. A small gauge c.o.c.k 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 bra.s.s in the water-pipes, two above the branches Q and two below them; they allow the water to pa.s.s 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 c.o.c.k coming from the force-pipe, so as it shall always be kept filled with cold water. Y Y. A c.o.c.k 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.
[Page 422]
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 ill.u.s.trious Watt, whose portrait heads the first chapter on Heat in this book.