STEAM AND STEAM-EXUIXE. 



STEAM AND STEAM-KNOINE. 



784 



Watt and <'f Southern ui>n this subject which had previously been 

 received. Kvgnault found that at the ordinary atmospheric pressure it 

 required 540 thermal unit* of the French scale to convert 1 gramme of 

 water into steam (971,636 English thermal units to convert 1 pound 

 avoirdupois) ; and thus far hU experiments (recorded in the ' MiS- 

 iu<iirrs de I'Acadcuiiu des Science*,' voL zxi.) agreed with those of 

 other observers. Watt, however, had laid down the law " that the 

 quantity of heat necessary to vaporise a given weight of water was the 

 am at every degree of toe thermometer ; " and Southern had stated 

 " that the latent heat of vaporisation was the same under every degree 

 of pressure ; " De Pambour's observations appeared also to show that, 

 up to a pressure of about 65 Ibs. on the superficial inch, Watt's law 

 was substantially correct. Regnault, on the contrary, found that 

 Watt's law was not exact, and that Southern's was still more falla- 

 cious ; for he found that when the tem]>eniture increased, the total heat 

 also increased, but the latent heat diminished. The results of his 

 experiments were given in the following formula, A = 606'5 + 0-30& ; 

 in which X is the total heat (on the centigrade scale), and ( the tempe- 

 rature of the steam ; the coefficient 606'5 being the value assigned by 

 him as the latent heat of vapour at 0, and 0-305 the specific heat of 

 steam. Regnault ascertained at the same time that between the 

 limits of and 392 there was hardly any difference in the specific 

 heat of water, so that there was no occasion to take that difference 

 into account. In the Me'moire wherein these observations are recorded 

 a table is inserted, showing the tensions, and the total heat of the 

 vapour given off at temperatures increasing by equal increments of 10 

 degrees centigrade, between and 230. The table in question is also 

 given in Daguin's ' Traite' de Physique,' t. i., part 2, p. 965. It may be 

 OB well to add that the laws of the latent heat of steam are practically 

 applied when buildings are heated by means of it; in these cases the 

 heat absorbed, or rendered latent in one place, is distributed by the 

 pipes which enable the steam to circulate over other parts of a 

 building. 



The following table of the densities of vapours is extracted from 

 Daguin's work ; it is based upon the experiments of KM. Gay-Lussac 

 and Dumas, and the density of air is token as unity. 



Compared with water at its greatest degree of condensation, the 

 density of steam at 212" Fahr. is exactly 1695 less than that of the 

 water, or nearly 1700, as was before stated; or in fact, one volume of 

 water yields nearly 1700 volumes of steam. This is worthy of remark; 

 for the volumes of the oxygen and hydrogen, contained in a given 

 volume of water, occupy under atmospheric pressure a space equal to 

 2500 times the volume of the latter. It has been suggested that the 

 o indentation which thus appears to have taken place during the com- 

 bination of the permanent gases referred to, may be explained by some 

 change in their electrical state; and it is well known that the evolution 

 of steam, under high pressures, does give rise to electrical phenomena 

 of a very remarkable but hitherto only partially studied description. 

 Messrs. Armstrong, Faraday, Schofthoentl, and Becquerel have, indeed 

 observed that when steam, charged with water in suspension, escapes 

 in such a manner as to exercise friction against a substance opposed to 

 its passage, a development of electricity takes place, and that generally 

 the water or the vapour is positive, and the opposing substances 

 negative. The form, the nature, and the temperature of the orifices 

 affect the development of the electricity to a great extent, and 

 especially does heat retard it; at the same time the amount of elic- 

 trical action depends on the purity of the water, for a small quantity of 

 salt or acid destroys the property, and a very small proportion of the 

 essence of turpentine causes the nature of the electricity to change ; 

 the steam in this case becomes negative. Becquerel evidently attri- 

 butes the development of the electricity, by the passage of steam under 

 the circumstances recorded in the experiments of Mr. Armstrong, to 

 the friction of the globules of water contained in the steam ; but this 

 interesting question has not yet been examined with sufficient accuracy 

 to allow the formation of any absolute opinions on the subject. 



Steam-Exyinc. In conformity with the plan of this Cyclopedia 

 general outline of the principles of the engine will be here given, the 

 reader being referred to different articles connected with the subject, 

 or to works written specifically on the steam-engine, for more detailed 

 information. 



The claim to the invention of the steam-engine has been made a 

 subject of national contention ; but the conclusion, arrived at from the 

 discussions which thin contention lias originated, seouis to be, that, in 

 common with all other important applications of physical principles, 

 no individual can. by claim to the invention. Whatever may have 



been the nature and date of its origin, it has been reared to its present 

 gigantic stature by the fostering care of different countries, and, with- 

 out detracting from or underrating the efforts of others, England may 

 be justly proud of her share of the glory, a shore readily conceded by 

 our competitors. 



Considering therefore dispute as unprofitable, and the discuN- 

 dates of patents and improvements as uninteresting, we shall im-r|. 

 rate all that is requisite of the history of the engine with our account 

 of it. 



A steam-engine may be defined generally as an engine by which the 

 force* arising from the properties of elasticity and of instantaneous 

 condensation possessed by steam are transmitted to produce a con- 

 tinuous rotatory motion, either of a fly-wheel designed to constitute a 

 reservoir of power for the purposes of driving machinery, or for any 

 other uses that force may be put to. 



Admitting this definition, the earlier steam-engines, as they are 

 commonly called, those of the Marquees of Worcester (1663), and the 

 improved forms contrived or suggested by others, and even Captain 

 Savery's (1698), which was long employed in this country, were only 

 pamff for raising water : a partial vacuum was formed in close vessels 

 by the condensation of steam within them, the atmospheric pressure 

 raised the water to a certain height ; from whence it was forced higher 

 by the elasticity of the steam admitted to act on its surface. 



Passing over all these therefore as foreign to our subject, t) 

 engine which it is necessary to describe is that of Newcomen (1705) ; 

 it constitutes the connecting link between the steam-pumps alluded to, 

 and the modern engine, of which it contained the germ, and into which 

 it was converted by the genius of Watt [WATT, JAMES, in Bioo. 

 Div.J 



In the subjoined diagram, A represents a cylinder open at the uppe 



Fig. 1. 



end, fitted with a ]>i*ton B, and rendered air-tight by having water on 

 it to the depth of several inches : the piston-roil was suspended by a 

 chain from the arched end of a beam c, turning on an axle, and having 

 a pump-rod at its other extremity, loaded so as to counterpoise the 

 weight of the piston, and to raise it to the top of the cylinder. This 

 cylinder was placed over the boiler D with which it communicated by 

 a steam-pipe i . furnished with a cock K to open or close the passage : 

 o is a cistern fixed above the cylinder, to the bottom of which a pipe 

 H passed, also provided with a cock i. 



When the piston was depressed to the bottom of the cylinder, it 

 drove out all the air before it, which escaped at the orifice of a pipe K 

 into the water of a smaller cistern L : the cock T being next opened, 

 the steam from the boiler filled the cylinder as the piston rose again 

 from the action of the counterpoise ; as soon as it arrived at the top, 

 the cock i' was closed and I opened, a jet of cold water from I lie cistern 

 o rushed into the cylinder, condensing the steam, and thus forming a 

 partial vacuum beneath the piston, the pressure of the air on its upper 

 surface forced it downwards, and caused the pump at the other end of 

 the beam to raise an equivalent weight of water to a height equal to 



