1822.] inmodifyingthe Specific Qravity of Gases, 421 



It has been found that water is more easily distilled ; namely, 

 with a less expense of fuel, at a high temperature than at a low; 

 and that high pressure steam engines do more work with less 

 fuel than low pressure ones. These things Dr. Thomson 

 advances as proofs of his inference of the diminution of latent 

 heat. Now Mr. Dalton has shown by experiment that water 

 evaporates nearly as the superincumbent pressure ; and, there- 

 fore, at 340°, the generation of steam is about nine times as 

 great as it is at 212°, though the temperature is only about one- 

 eleventh part higher. Therefore, if nothing else interfered by 

 increasing the temperature from 212° only about one-eleventh, 

 we might perform nine times the work. To explain the economy 

 of high pressure engines, we want, therefore, no new doctrine of 

 latent heat ; and hence the introduction of it appears to me to 

 be superfluous. 



By the experiments of Mr. Sharpe and Mr. Southern, the specific 

 gravity of steam in conjunction with its fluid has some proportion 

 to its elasticity. In the last volume of the Annals, p. 269, I have 

 shown that this specific gravity and elasticity cannot be cor- 

 rectly proportional under any consideration whatever, neither 

 from the theory 1 have advanced, nor from the experimental 

 results of that which is usually admitted. Dr. Thomson, how- 

 ever, in his present paper, having assumed that the proportion is 

 ■correct, I shall concisely show that it carmot be. Messrs. Dalton, 

 Gay-Lussac, Dulong, and Petit, have proved that the volumes 

 being the same, the elasticities ; and the elasticities being the 

 same, the volumes of a given portion of any gas at the tempera- 

 ture of 32° and 212° are as 8 to 1 1 ; and that in other cases, the 

 increments or decrements of the elasticity or volume are propor- 

 tional to the ascending or descending Fahrenheit temperature. 

 Therefore when the volume is the same, the 



elasticity = 448 + F ; 



and when the elasticity is the same, the 



volume = 448 + F, 



F denoting the corresponding Fahrenheit temperature. It has also 

 been found that at the same temperature the specific gravity is 

 proportional to the elasticity. And it has likewise been esta- 

 blished by the concurrent experiments of the French and English 

 philosophers, that with the exception of their not being able to 

 sustain more than a certain pressure according to the tempera- 

 ture, vapours are perfect gases, and follow precisely the same 

 laws of expansion and contraction. Let S be the specific gravity 

 of vapour, and t the tension at the temperature F, then at any 

 other temperature F'', the elasticity of this same vapour under the 

 same volume, would be 



1^+448 

 ■^ ^ fT"448' 



