investigating the Specific Heats of the Gases. 9 



its stop-cock was rapidly closed, that of the other opened, and the experiment 

 continued by means of pressure similarly applied to the gas. While matters were 

 thus proceeding, I kept my eye, armed with a common lens, steadily fixed on the 

 wet thermometer, and the moment that it acquired a stationary temperature, 

 (which, generally speaking, in consequence of the previous current of dry air, 

 occurred long before the entire of the gas was discharged,) its indication, and that 

 of the dry thei'mometer, were registered, and the experiment suspended. The 

 residual gas was now passed into a glass jar on the mercurial trough, with a view 

 to subsequent analysis, and both bladders being refilled with atmospherical air, a 

 second experiment was performed precisely as just described. 



The values of t and t', obtained in the first experiment, enabled us to calculate, 

 by aid of the equation 



_er_ 30 



the specific heat of the elastic fluid which was made to traverse the apparatus. 

 But this result belonged not to the pure gas, but to a mixture of it with a certain 

 quantity of atmospheric air, which enters the bladder upon the principle of 

 endosmose, and to infer from it the specific heat of the pure gas, which we shall 

 call a', it was necessary to know the amount of air present, and its specific heat. 

 Now the former of these was given by the analysis of the residual gas, as already 

 mentioned, and the latter by the results of the second experiment above recorded, 

 in which both bladders were occupied by air alone. 



Jf a' be the specific heat* of the gas, n the percentage of air, c its specific 

 heat, and a the specific heat of the mixture of air and gas, we will, on the principle 

 that the specific heat of the mixture, multiplied by its volume, is equal to the sum 

 of the products of the respective volumes of air and gas, multiplied by their re- 

 spective specific heats, have 



a' x( 100— n) + wc = o X 100, 



an equation from which we deduce 



, , (a—c)n . 



« = « + -ioo=« 



This is the specific heat of the pure gas in reference to that of air, as determined 



* The specific heats spoken of throughout this paper are those under a given volume. 

 VOL. XVIII. C 



