Section of Chemistry and Electricity. S87 



tain, by aid of the equation a=LZ_x— , the specific heat of the 



48a p 



elastic fluid which was made to traverse the apparatus. But this 

 result belongs not to the pure gas, but to a mixture of it with a cer- 

 tain quantity of atmospheric air, which entered the bladder upon 

 the principle of endosmose ; and to infer from it the specific heat of 

 the pure gas, which we shall call x, it was necessary to know, 1st, 

 the amount of air present, and 2nd, its specific heat. Now the for- 

 mer of these data was given by the analysis of the residual gas, as 

 already mentioned, and the latter by the results of the second expe- 

 riment above recorded, in which both bladders were occupied by 

 air alone. If x be the specific heat, and s the specific gravity of 

 the gas, n the per centage of air, c its specific heat, and a the spe- 

 cific heat of the mixture of air and gas, as already determined, we 

 shall, on the principle that the specific heat of a mixture multiplied 

 by its weight is equal to the sum of the products of the weights of 

 the gases mixed multiplied by their respective specific heats, have 

 *(100 — n)s + n c = a(lQ0— n s + n), an equation from which we de- 

 duce x — a + — ■ - — . This is the specific heat of the pure gas 



(100-w)s r " 5 



in reference to that of air, as determined by the second of the above 

 experiments ; and as both air and gas are dry, and must have been, 

 with at least a very high degree of probability, proportionally af- 

 fected by variations of pressure, the precise influence of these, about 

 which, indeed, philosophers are not agreed, do not require to be 

 taken into consideration ; nor is there anything further necessary 

 for rendering the result thus obtained strictly comparable with 

 those of other experimenters, than to reduce it, by the rule of three, 

 to what it would be if the specific heat of air were '267, the num- 

 ber by which it is usually represented in books at a mean altitude 

 of the barometer. The following experiments on air and hydrogen, 

 performed on the 4th of August, will illustrate the preceding de^ 

 scription. 



t t' d p 



Hydrogen 68 48 20 30*114 



Air 68 43 25 30*114 



f'e 30 

 By applying to these results the equation a = j— - x — , we get 



TfO U p 



Specific heat of air =-2767 



Approximate specific heat of hydrogen . ='4092 



But the gas, upon analysis, was found to contain 5 per cent, of air. 



Hence the specific heat of the hydrogen supposed pure as deduced 



fromthe equation x = a-\ — ^ a ~" c )n becomes -.097. And *2767: 

 ' (100 — n) s 



•5097 : : *2670 : '4914 = the specific heat of hydrogen compared to 



that of air under a pressure of 30, — when water is represented by 



unity, or, what amounts to the same, when air is *267. 



The following table exhibits the results thus obtained ; — referred 



to air as the standard, the number for nitrogen being the mean of 



3D2 



