TRANSACTIONS OF THE SECTIONS. 
31 
Matters being thus arranged, an assistant pressed, by means of a 
deal board, first upon the bladder A, containing atmospherical air, 
and, when it was exhausted, upon the bladder G, containing the gas 
which was the immediate subject of experiment. The air, in pass¬ 
ing through the oil of vitriol, was deprived of its vapour, and in 
subsequently traversing the tube containing the thermometers, pro¬ 
duced in the wet one such a reduction of temperature, that, upon 
continuing the experiment as rapidly as possible with the gas , the 
wet thermometer soon acquired a stationary temperature,—which, 
when attained, was, as well as the indication of the dry instrument, 
carefully noted. The residual gas was now passed into a glass jar 
on the mercurial trough, with a view to a subsequent analysis; and 
both bladders being refilled with atmospherical air alone, a second 
experiment was performed precisely as just described. 
From the values of 1 0 t' obtained in the first experiment, we ob- 
e 30 * 
tain, by aid of the equation a=-^—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, lst> 
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 
ic(100>—w)s + w c = a(100—w 5-j-w), anequation from which we de¬ 
duce x = a -j- • This is the specific heat of the pure gas 
in reference to that of air, as determined by the second of the above 
