of the Specific Heat of Gases under Constant Volume. 343 



to cause, by the increased pressure of the gas, the disruption of 

 the shell, when the whole experiment shall be concluded. 



2. It will be easy now to show how, by means of the know- 

 ledge of the capacity and the pressure of disruption of the shell, 

 the initial pressure and the initial temperature and weight of the 

 gas, and with the aid of the laws of gaseous elasticity and of 

 galvanic heating, the real specific heat of any gas subjected to 

 an experiment like the above may be accurately deduced. 



Let v be the volume common to both the shell and the gas, p 

 the initial pressure, and t the initial temperature of the gas ; then, 

 by the law of Boyle (to which, however, it would be easy to sub- 

 stitute any other more accurate formula), 



pv=. 1 ^{a + t) ; 



R being a constant characteristic of the nature of the gas, and a 

 the inverse coefficient of expansion. If P be the pressure of dis- 

 ruption, and T the corresponding temperature of the gas, then 



Pv = R(« + T). 



Hence, the increase of temperature owing to the heating of the 

 gas, 



6 = T-t=(Y-p)^ (I.) 



where (T— t) is expressed by quantities all of which are known. 

 It now remains to determine the quantity of heat by which this 

 increase of temperature is produced. According to Mr. Joule's 

 law, the quantity of heat given out by part of the circuit of a 

 galvanic battery in the unit of time is 



w=c .r .i 9 , 



where i denotes the intensity of the current, r the resistance of 

 the part of circuit considered, and c a constant dependent on the 

 unit of heat chosen. If the battery in the above experiment 

 have acted during the interval of time t, then the amount of heat 

 emitted by the spiral employed to heat the gas will be, the above 

 formula being now applied to this spiral, 



W = c .r . z 2 .r. 



Let it now be supposed that the same battery and spiral be 

 employed to heat, instead of the gas, a pound of water during the 

 unit of time ; the heat given out in this case will be immediately 

 measured by the increase of temperature, 



r x and \ x being the magnitudes now taking the place of r and i 

 in the former experiment. And since 



W= 7 % 



