IS 13.] Specific Heat of the different Gases. 375 



portional to the- quantity which parses through, it follows, from 

 the preceding experiments, that it" a volume f dry air raise the 

 temperature of the calorimeter l.VI.'°. an equal olume of 

 vapour would raise it i?9'7°, other things being equal, lience, 

 if the specific heat of air be I 000, that of the same volume of 

 vapour is 1*9G, and of the same weight, 8\136.* 



Section V. 



Determination of the Specific Heat of Air suljectcd to different 

 Degrees of Pressure. 



After having established the relation which exists between the 

 specific heat of the different gases, we endeavoured to ascertain 

 that which exists between the specific heat of the same gas sub- 

 jected to different degrees of pressure, or, which comes to the 

 same thing, having different densities. 



Does the specific heat of a gas increase with its density ? and 

 if it does, is the increase proportional to the density ? The 

 experiments of Gay-Lussac, the only ones, as far as we know, 

 which are capable of throwing light on the subject, seem to 

 decide the first of these questions in the affirmative; but they 

 are neither sufficiently direct nor precise to give an answer to the 

 second. 



The first process employed to determine the specific heats of 

 the different gases, appeared to us equally proper to furnish an 

 accurate answer to these two questions. It was sufficient to 

 circulate a current of the same gas through the calorimeter, 

 sometimes artificially compressed, and sometimes subjected only 

 to the pressure of the atmosphere, and to determine in both 

 cases the point at which the temperature of the calorimeter 

 became stationary. The following modifications in our apparatus 

 enabled us to make these experiments with facility : — 



We soldered to the stop-cocks, P and P', (fig. 8, Plate X ) a 

 tube in the form of a Y reversed. The two branches of the Y 

 united in a common tube, 1 1 1, which, rising vertically, and pass- 

 ing through an opening in the roof of the room, opened above a 

 tub, X, placed ID the room above. We carried to this room 

 the cylindrical glass vessels, A, A', and formed the communica- 

 tion between them and the reservoirs, B, B', by the long tubes 

 which passed down through the floor. In this apparatus the 

 height, H II, of the upper extremity of the tube, I I, above 

 the mouth of the stop-cocks, P, 1", determined the pressure to 

 which the gas was subjected. It amounted to 11-29 feet, f It 



* This is calcalated on the supposition thai the prelght of vaponr is lot t 

 of air us 10 : 16. Bee < iaj Lomoc, Ann. de Chim. Iwx. 218. 



i To enable tin- reiervo n t" beai this great pressure without danger, they 

 were firmly buund round with cords. 



1 



