M. V. Regnault on the Expansion of Gases. 135 



The values of y then became for the same pressure much 

 greater than in the preceding series, in which the expansion of 

 the gas took place entirely in the calorimeter. Thus the cooling 

 is far greater when the silver capillary tube debouches directly 

 out of the calorimeter into the external air than when the gas 

 on passing from the capillary tube can expand completely in 

 the boxes of the calorimeter, and then traverse them with a 

 small velocity before escaping. This obviously arises from the 

 circumstance that in the first case the gaseous molecules con- 

 stantly increase in velocity until their emergence from the calo- 

 rimeter, while in the second case the gas undergoes, on the con- 

 trary, a material loss of vis viva in the boxes of the calorimeter, 

 to which it thus abandons a considerable quantity of heat, which 

 diminishes by so much the cooling observed. 



These latter experiments show that the cooling is produced 

 during the circulation and by the expansion of the gas in the 

 silver capillary tube, while the end of the expansion on the out- 

 side, with the modifications which are the consequence of it, rather 

 gives rise to a disengagement of heat, owing to the destruction of 

 vis viva. I wished to establish this fact more directly by expe- 

 riment, and I had recourse to an apparatus consisting of two calo- 

 rimeters, A and B. The first calorimeter, A, small in capacity, 

 contains the silver capillary tube rolled spirally ; the first end 

 of this tube fits in the long copper worm immersed in the large 

 water-bath, and which brings the compressed air from the reser- 

 voir; the other end of the silver tube fits in the lower box of the 

 second calorimeter B, which is like those I have used to deter- 

 mine the calorific capacity of gases under the pressure of the 

 atmosphere. This second calorimeter terminates in a tube 

 through which the gas is liberated. This latter tube fits in a 

 larger tubulure, in which is kept a very delicate thermometer, 

 and which by a lateral tubulure conducts the gas to a meter. 



Experiments made with this new apparatus led to the follow- 

 ing conclusions : — 



1. The cooling effect of the expansion is produced almost en- 

 tirely in the silver capillary tube. Owing to the great conducti- 

 vity of silver and the smallness of the section of the tube, the 

 gas emerges from the capillary tube sensibly at the same tem- 

 perature as the water of the first calorimeter, but with a far 

 greater molecular velocity than it had on entering. 



2. A new expansion takes place in the superposed boxes of 

 the second calorimeter; this expansion is much weaker. The 

 small lowering of temperature which may be thus produced is 

 more than compensated by the heat which the gas abandons in 

 losing the greater part of its vis viva ; so that the total effect 

 consists in a considerable heating of this calorimeter. 



