M. V. Regnault on the Expansion of Gases. 131 



sation, because the gas always emerges from the calorimeter with 

 a great velocity. 



For atmospheric air, and especially for carbonic acid, the re- 

 sultant is a notable cooling. 



For hydrogen, the three causes, acting in contrary directions, 

 neutralize each other, especially owing to the small atomic weight 

 of the gas. 



Second case. — The compressed gas reaches the calorimeter 

 with a temperature much higher than that of the calorimeter, 

 so that there is not merely expansion but also cooling of the 

 gas. 



This second case is more complicated than the first, because 

 it comprehends the calorific effects produced by changes of 

 molecular velocity, the modifications produced in the consti- 

 tution of the gas by change of pressure, and those, moreover, 

 which arise from change of temperature. I have been led to 

 consider a special calorific capacity which comprehends the whole 

 of these effects. 



For air, this calorific capacity with expansion is appreciably 

 greater than the calorific capacity of air under constant pressure. 



For hydrogen it is the same. 



Lastly, for carbonic acid it is considerably smaller than the 

 calorific capacity under constant pressure at high temperatures, 

 and much greater at very low temperatures. 



II. Experiments to determine the heat which atmospheric air ab- 

 sorbs when it expands from a high pressure to the pressure of the 

 atmosphere, not suddenly as in the preceding chapter, but sue- 

 cessively. (Experiments of 1853.) 



In the preceding experiments the air compressed in the reser- 

 voir expands completely on emerging from a single orifice in the 

 interior of the calorimeter; the expanded gas circulates then in 

 the superposed boxes of the calorimeter, and acquires the tem- 

 perature of the water of the calorimeter before emerging into the 

 atmosphere. I have endeavoured in the experiments I am about 

 to describe to effect this expansion step by step at several periods 

 in the interior of the calorimeter, so as to ascertain whether this 

 circumstance exerts an influence. 



The special calorimeter which I used for these experiments, 

 and which I shall call calorimeter for successive expansions, con- 

 sists of a series of brass tubes A, B, C, D, . . . , 8 millims. in the 

 clear, connected with each other by tubulures. These tubes, 

 twelve in number, are vertical, and form a circular crown in the 

 interior of the calorimetric vessel. 



The reservoir containing the compressed gas communicates 

 with a long worm arranged in a bath of water. The end of this 



K2 



