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



3. The expansion is almost complete on emerging from the 

 second calorimeter ; but the gas still retains its velocity. If it 

 passes into a space of larger section, the velocity of its molecular 

 transport diminishes; a disengagement of heat ensues, which 

 produces an appreciable elevation of the temperature of the gas. 



4. To obtain the true quantity of heat taken from the sur- 

 rounding medium by the gas which expands under the conditions 

 of the experiment, and without change of temperature, the gas 

 should emerge from the second calorimeter destitute of vis viva 

 (a condition which in practice it is impossible to realize), or with 

 a vis viva equal to that which it had on entering. 



In continuation of these long researches I was led to construct 

 a single calorimeter in which are performed all the expansions 

 which successively take place in the two connected calorimeters. 

 I have definitively adopted this arrangement for atmospheric air 

 and for all other gases, because it seemed to combine most 

 guarantees for exactitude. I have endeavoured to define as 

 exactly as possible the conditions in which the gas undergoes its 

 successive expansions. 



Numerous experiments have given for y l a greater value than 

 that 'I obtained in the expansion of air through orifices in a thin 

 plate — that is to say, y x =. — o, 377 for a variation in pressure of 

 1 metre of mercury. This is the value I definitively assume for 

 atmospheric air when the expansion takes place under the clearly 

 defined conditions of the experiment. 



I have previously spoken of the experiments I made to deter- 

 mine the heat absorbed by carbonic acid in motion when it ex- 

 pands without altering its temperature. This quantity of heat 

 is far greater for carbonic acid than for air ; it appears moreover 

 to increase sensibly with the pressure. In these experiments 

 the absolute pressure never exceeded 9'9 metres of mercury. 



I was desirous of working with the new apparatus under far 

 higher pressures, especially under those which gaseous carbonic 

 acid retains in the reservoir of Thilorier's apparatus, in which 

 it has been liquefied. I conducted the experiment as follows. 



The reservoir of Thilorier's apparatus, containing about4kilogs. 

 of liquid carbonic acid, is kept in a large vessel of water at the 

 surrounding temperature^ which maintains it at a virtually con- 

 stant temperature. I assume that the metallic mass of this reser- 

 voir constantly restores the heat absorbed by the volatilization 

 of the liquid acid. A very strong copper tube connects the worm 

 of the large bath with the atmosphere of gaseous carbonic acid 

 of the reservoir. The calorimeter is arranged exactly as it was 

 for the experiments on atmospheric air; it is furnished with the 

 same thermometers. A continuous and perfectly regular agita- 

 tion mixes the layers of water of the calorimeter and those of the 

 vessel which contains the large worm. 



