M. Achille Cazin on Internal Work in Gases. 283 



Up to the present time a relation 



pv& = const (18) 



appears to be admitted, such as was established by Laplace and 

 Poisson before the appearance of the thermodynamic theory. In 

 the recent experiments which M. Hirn and myself have made 

 on the expansion of aqueous vapour, the value of ft varied very 

 little, so that we could accept it as constant by attributing 

 the variations to experimental errors. Such is, I believe, the 

 opinion of M. Hirn and M. Zeuner*. I have undertaken some 

 new researches on carbonic acid which may throw some light on 

 this matter. 



§ IV. On the passage of a gas from a reservoir where it is com- 



pressed, into a reservoir which contains a certain quantity of the 



same gas rarefied. 



The following problem, which relates to the experiments de- 

 scribed in the first part of this memoir, can be solved by means 

 of the relations established in the preceding sections.. 



Problem IV. — In a reservoir A, of volume Y v is a certain 

 weight of gas under the pressure p x and at the temperature T 2 . 

 In a second reservoir B, of volume V 2 , is another weight of the 

 same gas, under the pressure^ <j?i and at the same tempera- 

 ture T P These two reservoirs put into communication with one 

 another : to determine the condition of the gas when the disturb- 

 ances have ceased, supposing the sides to be impermeable to heat. 



Denote the weight of gas contained in reservoirs A and B by 

 m v m 2 respectively. It is easy to deduce these values from re- 

 lation (2) when p v p 2) and Tj are known. In fact we may de- 

 duce from this relation the specific volumes v Y and v^ and we 

 shall have 



Vi • v 2 



m ,= — i, m 2 = — *• 

 ...... 'Px. v 2 



Conceive the reservoir B to be of the form of a cylinder, and 

 a piston without mass to be applied against the orifice of reser- 

 voir A, supposed to be at first closed. When this orifice is 

 opened, the gas m x pushes the piston; some whirlings take 

 place on each side of the orifice, whilst the gas ??z 2 receives a 

 pressure which its elastic force balances at each moment. There 

 is one moment when, these whirlings having ceased, the condi- 

 tion of the gas m, is Vj + #, p' } T', and that of the gas m 2 is 

 V 2 — x } p', T". The problem thus stated does not differ, as to 

 the final effect, from that with which we are occupied, although 



* G. Zeuner, Ueber das Verhalten der uberhitztcn und der gemischten 

 Wasserdiimpfe {Civilingenieur, 13 e annee, 1867). . . 



U2 



