M. Achille Cazin on Internal Work in Gases. 93 



the final pressure p 1 , and op 2 the negative excess of the pressure 

 of the rarefied gas in reservoir B above the same final pressure, 

 the succession of the pressures in each of the reservoirs is repre- 

 sented by curves of the form p^ghie, p 2 g h i e. 



The abscissa of is less than 0*1 second. During this very 

 short period the compressed gas rushes into the reservoir B, 

 compresses the gas in the latter, and establishes equality in the 

 whole of the apparatus. From this moment the pressure common 

 to the two reservoirs increases at first rather rapidly, reaches a 

 maximum in about fourteen seconds, and afterwards decreases 

 very slowly and becomes stationary after two minutes. The final 

 pressure is greater by 14 centimetres at least (sulphuric acid) 

 than the pressure which existed at the moment when the ex- 

 pansion ceased, and less by 3 centims. than the maximum of the 

 variable pressure. 



It is during the period g hi that the mechanical and thermal 

 phenomena which interest us manifest themselves. They are due, 

 at least in part, to the properties of the gas and the action of 

 the sides, which can be disregarded at no part of the whole dura- 

 tion of the phenomenon. But, before seeking to explain the 

 latter, we must increase the number of experiments, and examine 

 attentively the various circumstances which appear likely to 

 exercise an influence either on the magnitude or on the direction 

 of the effects. 



§ V. Influence of the nature of the liquid contained in the mano- 

 meter. 



Most of the experiments relative to the accessory circum- 

 stances have been made since the publication of the earliest re- 

 searches of this series. They have gradually led me to the disco- 

 very of facts described in the preceding paragraph. If in my 

 exposition of these I have not observed their chronological order, 

 it was that I might first establish the experimental method as a 

 whole. The details which follow will, I hope, prove that I have 

 carefully avoided allowing myself to be directed in these re- 

 searches by any preconceived ideas ; and I shall only draw con- 

 clusions after having solved several questions which have succes- 

 sively presented themselves to my mind. 



In order to examine whether the nature of the liquid had any 

 influence, two series of experiments were made under the same 

 conditions, with the same value of 6, — the manometer Q, for ex- 

 ample, first containing sulphuric acid and then water. In the 

 latter case the interior level was covered with a thin layer of tur- 

 pentine to avoid the influence of the vapour of the water. For 

 the reservoir B, in these two series, the glass vessel was used. 



