M. V. Regnault on the Elastic Forces of Vapours 



Third Series. 

 Elastic force of the air at 0° C, 706-91 millims. 



It will be observed that this series presents still greater differ- 

 ences than the preceding, but this arises from the maximum 

 determinations only having been inserted. The observations at 

 the same temperature were made at intervals of half an hour. 



It would take up too much time to indicate here the different 

 circumstances under which the partial determinations for these 

 three series were effected, — these circumstances exercise a great 

 influence upon the values found for the elastic force of the vapour. 

 I shall content myself with saying, that very often a determina- 

 tion was not made until after the bath had been kept for several 

 hours at a constant temperature and in continual agitation. In 

 other cases the bath was allowed to cool very slowly, keeping it 

 constantly agitated, and the observations were made during this 

 period of descent in the temperature, which was very favourable 

 to saturation. 



The greatest value was obtained for the elastic force at a given 

 temperature, by suddenly cooling the balloon so as to induce an 

 abundant condensation of the vapour, and then rapidly re-esta- 

 blishing the original temperature. By making observations 

 afterwards every quarter of an hour, the temperature of the bath 

 remaining exactly the same, the elastic force will be found to 

 diminish gradually during several hours. If, on the contrary, 

 the temperature of the bath be raised gradually up to the sta- 

 tionary point, and observations be then made every quarter of 

 an hour, it will be seen that the tension of the vapour constantly 

 increases, without, however, attaining, not only the tension 

 which it presents in vacuo, but even that observed at the same 

 temperature in the experiments by refrigeration immediately 

 after the condensation of the excess of vapour. I shall give the 

 explanation of these facts hereafter. 



