270 M. V. Regnault on the Elastic Forces of Vapours 



ciple, to experimental verification, we must know, — I. the total 

 amount of heat contained in different clastic fluids at a certain 

 state of temperature and pressure ; II. the relations which exist 

 between the temperature and pressure for the same volume of 

 these different fluids. The knowledge of these elements is par- 

 ticularly important in the case of readily condensable vapours, 

 which are still the only elastic fluids employed in engines. 



In my preceding memoirs, which compose the twenty-first 

 volume of the Memoir es de VAcademie des Sciences , I have 

 published the results of my experiments on the elastic force of 

 aqueous vapour at saturation at different temperatures, and on the 

 total quantities of heat which this vapour at saturation possesses 

 imder different pressures *. In memoirs since presented to the 

 Academy, which will shortly be published in extenso in its 

 Memoir esy I have given the capacity for heat under a constant 

 pressure of a great number of permanent gases and super-heated 

 vapours, as well as the calorific changes undergone by perma- 

 nent elastic fluids during their expansion effected under certain 

 conditions. 



I now propose to bring before the Academy some experiments 

 which I have made on the elastic force, at different temperatures, 

 of saturated vapours other than that of water. I shall add 

 the results of numerous experiments which I have made in 

 studying the phsenomenon of vaporization in vacuo and in gases ; 

 a phsenomenon on which science as yet possesses but very vague 

 notions, deduced from a small number of experiments which are 

 in themselves very inconclusive. 



Although the greater part of these experiments were executed 

 between 1843 and 1850, I had proposed to defer their publica- 

 tion still longer, in the hope that I might be able to complete 

 them. But many physicists being now occupied upon the same 

 subject, I am compelled to give at all events a brief statement 

 of the results at which I have now arrived. I shall divide this 

 note into five parts. 



The first will include the results which I have obtained regard- 

 ing the elastic forces of vapours at saturation furnished by a 

 certain number of liquids, selected amongst those most easily 

 obtained in a state of purity, in large quantity and at a price 

 which does not preclude their employment in machinery. 



In the second part I shall treat of the elastic forces of saline 

 solutions, and of the application which may be made of them in 

 the study of various questions in physics and molecular chemistry. 



The third will include the phsenomena of the vaporization of 

 liquids in gases. 



The fourth will contain the results of my experiments on the 

 * [See Taylor's Scientific Memoirs, vol. iv. p. 559.] 



