in vacuo and in Gases. 23 



I have since made similar experiments upon two volatile 

 liquids which solidified at a readily obtainable temperature, 

 whilst still presenting a tension sufficiently strong to be mea- 

 sured with precision. These are hydrocarburet of bromine and 

 benzine. 



We may therefore admit, as proved by experiment, that the 

 molecular forces ivhich determine the solidification of a substance 

 exert no sensible influence upon the tension of its vapour in 

 vacuo. 



But I attached particular interest to similar researches made 

 upon monohydrated acetic acid. This acid is solid up to a tern-, 

 perature of +16° C; but when once liquefied, its congelation 

 presents great difficulty. It may be cooled sometimes to —8° of 

 -!-10° C. without solidifying, even when the flask containing it 

 is briskly shaken. The solidification takes place immediately 

 when the surface of the liquid is touched with a glass point, or 

 when a crystal of solid acid is thrown into it. Monohydrated 

 acetic acid consequently presented me with an instance of a 

 substance, the tensions of the vapour emitted by which, both in 

 a solid and liquid state, might be determined through a consi- 

 derable extent of the thermometric scale. 



The acetic acid employed in the two first series of experiments 

 was taken from a mass of 1 kilogramme, which to all appearance 

 solidified completely; but, for more certainty, only the last 

 solid fragments which remained after the liquefaction of the 

 greater part of it, were taken. 



The acid remained liquid through all these temperatures. To 

 make it crystallize, the water was taken out of the trough and 

 the balloon was made to vibrate strongly, but without success. 

 These vibrations at last fractured the mastic which established 

 the communication with the manometer, and the experiment 

 was obliged to be stopped. 



