838 



tensions according to Regnaui.t, which deviate little from the sum 

 of the vapour tensions of the pure substances. Regnault even asserted 

 that the tension of carbon tetrachloride-water mixtures is somewhat 

 hio-her than the sum, and thought he had to ascribe this to slight 

 contaminations; Gernez has shown later that the three-phase tension 

 is really slightly smaller than the sum of the vapour tensions, which 

 is therefore in harmony with the theory. I have now tried to inves- 

 tigate the two systems at higher pressure ; I haxe, however, not 

 succeeded in doing so with the system carbontetrachloride-water, as 

 the components act on each other at higher temperatures. The inves- 

 tigation is possible for the system benzene-water, and also this system 

 appeared really to furnish an example of the remarkable phenomenon. 

 Benzene free from thiophene (negative isatine reaction) was distilled 

 from phosphorus pentoxide; the boiling point under normal pressure 

 was 80°.2, and was therefore in perfect concordance with the value 

 given by Young. The vapour tension line of this benzene was deter- 

 mined, and then the three-phase tensions of a benzene-water mixture 

 were measured and compared with the vapour pressure line of water, 

 which was also determined by the aid of the same thermometers. 

 To avoid corrections I have measured the three pressure values 



TABLE IV. 



