837 



The values for the vapour tension of water have not been derix ed 

 from earUer observations, but determined by myself to prexcnt an 

 eventual deviation of the thermometer from vitiating the comparison. 

 All the observations have been carried out; with a normal thermo- 

 meter, and with an Anschützthermometer vcrilied by the boiling 

 point of pui-e aniline. 



We draw the conclusion from the last column of table 'A that 

 the three-i)hase tension is again greater than the sum of the vapour 

 tensions of the pentane mixture aji<l of pure water. The difference 

 appears again to be greatest at the critical endpoint - in all the 

 tables the critical values are piinted in bold type — ; with decrease 

 of temperature the difference decreases rapidly, and according to 

 the theory it must reverse its sign at temperatures where the saturate 

 vapours follow the gas laws. 



The abo\'e described example shows therefore again a case of 

 very high three-phase pressure. Though these e.xpei-iments would 

 have to be repeated with the pure substances to get perfect certainty 

 about the behaviour of the binary systems, the conclusion that the 

 pentanes and hexane behave analogously with respect to water, 

 seems yet sufticiently certain to me. Also the relative situation of 

 the critical end point with respect to the critical points of tiie com- 

 ponents is the same as for the hexane-water mixtures. 



Finally 1 will still point out that the abo\e only i)rovcs that there 

 exists a pentane-water mixture that possesses the repeatedly men- 

 tioned remarkable property, and this suffices also for my purpose; 

 other proportions of pentane mixture and water will probably give 

 rise to some change in the three-phase tensions because the pentane 

 mixture is not a simple substance; for the solubilities of the two 

 pentanes in water will probably not be in the same proportion as 

 the quantities of the pentanes in the pentane mixture ; the difference 

 in the fifth column can therefore undergo some modification for 

 another ratio of the two "components". 



§ 3. The experiments of § 2 confirming my supposition that the 

 abnormal value of the three-phase pressure would be a phenomenon 

 of frequent occurrence, 1 thought I had a great chance to find the 

 same peculiarity also for other binary systems. I have therefore 

 looked for binary systems of which it was known that for low 

 temperatures the threephase pressure lies higher than the vapour 

 tensions of the pure components separately and is about equal to 

 the sum. Dr. Büchner drew my attention to the systems carbon 

 tetrachloride- water and benzene-water, which possess three-phase 



