192 Messrs. J. P. Kuenen and W. Gr. Robson on 



all observation impossible ; and also the pressures required to 

 reach the critical points are very high, the critical pressure of 

 water itself being 190 atmospheres. 



For further experiments our attention was directed to 

 combinations of hydrocarbons and alcohols. In order to get 

 the phenomena for which we were looking within easy reach 

 of temperature we selected ethane, and we have combined 

 this substance with a number of the lower alcohols. 



A compression-tube was filled with ethane prepared from 

 sodium acetate by electrolysis, and purified in the manner 

 described in a former paper by one of us*. The substance to 

 be introduced into the ethane was poured on the top of some 

 mercury in a beaker, and boiled for some time in order to 

 expel dissolved air. The beaker was then quickly cooled, 

 the tube placed in the mercury, and by expelling some of the 

 ethane and lifting the tube a few drops of the liquid were 

 readily introduced without any chance of air getting in. 



The methyl and ethyl alcohols were dried by boiling with 

 finely powdered calcium carbide. After distillation the alco- 

 hols were treated with anhydrous copper sulphate, and finally, 

 just before use, they were distilled from a flask with Wurtz 

 head. The boiling-points, which were quite constant during 

 this last distillation, were for methyl alcohol 64°*49 0. at 

 760 mm., and for ethyl alcohol 78°*15 C. at 760 mm. 



The propyl alcohol was similarly treated with calcium 

 carbide and copper sulphate. It was then fractionated, a 

 long still-head containing platinum-gauze being used. The 

 portion boiling at 96° - 65 (at 760 mm.) was used for the 

 mixtures. The amyl alcohol was purified by repeated dis- 

 tillation, the distilling-flask being fitted with the deflegmator 

 described by Young and Thomas. The boiling-point of the 

 portion used for making the mixtures was 129 0- 23-129 0, 28 C. 

 at 760 mm. 



The isopropyl and butyl alcohols were used as they came 

 from Kahlbaum. Their boiling-points were respectively 

 80°-2-81°'3 C. and 113°-6-116°-8 C. (both at 760 mm.). 



The ethane was first tested. The values of the vapour- 

 pressures and critical constants (Table II.) agree with those 

 obtained on former occasions, and the small increase t of 

 pressure required for the total liquefaction (pb—p a ) shows 

 that the ethane was very pure. 



* Kuenen, Zeitschrift phys. Chem. xxiv. p. 694 ; Phil. 

 1897, p. 175. 



