4()o 



for 30 hoLus, then shaken with a siilpliurie acid-nitric acid mixture, 

 washed three times with a solution of potassium hydroxide, four 

 times witli water, dried on potassium hydroxide, and then fractionated. 

 Repeated fractionation, the last time on phosphorus pen toxide yielded 

 a large fraction, which distilled over within a range of 0°05. Boiling 

 point 69.0°. For the hexane purified in this way we found : 



tk = 234.6 ; Pk = 30.15 . 



The range of pressure for isothermal condensation, determined 

 about 10 degrees lielow the critical temperature, amounted to from 

 0.1 to 0.2 atmosphere. 



By means of this hexane the critical endpoint was determined 

 with a pretty considerable quantity of water. (47 mol. 7o H,0). 

 This experiment yielded : 



tk = 222,05 ; Pi = 52,05. 



These values ditfer but little from those which were obtained 

 with the impure hexane. So the stable part of the plaitpoint curve 

 on the hexane side extends over a range of 21,9 atm. and 12°,55. 



3. In order to investigate the mixtures with a great quantity 

 of hexane, I have, starting from pure hexane, prepared mixtures 

 with increasing quantity of water, till 1 reached the critical 

 endpoint. Of these mixtures I have determined the initial and the 

 final condensations of the hexane layer. I have had to relinquish 

 the thought of a determination of the disappearance or appear- 

 ance of the waterlayer here as in my in\'estigation of the 

 system ether-water, as a slight quantity of water again becomes 

 invisible here. Besides, we could dispense with these determinations 

 as well now as on the former occasion, as their knowledge is 

 not required for an insight into the phenomena. For if there is no 

 layer rich in water by the side of the vapour and the liquid 

 i-ich in hexane the pressure deviates from the three-phase pres- 

 sure ; if thei-e is one, the pressure gets on the three-phase line 

 which is equal for all the mixtures, and reversely from the fact 

 that the found pressure deviates or does not deviate from the three- 

 phase line, determined with excess of water, we may conclude 

 whether we have to do with a two-phase or with a three-phase 

 equilibrium. Besides, in the observation of one or more points of 

 the three-phase curve, which was possible for almost all the mix- 

 tures if oidy the temperature be low enough, I had a criterion of 

 the purity of the mixtures The observations of these three-phase 

 pressures have bee;i given in the subjoined table 1, and deviate 



