835 



I have shown in the cited paper that the conclusion that the 

 three-phase mixture will expel water througii a niembrane permeable 

 to water, is reallj correct, and that probably mutatis mutandis the 

 opposite thing will apply to hexane. Tiie error in the above reasoning 

 lies therefore only in the very last conclusion. 1 have pointed out 

 loc. cit. that it is, indeed, possible that two liquids, each under its 

 own vapour pressure, mix to a three-phase mixture that possesses 

 the property to get unmixed again into the pure components through 

 semi-permeable membranes; that this is not in contradiction with 

 the second law of thermodynamics, but that on the contrary this 

 jihenomenon will I)e tVequently met with in my opinion, also for 

 systems which do not present the special behaviour mentioned at the 

 head of this paper. Thus solutions of gases which are but sparingly 

 soluble in water will certainly expel water, when they are osmotic- 

 ally brought in contact with pure water of the saturate tension. The 

 observed phenomenon is therefore not in contlict with our theoretical 

 considerations. 



2. To get an answer to the question whether the system hexane- 

 water presents an exceptional behaviour in the appearance of a 

 three-phase pressure which is greater than the sum of the vapour 

 tensions of the components, I have investigated a number of other 

 systems in the hope of tindiug the remarkable phenomenon there too. 

 First of all I have chosen the system pentane-watei-. The pentane 

 wdiich I had at my disposal, was however Kahlbaum's "normal 

 pentane", which is no pure normal pentane, but a mixture of iiormal 

 and isopentane, wdiich can only be separated with great loss of 

 substance and time, as the boiling-points of the two substances lie 

 near room-temperature, and differ only little (slightly more than 

 8 degrees). This slight difïerence of boiling-point involves that the 

 pentane mixture behaves pi'etty well as a pure simple substance; 

 the isothermal pressure ranges for condensation are slight. I have 

 therefoie given up the separation of the two pentanes, and compared 

 the vapour tensions of the pentane mixture and of pure water with 

 the three-phase tension of a pentane-water mixture. It is clear that 

 both the pentane mixture and the three-phase mixture must possess 

 a tension dependent on the \olume at constant temperature, but 

 also the three-phase tension appeared to be only little dependent on 

 the volume. To execute this comparison of the pressures as exactly 

 as possible 1 have determined the pressures for tinal condensation 

 and for about equal volumes of gas and liquids both of the pentane 

 mixture and of the three-phase mixture. 



