6:42 ProL J. r. Kuenen on the 



develops out o£ the main curve near the critical point of 

 ethane ; at this moment a new critical point appears (C in 

 the p-t figure), the top layer in the tube divides into a vapour 

 and a liquid and the three-phase equilibrium, represented in 

 the V-.V diagram by a triangle, begins. The critical point of 

 this curve aj)proaches and finally coincides with the critical 

 point of ethane, while the three-phase triangle continues 

 down to the lowest temperature which was tried, viz. — 78° C. 



With ethyl- and the other alcohols the original critical 

 point remains near its normal position on the ethane side of 

 the saturation-curve ; after the subsidiary curve has made its 

 appearance the two phases which lie on either side of the 

 first critical point begin to approach each other nntil they 

 coincide ; at this moment the three-phase triangle and the 

 original critical point disappear, i. e. the lower critical point 

 (see above) is reached. The second critical point continues 

 its course until it reaches the ethane axis at the critical point 

 of this substance ; below this temperature nothing remains 

 but the ordinary vapour-liquid saturation-curve. 



It follow^s immediately from the above results ihat methyl- 

 alcohol and ethane mix completely by pressure, but at the 

 lower temperatures the pressures required become enormous. 



It is possible up to a certain point to produce the saturation- 

 curves in the v-.t diagram through points of intersection with 

 other saturation- curves into those regions where the metastable 

 and unstable conditions are represented^ and it follows thcit 

 the critical curves may also be considered beyond points of 

 intersection with three-phase curves. For a general discussion 

 of this question and of the special features of those curves in 

 the cases before us, we must refer to van der Waals^ researches 

 in the second volume of his treatise on the continuity of the 

 fluid states of matter *, and to a paper by the present writer 

 containing a criticism of some of van der Waals^ views f. 



In all probability mixtures like those of ether and water, 

 sulphur dioxide and water, and others would be found to 

 behave in a manner analogous to ethane and methyl-alcohol 

 if it were possible to investigate them in the critical region, 

 but the action of water on glass at high temperatures has 

 prevented this so far. 



b. ProiMne and Methyl-cdcoJioI. 

 The propane was prepared from propyl iodide and alcohol 

 by means of the zinc-copper couple; it was purified with 



* Van der Waals, Die Contimiitdt des gasformigen imd Jiussigen 

 ZiUstandes, II. Teil, 1900. Earth, Leipzig ; especially p. ] 75 sq. 



t Kuenen, Kon. Akad. van Wet, Amst.y Proceedings, September 1902. 

 Comp. van der Waaly, ibid. October 1902. 



