1056 



there is no unmixing in one system, whereas metastable unmixing 

 is assumed to take place in the other case, lies in the shape of (he 

 critical line in the stable region, in one case it is possible to join 

 the two stable parts of the critical line by a curve with a regular, 

 continuous course; in the other case the critical line would have to 

 present a peculiarly steep course with a strongly pronounced maxi- 

 mum. This latter is deemed less probable, and can also be explained 

 in a plausible way by the assumption that the critical line has two 

 cusps. I will, however, point out that also metastable unmixing in 

 the unstable region is possible for the system ether-anthraciuiTione, 

 and that for the system diphenylamine-carbonic acid the metastable 

 unmixing has not been proved, but has only been rendered probable. 

 Hence a sharp classification of these types of binary systems i8 

 impossible. 



A similar case is offered by the system sulphui-etted hydrogen- 

 ammoniac '). In this investigation I have theoretically examined what 

 phenomena occur in the stable region when a critical line intersects 

 tlie three phase line VLG\ it was not necessary to consider meta- 

 stable unmixing in that case, because it is clear that all the pheno- 

 mena in the stable region can be derived from a system without 

 unmixing. When now the ex|)eiiinental results of this research ai-e 

 examined, it appeal's tlmt the critical line, when it does not possess 

 cusps in the unstable rigion, must have a very steep course, just as 

 that in the system di|>henylamiue-carb()nic acid. (I have expressed 

 this graphically in my Thesis for the Doctorate). On the same grounds 

 that lead us for the system di|)henylamine carbonic acid to the con- 

 clusion of the existence of two cusps in the critical line, the system 

 sulphuretted hydrogen-ammoniac may be counted among the systems 

 with unmixing. As in my opinion this system would then be the 

 most elaborately examijied example of such systems, in which besides 

 unmixing also a compound occurs, 1 have indicated the second case 

 discussed by Büchner as the type sulphuretted hydrogen-ammoniac 

 in the cited paper. 



J Decembei' 1918. Delft. Teclmicdl University. 



1) Dissertatie Amsterdam 1909. Zeitschr f. physik. Ghem. 71. 214 and 671 (1910). 



