Chemistry. — ''On Metastahle Unmixing and the Classification o f 

 Binary Systems.'" By Pi-of. F. E. C. Scheffeh. (Comiiuinicated 

 by Prof. Böeseken). 



(Communicated in the meeting of .lanuary 25, 1919). 



J. Ill the leceiitly published work on systems with (wo liquid 

 phases Büchner discusses in §4 the different spacial figures of systems 

 in which besides two liquid layers there also occur compounds. *) 

 He successively discusses there the systems with quadruple points 

 VL^ L^G ( F==: compound), and those which present analogy in 

 behaviour with the system diphenylamine-carbonic acid, which was 

 closely examined by Büchner. 



In my recently published paper on the phenyl- and tolyl-carba- 

 minic acids') I have pointed out that the systems aniline, resp. 

 toluidine-carbonic acid belong to the categoiy first discussed by 

 Büchner, and that with a suitable choice of the homologues of 

 aniline a transition can appear in the second case discussed by 

 Büchner. The latter I have, however, indicated as the type sidphur- 

 etted hydrogen-ammoniac. In reference to this the following remarks 

 may be made. 



2. In all (he systems in which a three phase line Sfj(T intersects 

 the critical line [)art of the latter is not stable, and if retardations 

 are not possible, it is, therefore, not realizable. This not realizable 

 part of the critical line can be either entirely metastable, or partly 

 metastable, partly unstable. Neither possibility can be demonstrated 

 directly experimentally. 



In the system ether-anthraquinone examined by Smits it has always 

 been assumed up to now (hat the critical line has no cusps, and 

 that, therefore, no unmixing takes place in the unstable region ') ; 

 it has, howevei', been assumed in the system diphenylamine-carbonic 

 acid examined by Büchner that the critical line possesses two cusps 

 in the unstable regioti. In the stable i-egion the two systems exhibit, 

 however, a perfectly analogous behaviour. The reason to assume that 



') Bakhuis Roozbboom, Heterogene Gieicligewichle. II 2. (1918) S. 184. et seq. 



«) These Proceedings. 21. 644. (1919). 



') Bakhuis Roozeboom. Heterogene Gleichgewichte II. 1. (1904). S. 378 et seq. 



