670 



monotropv into enarïtlotropy can be explained in a simple way 

 by means of the theory of allotiopy. 



Now the question rises where the transition line eo^ starts from. 

 A possibility has been given in tig. 3, from which follows that the 

 transition line starts in a metastable point of transition under the 

 vapour pressure 0^. This is the view to which lead Ostwald's ^) and 

 Schaum's '^) assumptions on the existence of a metastable point of 

 transition under vapour pressure '). Now it is the question whetlier 

 this is tiie only possibility. It has been pointed out just now that 

 the metastable coexistence is confined between the two mixed crystal 

 series md and pe (see Fig. 4), and as the metastable point of 

 transition arises by intersection of the internal equilibrium line of 

 the solid phases with the above mentioned mixed crystal lines, it is 

 clear that it may happen that this intersection does* e.g. not exist 

 under the vapour pressure. 



If in such a case enantiotropy does occur at higher pressure, the 

 transition line will proceed in a metastable way up to that pressure 

 and that temperature at which for the tirst time an intersection 

 between binary mixed crystal lines and internal equilibrium lines 

 takes place, and there the transition line will then suddenly terminate 



in a point that indicates the 

 limit of existence of the 

 coexistence between two solid 

 phases which are in internal 

 equilibrium, as fig. 6 shows. 

 Now it is clear that the 

 main cause of the transition 

 from monotropy to enantio- 

 tropj can find its origin 

 exclusively in this that the 

 situation of the pseudo figure 

 varies more greatly with the 

 pressure than that of the 

 unary figure, but in by far 

 the most cases, namel}' there 

 y where the pseudo components 



Fig. 6. are different in molecular 



sizes, the situation of the pseudo figure will vary less with the 



1) Z. f. phys. Chem. 22, 313 (1897). 



2) Lieb. Ann. 300, 215. 



^) Cf. also Bakhuis Roozeboom, "Die Heterogenen Gleicbgewichte" I, 187. 



