C 619 ) 



in ether -j- alcohol, and the homogeneous mixed crystals obtained 

 on slow evaporation were individually iinestigated crystallographic- 

 ally and then their melting point was taken, namely the temperature 

 at which the last particle of solid matter disappears in the surrounding 

 fused mass. If one may assume that this last solid particle, in each 

 of the cases investigated, is really in stable equilibrium in regard 

 to the fused mass, the temperature thus found, by comparison with 

 the already found upper branch, indicates the molecule-percentage 

 composition of the mixed crystal under investigation. 



If we take little of the i?r-esler and much of the (7/-ester, we 

 obtain from the alcoholic solution momclinic mixed crystals which 

 possess quite the form and angular values of monoclinic C/-ester 

 itself. Of such crystals the melting point never exceeded 467,*'. If 

 the proportion of the components is reversed mixed crystals of a 

 rhombic form are de[»osited quite analogous to the i??'-ester. These 

 crystals gave melting i)oints from 797,° down to 47^ ; but not lower. 



Assuming that the melting point of the end terms of the mono- 

 clinic series does not ditfer practically from 47°, it then looks as 

 if rhombic mixed phases ma,y exist which, at 47° as transition tem- 

 perature, attach themselves immediately to the monoclinic terms. I 

 have found, however, that rhombic mixed crystals with various melt- 

 ing points kept together in a closed tube for four months become 

 turbid and partially opaque with a rough surface as soon as their 

 melting point falls heloin 65°. It is also remarkable that the rhombic 

 mixed phases of this kind are more and more badly formed and curve- 

 planed, and that they become more distorted, as if existing in a kind of 

 enforced condition, when their composition begins to ditfer from tliat at 

 65° towards the monoclinic side. It seems to me that when accepting 

 the above hypothesis, all rhombic mixed phases below 65° represent 

 metastable conditions, which, in tlie solid state, are very slowly 

 broken up, to be partly converted into monoclinic terms. 



That is to say the melting figure takes schematically the form of 

 fig. 9 ; the said metastable conditions are then points situated on the 

 extended part of the lower branch to the right, which indicates the 

 composition of the rhombic mixed crystals coexisting with the fused 

 mass. The stable hiatus in the mixing series then extends from 187„ 

 to 607o of the i?r-compound. 



From all this it follows that in consequence of the very slow 

 conversion of the mixed crystals, no sharp determination of the 

 mixing limits can be made in this manner when less than 607,, 

 Br-estev of monoclinic character is present. 



In the system CZ-ester + /-ester the matter is still more troublesome. 



