347 



taiitomers, are comparatively few as jet, but uiidonbtedl^- their 

 number will increase as the experiment is made more refined. 



It is obvious that a test of the just mentioned conclusion from 

 the theory of allotropy will be most easily carried out in the region 

 of organic chemistry, but on the other hand a test in the region of 

 anorganic chemistry will be, especially for elements, of greater scien- 

 tific interest. 



Accordingly the research is continued both in anorganic and 

 organic domain, and the purpose of this communication is to draw 

 attention to the gigantic field of research which is opened up for 

 us in organic region for a study in this direction. 



B.ANCROFT ') was the first to take into account tlie intluence of the 

 time in the study of systems of organic substances wiiieh can occur 

 in two different forms. In this consideration he came to three cases. 



1. The time element vanishes in consequence of the practically 

 immediate setting in of the (internal) ecpiilibrium. 



2. The setting in of the (internal) equilibrium takes place so 

 slowly that so-called "false equilibria" occur, for which case Bakhuis 

 RoozEBOOM ^) derived ditferent T, A'-figures. 



3. The (internal) equilibrium sets in with such a velocity that 

 the system behaves as a binary one in case of rapid working, as a 

 unary one in case of slow working. 



The substances belonging to the latter group, and their number 

 is undoubtedly enormously great especially in the domain of organic 

 chemistry, yield very satisfactory material of research. 



Bancroft was the first who discovered a pseudo binary system in 

 (Uchlorostilbene examined by Zinckk 'j and explained its behaxiour. 

 Z^^'CKE had discovered that when the form with the highest melting 

 point was kept in molten condition for a long time (200°), there 

 took place a lowering of the point of solidification from 192° to 

 160°, which was to be attributed, as Banckoft stated, to this that 

 the substance had assumed (internal) equilibrium at 200°, in which 

 the molecules of one form had been partially converted to those of 

 the other form. 



Among the organic substances which can occur in ditferent isomer 

 forms, variations of the melting point are met with in very many 

 cases accoi'ding to the literature, which variations must be attributed 

 to a conversion in the direction of the internal equilibrium or to a 

 retardation of the setting in of the internal equilibrium. 



1) Journ phys. Ghem. 2. 143 (1898). 

 S) Z. f. phys. Ghem. 28. 389 (1899). 

 ') Lieb. Ann. 198. 115 (1879). 



