211 



P AZOXY ANISOL 



Rising Temperature Fallinq Temperature 



Fig. 1. 



P A20XYBENZ0ËZURE AETHYLESTER 



Rising Temperature Falling Temperature 



Fig. 2. . 



When we consider these curves of extinction, the fact is obvious 

 that the extinction in the liquid-crystalline condition, proceeding 

 from melting of the solid phase ("ex-solid") is different from the 

 liquid-crystalline condition formed by cooling of the isotropic liquid 

 ("ex-liquid"). This different extinction is accompanied by an abso- 

 lutely different aspect. 



These differences are mostly conspicuous in the case of p-azoxy- 

 benzoe-acid-aethylester. With this substance the ex-solid condition 

 is milky-opalescent, the ex-liquid grainy -opalescent, and when the 

 preparation is heated the first condition always changes into the 

 other at the same temperature. In the curve that transition 

 appears by a leap-wise increase of the extinction. In the cooling- 

 branch of the extinction-curve we only found an indication that 

 at the sudden transition from liquid into liquid-crystal during a 

 short period the ex-solid state might inconstantly have existed as 

 instable, however by cooling very quickly we succeeded in obtain- 

 ing durably the ex-solid condition from the liquid state. 



With the three other substances examined, also a very obvious 

 difference in extinction between the ex-liquid state and the ex-solid 

 state (vid. fig. 1) shows itself, but contrary to p-azoxy-benzoe-acid 

 aethylester, with these three substances of both liquid-crystal con- 

 ditions the ex-liquid one is the most opaque. 



Another particularity of the extinction-curves are the different 

 bag-shaped drops. 



The drops at the transition from liquid-crystal into isotropic-liquid 

 and the reverse are not real, i.e. they have no meaning for the ex- 

 tinction as such. They are caused by the melting (resp. the getting 

 turbid) not occurring simultaneously in all parts of the substance. 



