Physics. — "Contribution to the research of liquid crystals. II. 

 The influence of the temperature on the extinction; further 

 experiments upon the influence of the magnetic field.'" By 

 Dr. W. J. H. Moll and Prof. Dr. L. S. Ornstein. (Commu- 

 nicated by Prof. Julius). 



(Communicated in the meeting of February 24, 1917). 



In the further research of the liquid crystals, the results of 

 which we intend to communicate hereafter, the same method as 

 described in a former communication was used again. (These 

 Proc. XIX p. 1315). The method was improved in a few respects 

 only, the principal change being that a copper-disk with a 

 central hole of about three millimeter diameter takes the place 

 of the glass-pieces in the oven. The substance is put between two 

 object-glasses, which lie on the disk. In this way we get the 

 advantage that the matter does not come into contact with the 

 copper, and that it is possible to examine several substances succes- 

 sively with the same oven. Though the narrow hole in the copper 

 diminishes the intensity of the image on the thermo-pile it secures 

 an absolutely homogeneous heating of the very small part of the 

 matter under observation. 



§ J . IVie in/iuence of the temperature on the extinction. 



The extinction in its dependence on the temperature was measured 

 in the following way. The matter that has been melted before 

 between two glasses and congealed afterwards, is put on the oven 

 the temperature of which is below the melting-point. Then such 

 a value is given to the heating current, that in the long the 

 melting to isotropic-liquid will be reached. Then if after some time 

 the substance has been molten, the current of heating is put off 

 (or diminished) so that the substance gets liquid crystalline again 

 and congeales afterwards. In the method described before the 

 extinction is registered during this rising and falling of temperature. 

 There were examined p-azoxy-anisol, p-azoxy-phenetol, anisaldazine 

 and p-azoxy-benzoeacid-aethylester. In fig. 1 and 2 the curves of 

 extinction are reproduced of two of these substances ^). 



1) p-azoxy-phenetol and anisaldazine produced melting-curves of the same charac- 

 ter as p-azoxy-anisol. 



