( 794 ) 



in olive-oil is much larger than in the first case and amounts to 

 about lO''. 



Recrjstallisation from petroleum-ether does not alter the properties 

 of a definite crystal species; all preparations, however have the same 

 meltingpoint and a complete identical crystalform. 



We are therefore confronted with the fact that the compound 

 CH(CgH4Cl)3, m. p. 92" occurs, under varying circumstances, in forms 

 which cannot be distinguished by chemical and crystallographical 

 means, but whose optical orientation is very different. Sometimes, 

 the crystals show a positive, sometimes a negative double refraction ; 

 one crystal shows a crossing of the axial planes for diverse colours, 

 another for only a single colour; others again for no colour what- 

 ever, the axial plane then being either {001 j or |010| whilst the 

 dispersion is sometimes : (> ^ v, sometimes ^ <[ v. 



Of course, the possibility is not excluded that exceedingly small 

 traces of foreign impurities cause this change of the so sensitive 

 optical orientation. The result of the investigation of Tri-p-Cldorocar- 

 binol showing its complete isomorphotropic relation to the said deri- 

 vative, renders it not improbable that a trifling admixture of this 

 oxidationproduct is the cause of the phenomenon. 



In accordance with this is the fact, communicated to me privately 

 by Dr. Montagne, that a turbidity of the transparant crystals never 

 occurs with the thin rapidly formed needles, but always with the 

 thick and short crystals of T'ri-p-Chlorotriphenylmethane, obtained by 

 sloiü crystallisation. 



But it is also conceivable that such large molecules as that of 

 Tri-p-Clilorotriphenylmethane might in different circumstances suffer 

 small deviations of their average atomistic configuration, which cannot 

 be demonstrated chemically or crystallographically, but which can 

 be shown optically. 



Of late years numerous investigations have been carried out which 

 must lead to the conclusion, that many properties of crystallised 

 matter such as the growth- and cohesion-phenomena must be con- 

 tributed to the regular molecular aggregation, whereas other ones 

 such as the optical properties would have their origin, at least to a 

 great extent, in the properties of the molecules themselves. This 

 view is strengthened by different observations made with the so-called 

 liquid crystals and doubly-refracting liquids; also by some experi- 

 ments made by Wallerant a.o. on the optical behaviour of deformed 

 solid crystals. And phenomena like those observed here with Tri- 

 p-Chloro-Triphenylmetltane may show that it is possible that the 

 spacial configuration of the chemical molecules is variable within 



