273 



in full agreement with the apparently holohedral symmetry of the 

 crystals, as inferred from their geometrical form. Groth points l ) 

 to the desirability of confirming this result by etching two adjacent 

 pyramid-faces. In any case, if hemihedrism here is also assumed, 

 it appears to be so feebly expressed, that no convincing proof 

 of its existence could hitherto be given; the optical rotation in 

 chloroform-solution, however, amounts here to: \a] D = + 63, 1. 

 This appreciable rotation surely bears no relation to the imper- 

 ceptible degree of hemihedral development. 



In an analogous way it was found 3 ) that cholestenon: C 27 # 44 0, 

 (nipt: 78 C.), prepared by Windaus, crystallises each time from 

 ethylacetate in the prismatic class of the monoclinic system. Here 

 also there can be no doubt about the apparent holohedrism of the 

 crystal- form. It is possible that in molecules of such a magnitude 

 the influence of the asymmetric carbon-atom is almost effaced, and 

 that, therefore, its presence is by no means revealed in the crystalline 

 form of the compound. 



28. With respect to the manifestation of hemihedrism, the 

 question may be asked, whether the two factors differentiated in 

 the above, namely: the influence of the stereometrical arrangement 

 on the one side, and that of the chemical inequality of the sub- 

 stitutes on the other side, have not a very different importance 

 in causing the occurrence of crystallographical hemihedrism and 

 that of optical activity respectively? 



Now the study of compounds which contain partially asym- 

 metric atoms (p. 244) might give some insight into this question. 



Investigations were, therefore, made in this laboratory into the 

 optical and crystallonomical properties of the salts of the trivalent 

 triethylene-diamine-cobalii-ion : [Co(Eine)^} , first prepared and 

 studied by Werner. Indeed, all substituents round the central 

 Co-atom are identical here: it will thus be only the influence of 

 the non-superposable configuration, that would be expressed in 

 the properties of the derivatives. We get rid here, therefore, of the 

 influence, which is in all these cases combined with the chemical 

 differences between the substitutes, as we have already explained 

 in dealing with the rotatory power of these substances. 



Notwithstanding the enormous rotation which these optically 



1) P. Groth, Chemische Krystallographie, III, p. 526, (1910). 



2) F. M. Jaeger, in Groth's Chem. Krystall., Ill, 536, (1910); A. Windaus, 

 Her. d. d. Chem. Ges., 39, 2008, (1906). 



18 



