260 



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? 



Now the study of compounds which contain partially asym- 

 metric atoms (p. 235) might give some insight into the question. 



Investigations were therefore made into the optical and crys- 

 tallonomical properties of the salts of the trivalent tri-ethylene- 

 diamine-cobalti-ion: {Co(Eine) s }' ' ', first prepared and studied 

 by Werner. Here indeed all substituents round the central 

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

 non-superposable configuration, that would be expressed in 'the 

 properties of the derivatives. Therefore we get rid of the influence 

 which is in all these cases combined with the differences between 

 the substitutes, as we have already explained in dealing with the 

 rotatory power of these substances. 



Notwithstanding the enormous rotation these optically active 

 salts exhibit, it was now found *) that, although in some cases 

 enantiomorphism was really manifested, this was however reduced 

 in several instances to an undetectably feeble degree. 



The d- and l-bromides: {Co(Eine) 3 }Br 3 -+- 2H Z 0, did not show 

 under any circumstances of crystallisation, the slightest indication 

 of hemihedrism; while in the case of the iodides: [Co(Eine) 3 }I s 

 + H Z 0, and of the rhodanides: [Co(Eine) 3 }(SCN) 3 , even the 

 corrosion-figures obtained were in full accordance with holohedral 

 symmetry, instead of being a proof of hemihedrism. If enantio- 

 morphism be present here, it is evidently manifested to such an 

 extremely slight degree that it is not detectable by any crystallo- 

 graphical method at hand. 



From this it appears evident that in this case there is surely 

 no rational proportion present between the enormous optical 

 activity of the molecules on the one hand, and the undetectable 

 hemihedrism on the other. The cause of this can only be the 

 equality of the dissymmetrically arranged substitutes : [C Z H^(NH 2 ) 2 ]. 



From this it becomes highly probable that, while the optical 



J) F. M. Jaeger, Proceed. Kon. Akad. v. Wet. Amsterdam. Vol. 18. 52, 56, 

 63, 65, 67. (1915); Zeits. f. Kryst. u. Miner. 55. 209. (1915); Chemisch Weekblad 

 14. 718727. (1917). 



