261 



that arrangement. Onlj in second instance \\\e mass and the rlwrn tea I 

 nature of the central-atom seem to be of intlnence, and more especial- 

 ly in so far as concei-ns the changes of the size of the rotation, when 

 the one kind of central atom is replaced by another isomorphons 

 element. 



It is worth remarking here, that the crystals of the optically - 

 active trl-ethylenediamine-cohalti-, and -rhodium-nitrate hei-e investiga- 

 ted, exhibit sphenoids of opposite algebraic signs in the case of active 

 salts rotating in the same direction: the laevo-%y vAia cobalti-salt 

 manifest the right-imnded sphenoid, while the /aevo-gyn\\e rhodium- 

 nitrate exhibits precisely the left-handed form. 



On the surface of it, it may seem to be correct to consider this 

 fact as an argument in favour of Werner's view about the anti- 

 logous configurations of cobalti- and rhodium-saUs of the same 

 rotation-direction. But this conclusion must appear completely un- 

 justified, as soon as the facts hitherto stated are" taken into account, 

 — scanty as these facts for the rest may be at this moment. The 

 question : in how far is there any rational connection between the 

 external appearance of form of a crystal and the stereometrical con- 

 iiguration of its molecules? — seems to be quite unanswerable at 

 the present moment, because this external appearance of the crystal, 

 depending on a great number of accidental circumstances during the 

 process of crystallisation, is a very capricious and variable phenomenon. 

 It is, for instance, well known, that the K-, (NH^)-, Rb-, and Co-dextro- 

 bitartrates, all undoubtedly having the same stereometrical configuration 

 (namely : of d-tartaric acid), may exhibit preferentially the forms |111| 

 or |1'I1| in a predominant way, if certain salts (e.g. sodium-citrate) 

 be purposely added to their solutions, or if circumstances during 

 the crystallisation be arbitrarily varied. In the case of the complex 

 salts under consideration, which, moreover, appear to vary their 

 outward appearance to a most intense degree under circumstances 

 only slightly altered, such arguments, based only on this external 

 form, can hardly have any value at all for judging the internal 

 structure of their molecules, unless full certainty is obtained that the 

 salts compared are deposited under exactly the same circumstances, 

 as e.g. this may be assumed in cases, where racemoids are separated 

 by so-called spontaneous crystallisation, the two kinds of crystals here 

 being deposited simultaneously from the same mother-liquid. 



At this moment the only conclusion can be, that the same con- 

 figuration must be attributed to the de.vtro-, respectively laevo-gyvate 

 complex-salts of cobalt and rhodiuu}, when they exhibit a rotation 

 of the same direction. 



