217 



still remains wholly outside the scope of mechanical explanation. 



More and rigorously systematical observations and experiments 

 must be made, before the required insight into this problem can be 

 said to be obtained. 



7. Fission of Racemoids by Combination with optically active 

 Substances. 



As a rule the method of fission dealt with in the preceding para- 

 graphs, does not lead to the desired result, because for some reason 

 or other, circumstances do not appear favorable for spontaneous 

 fission. In such cases a second, and from a practical standpoint, the 

 most important method of separation, also found by Pasteur, 

 is made use of. It is by this method that most substances which may 

 occur in two non-superposable mirror- images, have up till now, 

 been resolved into their components. 



The principle on which this method is founded, is, that when 

 two stereometrical arrangements which are non-superposable mirror- 

 inages A and A' of each other, are combined in a corresponding 

 way with another stereometrical complex /, being also different 

 from its mirror-image /', the two figures Af and A'f thus produced 

 will no longer be mirror-images of each other. 



The truth of this can be easily demonstrated; for if Af be reflected 

 in a mirror, it is changed into its mirror-image A'f. This figure 

 A'f, however, is certainly different from A'f, because /and /'are 

 non-superposable mirror-images of each other. Therefore, Af and 

 A'f can never be mirror-images of each other, unless / and f be con- 

 gruent, which, however, is not the case. 



If instead of /, we had used its mirror-image /', we should have 

 obtained the complexes Af and A 'f ; of course, these again will not be 

 each other's mirror-images. But A'f' and Af, and in the same way 

 A'f and Af, are truly two pairs of such mirror-images. As we shall 

 see, this last fact can be made use of for obtaining both antipodes 

 of a racemoid by the same method of fission. 



All right and left-handed isomerides have identical scalar pro- 

 perties, and also the same chemical constants. Thus they have the 

 same solubility in the same solvent, identical melting-, and boiling- 

 points, the same affinity-constants in their reactions with optically 

 inactive substances, the same densities, etc. Substances which are 

 not related as mirror-images, have, however, different solubilities 

 under similar circumstances. It will, therefore, be possible to separate 

 them by fractional crystallisation; thus e.g. Af and A'f, or Af and 



