270 



ly related, hemihedral crystalforms in the case of both tartaric 

 acids, and since he confirmed his original view by the study of a 

 great number of their crystallised derivatives, the question as to 

 the necessary mutual dependence of both phenomena has been 

 discussed several times by different authors. 



While there seemed to be no justifiable doubt about the validity 

 of Pasteur's view that molecular dissymmetry is always the cause 

 of optical activity in the sense employed in the foregoing, serious 

 doubt has arisen in later times as to the correctness of Pasteur's 

 conclusion that molecular dissymmetry is necessarily connected 

 with the occurrence of enantiomorphous hemihedral crystalforms. 



The reason of this is obvious. In fact, optical activity is a property 

 existing also in the amorphous state, in solution and in molten 

 masses. It is, therefore, a property which is directly and intimately 

 connected with the individuality of the single molecule and its 

 particular stereometrical configuration. The ' crystalform, however, 

 is one of the many ways in which the symmetrical and periodical 

 arrangement of the crystal-molecules, or at least, of the crystal- 

 units, manifests itself. 



It may be, and more recent experience seems to support this 

 view, -- that the crystal-molecules are identical with the chemical 

 molecules; or even that the conception of a single molecule in crystals 

 no longer holds. But also if this were true, the crystalline form, 

 while depending on the rather complicated arrangement of these 

 crystallographical units, is strictly speaking only a second-hand 

 phenomenon with respect to the inter atomistic forces, which deter- 

 mine the stereometrical configuration of the atoms in the molecule. 

 There are many substances known, which crystallise in well-developed 

 hemihedral forms differing from their mirror-images, but which 

 do not exhibit any rotatory effect in solution or in the liquid 

 state: sodium-chlorate, rhombic magnesium-sulphate, etc., are well- 

 known instances of this. Why should not the reverse eventually 

 be possible? 



Then, there seemed to be a number of apparent exceptions to 

 Pasteur's law, which gradually amounted to a considerable group. 



Thus, Be eke *) in 1889 gave a review of about seventy cases of op- 

 tically active substances, not exhibiting hemihedral crystalline forms. 

 However, in his opinion Pasteur's theory must be still adopted, 



F. Becke, Tscherm. Min. u. Petr. Mitth., 10, 464, (1889}; 12, 256, (1891). 



