257 



iiunon with respect to the inter-atomistic forn-s which determine 

 tin >ti ivometrical configuration of the atoms in the molecule. 

 I IK K an many substances known, which crystallise in well-developed 

 lit mill, dral 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 

 P a s t e u r's law, which gradually amounted to a considerable group. 



B e c k e x ) in 1 899 gave a review of about seventy cases of 

 optically active substances, not exhibiting hemihedral crystal- 

 line forms. 



However, in his opinion P a s t e u r's theory must be still adopted, 

 because there are a much greater number of valid cases, and 

 because the absolute proof of the presence or absence of hemi- 

 hedrism in many crystallographical researches was or could not 

 be given by the rudimentary development of the crystals, etc. 

 Of course, the first argument is of no significance, where just the 

 special question is put, whether the connection of both phenomena 

 be a necessary one? 



With respect to the absence of rotatory power in many hexa- 

 gonal and tetragonal crystals of these optically active substances, 

 he also agrees with the explanation of this given by Mallard 2 ) 

 and Wyrouboff 3 ), who, from their observations of crystals 

 exhibiting rotatory power, had already concluded that all these 

 crystals were really pseudosymmetrical intercalations, and warned 

 in 1894 against the dogmatic view that an obligatory connection 

 between optical activity and hemihedrism should exist. In 1896 

 and 1897 Wai den 4 ) again drew attention to the fact that the 

 number of cases in which a rotatory effect in solution was not 

 combined with the occurence of hemihedral crystal-forms, increased 

 more and more, their number gradually approaching that of tin- 

 cases in which such hemihedrism was concisely determined. 



He is therefore convinced that optical activity in solution or 



i) F. Becke, Tscherm. Min. u. Petr. Mitth. 10. 464. (1899); 12. 256. (1891). 

 -) E. Mallard, Trait6 de Christallographique //. p. 330. (1884). 

 3) G. Wyrouboff, Ann. de Chim. et Phys. (fi).8.416. (1886); (7). 1. 10. (1894); 

 A. Descloizeaux, Ann. des Mines (5). 14. 18. 



) P. Walden, Ber. d. d. Chem. Ges. 29. 1692. (1896); 80. 98. (1897). 



17 



