SEPARATION OF STEREO-ISOMERS 115 



substances to form salts. The method was first applied in 

 the case of racemic acid by Pasteur, who saturated the acid 

 with cinchonine and found that the cinchonine salt of the 

 laevo-acid crystallized first ; this has then obviously a 

 smaller, and therefore a different solubility \ in accordance 

 with the general rule that, so soon as asymmetrical optical 

 antipodes combine with the same asymmetrical active sub- 

 stance, a compound results no longer answering to a pair 

 of reflected images, as appears from Fig. 22. 



The two larger triangles represent dextro- and laevo- 

 tartaric acid, the two smaller, cinchonine ; the dextro and 

 laevo combinations cannot be arranged 

 symmetrically to one another, and con- 

 sequently differ in their properties like 

 ordinary isomers, e. g. in their solubility. 

 Direct measurements of solubility have 

 not yet been carried out for such a case, 

 so that the question is still undecided 

 whether racemism is possible in it, with 

 a transition temperature in the former sense 2 . If so, the 

 phenomena would be strictly comparable with the behaviour 

 of double salts. 



(b) Methods of Separation depending on Chemical Action. 



Separation by means of enzymes and organisms. Separa- 

 tion by means of enzymes and organisms is really the same, 

 for the function of an organism in such cases can be traced 

 to the action of peculiar substances formed in the organism, 

 and given off by it, to which the name of enzymes has been 

 given. An especially interesting example of this is to be 

 found in the isolation effected by Buchner 3 of the enzyme 

 of fermentation, zymase, from yeast, by breaking up the 

 yeast-cells (by rubbing with glass) and pressing out. If 

 we combine this fact with the discovery of Fischer 4 , that 



1 Marckwald, Berl. Ber. 31. 786. 



2 Ladenburg, 1. c. 31. 524, 937, 1969 ; Kiister, 1. c. 31. 1847. 



3 1. c. 31. 568, 1084, 1090. * 1. c. 23. 2620. 



H 2 



