206 



or at lower temperatures, and provided that supersaturation be 

 avoided in the case of lower temperatures. But if the transition- 

 temperature be too far removed from the ordinary temperatures of 

 crystallisation, in most cases it will be by no means possible to 

 resolve the racemoid into its components in the way described, and 

 then it becomes necessary to look for other methods of fission. 

 Cases of this kind are the most numerous: thus, e. g., that oi racemic 

 acid itself, and the dextro-, and laevogyratory tartaric acids, in 

 contradiction to the cases of their salts above dealt with. A similar 

 case is that, where no racemic compound could be obtained, although 

 both the optically active components be well-defined crystallised 

 substances. Such cases are for instance: d-, and l-asparagine: 1 ): 

 CO(NH Z )CH 2 CH(NH 2 )COOH + H Z 0, and the d-, and l-gulbnic 

 lactones 2 ) (mpt: 181 C.): C 6 H 10 G , which all have the symmetry 

 of the group D 2 , but whose racemoids have not so far been obtained. 

 Here also the temperature at which the inactive mixture is changed 

 into the racemic compound, when in contact with its solution, must 

 be supposed to lie too far removed, to allow its formation from the 

 components. 



5. Fairly soon however it appeared that the transformation of 

 the racemic compound into its active components could happen 

 also under circumstances in which the racemic compound itself must 

 be considered as undeniably stable. 



Gernez 3 ) first drew attention to the fact that from an optically 

 inactive solution of two active components, if supersaturated, the 

 excess of the solute was precipitated wholly as one of the active com- 

 ponents, if a small crystal of that component or of an isomorphous 

 or isodimorphous substance, was added to the supersaturated solution 

 as a nucleus of crystallisation. The same was demonstrated after- 

 wards by Pur die 4 ) in the case of zinc-ammonium-lactate , while in 

 1898 analogous experience was obtained to a certain extent by 

 Kipping and Pope 5 ), namely in so far that on recrystallising 

 sodium-ammonium-racemate from solutions in the open air and in 



') A. Piutti, Rend. Acad. d. Sc. Napoli (3). 10. 69. (1904); Gazz. Chim. It. 

 34. //. 36. (1904). 



2 ) E. Fischer and R. S. Curtiss, Ber. d. d. Chem. Ges. 25. 1025. (1892). 



3 ) D. Gernez, Compt. rend, de 1'Acad. d. Sc. Paris, 63. 843. (1866); Jahres- 

 ber. (1866), p. 400. 



4 ) T. Purdie, Journ. Chem. Soc. London 63. 1143. (1893). 



5 ) F. S. Kipping and W. J. Pope, Journ. Chem. Soc. London, 95. 103. (1909). 



