212 



without decomposition, there will be great probability that the 

 spontaneous fission mentioned above, really occurs, be it at higher 

 or at lower temperatures, and provided that supersaturation be 

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

 temperature is too far removed from the ordinary temperatures of 

 crystallisation, it will in most cases 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 of racemic 

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

 contrast with the case of their salts above dealt with. A similar 

 case is that, where no racemic compound could be obtained by com- 

 bining the two antipodes, although both the optically active compo- 

 nents be well-defined crystallised substances. Such cases are, for 

 instance: d-, and l-asparagine: 1 ): CO(NH Z )CH 2 CH(NH Z )COOH + 

 H 2 0, and the d-, and l-gulonic lactones 2 ) (mpt: 181 C.): C 6 # 10 6 , 

 which all have the symmetry of the group D 2 , but whose racemoids 

 have not so far been obtained from the combined antipodes. Here also 

 the temperature at which the inactive mixture is changed into the 

 racemic compound, when in contact with its solution, must be suppo- 

 sed 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 also happen 

 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 results were obtained to a certain extent by Kipping 

 and Pope 5 ), namely in so far, that on recrystallising sodium-ammo- 



!) 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). 



