207 



it seems better to deal more in detail with these various methods 

 of fission, and to consider at the same time the most important 

 facts relating to them, which have been detected since that period. 



2. Spontaneous Fission of Racemic Compounds into their 

 Components by mere Crystallisation from Solutions. 



The phenomenon first discovered by Pasteur, that a racemoid 

 by simple recrystallisation from a solution may deposit the crystals 

 of both its optically active components separately, has since been 

 observed in a restricted number of cases. It appeared, however, for 

 a considerable time to be quite fortuitous, whether the desired fission 

 of the racemic compound occurred in this way, because the special 

 circumstances under which it takes place seemed to be completely 

 unascertainable. Pasteur himself, who clung persistently to the 

 idea that molecular dissymetry could only be produced by the action 

 of living organisms, assumed that the fission by spontaneous crys- 

 tallisation was started by micro-organisms introduced from the 

 atmosphere. Since then it has been found that the phenomenon takes 

 place in cases, where the inactive mixture of the components is at 

 the same temperature less soluble than the racemic compound. This 

 signifies, that in those cases the racemic compound is the less 

 stable, or "metastable" solid phase with respect to the saturated, op- 

 tically inactive solution, in comparison with the crystalline mixture 

 of the active components. As, however, these relations are a function 

 of the temperature, it is necessary to consider this case more in detail. 



The classical example of a fission of this kind is that of Scacchi's 

 sodium-ammonium-racemate 1 ) : C^H 4 p 6 (NH l )Na -f- H 2 0. If this salt 

 be recrystallised from aqueous solutions at temperatures below 

 27 C., it is deposited as a mixture of right-, and left-handed crystals 

 of the corresponding optically active tartrates (-f- 4H 2 0), having 

 the axial symmetry D 2 . 



It was afterwards demonstrated by Van 'tHoff 2 ), that this 



!) A. Scacchi, Rendic. dell' Acad. di Napoli, (1865), 250; cf.: W. Sta- 

 del, Ber. d. d. Chem. Ges., 11, 1752, (1878); G. Wyrouboff, Compt. rend, 

 de 1'Acad. d. Sc. Paris, 102, 627, (1886); Bull, de la Soc. Chim., (2), 41, 210, 

 (1884); 45, 52, (1886). 



2 ) J. H. van 't Hoff and C. Van Deventer, Zeits. f. phys. Chemie, 

 1, 173, (1887); J. H. van 'tHoff, H. Goldschmidt, and W. P. Jorissen, 

 Zeits. f. phys. Chemie, 17, 49, 505, (1895); J. H. van 't Hoff, Vorlesungen 

 H. theor. u. phys. Chemie, II, (1899), p. 100; idem, Vorlesungen u. Spaltung und 

 Bildung von Doppelsalzen, (1897), p. 81 ; W. Meyerhoffer, Gleichgewichte der 

 Stereomeren, Leipzig, (1906). 



