201 



hitin^ to them, which ha\v been dete, u-d since that period. 



2. I. Sptiiitiiiu'iins l-'issi<>n af Racemic Compounds into their 

 Components by mere Crystallisation from Solutions. 



The |>lu'nomenon first discovered by Pasteur, that a racemoid 

 >\ simple recrystallisation from a solution deposits the crystal- -f 

 l)i>th its optically active components separately, h.i> since been 

 ohx-wed in a restricted number of cases. It appeared however for 

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

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

 ci remittances under which it takes place seemed to be completely 

 unknowable. Pasteur himself, who clung persistently to the idea 

 that molecular dissymetry could only be produced by the action 

 ot 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 the racemic compound is the less stable, or "metastable" 

 solid phase with respect to the saturated, optically inactive solution, 

 in comparison with the crystalline mixture of the active components 

 with respect to it. 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 t 9 (NH t )Na -f H Z 0. If this salt 

 recrystallised from aqueous solutions at temperatures below 

 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 't Hoff 2 ), that this 

 case of spontaneous fission is completely analogous to that of the 

 formation and decomposition of many double-salts, there being 



i) A. Scacchi, Kendic. dell' Acad. di Napoli (1865). 250; cf. W. Stft- 

 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). 



'-') J. H. van 't Hoff and C. Van Deventer, Zeit^. f. phys. Chemie 

 1. 173. (1887); J. H. van 't Hoff; H. Goldschmidt, and W. P. Jorissen, 

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

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

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

 Stereomeren, Leipzig, (1906). 



