io8 MOLECULAR STRUCTURE 



side by side, led to the first actual separation. This fact 

 has since acquired a certain general interest in natural 

 philosophy. Pasteur, who held the view that optically 

 active compounds could only be obtained by the action 

 of living organisms, attributed the so-called spontaneous 

 separation to the action of germs in the atmosphere. 

 Wyrouboff opposed this view, and since then the mechanical 

 explanation of the separation has become clear, viz. that 

 separation takes place regularly when the mixture of the 

 optical antipodes is less soluble than the racemic substance. 

 The phenomenon depends on temperature, and for some 

 bodies occurs only under restricted conditions of temperature, 

 as will be seen from the following more detailed account 

 of particular cases. 



Stadel found that the solution, which in Pasteur's hands 

 yielded the two sodium-ammonium tartrates, gave him only 

 a sodium-ammonium racemate ; this was more thoroughly 

 investigated by Scacchi, whilst WyroubofF found that the 

 appearance of one or the other from solution depended on 

 temperature ; that if supersaturation was avoided the 

 mixed tartrates appeared below 28, the racemate above. 

 Van 't Hoff and van Deventer 1 then showed that we have 

 here to do with a transition (Part I, p. 25). Just as with 

 Glauber salt, the separation of hydrate (Na 2 SO 4 . ioH 2 0) 

 or anhydride, according as one works below or above 33, is 

 associated with the complete transition of the salt at 33, 

 according" to the equation ,// -. 



Na 2 S0 4 . ioH 2 = Na 2 S0 4 + ioH 2 O, 



so the alternative crystallization of mixed '* tartrates or of 

 racemate is associated with a transition taking place at 28, 

 according to the equation 



CC 4 H 4 6 NaNH 4 . 4 H 2 + t)C 4 H 4 O c NaNH 4 V4 H 2 O - 

 (C 4 H 4 O fl NaNH 4 ) 2 2 H 2 O + 6 H 2 O; t \ 



The two phenomena may be observed in the/same manner. 



1 Zeitschr. f. Phijs. Chem. i. 173 ; van 't Hoff, Goldschm'idt,'Jorissen, 1. e. 

 17-49- - ' " - 



