MEANS OF SEPARATING ROTARY SUBSTANCES 43 



X 



MEANS OF SEPARATING THE RIGHT- AND LEFT- 

 HANDED SUBSTANCES 



We have to deduce from the preceding facts one of the 

 consequences which they allow. Now that we have 

 substances of the same composition into the molecule 

 of which we can introduce either an identity, or foreseen 

 and premeditated variations, let us ask ourselves if we 

 cannot impart to the two tartrates, right and left, which 

 precipitate at the same time from a solution of the double 

 paratartrate of soda and ammonia, a difference in solu- 

 bility great enough so that one will be deposited before 

 the other, when the liquid is left to evaporate. That 

 would be a great advantage. At present, we only know 

 how to separate them by hand, observing individually 

 their hemihedral facets in order to determine how they 

 are placed on the crystal. That demands time, patience, 

 and a profound knowledge of crystalline forms. Further- 

 more, when deposited, the crystals are generally in a 

 mass, and one is never sure that a right-handed crystal 

 which one detaches from the mass does not bear with 

 it fragments of a left-handed one. The separate crystal- 

 lization of the two salts would certainly yield them in a 

 much purer state. 



Let us search then in this direction, Pasteur surely 

 said, and he soon found, in reahty, that in crystallizing 

 the paratartrate of cinchonine, the left-handed tartrate 

 which is less soluble was deposited first, and to such an 

 extent that by decanting at a given moment the mother 

 liquid, and evaporating it anew, there was found in it 

 only the right-handed tartrate. It was a natural separa- 

 tion of the two acids, otherwise so similar. I imagine 

 that when Pasteur performed this experiment for the 



