314 NATURAL SCIENCE. Nov., 



It is not too much to claim for the discovery relating to racemic 

 acid that, in the domain of crystallography, it was the most important 

 of the present century ; while in chemistry it laid the foundation 

 of an entirely new branch of science, now known as stereo-chemistry; 

 one which has been more stimulating to research and more fruitful in 

 result than perhaps any other of modern date. 



Those who had the pleasure of hearing Professor Percy Frank- 

 land's evening lecture at the British Association meeting at Ipswich 

 will recollect as one of the most vivid reminiscences of the great 

 chemist's life how, when engaged upon his earliest important 

 research, he rushed from his laboratory, and, falling into the arms of a 

 friend, exclaimed enthusiastically, " Je viens de faire une grande 

 decouverte ! " 



The discovery was this. Both tartaric and racemic acids were 

 known to chemists ; so far as could be seen they were absolutely 

 identical in all their chemical and physical characters, with one 

 exception ; further, from them could be derived a series of tartrates 

 and racemates respectively which appeared to be also identical, with 

 the same exception. The difference lay herein, that while solutions 

 of racemic acid and the racemates were without action on polarised 

 light, solutions of tartaric acid and the tartrates rotated a transmitted 

 beam of plane polarised light to the right. Now Pasteur observed 

 that the crystals of the latter substances (if account be taken of certain 

 minute facets which they present) are dissymmetric ; that is to say, any 

 one of these crystals, when held before a mirror, has a shape different 

 from that of its image. It is precisely analogous to the case of a right 

 hand which, when viewed in a mirror, becomes a left hand. Now if 

 there be a relation between the form of the crystal and the properties 

 of the solution, it might be expected that a solution which turned 

 plane polarised hght to the left would furnish crystals having the 

 form of the mirrored image. On examining the crystals obtained 

 from the inactive solution of racemic acid, Pasteur found that they 

 consisted of equal quantities of two distinct sorts of crystals bearing 

 precisely this relation to each other : a solution of the one was dextro- 

 rotatory, and the solution of the other was Isevo-rotatory. In the 

 solution of racemic acid, which contains equal quantities of both, they 

 neutralise each other's effects, and the solution is without action on 

 polarised light. The two sorts of crystals resemble two similar spiral 

 staircases, one of which twists to the right and the other to the left. 

 Even if they be broken up we can take any one step and say 

 from its shape whether it belongs to the right- or to the left-handed 

 staircase ; and in the same way when the crystals are broken up and 

 dissolved, it is possible, from the optical action of the molecules in the 

 solution, to predict the sort of crystal which they Avill construct. 



Biot, hearing of this striking discovery, sent the young chemist 

 some crystals of racemate of sodium and ammonium and begged him 

 to separate them by their forms, in order to ascertain whether their 



