PASTEUR: THE TARTRATES 13 



the normal school and able to enter the laboratory as 

 ''preparateur/' he made ready to pursue them. In 

 order to accustom the eye and the hand to the things 

 with which crystallography deals, he conceived the ex- 

 cellent idea of taking as guide a rather extended treatise 

 on crystalline forms, proposing to repeat all the experi- 

 ments and all the measurements, and to compare his 

 results with those of the author whom he followed step 

 by step. He chose for this purpose a work by Provostaye 

 on the tartrates, a most fortunate choice, for among the 

 substances endowed with rotary power, the tartrates 

 are those which present in simplest form the phenomena 

 toward which the ambition of the young savant directed 

 him. With other salts he would have been obliged to 

 search much longer to find things not so clear, but he 

 would have found them in the end. 



He had, in fact, constantly present in his mind, this 

 correlation between hemihedrism and the rotary power 

 discovered in quartz. It was useless to say that it had 

 no apparent connection with the case of tartaric acid, 

 that is, that it resided in the arrangement of the mole- 

 cules, instead of in the molecule itself; the ideas of his 

 master as well as his own, reverting constantly to this 

 subject, told him that there ought to be something exter- 

 nal indicating the mode of arrangement of the atoms. 

 One of the best proofs that he searched for this some- 

 thing which his imagination had glimpsed in the memoirs 

 of BiO/t and Herschel, is that he saw at once on the 

 crystals of tartaric acid and the tartrates those hemi- 

 hedral facets which neither Provostaye nor Mitscherlich 

 had observed. The former, a conscientious worker but 

 without inspiration (sans flamme), had certainly seen 

 them but he had disregarded them. The second, whose 

 fame is well established, was occupied in his study espe- 

 cially with showing the isomorphism of the tartrates, 

 4 



