A LABORIOUS YOUTH 25 



other, within the molecule? And what would 

 be the resultant form of the molecule itself? 

 All these were questions on which no one had 

 any clear idea." 1 



Haiiy, who had made a very special study of 

 crystals, and had named their constructive 

 molecule the integrant molecule, considered 

 that this latter had no relation to the chemical 

 molecule, and that their different groupings 

 were produced by molecules identically the 

 same. Mitscherlich demonstrated that this the- 

 ory was not absolutely exact by replacing the 

 atoms of calcium with atoms of magnesium in 

 a crystallization of carbonate of lime, without 

 altering its form. This constituted the phe- 

 nomenon of isomorphism. Delafosse, a pupil 

 of Haiiy's, and one of Pasteur's professors, was 

 destined to study the phenomenon of hemi- 

 hedrism, that by which certain crystals evade 

 the law of symmetry and possess one facet 

 which has no corresponding one, but he was 

 unable to find the explanation. On the other 



1 Pasteur, the History of a Mind, by E. Duclaux, p. 40 



