THE PREDECESSORS OF PASTEUR 



By breaking a cubic crystal of marine salt we reduce it 

 to many little cubes which, pulverized in their turn, 

 would bring us, if it were possible to push the division 

 far enough, to the integral molecule, which also we may 

 suppose to be a cube. By superposing, or placing in 

 juxtaposition a sufficiently large number of these invisi- 

 ble cubes we can form a cubic crystal of any volume 

 whatever, and this example suffices very well to repre- 

 sent to us the integral molecule of Haiiy. But, in the 

 mind of this savant, these integral molecules of the 

 crystal bore no necessary relation to the chemical mole- 

 cule. In order to make an integral molecule of marine 

 salt it sufficed that eight chemical molecules, each formed 



?^^=^ 



c^ 



-o- 





Fig. 1. 



-Diagrams illustrating primitive conceptions of the distribution of 

 molecules in crystals. 



of one atom of chlorine and one of sodium, should group 

 themselves into the form of a cube. What these chem- 

 ical molecules, themselves, might be, spheres (as repre- 

 sented in Fig. 1), cubes, tetrahedrons, etc., was a matter 

 of entire indifference; their form had nothing to do with 

 it; it was their grouping alone that determined the form 

 of the integral molecule of the crystal and, consequently, 

 that of the crj^stal itself. 



This grouping, according to Haiiy, was determined by 

 the particular nature of the chemical molecule and 

 could only occur among molecules which were similar 

 and completely identical. The geometrical regularity 

 was evidence of the physical and chemical regularity. 

 The discovery of facts relating to isomorphism came 



