EXPERIMENTS IN CHEMISTRY 23 



sides of the crystals have a remarkable constancy, 

 regardless of whether the crystal is large or small. 

 During the process of crystallization the molecules 

 of the dissolved substance are added to the dif- 

 ferent faces of the crystal in definitely proportional 

 amounts, thus preserving the general form of the 

 whole. Crystals when broken may regenerate their 

 normal form if they are placed in a solution of their 

 own substance, material being added to the broken 

 surface much more rapidly than elsewhere until 

 the typical outline is restored. 



Under conditions in which there is a limited 

 supply of the dissolved material the substance for 

 restoring the broken end of the crystal may even 

 be obtained by dissolving away a certain amount 

 of the substance from other parts of the surface; 

 thus by taking material from one place and adding 

 it to another a completely regenerated crystal of 

 smaller size may finally be obtained. What forces 

 regulate the behavior of chemical molecules while 

 they are building themselves up into these beautiful 

 and regular geometrical forms is a fascinating sub- 

 ject of speculation which has attracted many minds. 

 That the process is dependent upon the chemical 

 nature of the substances concerned seems evident 

 from the constant and characteristic form which 



