WATER OF CRYSTALLIZATION. 



belong heulandite, stilbite, analcite, natrolite, and scolecite, which are 

 included in the present research. 



In these minerals the water of crystallization is very loosely held. 

 It is impossible to distinguish between water of constitution and water 

 of crystallization. The water continues to be gradually expelled as the 

 temperature is raised and may be replaced by other substances, such 

 as NH 3 , H 2 S, or C 2 H 5 OH. The dehydrated crystals absorb definite 

 quantities of these substances as a sponge absorbs water, the process 

 being accompanied by the evolution of heat. 



90% 



10 



O 2 3 4 5 6 7 8 



FIG. 7. Stilbite (a); Potassium alum. 



Since the per cent of water present varies continuously with the 

 vapor pressure it is generally concluded that the water of the zeolites is 

 not analogous to the water of crystallization of most hydrated salts, but 

 resembles more nearly the intermixture which occurs in solid solutions. 



In fig. 6 two curves of heulandite are given. The sections were about 

 the same thickness, and the great difference in transparency is due to 

 the fact that the crystals were of different homogeneity and trans- 

 parency. The curves show the presence of the water bands at 1.5, 2, 



