WATICR OF" CRYSTALLIZATION. 



of H 2 O. It would have been highly desirable to procure more minerals 

 which occur in the hydrous and anhydrous state, but none were obtain- 

 able. The artificially dehydrated minerals, such as copper sulphate, were 

 too opaque for examination after expelling all the water. The only 

 exception is selenite, the various curves of which will now be considered. 

 The anhydrite curve, b, is to be noticed first, from which it will be 



90% 



01 234 56 



FIG. 3. Anhydrite (d) Selenite. 



observed that there are small bands at 1.9, 3.2, 5.7, 6.15, and 6.55 p., 

 and an enormous band at 4.55 p, which will be shown later to be due 

 to the SO 4 ion. 



Turning to the selenite curve (a, fig. 2), it will be noticed that it is 

 less transparent for the same thickness, 0.65 mm., and that in its general 

 trend it is similar to the curve for water. All of its absorption bands 

 coincide with water, with the exception of the 4.75 //, band, which is 

 shifted to 4.6 /*. The shifting of this band is due to the SO 4 band at 

 4.5 fi, as was found on examining anhydrite. 



The curve, c, for a thickness of 2.57 mm. is due to Konigsberger 

 (loc. cit.). 



