4O INFRA-RED TRANSMISSION SPECTRA. 



melting began, the rock salt, containing the film, was removed. In the 

 same manner the film for curve c was obtained, but here it was not 

 permitted to melt entirely, so that the film was only semi-translucent. 

 Nevertheless, it does not show the water bands at 1.5 and 3 /x. It is 

 difficult to conceive how all the water was expelled in these two cases. 

 Curve d is curve c magnified 10 times at 3 p.. 



Out of a list of 32 substances examined containing water, generally 

 in the form of water of crystallization, this is the first exception to the 



90% 



6769 



FIG. 25. Brucine. 



rule tentatively assumed in this work. The second exception thus far 

 considered is cane sugar, which is not supposed to contain water of 

 crystallization. In fig. 40 Kieserite (MgSO 4 -)-2H 2 O) is to be noticed. 

 It has water bands at 1.5, 3, 4.55, and 6/u, the latter being complex 

 on account of the SO 4 groups. In fig. 42, cadmium sulphate QCd 

 SO 4 -|-8H 2 O) is also to be noticed, since it contains the water bands at 

 1.5, 2, 3, and 4.6/4. 



GROUP II: MINERALS CONTAINING WATER OF CONSTITUTION. 



The first part of this group contains minerals in which the oxygen 

 and hydrogen are present in the form of the univalent hydroxyl radical. 

 OH, and are known as hydroxides. The hydroxides when heated also 

 yield water, but it is a characteristic that they must be strongly heated 

 before they are decomposed. From previous work, already noticed, we 

 would expect an absorption band at 3 /* for hydroxides. 



