WATER OF CONSTITUTION. 



43 



DATOLITE (Ca(BOH)SiCu). 

 (Section ground to 0.23 mm. Curve c, fig. 28.) 



In this curve the OH band at 3 p. is shifted to 2.8 /*. The other bands 

 present are at 2, 3, 5.3, and 6.3 /*. Although the specimen was full of 

 cracks, it is rather transparent for a boro-silicate. 



AZURITB (2CuCO 3 .Cu(OH) 2 ). 

 (Translucent; section parallel to c; = 0.35 mm. thick. Fig. 29.) 



The section was ground from a group of crystals all of which were 

 apparently piled parallel to c. There are absorption bands at 2.5, 3.05, 

 3.58, and 4.05 ju. and complete opacity beyond 5.5 /*. 



The 3.05 /A band is shifted slightly from the position common to 

 substances containing OH groups. 



a 



4-56789 



FIG. 29. Brucite (a and b) ; Azurite. 



<0 



BRUCITE (Mg(OH),). 



(From Woods Mine, Lancaster County, Pennsylvania. Foliated; massive; lamina 

 parallel to c; { = 0.05 and t = o.ig mm. Fig. 29.) 



As mentioned elsewhere, the fact that brucite did not show an 

 absorption band at 3 //,, which is the maximum of the hydroxyl group 

 in a series of organic compounds previously studied, made a reexamina- 

 tion highly desirable. Of course, as will be noticed in curve b, by 

 straining matters one might have concluded that the band at 2.5 /*, 

 which evidently is complex, containing the 3 /* band. In the present 



