WATER OF CONSTITUTION. 



45 



which have a wide band from 3 to 4 /A and a transparent region from 

 4-5 to 5-5 /"-, followed by opacity beyond 6/x,. 



It is known that for alcohols the large band in the region of 3 /A 

 is the composite of two bands situated at 3 and at 3.43 /A. 



CHLORAL HYDRATB (CC1 S CH(OH) 2 ). (Curve b, fig. 31.) 



The constitution of this compound is uncertain. For the present 

 examination the crystals were melted between plates of rock salt, and 

 placed over P 2 O 5 to dry and recrystallize. The transmission curve 

 shows ail the water bands ; although it is not considered water of 

 crystallization, curve c shows the region at 3 /* after the film stood over 

 P,O 5 for six days and had crystallized into an opaque mass. Chloral 



to 



3 4 S 6 7 8 



FIG. 31. Mantiite(a); Chloralhydrate. 



hydrate has the following bands: 1.5, 2, 3, 3.2, 3.7, 4.7, 5.1, 5.7, 6.2, 

 7.2, and 8 p. Curve c is b after crystallizing several days. 



In the foregoing dozen minerals containing hydroxyl groups there is 

 only one, or possibly two, viz, manganite and datolite, which appear to 

 be exceptions to the rule that hydroxyls have a band at 3 p. It will, of 

 course, be understood that this decision is also based upon previously 

 studied compounds referred to in the text. 



Several other minerals in which the constitution is less understood, 

 but which are supposed to contain hydroxyl groups, for example ser- 

 pentine and epidote, will be considered later on, where it will be found 

 that the 3 /n band is also very evident. 



