38 PROCEEDINGS OP THE AMERICAN ACADEMY 



moreover, in whicli the ratio between the atomicity of the basic and acid 

 radicals has a constant value, all hydrogen, which represents water of 

 constitution, will supplement the other basic radicals, and added to 

 them will complete the relative amount of basic radical which the given 

 class of salts require ; while the hydrogen, which represents water of 

 ciystallization, will be in excess of that amount. 



In mineral silicates these relations are complicated by the phenomena 

 of isomorphous replacements, and, although there may be some question 

 in regard to the replacing capacity of hydrogen, we cannot expect the 

 same constancy in the amount of water of constitution, which these 

 minerals contain, as in the case of simple salts. The amount of water 

 of crystallization, however, must be as invariable in one case as in the 

 other, and the hydrogen must bear the same relations to the atomic 

 ratio of the compound. Thus, if the mineral is an orthosihcate in 

 which the atomic ratio between the su7n of the basic radicals and the 

 silico7i is 1:1, all hydrogen in excess of the amount which this ratio 

 requires must represent water of crystallization, while all required to 

 complete the ratio must represent water of constitution ; and we thus 

 have a means of distinguishing between these two states of combination 

 where the class of compounds to which the mineral belongs is known. 



Now, it is true of each of the minerals we have distinguished among 

 the vermiculites, — 



First. That the water is driven off at a temperature below a red 

 heat. 



Secondly. That the loss of the water is attended with a complete 

 disintegration of the mineral. 



Thirdly. That the amount of the basic radicals, exclusive of the 

 hydrogen, is sufficient to saturate the silicon, and that the amount of 

 hydrogen is wholly in excess of the amount which the atomic ratio 1 : 1 

 requires. 



Could it be proved that the vermiculites are orthosilicates, the last of 

 the three facts just stated would be alone sufficient to establish the cor- 

 rectness of our conclusion. Unfortunately such absolute proof cannot 

 be obtained ; and we only claim that the crystallographic and chemical 

 relations of the vermiculites to each other, and to the magnesian micas, 

 gives a very high degree of probability to our theory that they are 

 orthosilicates. 



From these facts we have concluded that the water which enters into 

 the composition of the vermiculites is water of crystallization. For the 

 evidence of the facts, we refer to the descriptions of the several species 

 given below. But, further, in order to justify our conclusion, we pro- 



