DR T. THOMSON'S Analysis of some Minerals. 465 



Sulphuric acid, 30.225 



Alumina, 5.372 



Peroxide of iron, .... 8.530 



Potash, 1.172 



Water, 36.295 



81.594 

 Insoluble matter, .... 15.310 



Total, . . . 96.904 

 Loss, . . . 3.096 



100.000 



This loss was doubtless water. For the 36.295 per cent, of 

 water were obtained by simply exposing the matter to heat on 

 the sand bath. I had ascertained, by previous experiments, that 

 it is impossible to deprive sulphate of alumina of the whole of 

 its water, without at the same time driving off some of the sul- 

 phuric acid. 



The constituents thus found are equivalent to 



24 atoms sulphate of alumina. 

 9 atoms bipersulphate of iron. 

 1 atom bisulphate of potash. 

 42 atoms water. 



The American sulphate of alumina differs from that of Camp- 

 sie in three remarkable particulars. It contains soda, while the 

 alkali in the Campsie mineral is potash. The Campsie mineral 

 contains a notable quantity of bipersulphate of iron, while, in the 

 American mineral, the quantity is trifling. In the American 

 mineral, all the saline contents were neutral, while in the Camp- 

 sie mineral almost one-half of the saline contents are in the state 

 of bisulphates. 



