OF ALUMINA. 



This salt is capable of congealing though it con- 

 tains a slight excess of acid. I have obtained it 

 composed of 



Sulphuric acid 5-625 

 Alumina 2-25 



Water 7-875 



15-75 



The excess was just the ith of an atom of sul- 

 phuric acid. To prevent any such excess we 

 must continue the digestion over alumina for a 

 considerable time ; for the action of the acid, 

 when nearly saturated, becomes very feeble. 



2. Trisulphate of alumina. This is a fineTnsui. 

 white aluminous looking mineral, found in Sus- P 

 sex and in other places, and distinguished among 

 mineralogists by the name of aluminite. Its con- 

 stituents, as appears from the analysis of Stra- 

 in ever, are 



1 atom sulphuric acid 5 

 3 atoms alumina 6*75 



9 atoms water 10-125 



21-875 



I have already noticed disulphate of alumina in 

 a preceding chapter. 



3. Dinitrate of alumina. This salt was ob- 

 tained by digesting hydrate of alumina in dilute 

 nitric acid till the acid refused to dissolve any 

 more of the hydrate ; the liquid was then con- 



U4 



