464 DR T. THOMSON'S Analysis of some Minerals, 



luring of alum. After having examined the sulphate of alumina 

 from Rio Soldano, it occurred to me that the white bands at 

 Campsie bore a certain resemblance to it. I, therefore, request- 

 ed Mr MACINTOSH to procure me a specimen of it for examina- 

 tion, which, with his usual polite kindness, he speedily did. 



Its colour is greyish-white, intermixed with portions having 

 a yellow colour, and which are unequally distributed. 



Fracture earthy. 



Opaque. 



Friable. 



Taste acid, astringent, and sweet. 



Specific gravity 1.887. 



When digested in water it dissolved, with the exception of a 

 white powder, which amounted to 15.31 per cent, of the whole. 

 This white powder proved, on examination, to be a subsulphate 

 of alumina. 



When heated, it melts somewhat like alum, and gives out 

 pure water. When heated to redness, it swells up like alum, 

 and finally leaves a yellowish-white, porous, tasteless matter, 

 nearly similar to what would be left by alum, making allowance 

 for the colour. 



Being carefully analyzed, its constituents were found to be, 



1. Matter insoluble in water 15.31, composed of 



Sulphuric acid, . .-' 'V$ .. . 10.2 

 Alumina, ....... 5.11 



2. Matter soluble in water composed of 



