314 EARTHS PROPER. 



The first of these salts constitutes common sul- 

 phate of alumina, and it is an essential consti- 

 tuent of alum. The third of these salts is the 

 mineral found in Sussex and other places, and 

 known by the . name of aluminite. For Stro- 

 meyer has shown that it is a compound of 1 

 atom sulphuric acid, 3 atoms alumina, and 9 

 atoms water. If potash be poured into a boiling 

 hot solution of alum, an earthy precipitate falls, 

 precisely similar in its nature with the substance 

 which chemists formerly called alum saturated 

 with its earth. This precipitate is a compound 

 of 1 integrant particle of sulphate of potash, and 

 3 integrant particles of trisulphate of alumina, as 

 was first proved by Riffault.* I find that the 

 second of these salts, to which I give the name 

 of disulphate of alumina, may be obtained by a 

 process similar to the one followed by Mr. Phil- 

 lips ; but not carried so far. It is soluble in 

 water, and still possesses an astringent and 

 sweetish sour taste. 



Mr. Phillips' salt was a mixture or compound 

 of disulphate of alumina and trisulphate of alu- 

 mina, in the proportion of 3 atoms of the former 

 salt to 1 atom of the latter. It was the trisul- 

 phate which precipitated when the solution was 

 poured into water ; and it was its tendency to 

 fall down that explains the phenomena which 



* Ann. de Chim. et de Phys. XVI. 355. 



