310 SALTS 



nesia varies more in the different species, than in 

 any of the preceding genera of salts. Two of 

 the species are anhydrous three contain 1 atom 

 of water three contain 2 atoms one contains 

 3 one 5 one 6 two contain 7, and one con- 

 tains 8 atoms. 



8. SALTS OF ALUMINA. 



Sulphate, i. Sulphate of alumina. This salt does not 

 crystallize regularly; but if we digest dilute 

 sulphuric acid over hydrate of alumina for two 

 or three days, and set the solution aside after 

 having concentrated it sufficiently, it gradually 

 congeals into a beautiful, white, soft, light, semi- 

 transparent mass, which may be dried upon 

 blotting paper, and is not altered by exposure to 

 the air. It always reddens vegetable blues how 

 long soever the liquid be digested over the alu- 

 mina; I continued the digestion for a month 

 without altering this property. All the salts of 

 alumina, so far as I have tried them, redden 

 vegetable blues. Sulphate of alumina is com- 

 posed of 



1 atom sulphuric acid 5 

 1 atom alumina 2-25 



7 atoms water 7*875 



15-125 



