310 Mr. Ceum on the Acetates of Alumina. 



cent, of sulphuric acid. 19'715 grains mixed with 16 grains sulphuric acid 

 in a platinum crucible were tirst heated with a spirit lamp, and then 

 exposed to a white heat. It left 8'51 grains =i4316 per cent, of alumina. 

 Another experiment gave 42-94 per cent. The mean is 43-05. The 

 composition of the substance is therefore — 



Sulphuric acid, 17-29 SO3 17-18 



Alumina, 43-05 2A1,03 44-16 



Water, 39 66 , lOHO 38-66 



100-00 100-00 



When the solution from alum and sugar of lead was heated before the 

 restoration of its sulphate of potash, a very slight precipitate was formed. 

 The addition of that salt completed the precipitation, but the substance 

 thrown down was more transparent, and dried into a brownish, horny- 

 looking matter. Its analysis, however, gave nearly the same results. 



Sulphuric acid, 17-23 



Alumina, 43-51 



Water, 3926 



100-00 



But when the solution was boiled for two hours before the addition of 

 the sulphate of potash, a quantity of alumina seems to have gone down 

 with the sub-sulphate, for its analysis gave in 100 parts 



Sulphuric acid, 13-73 



Alumina, 50-71 



It had an appearance similar to the preceding product. In the moist 

 state the sub-sulphate is soluble in cold acetic acid, as well as in the 

 mineral acids. It dissolves in three atoms of sulphuric acid to form two 

 of the bisulphate, which, on the addition of water is resolved into the 

 tersulphate of alumina, and the insoluble monosulphate. 



2A1A,S03-1-3S03=2(A1A, 2SO3.) 

 = AL03, SO3+AIA, 3SO3. 



The same mixture of teracetate of alumina and sulphate of potash, 

 which in a diluted state produces subsulphate of alumina on the applica- 

 tion of heat, gives a precipitate of binacetate of alumina when heat is 

 applied to it in a concentrated state. A quantity of sulphate of potash, 

 however, adheres to the insoluble binacetate even after abundant washing. 



salt of baryta complete without a considerable excess of the barytic salt, and vice 

 versa. The point sought for in the present instance is that at which an equal pre- 

 cipitate is formed on adding an excess of either salt. 



