Mr. Ckum on the Acetates of Alumina. 305 



does not deposit its iron in like circumstances ; a difference wbich may 

 be accounted for from the fact that the binacetate of the sesquioxide of 

 iron is more readily decomposed than the teracetate of that base. 



Spread very thinly over a sheet of glass, it evaporates at 60° or at 

 100° Fahr., without running into large drops so much as the teracetate, 

 and without having an equal tendency to produce the insoluble binacetate. 

 The scales into which it forms in drying are transparent and soluble in 

 water. 



Burned with oxide of copper for acetic acid, and calcined for alumina, 

 100 parts were found to contain — 



Acetic acid, 55-2 1 



Alumina, 3 1 "3 1 



But the alkalimeter had shown, that in the solution the same quantity of 

 alumina had been combined with — 



Acetic acid, 59 • 1 3 



More than 4 per cent, therefore had been lost by evaporation at 100° 

 Fahr. 



After some other attempts, I was obliged to conclude that the only 

 way to obtain the dry soluble binacetate in something like atomic pro- 

 portions, was the unsatisfactory one of evaporating in the air a solution 

 of binacetate, mixed with such a proportion of acetic acid or of teracetate 

 as is found by trial to produce it. 



On the question, as to which of the soluble acetates of alumina 

 can be considered as a definite compound, it has already been stated of 

 the teracetate, that when evaporated rapidly enough, and at a heat just 

 low enough to prevent the formation of the insoluble salt, it leaves a pro- 

 duct whose composition is nearly that of a binacetate. It may be added, 

 that the solution of teracetate gives off acetic acid as freely in the cold, 

 as if a third part of its acid were free. On making an experiment with 

 two solutions of acetate of lead — one of which was decomposed by sul- 

 phuric acid, and the other (which was three times as strong) by tersul- 

 phate of alumina — it was found that the aluminous solution gave a smell 

 of acetic acid considerably stronger than that in which the acid was 

 known to be free. It may be doubted, then, whether there exists a com- 

 bination of acetic acid with alumina corresponding to the tersulphatc of 

 alumina. The solution of binacetate has no smell of acetic acid at ordi- 

 nary temperatures. 



BiHYDRATE OF AlUMINA SOLUBLE IN WATER. 



AlA -f 2110. 



Hydrate from the soluble Binacetate. — By the continued action of heat on 

 a weak solution of binacetate of alumina, a permanent separation of tho 

 constituents of the salt takes jjlacc, although no acid escapes, and no 



