302 Mr. Crum on the Acetates of Ahunina. 



The formula, AIA, 2A + 2H0, requires— 



Acetic acid, 59'51 



Alumina 29'99 



Water, 10-50 



100-00 



Numerous specimens of this salt were formed by precipitation from solu- 

 tions of various sti-engtbs, at various temperatures below boiling water, and 

 analyzed for acetic acid and alumina. Tbey generally agreed in tbe pro- 

 portions of acid and base, but varied in the absolute quantity ; indi- 

 cating a range of from 3 to 5 equivalents in the proportions of water. The 

 two salts which have been described as deposited, one at 60° and the 

 other at a boiling heat, gave results nearly uniform. 



When heat is applied to a solution of teracetate of alumina weaker 

 than that which has been described ; to one, for example, containing 3 

 per cent, of alumina, it also yields the insoluble binacetate, but, in that 

 case, not acetic acid alone, but a considerable quantity of acetate of 

 alumina remains in the solution. Solutions containing 2 per cent, of 

 alumina are precipitated by boiling, if they have been kept some weeks, 

 but not if recently prepared. It appears from these experiments, that 

 the presence of free acetic acid favours, in some way, the production of 

 the insoluble binacetate of alumina from a solution of teracetate. It was 

 found, accordingly, that a solution of teracetate containing |- per cent, 

 of alumina, and which could not therefore be precipitated by boiling, 

 acquired that property when made to contain acetic acid equal to a solu- 

 tion of teracetate, with 4 per cent, of alumina. 



In whichever way deposited, this substance is exceedingly insoluble in 

 water, either cold or hot, and it is equally insoluble in acetic acid. When 

 one part of it is digested for an hour and a-half in two hundred parts of 

 boiling water, it dissolves ; and the solution consists partly of soluble 

 binacetate of alumina, and partly of acetic acid and tbe bihydrate of 

 alumina to be afterwards described. 



It dissolves in two equivalents of sulphuric acid, or of hydrochloric, or 

 nitric acid, forming bisalts of alumina, and liberating the two atoms of 

 acetic acid. It also dissolves in a strong solution of tersulphate of 

 alumina, with the assistance of heat, forming bisulphate of alumina and 

 free acetic acid. 



2(AL03. 3SO3) + ALO5, 2 A = 3(Al,03, 2SO3) + 2 A 



The mixture does not precipitate on the addition of water like the 

 bisulphate alone, and must therefore be changed by water into tersul- 

 phate and binacetate of alumina. 



2(A1A, 3SO3) + AI0O3, 2A 

 A solution of potash alum dissolved this binacetate in the same cir- 

 cumstances, but on the heat being continued for some time, a precipitate 



