304 Mr. Crum on the Acetates of Alumina. 



Acetic acid, 52 "38 



Alumina, 26-40 



Water, 18-49 



97-27 



The excess of acetic acid = 3 44 per cent, over the proportions of a bin- 

 acetate, was presumed to be free acid adhering to the product. To 

 remove that excess, a portion of it was heated in a water bath, and after- 

 wards treated with water. A considerable quantity of insoluble matter 

 was left, and the solution on being evaporated to dryness, at a gentle 

 heat, produced a soluble acetate, of which 100 parts contained — 



of acetic acid, 49-55 



and of alumina, 32-47 



corresponding, therefore, in composition, to a sesquiacetate ; but it can 

 only be looked upon as an accidental mixture, for every fresh portion 

 that was produced in a similar way gave a different result — the amount 

 of acid depending upon the extent and duration of the heat. 



The binacetate of alumina may be produced at once in solution ; and 

 as it is the most suitable combination from which to form the dry soluble 

 binacetate, as well as other bodies, I shall describe particularly the 

 manner of obtaining it. Dissolve 24 parts of precipitated binacetate of 

 alumina in 15 of rectified sulphuric acid, and 40 of water. Dilute 

 further with 80 parts of water, and add carbonate of lead (about 44 

 parts) to precipitate the sulphuric acid. 



AI2O3, 2 A + 2SO3 + 2(PbO, CO2) 

 = AI2O3, 2A + 2(PbO, SO3) + 2CO3 



Filter the solution, and pass sulphide of hydrogen through it until it 

 ceases to precipitate lead, and then add acetate of baryta, so long as it 

 is precipitated by the sulphuric acid of the sulphate of lead which had 

 remained in solution. When in this state, if the mixture be well agitated 

 for half an hour in an open vessel, the excess of sulphide of hydrogen will 

 be removed, and it may be filtered without the danger of the filtrate 

 becoming afterwards milky, from the effects of the sulphide. 



A solution of binacetate of alumina is thus obtained, containing about 

 5 per cent, of alumina, and a minute portion of iron ; the last traces of 

 which it was, for a long time, difficult to remove from these acetates. 

 Iron is found in all the solutions, and in both of the insoluble binace- 

 tates. Traces of it exist even in the binacetate which has been freed, 

 by a second precipitation, from all its other impurities. It was at last 

 observed that a solution of binacetate of alumina, at 5 per cent., which 

 is strong enough to form, after some time, a crust of the binacetate, 

 deposited its iron along with the first portions of the crust, and left the 

 solution altogether free from that impurity. The teracetate of alumina 



