308 Mr. Ckum on the Acetates of Alumina. 



the change, for after that time the solution has no longer any taste of 

 alum, and the power of coagulating with acids does not increase. 



6'93 grs. of this hydrate, which had been dried at a steam heat, were 

 moistened with sulphuric acid, which was then gradually expelled by a 

 spirit-lamp, and the residue, when kept forty minutes at a white heat, 

 left 520 grs. of alumina, indicating 24*97 per cent, of water. The 

 mean of this and the previous experiment gives for the composition of the 

 hydrate — 



Alumina, 7468 



Water, 25-32 



100-00 

 A bihydrate requires — 



Alumina, 74'06 



Water, 25-94 



10000 

 Acetates of Sesquioxide of Iron. 



The analogy between the salts of alumina and those of the red oxide 

 of iron, induced me to inquire whether there might not exist allotropic 

 acetates of iron, corresponding with those of alumina. 



A solution of sulphate of iron, to which was added half an equivalent 

 of sulphuric acid, was acted upon by strong nitric acid, and the tersul- 

 phate so obtained was converted into the teracetate by decomposition 

 with neutral acetate of lead. A binacetate was also produced by decom- 

 posing with a mixture of acetate and carbonate of lead. Both solutions 

 had the same intense red colour which is peculiar to the peracetate of 

 iron. 



The teracetate of iron, whether concentrated or weak, is little liable to 

 decomposition in the cold. Boiling causes the deposition of a hydrated 

 peroxide, but the decomposition is only partial, and the hydrate difficult 

 to collect. 



The binacetate soon begins to let fall an oxide in the cold ; and at the 

 heat of boiling water a complete separation takes place. A rich deep, 

 coloured hydrate goes readily down, and the whole of the acetic acid 

 remains in the liquid, which is perfectly colourless. No allotropic acetates 

 of iron, corresponding to those of alumina, appear therefore to exist. 



BiBASio Sulphate of Alumina. 



2A1A, SO3 + lOHO. 



It is well known that when teracetate of alumina is boiled along 

 with sulphate of potash, a gelatinous precipitate is formed, which re- 

 dissolves when the solution becomes cold. M. Ka3chlin-Schoueh''= found 

 it to be a subsulpliate of alumina, 



* Sui' Ic Mordant Rouge, &c. Bulletin de la Societe Industriclle de Mulhausen 

 I. 299. 



