Mr. Ckum on the Acetates of Alumina. 303 



was formed anew, wbich appeared from a qualitative analysis to be the 

 monosulpbate of alumina and potash, 



K0,S03 + SCAl^Og, SO3) 



the substance which is formed when hydrate of alumina is boiled with 

 alum. The same substance is found native, under the name of alum- 

 stone, at La Tolfa, the seat of the celebrated manufacture of Roman 

 alum, near Civita Vecchia ; and was ascertained, by Collet Descotils, to 

 be formed of — 



KO, SO3 + 3(A1A, SO3) + OHO 



Soluble Acetates of Alumina. 



Soluble Binacetate of Alumina. AI2O3, 2A + 4H0. Notwithstanding 

 the tendency of a concentrated solution of the ter- acetate of alumina 

 to deposit the insoluble salt, it may be evaporated, with certain precau- 

 tions, to a dry substance soluble in water. For this purpose it must be 

 spread very thin over sheets of glass, or of porcelain, exposed to a heat 

 not exceeding 100" Fahr., and, as it runs together into drops, like water 

 upon an oiled surface, it must be constantly rubbed with a thin platinum 

 or silver knife. If these precautions are neglected, a mixture is obtained 

 of the insoluble with a soluble acetate. 



The soluble salt is thus produced in scales, having the appearance of 

 gum when moistened, and leaving no residue when dissolved in water. 



For analysis it \^ as reduced to powder, and dried in the air twenty-four 

 hours, at the temperature of 100" Fahr. The alkaliraetric method was first 

 employed, and it indicated 548 per cent, of acetic acid; but the more 

 accurate method, by oxide of copper, gave 55-82 per cent, of acid. In 

 experiments for the alumina 26'4 per cent, was obtained. The composi- 

 tion of the substance was thus — 



Acetic acid, 55'82 



Alumina 2640 



Water, 17-78 



100-00 



But the solution from which this subtance was obtained was a terace- 

 tate, and contained for the same quantity of alumina, 



Acetic acid 78'58 



It lost, therefore, during gentle evaporation, nearly one-third of its acetic 

 acid, and was reduced almost to a binacetate, the formula of which — 



Al/Ja, 2A + 4H0 — requires — 



