Gooch and Osborne — Potassium Aluminium Sulphate. 167 



Art. XVI. — The Reaction between Potassium Aluminium 

 Sulphate and a Bromide- Bromate Mixture; by F. A. 

 Gooch and R. W. Osborne. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clx.] 



"When the water solution of a neutral aluminium salt is boiled, 

 hydrolysis may take place until an equilibrium is brought 

 about between the free acid formed and other active products. 

 If a product is inert toward the acid set free in the liquid, or 

 if the acid is continuously removed or destroyed, the process 

 goes on until no further hydrolytic action is possible under the 

 conditions. 



In the basic acetate process for the separation of alumina, 

 the insoluble aluminium compound is a basic salt inert toward 

 the free acetic acid formed under the conditions. 



In Chancel's method of precipitating alumina, by the action 

 of sodium thiosulphate upon the boiling solution of the soluble 

 aluminium salt, the insoluble product is likewise a basic salt, in 

 this case the sulphate, and the sulphuric acid set free is fixed 

 as sodium sulphate while the thiosulphuric acid formed in meta- 

 thesis is destroyed at the temperature of the reaction with 

 formation of the comparatively inactive sulphur dioxide and 

 sulphur ; though as Norton has shown* the basic salt is not 

 quantitatively insoluble until the mixture is superheated under 

 pressure. 



In Stock's processf for the determination of alumina, alumin- 

 ium sulphate in solution is heated at the boiling temperature 

 with a mixture of potassium iodide and potassium iodate. 

 The sulphuric acid produced hydrolytically is fixed by the 

 iodide-iodate mixture and comparatively inert iodine is set free 

 and taken up by sodium thiosulphate to form sodium iodide 

 and sodium tetrathionate. In this process, as Moody has 

 shown:};, the first insoluble product is a basic salt ; but pro- 

 longed boiling of the mixture of aluminium sulphate, potas- 

 sium iodide and potassium iodate finally brings about the 

 complete hydrolysis of the insoluble basic salt, so that the 

 entire amount of iodine set free in the process, when properly 

 collected and titrated, may serve as an accurate measure of 

 the acid produced and therefore of the acidic ion of the alumin- 

 ium salt. 



In an extension of this process to other elements Moody 

 found that a sufficiently prolonged treatment with the iodide- 

 iodate mixture completely liberated the acidic ion from the 



*Ber. Dtsch. Chem. Ges., xxxiii, 548, 1900. 

 f Norton, this Journal, xii, 118, 1901. 

 \ Moody, this Journal, xx, 181, 1905. 



