Transactions of the Royal Society of Canada 



SECTION III 

 Series III JUNE 1917 Vol. XI 



Studies on the Solubility of Aluminium Hydroxide. 



By E. H. Archibald and Y. Habasian. 



Presented by Dr. D. Mcintosh, F.R.S.C. 

 (Read May Meeting, 1917.) 



The determination of aluminium usually involves its precipita- 

 tion as the hydroxide, followed by ignition and weighing as the oxide. 

 The solubility of the hydroxide renders the exact estimation of this 

 metal under many conditions, very uncertain. But slight variations 

 in the concentration of the precipitating reagents has a marked in- 

 fluence upon the solubility, while the temperature at which precipita- 

 tion takes place is not without appreciable effect. The difficulty 

 of ascertaining the exact conditions under which equilibrium is attained 

 probably accounts for the very few direct estimations of the solubility 

 in ammonium hydroxide. The method usually adopted in ascertaining 

 the extent to which the precipitated aluminium hydroxide has dis- 

 solved, is to evaporate a portion of the wash water or filtrate that has 

 been in contact with the precipitate for a certain length of time, 

 frequently at a boiling temperature. Unfortunately there is no 

 way of telling how nearly the solution is saturated with respect to the 

 aluminium hydroxide, or what the concentration of the ammonia 

 will be after the solution has been heated in the open beaker. It 

 was thought that it would be of interest to make, by direct methods, 

 a study of the solubility of aluminium hydroxide in solutions of am- 

 monium hydroxide, and also in solutions containing those ammonium 

 salts that are usually present when aluminium hydroxide is precipitated. 



The results of several previous investigations have a bearing on 

 the present problem. C. Renz^ made some indirect estimations of the 

 solubility of aluminium hydroxide in ammonium hydroxide; he slates 

 that when aluminium hydroxide is precipitated, by an excess of am- 

 monia from a solution containing ammonium nitrate, a small quantity 

 of aluminium hydroxide remains dissolved. This portion in solution 



1 Ber. der deut. Chem. Ges. 36, 275 (1903). 



Sec. Ill, Sig.l 



