SECTION III, 1916 [69] TRANS. R.S.C 
The Solubility of Aluminium Hydroxide in Solutions of Ammonia and 
of Ammonium Salts. 
By E. H. ARCHIBALD and Y. HABASIAN 
(Presented by Dr. R. F. RUTTAN, F.R.S.C.) 
(Read May Meeting, 1916) 
The solubility of Aluminium hydroxide renders the exact estima- 
tion of this substance, under many conditions, very uncertain. But 
slight variations in the concentration of the precipitating reagents has 
a marked influence upon the solubility, while the temperature at 
which the precipitation takes place is not without appreciable effect. 
The difficulty of ascertaining the exact conditions under which equilib- 
rium is attained probably accounts for the fact that, up to the present, 
no direct estimations of the solubility in ammonium hydroxide have 
been made. 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 ammonium hydroxide and in solutions containing am- 
monium salts that are usually present when aluminium hydroxide is 
precipitated. 
All the chemicals used were purified by standard methods. 
For instance, in the case of the aluminium salts, impurities consisting 
chiefly of iron and nickel were eliminated by converting the aluminium 
into soluble sodium aluminate and after removing the iron, decom- 
posing the aluminate with carbon dioxide. The resulting aluminium 
hydroxide was dissolved in nitric acid and reprecipitated with am- 
monium hydroxide. This process was repeated eight times when all 
traces of sodium had disappeared. The alumina was then converted 
into the particular salt desired. 
The solutions studied were sealed in glass tubes; this being 
necessary on account of the volatility of the ammonia. After equi- 
librium had been reached, in a bath provided with a properly regulated 
thermostat, the tubes were opened under conditions that insured 
no appreciable loss of ammonia; and the necessary analysis of the solu- 
tion was then carried out. 
It was found that the solubility of aluminium hydroxide increases 
with the strength of the ammonium hydroxide up to a certain concen- 
tration—that beyond this concentration the solubility diminishes 
owing to the formation of a more crystalline variety of aluminium 
compound. 
