archibald-habasian] solubility OF ALUMINIUM HYDROXIDE 



the substance to be practically pure aluminium hydroxide, while 

 under the microscope it appeared to be quite amorphous. 



It should be noted that the formation of the non-gelatinous 

 precipitate takes place more quickly in the solutions that are con- 

 centrated with respect to the ammonia. There is of course the pos- 

 sibility that the aluminium hydroxide held in solution is present 

 in the colloidal state, but it is thought that the proportion held in this 

 form is small and that practically all in solution is present as ammon- 

 ium aluminate. This is also in agreement with the results obtained 

 by Blum\ who concluded from his measurements that ammonium 

 aluminate was formed in these solutions as was the case with the 

 solutions of aluminium hydroxide in sodium and potassium hydroxide. 



The next set of measurements was carried out in ammonia 

 solutions containing different amounts of ammonium nitrate. The 

 results obtained are shown below. The temperatures were 20°C. 

 and 30°C, and the values given show the weight of A1(0H)3 found 

 in 100 c.c. of solution. Equilibrium was much more quickly attained 

 in the presence of the ammonium nitrate. 



Table II. 



These results serve to illustrate the considerable influence of the 

 ammonium nitrate in lowering the solubility of aluminium hydroxide; 

 the solubility decreasing as the concentration of the ammonium 

 nitrate increases. We note, too, that as might be inferred from the 

 results in Table I, the solubility increases with the concentration of 

 the ammonia. The effect of a rise in temperature is to cause more of 

 the hydroxide to dissolve, this effect being more marked in the case 

 of those solutions which contain the more ammonia. This is perhaps 

 due to the breaTcing up of the aluminate with the rise in temperature. 



^ Loc. cit. 



