296 



On Chemical Tests. 



with a very small proportion of water — no free acid produces a precipi- 

 tate in aluminous salts. 



Potash produces in neutral solutions a bulky precipitate of the hy- 

 drate of alumina soluble in excess of the potash. Muriate of ammonia 

 (if the precipitate be re-dissolved by the potash) produces in such so- 

 lution a precipitate of alumina. c 



Ammonia gives a voluminous precipitate insoluble in an excess of 



the ammonia. The presence of muriate of ammonia does not prevent 



the production of this precipitate, (see 34) nor yet of the precipitates 



by the following re-agents, on which account salts of alumina cannot be 



mistaken for those of magnesia. 



Carbonate of potash....') » , . • . . . , . 



Carbonate of ammonia [ A precipitate soluble m acids, 



Phosphate of soda . . . . j ancl ln a solutlon of P otash ' 



Oxalic acid, neutral oxalates, prussiate of potash, tartaric acid, 



liquid sulphuretted hydroye c t and sulphuretted hydrogen gas produce 



no precipitates. 



Hydrosulphuret of ammonia produces a precipitate of pure alumina 

 and so does muriate of ammonia, see 34 and 36. 



a. Aluminous minerals before the blow-pipe on charcoal produce 

 a blue flame if moistened with nitrate of cobalt. 



b. Salts of alumina are distinguished by a sweet astringent taste. 

 They are not precipitated by oxalate of ammonia, nor tartaric acid, 

 which distinguishes them from salts of yttria ; nor by tincture of galls, 

 or prussiate of potash, in which they differ from the salts of yttria and of 

 glucina. If sulphuric acid, and then sulphate of potash be dropped into a 

 solution of alumina, or its salts, and the liquid be allowed to repose, crys- 

 tals of alum soon make their appearance. 



e. Solutions of alumina are distinguished from those of alkaline 

 salts by producing a wfiite precipitate with ammonia : from solutions, of 

 barytes,stronia,andlime by a white precipitate with ammonia,and no pre- 

 cipitate with sulphuric acid which produces a precipitate in those earths 

 except in the case of dilute solutions of lime. Alumina is distinguish- 

 ed from magnesia in solution by its behaviour with potash, and muriate 

 of ammonia. In neutral aluminous solutions, potash produces a 

 bulky precipitate, which wholly re-dissolves in an excess of potash ; 

 and in such a solution of alumina in potash, muriate of ammonia 

 produces a precipitate of alumina. Distinguished from glucina, see 

 57, a. 



d. The hydrate requires very careful washing and long continued 

 heat in drying for quantitative analysis. 



