§ 51. ALUMINIUM. 65 



dissolve the residue in water acidified with hydrochlorio 

 acid, filter if necessary, and then to precipitate the mag- 

 nesium in the usual manner with hydric disodic phosphate. 



c. If but little calcium is mixed with considerable mag- 

 nesium in the substance to be analyzed, evaporate the 

 solution to dryness, and ignite the residue gently to ex- 

 pel ammoniacal salts completely, dissolve this residue in a 

 very little water mixed with a few drops of hydrochloric 

 acid, add strong alcohol and a slight excess of pure con- 

 centrated sulphuric acid, and digest the mixture in the 

 cold several hours. Collect the precipitated calcic sul- 

 phate on the filter, wash it first with almost absolute al- 

 cohol and finally with alcohol of about 40 "1^, dry, ignite 

 and weigh. 



Expel the alcohol from the filtrate and washings by 

 heat, and determine magnesium in the usual manner with 

 sodic phosphate. 



ALUMINIUM. Al. 27.5. 



51. Compounds of aluminium with phosphoric and 

 silicic acids, and fluorine, are insohible in water. The 

 silicate is insoluble in acids. 



Reactions. — Solutions containing aUiminium give a pre- 

 cipitate, Al^OgjSH^O, or Al^HgO^, with ammonic or sodic 

 hydrate ; the precipitate is dissolved in an excess of the 

 latter reagent, but not in the former. 



When a compound of aluminium is fused on platinum 

 foil with four or five times its bulk of sodic and potassic 

 carbonate, the fused mass dissolved in a very little water, 

 and the solution filtered if necessary, nitric acid added to 

 the filtrate carefully until effervescence ceases, and then a 

 few drops of ammonia until the solution emits a faint 

 odor of the reagent, a white flocculent precipitate appears, 

 at once, or after standing some time ; it will appear soon- 

 er, or be more readily perceived, on heating the liquid 

 gently for a time. 



