204-210] TESTS FOR ACID-RADICALS 63 



PHOSPHATE ("'P0 4 ).— Use sodium-hydrogen-phosphate 

 (Na 2 HP0 4 .i2H 2 0) solution. 



204. Magnesium Sulphate (Mg 2 S0 4 ) to which 

 has been added ammonium chloride (NH 4 C1) and a 

 little ammonium hydrate (NH 4 OH), gives a white crystal- 

 line precipitate of magnesium - ammonium phosphate 

 (MgNH 4 P0 4 .6H 2 0), soluble in acids. 



205. Ferric Chloride (FeCl 3 ) added after acetic 

 acid and sodium acetate gives a pale yellow precipitate of 

 (erric phosphate (FeP0 4 ), soluble in hydrochloric acid. 



206. Ammonium Molybdate (NH 4 HMo0 4 ) when 

 warmed with a little phosphate solution gives a yellow 

 precipitate. The ammonium molybdate should be in large 

 excess, and the solution should be acidulated with nitric acid. 



207. Silver Nitrate (AgN0 3 ) gives a yellow precipi- 

 tate, soluble in ammonium hydrate (NH 4 OH) or in nitric 

 acid (HN0 3 ). 



SILICATE (""Si0 4 ).— Use sodium silicate (Na 2 Si0 3 ) solu- 

 tion for liquid, and finely ground sand (Si0 2 ) for solid. 



208. Hydrochloric Acid (HC1) gives a gelatinous 

 precipitate of silicic acid (H 4 Si0 4 ). This, however, some- 

 times remains in solution, in which case the liquid should 

 be evaporated to dryness in a basin, moistened with strong 

 hydrochloric acid, and boiled with water. An insoluble 

 residue of silica (Si0 2 ) will remain. 



209. If solid silica (Si0 2 ) be fused into a bead of sodium 

 carbonate it causes the melted bead to froth, from the 

 liberation of carbon dioxide. 



210. If solid silica be fused into a bead of microcosmic 

 salt (NaNH 4 HP0 4 ) it is not dissolved, but floats about in 

 semi-transparent particles. 



