53 PRACTICAL AGRICULTURAL CHEMISTRY [174-180 



turns brown in the air. This is best seen by pouring the 

 precipitate on to a filter-paper. If, however, ammonium 

 chloride (NH 4 C1) has been added before the NH 4 OH, the 

 precipitate will not be formed. 



174. Potassium Hydrate (KHO) gives the same 

 precipitate as ammonium hydrate, even in the presence of 

 AmCl. 



175. Ammonium Sulphide, (NH 4 ) 2 S, gives a flesh- 

 coloured precipitate of manganous sulphide (MnS). This 

 precipitate often appears yellow from the excess of the 

 (NH 4 ) 2 S, which has been added. On filtering off this liquid 

 the true colour may be seen. The colour of the precipi- 

 tate darkens on standing in the air. 



176. If a solid substance containing manganese be 

 mixed with three times its weight of sodium carbonate 

 (Na 2 C0 3 ), and a third as much potassium nitrate 

 (KNO3), an d tn e mixture fused on platinum foil, a bluish- 

 green mass is obtained on cooling. 



177. Borax Bead (27). — In the outer flame violet 

 whilst hot, amethyst when cold. In the inner flame colour- 

 less both hot and cold. 



CALCIUM (Ca).— Use calcium chloride (CaCl 2 '6H 2 0) 

 solution. 



178. Ammonium Carbonate, (NH 4 ) 2 C0 3 , added 

 after ammonium chloride (NH 4 C1) gives a white precipitate 

 of calcium carbonate (CaC0 3 ), soluble in acetic acid. 



179. Ammonium Oxalate, (NH 4 ) 2 C 2 4 , gives a 

 white precipitate of calcium oxalate (CaC 2 4 ) soluble in 

 hydrochloric acid (HC1), and insoluble in acetic acid (HA). 



180. Sulphuric Acid (H 2 S0 4 ) gives a white preci- 

 pitate of calcium sulphate (CaS0 4 ), which forms at once in 

 strong solutions, but only on being boiled, in dilute solutions. 



