60 PRACTICAL AGRICULTURAL CHEMISTRY [188-193 



POTASSIUM (K). — Use potassium chloride (KG) 

 solution. 



188. Platinum Chloride (PtCl 4 ) added to some of 

 the potassium chloride in a watch-glass and stirred with 

 a glass rod, gives a yellow crystalline precipitate of 

 potassium platinum chloride (K 2 PtCl 6 ). The precipitate 

 forms only in moderately strong solutions, and is hastened 

 by the addition of alcohol. 



188a. Sodium Picrate added to a little KC1 solution 

 placed in a watch-glass gives golden yellow needle-like 

 crystals of potassium picrate. The reaction is promoted 

 by addition of alcohol and stirring. 



189. Flame Coloration (26).— Pale violet. When 

 viewed through the indigo prism or cobalt-blue glass the 

 colour appears crimson. This colour is seen through the 

 prism in the presence of sodium salts. 



190. Potassium chloride heated on platinum foil behaves 

 exactly like sodium chloride. 



AMMONIUM (NHj). — Use ammonium chloride 

 (NH 4 C1) solution, 



191. Potassium Hydrate (KHO) poured either into 

 the solution or on to some solid ammonium chloride in a 

 test-tube and heated, gives off ammonia gas (NH 3 ), which 

 may be recognised by its smell, or by holding a piece of 

 moistened yellow turmeric-paper over the mouth of the test- 

 tube, when it will be turned brown. 



192. Platinum Chloride (PtCl 4 ) stirred in a watch- 

 glass with the solution gives a yellow crystalline precipitate. 



192a. Sodium Picrate, when stirred with AmCl 

 solution, gives golden-yellow needle-like crystals (188a). 



193. Solid ammonium chloride, if heated in an ignition- 

 tube, volatilises completely, and forms a white sublimate on 

 the cold part of the tube. 



