70 CHEMICAL PROPERTIES OF SOIL 



N 

 distillation is stopped, and — caustic soda is run into 



the distillate until it just turns yellow. Each cubic 



N 

 centimetre of— sulphuric acid used up during the dis- 

 tillation is equivalent to 0-007 gram of nitrogen. From 

 this may be calculated the nitrogen in 250 c.c. of the 

 original solution. 



(J?) Sodium Phosphate. — Fifty c.c. of the solution are 

 mixed with a quantity (about i gram) of ammonium 

 nitrate, and treated with 20 c.c. of ammonium-molybdate 

 solution. The mixture is stirred well, and allowed to 

 stand in a warm place for a day. The precipitate is 

 then carefully washed once or twice by decantation, 

 completely transferred to a porcelain evaporating basin, 

 and taken down to dryness on the water-bath. The 

 residue is carefully heated until all the ammonia is 

 given off and the substance assumes a uniform dark 

 blue colour. Each part of the residue contains 0-0396 

 part of P2O5. From this the content of PgOg in the 

 solution may be calculated. 



(c) Potassium Chloride. — Fifty c.c. of the potash 

 solution are acidulated with a little concentrated hydro- 

 chloric acid. A strong solution of platinic chloride 

 (10 per cent.) is added in moderate excess, and the 

 liquid evaporated on the water- bath to a thick paste. 

 The residue is digested with 80 per cent, alcohol, then 

 washed by decantation with the same liquid, and finally 

 transferred to a tared filter, where washing with diluted 

 alcohol is continued until the washings are colourless. 

 The residual precipitate is dried to constant weight at 

 100° C. It consists of KgPtClg, and the weight multi- 

 plied by 0-1937 gives the weight of potash, KgO, in the 

 solution taken. 



id) Sodium Nitrate. — One hundred c.c. of the 



