114 ARTIFICIAL NITROGENOUS MANURES 



mercury instead of water. To allow for the errors 

 introduced by the use of water it is advisable to control 

 the result by carrying out an experiment, under exactly 

 the same conditions, with chemically pure sodium or 

 potassium nitrate. The purity of the fertiliser under 

 examination may then be measured by direct com- 

 parison without further calculation. 



95. {c) Estimation by Reduction to Ammonia. — With 

 manures containing only small quantities of nitrates it 

 is advisable to use the reduction process already 

 described (48 (</), p. 70). By using small quantities 

 (0-5 gram or less) the method may also be employed for 

 the estimation of nitrates in nitrate of soda, etc. 



Existence of Perchlorates in Nitrate of Soda. 



Nitrate of soda frequently contains perchlorates (chiefly of 

 sodium and potassium) in quantity varying from 0-14 to 679 per 

 cent. These salts have a very injurious effect on vegetation and, 

 in particular, considerably retard germination and cause the leaves 

 of plants to wilt. Rye and maize are the most susceptible crops, 

 but other cereals are similarly affected. The determination of 

 perchlorates in nitrate of soda may therefore be of considerable 

 importance. 



96. Estimation of Perchlorates in Nitrate of Soda. 



Five grams of the fertiliser sample are dried in the 

 oven, mixed with 7 to 8 grams of pure slaked limxC, and 

 the mixture heated in a large covered crucible over the 

 Bunsen flame for fifteen minutes. The ignited mass is 

 extracted with water, filtered, and thoroughly washed, 

 and the filtrate then neutralised exactly with nitric acid. 

 The chlorine present in the solution is determined by 

 direct precipitation or volumetrically by titration with 

 silver nitrate, using potassium chromate as indicator 

 (92 (<:), p. 108). One part of CI is equivalent to 3-45 

 parts NaClO^. 



