NITEOGENOUS MANURES 263 



and traces of iodates and some other salts are also 

 generally present. Perchlorates are an impurity of much 

 greater importance, as they are injurious to plants. 

 These compounds have been found in samples of nitrate 

 of soda in quantities equal to between 6 and 7 per cent, 

 of sodium perchlorate. Their presence was originally dis- 

 covered in the course of investigations into the cause of 

 injuries done to crops by the application of nitrate of 

 soda. Anything over 1 per cent, of sodium perchlorate 

 is likely to prove harmful. Happily, a larger proportion 

 than this is not of very frequent occurrence. 



Adulteration. Any tendency to fraudulent adulteration 

 of nitrate of soda is largely held in check by the fact that 

 so many samples are submitted to analysis the only 

 means by which its purity or quality can be determined. 

 In view of the high price which the substance commands, 

 it is very important that this should be done, in order to 

 make sure that it is neither deliberately adulterated nor 

 contains any undue quantity of accidental impurity. 

 There are no simple tests, beyond the fact that the sub- 

 stance should be practically completely soluble in water. 

 Chlorides can be detected by the addition of a drop of 

 silver nitrate, and sulphates by the addition of barium 

 chloride to a solution of the nitrate, but as both of these 

 are commonly present in good commercial samples, such 

 qualitative tests are of very little value. 



Manurial Value. The manurial effects of nitrate of 

 soda may be ascribed to the fact that it is a highly con- 

 centrated nitrogenous manure, contains the nitrogen in 

 the form most suitable for the nourishment of plants, 

 and is extremely easily soluble in water. The solubility 

 cannot be too strongly insisted upon. It is, in fact, the 

 key to the character of the substance. When nitrate of 

 soda is applied to a growing crop its effects are generally 

 manifest within a very short time, even when no rain 



