io8 ARTIFICIAL NITROGENOUS MANURES 



Commercial nitrate of soda may contain up to i per cent, of 

 sodium chloride, small quantities of sulphates, and occasionally a 

 little sodium iodate. The fertiliser is very hygroscopic, and the 

 estimation of moisture is thus of some importance. 



91. Qualitative Examination of Nitrate of Soda. 



The sample should be examined qualitatively for 

 S7ilphates and chlorides in the usual manner, and observa- 

 tion made of any insoluble or difficultly soluble matter 

 present. 



lodates should be tested for as follows : — About 0-5 

 gram of the nitrate of soda is dissolved in a little 

 water, acidified with dilute hydrochloric acid, and then 

 mixed with a solution of sulphurous acid. The iodic 

 acid is thus reduced with the formation of free iodine, 

 which will give a blue coloration on the addition of 

 starch paste. 



92. Analysis of Nitrate of Soda. 



{a) Moisture. — Two or 3 grams of the well-drawn 

 fair sample are weighed into a porcelain dish and dried 

 to constant weight in the steam oven. The loss in 

 weight is moisture, 



{U) Insoluble Matter and Sand. — Twenty grams of 

 the manure are dissolved in water, the insoluble matter 

 collected on a filter paper and well washed. The 

 residue is dried and ignited together with the filter 

 paper in a weighed crucible, and is weighed as sand. 



The filtrate and washings from the insoluble material 

 are made up to i litre with distilled water and the 

 solution retained for further experiments. 



if) Chlorides. — The chlorides present are best 

 estimated volumetrically by standard silver nitrate 

 solution, using potassium chromate as indicator. One 

 hundred or 200 c.c. of the solution from {b) are taken 



