CH. vii] Potassium and Calcium Nitrates 131 



reduced to a minimum : there is the further advantage 

 that the nitrate of soda does not come in contact with 

 the superphosphate (which is drilled with or before the 

 seed) : unless thej'^ are very dry these two fertilisers do 

 not mix well although if put on at once the mixture can 

 be used where labour is scarce. Heavy dressings such as 

 are used in market gardens should be applied in two or 

 three lots and not all at once. 



Perchlorates are occasionally present in nitrates and are 

 very dangerous, as little as 1 lb. per acre causing injury. 



The ordinary nitrate of soda of commerce contains 

 15-5 per cent, nitrogen and its pre-war price was about 

 11 per ton f.o.r.^; each per cent, or "unit^" of nitrogen 

 therefore cost 14s. ^d., and each pound of nitrogen cost 

 8d. Since the war it has been practically unobtainable 

 by farmers. 



Nitrate of fotash (KNO^) 



This substance is dearer than a mixture of nitrate of 

 soda and sulphate of potash supplying the same ingre- 

 dients, and therefore it is not used in this country. But 

 being much less bulky than the mixture it finds con- 

 siderable application in countries where valuable crops 

 are raised and freights are high: thus it is used in the 

 Canary Islands and elsewhere under similar conditions. 



Commercial nitrate of potash contains nearly 14 per 

 cent, of nitrogen. 



Nitrate of lime 



Of recent years a considerable quantity of nitrate of 

 lime has been manufactured and prior to the war was 

 put on the market for use as a fertiliser. The industry 



^ F.o.r. =free on rail. Prices delivered to the buyers station may 

 average about 10s. per ton extra. 

 - Sec p. 206. 



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