36 THE CHEMISTEY OF THE FARM. 



The ammonia is converted into nitrates in a few days 

 or weeks after the application of the salt to a moist, fer- 

 tile soil. The use of sulphate of ammonium is attended 

 with some loss of lime to the soil, as both the sulphuric 

 acid, and the nitric acid subsequently formed, unite with 

 the lime of the soil, and the resulting salts are more or 

 less removed by drainage. Ammonium salts produce 

 little effect in soils destitute of lime. 



Nitrate of Sodium. An enormous deposit of the 

 crude salt, containing much chloride of sodium, is found 

 in Peru. The nitrate sent to this country has been puri- 

 fied by crystallisation; it contains 95 96 percent, of real 

 nitrate, or 15 '6 15*8 per cent, of nitrogen. The most 

 usual impurity is common salt. 



This manure, like the preceding, is valuable solely for 

 its nitrogen. It is an excellent manure for all crops re- 

 quiring artificial supplies of nitrogen, especially corn 

 crops and mangels. For corn crops it is best employed 

 together with superphosphate. Nitrate of sodium should 

 not be mixed with a damp superphosphate, else nitric 

 acid will be lost on keeping. The two manures may be 

 mixed immediately before use; or the superphosphate 

 may be sown with the corn, and the nitrate applied 

 afterwards as a top dressing. 



The return from the use of nitrate of sodium is 

 generally greater than from the use of the same quantity 

 of nitrogen as sulphate of ammonium. The nitrate is 

 especially better in dry seasons ; in wet seasons the am- 

 monium salt sometimes has the advantage. 



Nitrate of sodium is especially suited for clay land. 

 The soda which it leaves in the soil apparently helps to 



