72 FIRST PRINCIPLES OF AGRICULTURE. 



this country. It is completely soluble in water, diffuses 

 readily throughout the soil, and, since it forms no in- 

 soluble compound with soil constituents, is liable to be 

 washed into the lower layers of the soil, and finally into 

 the drains, if applied in the fall of the year, or in too 

 large quantities. It is very beneficial for early and 

 quick-growing crops, particularly upon light sandy soils, 

 because it is ready for use as soon as applied. 



The soda with which the nitrate is combined does not 

 possess any value as a plant-food constituent, though 

 it is believed to exert a beneficial effect upon the phys- 

 ical character of soils. This value is not taken into 

 account in commercial transactions. 



The use of nitrate is rapidly increasing where its ad- 

 vantages are well known. 



Nitrate of potash, or saltpetre, is another nitrate salt 

 used to some extent, though its cost of production is 

 too great to admit of its competition with the nitrate 

 of soda. It is a concentrated product, and furnishes 

 potash in addition to the nitrogen. 



Sulphate of Ammonia. Ammonia for fertilizing 

 purposes is secured almost entirely from sulphate of am- 

 monia, which is another chemical salt of definite com- 

 position, and is one of the most concentrated forms in 

 which nitrogen occurs. It contains, when pure, twenty- 

 one and two-tenths per cent of nitrogen. It is derived 

 chiefly as a by-product from the manufacture of gas by 

 the dry distillation of coal, and is also secured in smaller 

 quantities in the manufacture of bone-black for sugar re- 

 fineries, and in the distillation of refuse animal matter. 



The nitrogen contained in these products is, by the 



