88 AGRICULTURE. 



slowly, and hence the nitrogen is very slowly 

 available. 



One of the best vegetable nitrogenous fertil- 

 izers is cottonseed-meal. It is largely used in 

 the South, but its usefulness as a food for cattle 

 makes it too expensive, in many cases, for a fer- 

 tilizer. Castor pomace, obtained as a waste 

 product in extracting the oil from the castor 

 bean, is of no value as a food, and decays 

 rapidly in the soil, hence makes a useful and in- 

 expensive fertilizer, though it contains only 

 about one-half as great a per cent, of nitrogen 

 as chemically pure sodium nitrate. 



Mineral Sources. -Soluble nitrate is com- 

 monly obtained as nitrate of soda, or "Chile 

 saltpeter," which is found in deposits in the rain- 

 less regions of the Peruvian coast. It contains 

 a large per cent, of common salt, but when 

 purified, as prepared for commerce, it is 95 

 per cent., or more, pure sodium nitrate 

 (NaNO 3 ), and about 15 or 16 per cent, of this is 

 nitrogen. 



Sulphate of ammonia, (NH 4 ) 2 SO 4 , is formed 

 from coal as waste material in the manufacture 

 of gas and coke, also from the dry distillation 

 of animal bone in the making of bone-black. 

 It generally contains about 20 per cent, of 

 nitrogen, making it the richest in nitrogen of 

 any of the commercial fertilizers. It is quick 

 to act, and is readily distributed in the soil, and, 



