ARTIFICIAL AND CONCENTRATED MANURES. 73 



process of distillation, viz., in the absence of air, driven 

 off in the form of ammonia gas, which is conducted 

 into receptacles containing sulphuric acid, which fixes 

 the ammonia in the form of a sulphate. This is a 

 crude product, and is usually dissolved, recrystallized, 

 and purified, and is then reasonably uniform in compo- 

 sition, and contains on the average twenty and one-half 

 per cent of nitrogen. When sold without this method of 

 purification, it is called "brown sulphate of ammonia;" 

 this is more variable in composition, with moisture, and 

 insoluble and oily matters as impurities. Brown sulphate 

 often contains less than eighteen per cent of nitrogen. 

 Sulphate of ammonia, while freely soluble in water, is 

 readily absorbed by the soil, and may be applied in the 

 fall without danger of serious loss, and is, next to ni- 

 trate of soda, one of the best forms of nitrogen for 

 fertilizing purposes. It is a particularly useful form on 

 clay and clay loam soils. 



Nitrates and ammonia salts possess two chief advan- 

 tages; viz., solubility, hence ease of distribution in the 

 soil, and availability, or quick usefulness to the plant. 



The cost per pound of nitrogen in the form of am- 

 monia is usually greater than for the nitrate of soda, 

 because of the comparatively limited supply, and be- 

 cause more largely used in the arts. 



Organic Nitrogen. — Organic nitrogen is obtained 

 from a wide variety of sources, and is composed of both 

 animal and vegetable matter. The commercial materi- 

 als, from whatever source derived, unlike the salts men- 

 tioned, are not definite chemical compounds; those of 

 the same name, even, vary in their composition, and 



