[299] SCIENTIFIC MANUAL. 13 



their roots from the soil in the form of nitrogen, its supply 

 in plant nutrition being derived exclusively from nitric acid 

 and ammonia. 



Ammonia. This important compound, is a combina- 

 tion of nitrogen and hydrogen. It is formed by the de- 

 cay, or decomposition, of organic matter, both animal and 

 vegetable, containing nitrogen. 



Ammonia gas is formed by the union of one atom of 

 nitrogen with three of hydrogen. It has a very pungent 

 and penetrating odor, and is strongly alkaline in property, 

 instantly changing red litmus paper blue. With different 

 acids it forms salts : with sulphuric acid it forms sulphate 

 of ammonia; with nitric acid, nitrate of ammonia; with 

 carbonic acid, carbonate of ammonia, etc. 



It is called the "volatile alkali," because of its being 

 easily driven off by heat, or displaced by other stronger 

 alkalies and separated from its compounds. It is the most 

 costly constituent of commercial fertilizers, and a necessary 

 component of every fertile soil. It exists in very minute 

 proportion, as free ammonia, in the atmosphere, from 

 which it is absorbed as carbonate of ammonia by plants, 

 or carried down to the soil by the rain, which absorbs it 

 during its fall. 



The principal sources from which ammonia for agricul- 

 tural use is derived are dried blood, dried flesh, fish scraps, 

 gas works, human excrement, (hoofs, horns and leather 

 scraps, with exhaustive distillation), sewage and natural 

 guano, or the accumulated deposits of marine birds. The 

 principal natural sources on Georgia farms are cotton seed, 

 stable manure, and the vines, roots and foliage of field peas. 

 It performs a most important part in the growth of all veg- 

 etation, and is rapidly exhausted from soils under continu- 

 ous clean culture. 



Carbon is one of the most abundant elements in nature 

 forming nearly one-half of the material of the vegetable 

 kingdom, and a very important constituent of many rocks, 



