250 ARTIFICIAL MANURES [chap. 



Among the fertilising constituents nitrogen must be 

 given the first place. Not only is combined nitrogen 

 much more expensive than either potash or phosphoric 

 acid, I lb. costing about 6d. (12 cents), but as a 

 fertiliser it seems to have a much more direct and 

 immediate action upon a plant than the other two 

 substances, which are at bottom equally indispensable. 

 We find that nitrogen pushes on the first vegetative 

 development of the plant, promotes its growth in fact, 

 thus enabling it to search the ground more thoroughly 

 for phosphoric acid and potash which may there be 

 present. For some little time, indeed, crops may be 

 grown by the aid of nitrogenous fertilisers alone, and 

 there is always some tendency to use an excess of these 

 substances in comparison with manures containing 

 phosphoric acid and potash, which make less immediate 

 show. Of the purely nitrogenous fertilisers there are 

 five which are commonly employed ; sulphate of 

 ammonia, the most concentrated, contains about 20 per 

 cent, of nitrogen, and nitrate of soda contains about 1 5^ 

 per cent. To these concentrated fertilisers two new 

 rivals have recently arisen in the shape of calcium 

 cyanamide or nitrolim, containing about 18 per cent, of 

 nitrogen, and nitrate of lime, containing about 1 3 per 

 cent. These latter materials are manufactured artificially, 

 the nitrogen they contain being derived from the 

 atmosphere. Lastly comes soot, a waste material which 

 contains a small quantity of ammonia, showing from i 

 to 5 per cent, of nitrogen according to its purity and the 

 nature of the material from which it has been derived. 



Sulphate of ammonia is a product recovered in 

 the manufacture of coal-gas, coke, and other industries 

 involving the destruction of coal. It is a pale grey, 

 crystalline substance that is freely soluble in water, 

 though it remains dry, and does not naturally run down 



