ARTIFICIAL AND CONCENTRATED MANURES. 69 



are more immediately available to the plant. The manu- 

 rial elements, if in a form in which plants can nse 

 them, are quite as much actual plant-food when contained 

 in these materials as when furnished by the more familiar 

 natural manures. 



Natural manurial products, or homemade materials, 

 are used in their original state or applied directly to the 

 soil. Artificial products, as a rule, require treatment 

 previous to their use. 



Nitrogen. — Mtrogen is the most costly element of 

 manures. It is absolutely essential to all organized life, 

 whether animal or vegetable; it is the basis of the al- 

 buminoids of plants, the casein of milk, and the fibrin 

 of blood. Nitrogen occurs in three forms, and all these 

 forms- exist as commercial manure products. The form 

 means its combination with other chemical elements; 

 namely, nitrogen as nitrates, nitrogen as ammonia, and 

 nitrogen as organic matter. 



Forms of Nitrogen. — Nitrogen in the form of a 

 nitrate means its combination with oxygen in such pro- 

 portions as to form nitric acid, united with a base like 

 soda or potash; thus, we have nitrates of soda, potash, 

 lime, etc. 



Nitrogen as ammonia means its combination with 

 hydrogen in such proportion as to form ammonia. Am- 

 monia gas consists of one part of nitrogen and three 

 of hydrogen. This gas readily combines with various 

 acids, as sulphuric, nitric, etc., to form ammonia salts. 



Nitrogen in the form of organic matter means its com- 

 bination with the chemical constituents, carbon, hydrogen, 

 and oxygen, either as animal or vegetable substances. 



