New York Agricultural Experiment Station. 43 



(2) Nitrogen in Ammonia. — Nitrogen combined with the ele- 

 ment hydrogen forms ammonia. Ammonia is present in the air in 

 very small quantities. Ammonia is formed when vegetable and 

 animal substances containing nitrogen decompose. 



Ammonia is a colorless gas, and it is this gas dissolved in water 

 which is familiar to us as ammonia water or " Spirits of Hartshorn," 

 and which causes the peculiar odor of " hartshorn." 



Ammonia unites with different acids and forms salts somewhat as 

 metals do ; these salts we call amnhonium salts, compounds wliich 

 do not generally have any odor like ammonia. Thus, ammonia 

 combined with sulphuric a,cid iorms ammoniuTn sulphate, commonly 

 called sulphate of ammonia ; ammonia, combined with hydrochloric 

 acid, forms amynonium chloride, sometimes called muriate of 

 ammonia, also known as sal ammoniaG. 



(3) Nitrogen in Nitrates. — Nitrogen, combined with hydrogen 

 and oxygen, forms nitric acid or aqua fortis. If in nitric acid a 

 metal as sodium, for example, takes the place of hydrogen, we have 

 formed a sodium salt of nitric acid or a nitrate, called sodium 

 nitrate, or nitrate of soda. 



When animal and vegetable substances decompose in rather warm, 

 moist places, the nitrogen is changed into nitrates. This change of 

 the nitrogen of oi'ganic matter into nitrates is caused by germs called 

 hacteria, which are very small living vegetable organisms, and 

 which exists everywhere in enormous numbers. The process is 

 known as " nitrification^ 



(4) Nitrogen in Animals and Plants or Organic Nitro- 

 gen. — Nitrogen, combined with the elements, hydrogen, carbon 

 and oxygen occurs in plants and in animals. Such substances for 

 example are the casein or curd of milk, the gluten or gummy portion 

 of wheat, the fibrin of blood, the white of Q%%, etc. Wlien such 

 compounds decompose, the nitrogen is first changed into ammonia, 

 and then, under proper conditions of warmth, moisture and access 

 of air, into nitric acid or nitrates. The nitrogen existing in ani- 

 mals and plants is generally called orgoMic nitrogen. 



(b) In what Forms Nitrogen is Useful to Plants. — Plants can 

 use nitrogen in three different forms, viz. : 



(1) As nitrogen gas or uncombined nitrogen. 



(2) In the form of ammonia. 



(3) In the form of nitrates. 



