CHAPTER VI 

 Nitrogen 



43. Occurrence. Nitrogen occurs abundantly in a free 

 state in the air, nearly four-fifths by weight being uncom- 

 bined nitrogen. It also forms a part of some of the com- 

 pounds which make up animal and plant tissues, where 

 it is in chemical combination with carbon, hydrogen, and 

 oxygen. Nitrogen is present also in the soil, forming a 

 part of the decaying organic matter ; it is one of the ele- 

 ments of ammonia gas and ammonium compounds, and is 

 present in combination with other elements, as in nitrates. 



44. Preparation. Nitrogen is usually prepared from 

 air by removing the oxygen with which it forms a me- 

 chanical mixture. Since air is composed of both oxygen 

 and nitrogen, if the oxygen in a given volume of air, as 

 in a cylinder, is chemically united with phosphorus or 

 carbon, forming soluble products, there is a residue of 

 nitrogen left in the cylinder. Nitrogen produced in this 

 way is not pure, but con tains traces of other elements and 

 compounds. For experimental purposes, it may, how- 

 ever, be considered as nitrogen. Nitrogen can also be 

 produced from its compounds, as by the removal of the 

 hydrogen from ammonia gas. The method of prepara- 

 tion in the laboratory is as follows : 



Experiment 3. Insert a long pin through the center of a 

 large flat cork. Fasten a short piece of candle to the cork by 

 means of the pin. Nearly fill the pneumatic trough with water. 

 Light the candle and float it upon the surface of the water. In- 

 vert the large cylinder over the candle, having the mouth of the 



