CHAPTER XXIV 

 NITROGEN. THE ATMOSPHERE 



IT is time now to return to the atmosphere, of which the most 

 active component, oxygen, has already been discussed. The 

 other chief component, nitrogen, will lead us to ammonia NH 3 

 and nitric acid HNO 3 , both of which are of great commercial 

 importance, and have interesting derivatives. 



Occurrence of Nitrogen. Aside from the free nitrogen^ 

 which forms nearly four-fifths of the bulk of atmospheric auv_ 

 much nitrogen is found in nature in combination. 

 Potassium nitrate KyOt is formed in the soil by the 

 action of bacteria upon animal matter, and sodium 

 nitrate NaNOa is obtained from an immense deposit 

 in Peru and Chili. Nitrogen is an essential constitu- 

 ent of an important class of organic substances called 

 the proteins, which are found in plants, particularly 

 in the fruit, and in the muscles and other tissues of 

 the animal body. 



Preparation. Nitrogen may be obtained from 

 the air by simply removing the oxygen. This 

 nitrogen is not pure, however, as it retains about one 

 per cent of other gases the " inert gases " of the 

 atmosphere. The oxygen can be removed by allowing pieces 

 of moist phosphorus (Fig. 72) slowly to oxidize in an enclosed 

 specimen of air. The phosphoric acid H 3 PO 4 and other products 

 of the oxidation of the phosphorus dissolve in the water. 



Pure nitrogen can be obtained from pure compounds of nitrogen. 

 Thus, ammonia gas may be passed over heated cupric oxide 



286 



FIG. 72 



