CHAPTER XV 



NITROGEN 



(Nitrogen = N) 



Occurrence. Nitrogen is another element that plays 

 an important part in plant and animal life. In com- 

 bination with carbon, hydrogen, and oxygen, it forms 

 protein, one of the main classes of foodstuffs. It is 

 an essential constituent of all living organisms. It is 

 also found in nature in the form of potassium nitrate, 

 a compound commonly called niter, from which fact it 

 derives its name. As an element it forms about four- 

 fifths of the air. 



Preparation. For class use nitrogen is usually 

 obtained from the air. 

 Since oxygen and nitro- 

 gen make up more than 

 99% of the atmosphere, 

 when oxygen is removed, 

 nitrogen is left sufficiently 

 pure for the study of its 

 physical properties. Oxy- 

 gen is removed by combin- 

 bining it with any element 

 whose oxide is readily 



Fig. 41. Experiment to determine 

 the composition of air. 



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