STUDY Of AIR. 11 



physical properties of nitrogen in the 

 air? Is, therefore, the nitrogen in the 

 bottle pure? 



2. Place a piece of phosphorus on the burning 



spoon and light it. Carefully remove 

 the glass cover sufficiently to lower the 

 burning phosphorus into the jar of nitro- 

 gen. Cover again as quickly as possible. 



a. What do you observe? 



b. What, then, is the most striking dif- 



ference between the effect of oxy- 

 gen and nitrogen on heated phos- 

 phorus ? 



3. If you are sure that air has been kept out 



of the jar, see if sulphur, carbon, or iron 

 will burn in nitrogen. 



a. What do you conclude? 



b. Did the nitrogen itself burn in any of 



the preceding experiments? 



c. Does nitrogen make things burn? 



d. What is the advantage of having air 



composed of both oxygen and nitro- 

 gen? 

 C. Percentage composition of air. 



1. Pour the water at the bottom of the jar 



into a cylindrical graduate. How much 

 water is there? (This water took the 

 place of the oxygen as fast as the latter 

 was removed from the air by the burn- 

 ing phosphorus.) What, therefore, was 

 the volume of oxygen in the air? 



2. Fill the jar with water and then pour it into 



