16 PRELIMINARY EXPERIMENTS 



With students it is always safest to interpose a wash bottle (e) 

 between the generator and the flame so as to prevent damage in 

 case of an explosion. If potassium permanganate is put in the 

 wash bottle, impurities will be removed. 



5. NITROGEN 



Object. To learn something of the preparation and 

 properties of nitrogen, and the composition of air. 



Apparatus. A small piece of phosphorus, forceps, a cork float, 

 a large vessel of water, a bell jar, a support for the bell jar, and 

 several wide-mouth bottles. ' 



Method. Place a crumb of phosphorus upon the cork 

 float, using the forceps for handling it. Dry it with a piece 

 of blotting paper, but under no circumstances let it touch the 

 skin. 



Let it ignite spontaneously if there is time. Otherwise, 

 ignite it with a burning splinter, and immediately invert 

 the bell jar over it. 



Note the color of the flame and smoke, the behavior of 

 the water, and the height to which it rises in the bell jar. 

 -Why does it rise only about \ the height of the jar? What 

 has been consumed ? How much oxygen must there be in 

 a given amount of air? What becomes of the white fumes 

 which come from the burning phosphorus? 



After all the white fumes have disappeared and the con- 

 tents of the bell jar have become clear, the gas may be re- 

 moved into wide-mouth bottles and tested. To remove the 

 gas into a bottle, fill the bottle with water, invert, keeping 

 the mouth beneath the surface, and tilt the bell jar so that the 

 bubbles of gas can escape upward into the bottle. Test the 

 nitrogen thus obtained, with burning a stick, with limewater, 

 and by tasting and smelling. 



