LESSONS IN CHEMISTRY IB 



we thrust in the glowing stick. It immediately bursts into 

 flame and burns brightly until all the oxygen is used. 

 Brilliant fireworks can be made by burning phosphorus or 

 sulphur in the other bottles we filled. Even a steel watch- 

 spring, or piece of picture wire, if the tip is dipped in burn- 

 ing sulphur, catches fire in pure oxygen and throws oft' 

 flashing sparks of burning metal. We see, then, that the 

 most important chemical property of oxygen is its power to 

 make things burn. When any combustible substance is 

 heated sufficiently, the elements of which it is composed 

 unite with the oxygen, and thus are formed the compounds 

 we have called oxids. 



Preparation of Nitrogen. 1 The other gas found in air is 

 called ni'tro-gen. These two elements, oxygen and nitrogen, 

 are not chemically united ; 

 they are simply mixed, as 

 we might mingle sand and 

 sugar. We can easily take 

 the sugar from the sand 

 by putting the mixture 

 in water ; the sugar is dis- FlG 2 _ reparation of Nitrogen, 

 solved, while the sand re- 

 mains untouched. Chemists can also remove the oxygen 

 from a certain quantity of air, leaving free nitrogen. 



The materials required for the experiment are a tray of 

 water, a wide-mouthed bottle, a bit of phosphorus the size 

 of a pea, and a piece of cork large enough to float the phos- 

 phorus on the water. Placing the phosphorus on the cork 

 and lighting it, we quickly cover it with the mouth of the 

 bottle in such a way that the rim reaches just beneath the 

 surface of the water. The phosphorus burns readily for a 

 time, and the bottle is soon filled with the white fumes of 

 oxid of phosphorus. When all the oxygen has been used, 

 the flame dies out. As we watch the experiment, the white 

 fumes are seen to be gradually settling toward the surface 

 1 See "Laboratory Exercises," No. 3. 



