CHAPTER VII 

 OXYGEN AND OXIDATION 



33. The Air which we try to keep pure in our room 

 and which we breathe is composed of several gases which 

 are thoroughly mixed. These gases are nitrogen, oxygen, 

 carbon dioxide, and a few others which are not so 

 useful to man. Evaporated water is in the air in varying 

 amounts and is very necessary for health. A person can- 

 not study well in a room where the air is too dry. How 

 can we keep the air from getting too dry for health? 



The three important gases that make up about 99 per 

 cent of the air do not vary much in amount. Each one 

 is always present in about the same per cent where the 

 air is unconfined and free to move about as wind. 

 Nitrogen composes about 79 per cent of the air, and its 

 use, as far as oxidation is concerned, is to dilute the oxy- 

 gen and prevent too rapid burning. Carbon dioxide 

 composes about .03 per cent of the air and is formed by 

 burning coal, gas, or wood. Oxygen, which composes 

 about 20 per cent of the air, is the gas that is necessary 

 in the process of burning and of breathing. 



34. Preparation of Oxygen. Weigh out about six 

 grams of potassium chlorate (KC1O 3 ) and the same 

 amount of manganese dioxide (MnO 2 ). Mix these two 

 compounds in powdered form on paper and place the 

 mixture in a test tube. Have the test tube perfectly 

 dry inside and outside. Close the test tube by a rubber 



