COMBUSTION AND OXIDATION 



75 



and on the other water (H 2 0) . Hydrogen gas burning by itself 

 produces no carbon dioxide of course. In many cases even 

 when hydrogen is present, carbon only is oxidized and the 

 hydrogen unites with the oxygen in the material to form water. 

 Smoke is not a product of burning. On the contrary, it con- 

 sists of particles of unburned carbon which, if allowed to 

 escape into the air, is a waste of good material. All fires should 

 be so stoked as to prevent smoke from escaping. When soft 

 coal is burned at home, wetting the coal aids in reducing the 

 smoke. Though ashes are left when coal and wood are burned, 

 these are not products of burning. They simply represent the 



FIG. 25. A common way of preparing oxygen. 



mineral matter which was mixed with the combustible 

 material. 



72. Preparing Oxygen and Carbon Dioxide. There are 

 various simple methods of preparing oxygen for study. A 

 little water added to a few cubic centimeters of sodium peroxide 

 (Na202) in a bottle or jar will result in the immediate liberation 

 of oxygen. The gas may also be obtained by pouring a small 

 quantity of hydrogen peroxide over a few crystals of potassium 

 permanganate. The customary way of obtaining oxygen is to 

 put about 20 grams of potassium chlorate and an equal amount 

 of manganese dioxide in a large test-tube and heat the mixture 

 over the bunsen burner. The test-tube should be closed with 



