82 



GENERAL SCIENCE 



FIG. 83. Preparation of Oxygen. 



is a white crystalline solid which gives off its oxygen when 

 sufficiently heated. If manganese dioxide or iron rust 

 is mixed with potassium chlorate, it gives off its oxygen 

 more uniformly and at a lower temperature. 



Figure 83 shows the arrangement of apparatus for 

 preparing and collecting oxygen. A test tube contains 



the mixture of po- 

 tassium chlorate 

 and manganese di- 

 oxide. A delivery 

 tube leads from 

 the test tube to a 

 pneumatic trough, 

 where several bot- 

 tles have previ- 

 ously been filled 

 with water and 

 inverted ready for collecting the gas. Heat is then applied 

 to the test tube and the escaping gas is collected in the 

 bottles over water. 



Oxygen may also be prepared by allowing a solution 

 of hydrogen peroxide to drop into a flask containing some 

 crystals of potassium permanganate covered with a 

 dilute solution of sulphuric acid. 



Having collected several bottles of oxygen, we may 

 test its properties. 



Experiment 19. Ignite a pine splinter and extinguish the 

 flame. While it is still glowing introduce it into one of the bottles 

 of oxygen. This was the test used by Priestley. 



Experiment 20. By means of a piece of wire hold a small piece 

 of charcoal in the flame until it is aglow and then introduce it 

 into a bottle of oxygen. It should burn vigorously, giving off a 

 brilliant light. The product is the colorless- gas, carbon dioxide. 

 If limewater is put into the bottle in which the charcoal has been 



