THE PREPARATION OF OXYGEN 79 



Materials: Potassium chlorate (powdered), manga- 

 nese dioxide, splinters of wood. 



a. Mix equal parts of potassium chlorate and man- 

 ganese dioxide on a piece of paper, and pour into a test 

 tube. Hold the test tube in the flame of the burner, by 

 means of the test-tube holder, until it becomes very hot. 

 Then light a splinter of wood, let burn for a while, blow 

 out the flame, and insert the glowing end into the tube, 

 continuing to heat the tube. What happens? There is oxy- 

 gen coming from the mixture in the tube. Does wood 

 burn better in oxygen than in air? Is oxygen invisible or 

 visible? Colored or colorless? 



Review Question, 17. 



1. Why does the skin become tanned? 



2. If you run toward your image in a mirror going 

 ten feet a second, how fast will you approach your image? 



3. How should the lights of a house be arranged to 

 give the best light for the eyes? 



4. Why are woolen underclothes better protection 

 from cold than cotton garments? 



5. Should the thermometer hang near the floor, on 

 the level of your head, or near the ceiling of a room to be 

 of use to us? 



6. How can you show that there is air in water? 



7. Give all the reasons which make you think that 

 there is water in the air. 



8. How can you show that about four-fifths of the 

 air is nitrogen? 



9. Why does pure oxygen support combustion 

 better than air? 



10. What is one cause of headaches? 



