4 8 



GENERAL SCIENCE 



stopper with a glass tube through it as shown in the illus- 

 tration, letting the other end of the glass tube extend 

 under the mouth of a bottle on the shelf in the pneumatic 

 trough. Fill several large-mouthed bottles with water, 

 cover with a glass plate, and invert them on the shelf 

 of the pneumatic trough over a hole; then remove the 

 glass plate. With a Bunsen burner held in the hand, 



PREPARING OXYGEN 



By heating a mixture of equal amounts of potassium chlorate and 

 manganese dioxide. 



apply heat to the test tube very carefully; see that the 

 flame does not stay in one place, and that the entire end 

 of the test tube containing the compounds is equally 

 heated, or the test tube may be broken and then all the 

 oxygen will escape without going into the bottle. The 

 first gas that comes from the test tube through the de- 

 livery tube is air and should be allowed to escape before 

 placing the end of the delivery tube under the inverted 

 bottle. As the bottles are filled with gas the water will 

 flow out because of its own weight. When a bottle is 



