114 



THE VITAL PROCESSES 



length and of the right shape to convey the escaping gas to a small 

 trough or pan partly filled with water, on the table. Fill four large- 

 mouthed bottles with water and, by covering with cardboard, invert 

 each in the trough of water. Arrange the test tube conveniently for 



FIG. 58. Apparatus for generating oxygen. 



heating, letting the end of the glass tube terminate under the mouth of 

 one of the bottles (Fig. 58). Using an alcohol lamp or a Bunsen 

 burner, heat over the greater portion of the tube at first, but gradually 

 concentrate the flame upon the mixture. Do not heat too strongly, and 

 when the gas is coming off rapidly, remove the flame entirely, putting it 

 back as the action slows down. After all the bottles have been filled, 

 remove the end of the glass tube from the 'water, but leave the bottles 

 of oxygen inverted in the trough until they are to be used. On remov- 

 ing the bottles from the trough, keep the tops covered with wet card- 

 board. 



1. Examine a bottle of oxygen, noting its lack of color. Insert a 

 small burning splinter in the upper part of the bottle and observe the 

 change in the rate of burning. The air contains free oxygen, but it is 

 diluted with nitrogen. Compare this with the undiluted oxygen in the 

 bottle as to effect in causing the splinter to burn. 



2. In a second bottle of oxygen insert a splinter without the flame, 

 but having a small spark on the end. As soon as the oxygen kindles 

 the spark into a flame, withdraw from the bottle and blow out the flame, 

 but again insert the spark. Repeat the experiment as long as the spark 

 is kindled by the oxygen into a flame. This experiment is usually per- 

 formed as a test for undiluted oxygen. 



3. Make a hollow cavity in the end of a short piece of crayon. 

 Fasten a wire to the crayon, and fill the cavity with powdered sulphur. 



