WORK OF LEAVES: PHOTOSYNTHESIS 



99 



funnel is inverted over it, leaving a few sprigs projecting under 

 the edge of the funnel so as to hold the edge of the funnel off the 

 bottom of the jar and permit a free circulation of water and 

 gases. The small end of the funnel must be immersed. A 

 very short section of rubber tubing is slipped over the end of 

 the funnel. A test tube is filled with the water, inverted, and 

 the open end immersed so 

 there will be no air in the 

 tube. It is then slipped 

 over the end of the funnel 

 and squeezed far enough 

 down on the piece of rubber 

 tubing to hold it firmly in 

 place. The apparatus is now 

 placed in the sunlight, where 

 it will receive the sun during 

 the entire day. The bub- 

 bles of gas rise into the test 

 tube and displace the water.* 

 When the tube is nearly full 

 of gas the test can be made. 

 With one hand the tube is 

 removed, at the same time 

 holding the thumb over the 

 mouth to prevent the escape 

 of the gas. The tube is now 

 tipped so that the small 

 amount of water will flow to 

 the bottom. A soft wood 

 splinter is now lighted. After 

 it has flamed for a few seconds the flame is extinguished by 

 blowing. The glowing splinter is inserted in the mouth of the 

 tube. It flames again. This indicates that the gas is oxygen. 



* The water should be changed each morning until the tube is nearly 

 full of gas. To do this slip the tube off the funnel into a tumbler of water. 

 The funnel can then be removed, the water emptied and fresh water put in 

 the jar. The tube is then placed in position again. 



Fig. 85. 

 Apparatus to catch oxygen from aquatic plants. 



