EXERCISE 39 



WHAT IS THE NATURE OF THE GAS GIVEN OFF DURING CHLOROPHYLL WORK? 



Materials. Deep glass jar or aquarium ; large glass funnel ; test tube. 



Directions. Collect some of the gas which arises from the plants under the conditions of Exercise 

 38. Test it in the different ways which you used in earlier experiments, to find out if it is one of the 

 gases with which you are familiar. 



The collection may best be done in the following manner: Put the plants under an inverted 

 glass funnel in a deep jar. The funnel must be wholly submerged. Fill a test tube with water and 

 invert it over the stem of the funnel. The bubbles which arise from the plants will pass up into the 

 test tube, which may be removed for the tests when a sufficient quantity has been collected. To col- 

 lect a sufficient quantity of the gas within a reasonable time it will be necessary to use a large 

 quantity of plants and therefore a large funnel. 



Additional problems. In what sense is it true that a green plant is an oxygen-producing machine ? 



Of what significance is it to other living things to have large quantities of oxygen set free by green plants ? 



Can animals contribute to the supply of free oxygen in the air ? Can mushrooms and molds ? 



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