EXERCISE 34 

 CAN THE GREEN COLORING MATTER BE REMOVED FROM LEAVES? 



Materials. Some fresh green leaves, those of the geranium and nasturtium ; a beaker or 

 metal dish in which to boil water ; a smaller beaker which may be placed within the preceding 

 one ; alcohol. 



Directions. Since the common tests for the presence of food materials depend upon color changes, 

 it is necessary to bleach the leaf before applying a test such as is mentioned in the following 

 experiments. It will often be better for the teacher to perform the experiment, but the results 

 should be seen and handled by each pupil. 



Dip each leaf in boiling water once or twice, keeping it in the water only long enough to kill it, 

 as indicated by its becoming limp as if wilted. Place all the leaves in a beaker or other convenient 

 container with enough alcohol to cover them. Heat the alcohol to about 75 C. for ten minutes. 

 Since alcohol is inflammable, the heating is best accomplished by setting the vessel containing the 

 alcohol in the vessel containing hot water, using the principle of the double boiler. 



At the end of this ten minutes' heating, remove the leaves and rinse in water. Examine both 

 leaves and alcohol. What has happened to the green coloring material of the leaves ? This coloring 

 material is called chlorophyll. 



NOTE. The experiment can be performed without the use of heat, but the operation takes much longer 

 in this case. Pupils may perform the experiment at home by immersing leaves in cold alcohol for 24 hours 

 or longer. In this case keep the dish or bottle tightly closed to prevent evaporation of alcohol. 



Wood alcohol has the same effect upon the chlorophyll as common or grain alcohol, but because of the 

 poisonous nature of wood-alcohol fumes it is better to use grain alcohol. 



Additional problems. How do you account for the peculiar appearance of shoots and leaves of plants 

 such as potatoes, asparagus, etc., which have grown entirely in darkness ? 



Plant mustard seeds, or those of wheat, oats, and beans, in darkness, and remove them to the light when 

 the plants are an inch tall. What color changes follow removal to the light ? 



Evaporate the alcohol in which chlorophyll was dissolved, evaporating it slowly by allowing the dish 

 to stand in a draft. What is left in the dish ? 



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