54 PROXIMATE CONSTITUENTS OF PLANTS 



Chlorophyll. 



Chlorophyll is the name given to the green colouring-matter 

 of plants, in the economy of which it plays a highly important role. 

 The function of chlorophyll is the assimilation of carbon dioxide 

 from the air and its elaboration into cane sugar, and ultimately 

 other sugars, starches, and cellulose. This assimilative action of 

 chlorophyll takes place in conjunction with the protoplasm also 

 present, and proceeds only in the presence of light. The rapidity 

 of the action varies with the colour of the light, being most 

 vigorous under the influence of those rays (red, orange, yellow, 

 blue) which are absorbed by the chlorophyll. (Engelmann.) 



Although magnesium is stated to be an invariable constituent 

 of the substance, the chemical structure of the chlorophyll molecule 

 is unknown ; in fact, the substance is probably a mixture of different 

 compounds. The presence of iron in the plant is indispensable for 

 chlorophyll formation, although this element does not enter into 

 its constitution. 



Chlorophyll is insoluble in water, but dissolves readily in ether, 

 carbon bisulphide, and alcohol. 



33. Preparation and Qualitative Examination of 

 Chlorophyll, 



Twenty grams or so of fresh green leaves are cut 

 into small pieces and bruised in a mortar. They are 

 then placed in a filter-paper cartridge and extracted 

 with ether for an hour in a Soxhlet extractor on the 

 water-bath. The bright green ethereal solution of 

 chlorophyll is evaporated to about one-third of its 

 volume, and the following properties of the resulting 

 solution noted : — 



(i.) Chlorophyll solutions show a marked red 

 fluorescence, especially when viewed by reflected light. 



(ii.) Chlorophyll is soluble in alcohol, ether, CSg, but 

 insoluble in water. A small quantity of the ethereal 

 solution is shaken up with water in a test-tube, and 

 allowed to stand. It will be seen that all the chlorophyll 

 remains in the top ethereal layer, the lower aqueous 

 layer being only slightly coloured. 



