The Action of Light on Chlorophyll. 



401 



bleached in the light. It is important, however, that further experiments 

 should be made in which the carbon dioxide determinations can be made 

 more accurately. 



The Photo-decomposition of the Green and Yellow Pigments of Chlorophyll. 



The green and yellow pigments were obtained by shaking up an alcoholic 

 solution of grass chlorophyll with ' benzene. The alcoholic solution of the 

 yellow pigment was then evaporated to dryness and extracted with 

 petroleum ether. The benzene solution of the green pigment was treated in 

 the same way. Thin films of these two colouring matters were then 

 exposed to light (a) in the absence and (b) in the presence of carbon dioxide. 

 In both cases the yellow pigment bleached rapidly, and gave a very strong 

 reaction both with Sehiff's solution and with potassium iodide. The green 

 pigment bleached much more slowly and did not give quite as strong 

 a reaction with either Sehiff's solution or potassium iodide. Similar results 

 were obtained with strips of paper tinged with the green and yellow 

 pigments respectively. Thus, paper tinged with yellow pigment from grass 

 chlorophyll gave, after 40 minutes' exposure to diffuse sunlight in January, 

 a strong reaction both with Sehiff's solution and potassium iodide. The 

 green pigment under the same conditions gave no reaction. Paper tinged 

 with ordinary grass chlorophyll gave a slightly stronger reaction than the 

 yellow pigment. At the end of two hours the green pigment gave a very 

 slight reaction with Sehiff's solution, but a strong reaction with potassium 

 iodide, the yellow pigment a strong reaction in both cases. 



The more rapid oxidation of the yellow pigment can also be seen by 

 lining narrow glass tubes (a) with the yellow and (b) with the green 

 pigment. These are then placed with their open ends downwards in water 

 and exposed to bright sunlight. The water rises very rapidly in the tube 

 with the yellow pigment, showing a rapid absorption of the oxygen, but 

 more slowly in the tube with the green pigment. In both cases, however, 

 the whole of the oxygen in the tube ultimately becomes used up, and the 

 water rises to the same level in each. 



The tubes were 39 - 4 cm. long. After exposure to light the water rose 

 8'6 cm. The height of the water in a control tube of the same length was 

 0"5 cm. Consequently on subtracting this both from 39'4 and 8'G, the ratio 

 8"1 to 38"9 gives 20 - 82 as the percentage of oxygen absorbed. 



The Action of Oxidising Agents upon Chlorophyll. 



As the decomposition of chlorophyll by light appears to be an oxidation 

 process brought about by the oxygen of the air in the presence of light, 



