The Action of Light on Chlorophyll. 



391 



merits 1 and 2. This was then cut longitudinally into two, and the two 

 strips were then placed in Schiff's solution and in potassium iodide solution 

 respectively. In both cases a strong reaction was obtained in those portions 

 exposed to light. On comparing the results with the same paper not tinged 

 with chlorophyll it was found that the reaction both in Schiff's solution and 

 in potassium iodide solution was very strong with the chlorophyll-tinged 

 paper but slight and almost negligible with the plain paper. Prolonged 

 exposure of the plain paper to light gives a stronger reaction, but in no case 

 as strong as the chlorophyll-tinged paper. 



It was important to determine whether the solution of chlorophyll itself 

 is able to give the reaction, apart from the paper. As alcohol gives a strong 

 reaction with Schiff's solution it was necessary to dissolve the chlorophyll in 

 some other solvent. For this purpose petroleum ether is suitable, as it does 

 not give any reaction with Schiff's solution or with potassium iodide solution 

 either in the dark or in the light. 



Experiment 5 : Four small test-tubes were partly filled with a solution of 

 chlorophyll in petroleum ether and tightly corked. Two were exposed to the 

 light and two kept in the dark. When those exposed to light were con- 

 siderably decolorised, a small quantity of Schiff s solution was added to one 

 and a small quantity of potassium iodide plus starch solution was added to 

 the other. These solutions did not mix with the petroleum ether, but on 

 shaking up the test-tubes the Schiff's solution became bright pink, the 

 potassium iodide and starch solution became bluish-brown. The petroleum 

 ether solutions which had been kept in the dark were treated in the same 

 way with Schiff's solution and potassium iodide starch solution respectively, 

 and in neither case was any reaction observed. 



These experiments show clearly that the decomposition of chlorophyll is 

 accompanied by the formation of an aldehyde and of a substance capable of 

 oxidising the potassium iodide and setting free the iodine. It is extremely 

 interesting to find that the same reactions are obtained with some kinds of 

 paper when exposed to light. This is probably clue to the decomposition of a 

 substance. in the paper the nature of which is unknown. 



The same results are obtained when films of chlorophyll on glass are 

 exposed to the light, and it can be further shown that the oxidising substance 

 produced is a gas soluble in water. 



Experiment 6 : About 5 c.c. of a strong petroleum ether solution is carefully 

 evaporated in a 50 c.c. flask so as to leave a thin film of chlorophyll on the 

 sides and bottom of the flask. The ether should be completely evaporated, 

 and a stream of air forced through the flask to remove all traces of the ether. 

 The neck of the flask should be surrounded with black paper. A few drops 



