The Action of Light on Chlorophyll. 



403 



more powerful oxidising agent than hydrogen peroxide in its action upon 

 chlorophyll. In the dark a very pronounced bleaching is obtained in half an 

 hour, and nearly complete decolorisation is effected in about two hours, with a 

 correspondingly strong reaction for aldehyde. In the light the bleaching 

 takes place slightly more rapidly than in the dark. 



The yellow colouring matter of chlorophyll bleaches very rapidly, the 

 green colouring matter very slowly in permanganate of potash and sulphuric 

 acid. Two films of equal size were prepared in two test-tubes, (1) of the 

 yellow colouring matter, and (2) of the green colouring matter of grass 

 chlorophyll, and equal quantities of the permanganate solution were poured 

 into each with the following results : — 



(1) Yellow colouring matter : In 50 seconds the permanganate solution 

 was nearly colourless. At the end of two minutes it was poured off : the 

 film was quite bleached and gave a strong reaction for aldehyde with 

 Schiffs solution. The experiment was repeated with the yellow pigment 

 from leaves of Chrysanthemum jparthcnium (Feverfew) with a similar result. 



(2) Green colouring matter : At the .end of one hour the permanganate 

 solution was not quite colourless ; the film still showed a yellow-green 

 coloration, but was more strongly bleached in the thinner parts. In order 

 to ensure more complete bleaching, fresh quantities of permanganate 

 solution were added from time to time, but even at the end of 12 hours the 

 bleaching was not complete. On testing with Schiffs solution, the film 

 gave, however, a strong reaction for aldehyde. 



None of the films bleached by oxidising agents, either in the dark or in 

 the light, gave a reaction with potassium iodide. 



Experiments with strips of paper tinged with (1) grass chlorophyll, (2) 

 the yellow pigment, and (3) the green pigment from grass chlorophyll, gave 

 similar results on treatment with the permanganate solution. (1) and (2) 

 began to bleach at once, and at the end of half an hour gave a strong 

 reaction for aldehyde ; (3) showed a slight reaction only at the end of two^ 

 hours. 



From these experiments we may draw the extremely interesting- 

 conclusions that, so far as the production of an aldehyde is concerned, the 

 oxidation of chlorophyll in the dark by means of solutions of hydrogen 

 peroxide and permanganate of potasli brings about a similar change to that 

 which is effected when chlorophyll is acted upon by light in the presence of 

 oxygen. 



We have seen that the yellow colouring matter obtained both from grass 

 chlorophyll and from the chlorophyll extracted from the leaves of Chrysan- 

 themum parthcnium bleaches very readily in the light, and also in 



vol. lxxxvii. — B. 2 II 



