The Action of Light on Chlorophyll. 395 



peroxide were then tried, but all gave a negative result. The following are 

 some of the results obtained : — 



Dilute solution of chromic acid with sulphuric acid. This gives a 

 distinct blue coloration with 1/1,000,000 of hydrogen peroxide, but no 

 reaction with the chlorophyll solution. 



One of the most delicate tests for hydrogen peroxide appears to be that 

 given by Eoscoe and Schorlemmer in their text-book. When hydrogen 

 peroxide is added to a solution of potassium iodide ,and ferrous sulphate, 

 iodine is set free. Other oxidising agents have the power of liberating 

 iodine from potassium iodide, but not in the presence of ferrous sulphate. 

 I have obtained a distinct reaction with 1/50,000 of hydrogen peroxide and 

 a reliable reaction with 1/1,000,000. In the presence of ferrous sulphate the 

 chlorophyll derivative gives no reaction, although the same solution gave a 

 strong reaction with potassium iodide and starch alone. 



Leuchter's test* : With this I obtained a very clear reaction with 

 1/500 hydrogen peroxide, but no reaction with 1/50,000. No reaction was 

 obtained with a bleached chlorophyll solution. 



Titanium dioxide in concentrated sulphuric acid gives an orange-red colour 

 with 1/5000 of hydrogen peroxide, and a distinct yellow colour with 1/50,000 ; 

 no coloration was given with the chlorophyll solution. 



Experiments were also tried with a solution containing ferric chloride and 

 potassium ferricyanide. This gives a precipitate of Prussian blue with 

 solutions of hydrogen peroxide ; solutions of the chlorophyll derivative only 

 give a greenish yellow colour. 



All these tests indicate, therefore, that the chlorophyll derivative is not 

 hydrogen peroxide. 



The experiment was then tried of exposing a film of chlorophyll in the 

 dark to the action of a 20-per-cent. solution of hydrogen peroxide. If, as 

 Usher and Priestley state, the decolorisation is brought about by hydrogen 

 peroxide, we ought to get a very pronounced effect with so strong a solution. 

 The experiment, however, showed that even after ten days' exposure to the 

 hydrogen peroxide, the chlorophyll was far from completely bleached, and 

 was still of a yellow or yellowish green colour. The experiment was tried 

 many times in different ways, but always with the same result. The 

 bleaching of chlorophyll in the light appears not to be due, therefore, to the 

 action of hydrogen peroxide, and the most probable explanation seems to be 

 that the light absorbed brings about a combination of the chlorophyll with 

 oxygen resulting in the formation of an organic peroxide. 



It is interesting to note that other colouring matters react to light in the 

 * 'Chem. Zeit., ; 1911, see 'Chem. Soc. Journ.,' Abstracts, 1911. 



VOL. LXXXVII. — B. 2 G 



