On the Function of Chlorophyll. 



5 



but carotin and xanthophyll show the same reaction when exposed to light. 

 A long series of tests showed, however — (1) that the reaction was given only 

 when actual contact was assured with the substance undergoing oxidation ; 

 (2) that it was not due to any volatile product of decomposition ; (3) that 

 none of the products of decomposition had any power of liberating iodine 

 from potassium iodide ; (4) that partially bleached paper treated with starch 

 and potassium iodide and then kept in darkness gave no blue at whatever 

 stage the bleaching was stopped ; and (5) that no alkalinity was produced 

 (red litmus paper + chlorophyll + potassium iodide). This last test shows that 

 no hydrogen peroxide is formed. 



A curious point worth noting is that moist blue litmus paper bleaches much 

 more rapidly in sunlight than red litmus paper, and that the presence of a 

 little chlorophyll, carotin, or xanthophyll on the paper hastens the bleaching, 

 especially with the blue litmus. 



The conclusion seems justified that chlorophyll, xanthophyll, carotin, etc., 

 when exposed to sunlight, act not merely as oxidases to themselves but may 

 also accelerate the oxidation of other substances, if in contact with them 

 and if the supply of oxygen is abundant. This is borne out by the fact that 

 if a watery solution of xanthophyll with a supernatant layer of guaiacum is 

 exposed to sunlight, a green or blue layer forms between the two liquids 

 which soon disappears again. All these actions are only shown when an 

 abundance of oxygen is present, as when films are exposed to air. If the 

 potassium iodide and starch are mixed with a watery solution of xanthophyll, 

 or with a watery emulsion of carotin or chlorophyll, no perceptible liberation 

 of iodine takes place on exposure to light. In the case of chlorophyll films 

 or of carotin and xanthophyll films on filter paper, the possibility of .traces 

 of liberated potash combining with the chlorophyll or filter paper would 

 naturally favour the liberation of appreciable amounts of iodine. 



There is, therefore, no evidence that peroxidases, either organic or 

 inorganic, are among the products of the decomposition of chlorophyll by 

 oxygen and sunlight. The " iodoxidase " reaction in this case merely 

 indicates that oxidation has been taking place. A slight liberation of 

 iodine may even take place on a dry filter paper impregnated with chloro- 

 phyll and potassium iodide and then bleached, a blue colour showing on 

 moistening. 



The Oxidation of Chlorophyll. 



Dry chlorophyll films will bleach fully when exposed to sunlight in dry 

 air, but usually take five to ten times as long as similar films in moist air. 

 If the chlorophyll film is at all thick, the bleaching is greatly retarded by 

 the fact that the colourless products of oxidation form a waxy film on the 



