2 



Prof. A. J. Ewart. 



exposed to light do not bleach much more rapidly than similar films exposed 

 to ordinary air. 



In addition I was able to show* that formaldehyde is a direct product of 

 the oxidation of chlorophyll when exposed to light, that none is produced in 

 an atmosphere of pure carbon dioxide, and that when chlorophyll is exposed 

 to light in the presence of oxygen and of carbon dioxide, oxygen is absorbed 

 instead of being liberated. I pointed out that these observations supported 

 the old view that chlorophyll itself is a stage in photosynthesis. Schryverf 

 found that more formaldehyde was formed in the presence of carbon dioxide 

 than in its absence, and suggested that any excess of formaldehyde might 

 combine with the chlorophyll and be set free again on exposure to light. 

 Direct tests by myself, using chlorophyll films and formaldehyde solutions 

 kept in pure nitrogen in darkness, failed to give any support to this view. 

 With various interruptions work in this direction has been in progress during 

 the last five years. The appearance of an interesting paper by H. Wager, on 

 the action of light on chlorophyll,! leads me to give an account of my own 

 work up to the present time, leaving various points of detail for further 

 papers. 



Wager's conclusions are, in brief, that in sunlight, chlorophyll absorbs 

 oxygen and decomposes into aldehydes, of which a small portion is formal- 

 dehyde, and into an oxidising agent capable of liberating iodine from 

 potassium iodide, which is not hydrogen peroxide but may be an organic 

 peroxide. This action takes place in the absence of carbon dioxide, and 

 Wager inclines to the'view that the production of sugar in the green leaf 

 may be initiated by the photo-oxidation of the chlorophyll and the 

 subsequent polymerisation of the aldehyde thus formed, rather than by the 

 direct photosynthesis of carbon dioxide and water. 



A possible objection that might be raised to these observations is that the 

 methods of extraction given would not yield pure chlorophyll but a mixture 

 of it with xanthophyll, carotin, lecithin, phytosterin and waxy substances. It 

 is obviously of great importance to distinguish between the action of light 

 upon these different substances, which can only be done by using them in 

 pure form. 



Separation and Purification of Chlorophyll, Carotin, and Xanthophyll. 



The methods described by Willstatter for extracting and purifying chloro- 

 phyll were used with slight modifications. Grass leaves were immersed for 



* ' Koy. Soc. Proc.,' B, vol. 80, p. 30 (1908). 

 t ' Eoy. Soc. Proc.,' B, vol. 82, p. 226 (1910). 

 t 'Roy. Soc. Proc.,' B, vol. 87, p. 386 (1914). 



