Some Photochemical Experiments with Pure Chlorophyll. 345 



As regards photochemical reactions- we have mainly dealt with those which 

 affect the chromogen complex of the chlorophyll molecule. In regard to 

 •these we have found no qualitative difference in relation to the source of 

 light used, whether daylight, an arc lamp, or ultra-violet light from a quartz 

 mercury-vapour lamp. For the sake of convenience and rapidity of work we 

 have employed a mercury-vapour lamp since it gives a very intense and 

 constant illumination. 



The present investigation does not in any way claim to deal adequately 

 with the photochemistry of chlorophyll. Its object has been to deal with the 

 question as to how far certain observations described by previous investi- 

 gators can be justly used in support of their theories. The production of 

 formaldehyde by crude chlorophyll is used, for instance, by Usher and 

 Priestley as the basis of their theory of carbon assimilation ; also the 

 supposed formation of xanthophyll from chlorophyll in vitro is used by 

 Ewart in support of his contention that chlorophyll combines with carbon 

 dioxide with the production of xanthophyll and oxygen, the xanthophyll 

 being oxidised in presence of water to produce hexose sugars. 



Chlorophyll Extraction and Purification. 



The method used for the extraction and purification of chlorophyll is 

 described in detail by Willstatter and Stoll (13, pp. 133-135 ; see also 

 Jorgensen and Stiles (3)). The principle of this method for the isolation of 

 chlorophyll is that suggested by G. G-. Stokes in 1864, by which substances 

 are separated from one another by their distribution between two immiscible 

 solvents. 



The material used consisted of nettle leaves dried at 30 to 40° C, and 

 ground to a fine powder. 



The chlorophyll and accompanying substances are extracted with 80-per- 

 cent, acetone, and from this solution they are transferred to petrol-ether of 

 S.G. 0'64 to - 66. From this petrol-ether solution the colourless impurities 

 are removed by washing with 80-per-cent. acetone. The xanthophyll is next 

 removed by washing the petrol-ether with 80-per-cent. methyl alcohol. 



Pure chlorophyll is insoluble in petrol-ether, but is soluble if small 

 quantities of other substances, as, for instance, methyl alcohol, are present. 

 The last traces of methyl alcohol and acetone have therefore to be removed 

 by repeated washing with water. The chlorophyll is then precipitated 

 generally as a fine suspension while the carotin remains in solution. The 

 chlorophyll is obtained by filtering off the suspension through a layer of 

 powdered talc, and is purified by dissolving it in pure, redistilled ether. It is 



2 F 2 



