Oxidation Product of Chlorophyll Extracts. 383 



oxidising action of hydrogen peroxide. Less important evidence tending in 

 the same direction has been obtained by treating films which have been 

 exposed to light and air with potassium iodide, ferrous sulphate and acetic 

 acid. A small amount of iodine was slowly liberated, while films which had 

 been kept in the dark when treated with the same reagents caused no 

 liberation in an equal time. A film which had been illuminated in a sealed 

 tube containing moist oxygen-free carbon dioxide was not bleached and did 

 not give the above reaction, although iodine was set free by a film similarly 

 exposed in air over potash solution ; this film was very distinctly bleached. 

 It is, of course, not to be expected that such an unstable substance as hydro- 

 gen peroxide would accumulate in any quantity in these films. 



There thus seems to be good ground for believing that the bleaching of 

 chlorophyll in oxygen is due partially, if not entirely, to the action of hydro- 

 gen peroxide. Since bleaching does not occur in oxygen-free carbon dioxide, 

 however, there is no evidence that carbon dioxide plays any part in the 

 formation of the peroxide, which substance is obviously produced through the 

 agency of atmospheric oxygen. The somewhat greater readiness with which 

 bleaching takes place in moist air as compared with air which is relatively 

 dry, is doubtless related to these facts, although it would seem that the 

 change can be effected in the presence of only a very small amount of water. 



Usher and Priestley* found that chlorophyll films in a carbon-dioxide- 

 containing atmosphere which previously produced no effect on Beyerinck's 

 " luminous " bacteria, caused glowing after exposure to light. This does not 

 by any means necessarily point, as these authors consider, to the decomposition 

 of carbon dioxide with the formation of oxygen or hydrogen peroxide. It is 

 more probable that, although the gas did not originally contain sufficient 

 oxygen to cause visible luminosity of the bacteria, sufficient was present to 

 form hydrogen peroxide under the action of light, and the peroxide, according 

 to Usher and Priestley, has more effect upon these organisms than oxygen.f 

 The same criticism is applicable to Molisch's$ statement that assimilation can 

 be carried out by chloroplasts from dried and apparently lifeless cells, and 

 probably to other observations depending upon the use of bacteria also. 



Since the production of formaldehyde always accompanies the disappearance 

 of the green colour of chlorophyll in air, it is probable that in this bleaching 



* ' Koy. Soc. Proc.,' B, vol. 84, p. 105 (1911). 



t Usher and Priestley found that a certain amount of glowing was produced in the 

 presence of catalase ; hence it may be argued that the effect is not due to the action of 

 hydrogen peroxide formed in the manner here suggested. It is practically impossible, 

 however, that under the conditions of the experiment (q.v.) the catalase could render 

 the peroxide entirely ineffective. 



X ' Bot. Zeit.,' vol. 62, p. 1 (1904). 



