382 Mr. C. H. Warner. Formaldehyde as an 



exposed over potash solution under the same conditions, showed a very 

 marked formation of the aldehyde. 



Usher and Priestley* thermo-electrically determined the temperatures of 

 two similar films of chlorophyll extract exposed to light, carbon dioxide being 

 present in the surrounding atmosphere in one case and absent in the other. 

 They found that the temperature of the film in contact with carbon dioxide 

 was the lower, a result which they regard as evidence that synthesis had 

 taken place consequent on the absorption of energy by the film. This result 

 is in no way conclusive, and may be quite valueless, since, apart from the 

 difficulties due to the conditions of the experiment, there is the fact that 

 oxidation must have been proceeding in both cases, and the observed tem- 

 perature difference was in all probability due to the excess of oxidation of 

 the film in air as compared with that of the one in air diluted with carbon 

 dioxide. The greater proportion of oxygen in the air from which carbon 

 dioxide was absent would certainly account for the observation that " the film 

 in CCvfree air was scorched and destroyed sooner than the other." The 

 experiment should be repeated with nitrogen as an atmosphere for the 

 control film. 



The Bleaching of Chlorophyll. 



Chlorophyll in air becomes bleached by light both in the presence and 

 absence of carbon dioxide, and it has been found that formaldehyde has been 

 produced whenever bleaching has occurred. The bleaching was not more 

 marked in moist air containing carbon dioxide than in air standing over a 

 solution of potassium hydroxide, but when the effect of air containing appre- 

 ciable quantities of water vapour was compared with that of an atmosphere 

 relatively dry, it was found that the degree of decolorisation (especially in 

 the case of rather short exposures to comparatively dull light) was somewhat 

 greater under the moist conditions. In all 'of the experiments previously 

 mentioned in which films were exposed in tubes containing no oxygen, 

 including the four for which oxygen-free carbon dioxide was used, no bleach- 

 ing could be detected. It will be observed that these results agree with those 

 which were described when the production of formaldehyde was under 

 consideration. 



The Formation of Hydrogen Peroxide. 



The observations of Usher and Priestley on the action of sheep's liver 

 catalase in preventing the bleaching of chlorophyll have been confirmed. 

 These observations point to the conclusion that the bleaching is due to the 



* ' Roy. Soc. Proc.,' B, vol. 84, p. 107 (1911). 



