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



and in no case was formaldehyde found in such a film whether carbon 

 dioxide had been present or not. 



In some, at least, of the experiments which yielded indications of the 

 photo-synthesis of formaldehyde to previous investigators, either lime, soda- 

 lime, or solid potash was used to obtain a control atmosphere free from 

 carbon dioxide. A number of additional experiments have been carried out 

 under these conditions, which are, however, entirely unsatisfactory, since the 

 effect of a moist atmosphere containing carbon dioxide is compared with that 

 of dry carbon-dioxide-free air. In a few of these experiments, particularly 

 when short exposures to rather dull light were given, distinctly more 

 formaldehyde was formed in the films exposed to carbon dioxide than in the 

 controls ; in the remainder no appreciable difference was observed. 



In order to further investigate the influence of moisture upon the 

 production of formaldehyde, several experiments were performed in such a 

 way that the effects of moist and dry carbon-dioxide-free air could be 

 compared. Films were exposed in pairs, one in air over potash solution, and 

 the other in air over lime or soda-lime, a tube of concentrated sulphuric aeid 

 being present in addition in some cases. In this series also it was noticed in 

 some instances that the comparatively dry films contained distinctly less 

 formaldehyde than the moist ones. These experiments, taken as a whole, 

 appear to show that, while there is no appreciable difference between the 

 amounts produced by snch chlorophyll films in moist air containing carbon 

 dioxide and in similar air free from that gas (such differences as have been 

 observed being chiefly due, as shown by later experiments, to the air diluted 

 by carbon dioxide causing less oxidation), the aldehyde is formed more 

 readily in moist than in dry air. 



It is evident that formaldehyde was being produced in these experiments 

 as the result of photo-chemical decomposition of the films. This is one of the 

 points to which attention was drawn by Ewart (loc. cit.), who found that an 

 aldehyde was formed by chlorophyll under the action of light both in air in 

 which carbon dioxide was present and in that from which it was absent, nor 

 could he observe any difference in colour intensity between the two cases 

 when Schiffs reaction was applied. In this connection Ewart relied chiefly 

 upon observations on killed leaves, a method of experimentation very 

 difficult to control ; in addition to chlorophyll, the number of substances 

 present, some of which (such as organic acids) may give formaldehyde on 

 exposure to light, is very large, much greater than in an ether or petroleum 

 extract ; also, it is considerably more difficult to ensure freedom from carbon 

 dioxide for control experiments in such leaf material than in the thin films 

 obtained in the manner described. Again, the rosaniline test, apart from its 



