PHOTOCATALYTIC ACTION OF CHLOROPHYLL 49 



paraldehyde which absorbs long wave-length ultra-violet light, 

 the formaldehyde formed by the short wave-length is protected 

 from polymerization. To photocatalyse the production of 

 formaldehyde from carbon dioxide and water, Baly and 

 Heilbron employ malachite green which has the same infra-red 

 frequency as carbon dioxide and forms an additive compound 

 with this substance ; methyl orange and /-nitrosodimethyl aniline 

 may be used in place of malachite green. 



A coloured substance which can photocatalyse the poly- 

 merization of formaldehyde to carbohydrate has not yet been 

 found. It is assumed that chlorophyll is an ideal substance for 

 photocatalysing both reactions; it absorbs visible light from 

 the sun and possesses the power of forming an additive com- 

 pound with carbonic acid, as shown by Willstatter and Stoll ; by 

 absorbing those rays which tend to decompose carbohydrate, the 

 chlorophyll will, moreover, shift the equilibrium towards the side 

 of the carbohydrate and the plant will thus be able to synthesize 

 carbohydrate even when the concentration of carbon dioxide is 

 low. In the opinion of Baly and Heilbron the formaldehyde 

 peroxide compound of Willstatter and Stoll can have only a 

 very transient existence. The formaldehyde as it is split off is 

 instantly polymerized to a sugar which would account for the 

 inability to identify formaldehyde in active leaves. 



VOL. II. 4 



