ULTRA-VIOLET RADIATION 39 



with a number of fellow-workers,* modifies his original views 

 and suggests that the formaldehyde obtained in the earlier 

 experiments arose from the secondary decomposition of the 

 photosynthesized carbohydrate. 



They find, moreover, that if carbon dioxide be exposed to 

 the action of ultra-violet light in the presence of such sub- 

 stances as barium sulphate, aluminium powder, the basic 

 carbonates of aluminium, zinc or magnesium, which present a 

 surface upon which the gas may be absorbed, a condensation 

 compound is produced which is charred by sulphuric acid and 

 reduces Benedict solution after hydrolysis ; the exact nature 

 of this substance has yet to be determined, but it possibly 

 contains carbohydrate. 



Of more immediate interest in the problem of natural 

 photosynthesis are the results obtained with the use of visible 

 light, from an ordinary tungsten filament lamp or a 100-watt 

 half-watt lamp, in place of ultra-violet radiation ; using 

 coloured absorbing surfaces such as the basic carbonates of 

 nickel or cobalt, these authors were able to obtain a larger 

 yield of organic material than with the colourless substances 

 and ultra-violet light mentioned above. This material is a 

 mixture one component of which is a carbohydrate as is 

 indicated by the facts that it gives the reactions of Molisch 

 and Rubner, it reduces Benedict's solution and also forms a 

 solid ozazone. The material also contains a more complex 

 substance which reduces Benedict's solution after hydrolysis 

 with acid. In these experiments no free oxygen is given off ; 

 it is suggested that it is absorbed on the surface of the powder, 

 possibly forming a peroxide, and this in time may poison the 

 surface and stop the photosynthetic action. Thus with a 

 light of medium intensity, photosynthesis stops after two 

 hours ; in a stronger illumination the organic material first 

 formed may be decomposed ; with a decreasing intensity of 

 light, the amount of material synthesized by unit quantity of 

 light increases. 



* Baly, Davies, Johnson and Shanassy : " Proc. Roy. Soc," 1927, A 

 116, 197. Baly, Stephen and Hood, id., 212 ; Baly and Davies, id., 219. 



