Some Photochemical Experiments with Pure Chlorophyll. 355 



formaldehyde might be produced in large quantities. This does not exclude 

 the possibility that the complete breaking down of the chromogen complex 

 may also yield formaldehyde among its oxidation products. 



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Curves of Formaldehyde Production in the Photo-oxidation of Chlorophyll Sols. 

 These curves are based on the data given in Table II. In the case of curves A and D 

 glass tubes were used, but the glass was thick in D, thin in A ; also the traces of 

 ethyl alcohol were removed in the case of D, but not in the case of A. In the case 

 of curves B and C a quartz vessel was used ; the alcohol was removed in the case 

 of B, but not in the case of C. 



It will be observed from the curve (fig. 2) that the quantity of formaldehyde 

 produced reaches a maximum, and then decreases in amount. This is 

 probably due to further oxidation of the formaldehyde to formic acid. The 

 liquid, indeed, increases in acidity from the beginning of the experiment. 



•.Criticism of Previous Theories of the Function of Chlorophyll in 

 Carbon Assimilation in view of the Experimental Data obtained 

 in this Investigation. 



a. Theory of Usher and Priestley. 

 In a series of papers (10) on the mechanism of carbon assimilation, these 

 authors have expressed the opinion that the initial stages of this process are 

 ''entirely non-vital and can be reconstructed in vitro!' They consider the 

 first stage as consisting of the photolysis of aqueous carbonic acid with the 

 production of formaldehyde and hydrogen peroxide, the evolution of oxygen 

 being due to the decomposition of the latter substance by catalase. 



