88 PROCESSES OUTSIDE THE LIVING CELL CHAP. 4 



Saunders and Morrison {cf. Baly 1940) claimed to have photosynthesized an amino acid, 

 an alkaloid, and even a protein, by the ultraviolet illumination of mixtures of nitrite and 

 formaldehyde. Baly suggested that the "co-assimilation" of carbonates and nitrites 

 is the source of organic nitrogen compounds in plants: 



OH 



light y 



(4.26) HNO2 + CO2 + 6 H > HC +2 H2O 



\ 

 NOH 



These speculations have even less of an experimental foundation than Baly's hypotheses 

 concerning the synthesis of carbohydrates. 



In another series of papers on photosynthesis in vitro — those of Dhar 

 and coworkers, it was claimed that positive tests for formaldehyde were 

 obtained after the exposure of carbon dioxide or carbonate solutions in 

 open vessels for several hours to "tropical sunlight." (In what respect 

 this light is different from sunlight elsewhere, or from the light of a 

 strong artificial source, was not made clear.) 



According to Dhar and Sanyal (1925), Rao and Dhar (1931''*), Rajwanshi and 

 Dhar (1932) and Dhar and Ram (1932), formaldehyde can be detected after irradiation, 

 even in pure solutions of carbon dioxide or sodium bicarbonate; the yield can be increased 

 by the addition of the following sensitizers: In carbon dioxide solutions: FeCls, Fe(0H)3, 

 FeS04, NiS04, C0CO3, CUSO4, CuCOa, copper acetate, Cr2(S04)3, Cr203, Cr(0H)3, 

 MnCl2, V2O6, NH4-Ce-nitrate, Pd(N03)2, U02(N03)2, methylene blue, methyl orange 

 and malachite green; in sodium bicarbonate solutions: Fe(0H)3, C0CO3, NiC03, ZnO, 

 Mg and FeCOs. No formaldehyde was found in solutions "sensitized" by cerous 

 oxide, molybdic acid, rhodamine and safranine. The largest concentration of form- 

 aldehyde, obtained in carbon dioxide solutions after four hours of irradiation (in the 

 presence of manganous chloride) was 8 X 10~^%, while in bicarbonate solutions yields 

 up to 4 X 10"'% have been obtained. In the presence of zinc oxide or magnesium, 

 Dhar and Ram (1932) obtained, in four hours, 1-3 mg. of formaldehyde. 



Results similar to those of Dhar were obtained by Mezzadroli and 

 Vareton (1928), Mezzadroli and Babes (1929) and Gore (1934); but 

 Burk (1927), Reggiani (1932), Qureshi and Mohammad (1932) and 

 Mackinney (1933) were unable to confirm them. Some formaldehyde 

 was found in experiments with dyestuffs. Since its occurrence, however, 

 did not depend on the presence of carbon dioxide, it must have originated 

 in the decomposition of the dyestuff {cf. page 68). 



In refusing to accept as significant, from the point of view of photo- 

 synthesis, the results of Dhar's experiments, we take into consideration 

 not only the danger of contamination and the generally unsatisfactory 

 experimental technique, but also the general proposition, formulated on 

 page 83, that as long as quantum yields remain extremely small (of the 

 order of 10~^ or 10~^) "everything is possible in photochemistry." This 

 applies not only to direct effects of ultraviolet light but even to sensitized 

 reactions brought about by the comparatively small quanta of visible 



