The photosynthesis of naturally occurring compounds. I.—The action of ultra-violet light on carbonic acid

Abstract
When an aqueous solution of CO2 in quartz tubes is exposed to ultra-violet light, a photostationary state is established. Ordinary formaldehyde is not a component of this equilibrium, but there is present an organic compound which is probably a complex aldehyde. Ferrous bicarbonate in aqueous solution is converted by ultra-violet light in the absence of 0 into Fe(OH)3, organic compounds with reducing properties being simultaneously formed. This reaction appears to take place mainly on the surface of the quartz tubes in which is maintained a stream of CO2, and when the whole is exposed to ultra-violet light, complex organic compounds are synthesized. These may be recovered by evaporation of the solution after removal of the insoluble powder. The following materials are effective:[long dash]Al powder, BaSO4, freshly precipitated Al (OH)3, and the basic carbonates of Al, Mg, and Zn. After remaining in contact with water for some hrs., A1(OH)3 loses its efficacy, due to the well-known fact that it then has no measurable affinity for H2CO3. Since the experimental details were identical in this case with those when the other powders were used, this result excludes the possibility that the results observed in the other cases were due to impurities. Since quartz develops a marked opacity to rays of short wave-length when exposed to ultra-violet light, it is necessary when the photosynthesis is carried out in quartz tubes that these should be heated in the blast name before use. The total quantity of organic compound produced is about 0.02 gm. in 2 hrs. when 8 quartz test tubes (9X1 in.), containing in all 720 cc. of water and the suspended powder, are exposed to the light from a 220-volt U-shaped lamp at an average distance of 6 cm. The organic compounds thus produced seem to be of the nature of complex carbohydrates. They char readily when heated alone or with concentrated H2SO4. The quantity obtained in each experiment gives no visible reduction of Benedict''s solution, but after hydrolysis with HC1, reducing power was developed in the great majority of cases. In the presence of ammonium bicarbonate, complex organic material containing N also takes place when KN02 or Ba(NO2)2 is present. Exhaustive tests proved that the CO2 and other materials used were free from all organic impurity; numerous control experiments were carried out, which consisted in the irradia-dion of a powder, incapable of adsorbing H2CO3, suspended in water by means of CO2. Since entirely negative results were invariably obtained, and since the only variable factor is the nature of the surface, possibility of the results now recorded being due to organic impurities seems to be completely excluded.

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