64 



SCIENCE 



[N. S. Vol. XXXIV. No. 863 



But an alkaline area in connection with 

 the chlorophyll can be of even greater im- 

 portance. It is, in fact, highly probable that 

 the reduction of carbon dioxide itself takes 

 place in an alkaline solution, or better in the 

 form of a bicarbonate. It will be remembered 

 that while in the various attempts of Lieben,' 

 Ballo* and of Fenton,° to reduce carbonic acid 

 by chemical means, formic acid only was pro- 

 duced, the reaction took place either only with 

 the alkaline bicarbonate or it was greatly 

 accelerated by the presence of alkali. 



While the experiments of Herchenfinkle,' 

 and of Berthelot and Gaudechon' on the de- 

 composition of carbon dioxide into carbon 

 monoxide and oxygen in ultra-violet light 

 are a valuable contribution to the chemistry 

 of carbon dioxide. It must be borne in mind 

 that in the plant leaf we are dealing with a 

 substance of very different properties, namely, 

 metacarbonic acid or its salts. 



That certain plants are capable of liberat- 

 ing oxygen and synthesizing carbohydrates 

 from solutions of alkaline bicarbonates has 

 been demonstrated by Draper, Hassak, 

 Nathanson, Anglestein' and others. These re- 

 sults can not be interpreted to mean that the 

 plant is capable of utilizing the alkaline bi- 

 carbonates directly, but as the liberation of 

 oxygen decreases with increasing alkalinity, 

 it is clear from the equation, 



NaHCOs 4- HOH ^ NaOH + H^COs, 



that the plant is utilizing the H.COj formed 

 by hydrolysis of the sodium bicarbonate. As 

 McCoy' has shovm, the amount of sodium 

 hydroxide present in the above reaction is de- 

 creased to about one twentieth of the 

 amount calculated for a normal hydrolysis, 

 because of the secondary reaction: 



NaOH -I-' NaHCOa ±5 HjO +Na,C03. 



Thus it is clear that the plant has considor- 



^Monatsh. f. Chem., 1895 and 1897. 



* Berl. Ber., 1884, 6. 



'^ Jour. Chem. Soe. London, 91, 689. 



'Compt. reiid., 149, 395. 



'76id., 151. 



' Dissertation, Halle, 1910. 



' Amer. Chem. Jour., 29, 437. 



able carbonic acid at its disposal, which it can 

 utilize until the solution becomes too strongly 

 alkaline. It must be noted that from the be- 

 ginning, the action is taking place in an alka- 

 line medium. Of special importance in this 

 connection are the observations of Klebs" and 

 of Hassak" who found that various forms of 

 algse growing in distilled water produce alka- 

 linity therein during active appropriation of 

 carbon dioxide in the sunlight. 



In view of these facts, how then can the re- 

 duction of carbonic acid be pictured? Nef" 

 has suggested that the first step in photo- 

 synthesis is as follows : 



HO. H— O 



Nco^ I -t->co. 



HO^ H— O 



Now it is highly probable that the degree of 

 dissociation brought about by light is greatly 

 increased in the case of the alkaline bicar- 

 bonate : 



K— O. K— O 



\C0-^ I +>C0. 



H— O^ H— O 



This decomposition is, of course, similar to 

 the decomposition of carbon dioxide into car- 

 bon monoxide and oxygen by means of ultra- 

 violet light studied by Herchenfinkle. The 

 potassium hydrogen peroxide decomposes, re- 

 forming potassium hydroxide, and liberating 

 oxygen. The 0C< is immediately reduced 

 to formaldehyde by an action analogous to 

 the catalytic reduction of the nitrates as 

 given above: 



M + 2H0H -> M(OH), + 2H, 

 2H-h >CO-^H„.CO, 

 2M(0H), ^ M + 2H2O + O2. 



The detailed steps in the argument have 

 not been fully developed in the above brief 

 notice. Further work along these lines, as 

 well as on the relation between plant acids 

 and protein synthesis, are in progress, and 

 will be published fully elsewhere. 



Herman A. Spoehr 

 Department op Botanical Research, 

 Carnegie Institution op Washington 



"• Unters. Bot. Inst. Tuebingen, 2, 340. 



^Ihid., 465. 



^Ann. Chem. (Liebig), 357, 253. 



