134 



SCIENCE 



[N. S. Vol. XXXIII. No. 839 



the one that the sugars are formed directly 

 from the carbonic acid. This formation 

 could be satisfactorily accounted for as fol- 

 lows: Through the combined action of 

 chlorophyll and sunlight carbon dioxide 

 suffers dissociation into carbon monoxide 

 and oxygen. The oxygen is evolved while 

 the carbon monoxide combines with the 

 chlorophyll much as it does with the haemo- 

 globin of the blood. By the action of 

 hydrogen, obtained by the dissociation of 

 water, the carbon monoxide is then changed 

 into formaldehyde from which the sugar 

 results by condensation. The essential 

 points in Baeyer's hypothesis are there- 

 fore, first, the production of formaldehyde 

 from carbon dioxide and water, and sec- 

 ond, the formation of sugars by the poly- 

 merization of the aldehyde. Other investi- 

 gators have suggested certain modifications 

 of this theory, mainly in the method of 

 generation of the formaldehyde. Thus, 

 Erlenmeyer* in 1877 from certain observa- 

 tions made on the action of water on hy- 

 droxy acids was led to conclude that the 

 carbonic acid would be acted upon by 

 water under the conditions existing in the 

 plant with the production of formic acid 

 and hydrogen peroxide in accordance with 

 the following equation-. HO.COOH+HOH 

 -^H„0„4-H.C00H. The formaldehyde 

 would then result from the reduction of 

 the formic acid. Bach," on the other 

 hand, assumes the decomposition of the 

 carbonic acid directly into formaldehyde 

 and an unstable perearbonic acid, H2CO4, 

 which would break down into hydrogen 

 peroxide with regeneration of carbon diox- 

 ide. Usher and Priestley^" as well as Pol- 

 lacci^^ have also suggested certain modifi- 

 cations of the general assumptions. 



^ Ber. d. ohem. Gesell., 10, p. 634. 

 ^Vompt. rend., 116, pp. 1145, 1389; 126, p. 479. 

 '^Proo. Rayal Soc, B, 77, p. 369; 78, p. 318. 

 "Sot. ZentralU. for 1904 and 1905. 



The principal researches which have a 

 direct bearing on the validity of Baeyer's 

 hypothesis may be classified in regard to 

 their bearing on the following problems: 

 First, Is it possible to produce formalde- 

 hyde in the laboratory from carbon dioxide 

 and water under conditions approximating 

 those existing in the plant? Second, Is 

 formaldehyde actually present in the living 

 organism? Third, Is it possible for the 

 organism to assimilate formaldehyde? 

 Fourth, Is it possible to produce carbo- 

 hydrates directly from formaldehyde? 



It is my purpose to discuss briefly the 

 more important researches carried out in 

 these fields of investigation. 



PRODUCTION OF FORMALDEHYDE THROUGH 

 THE REDUCTION OP CARBONIC ACID 



The production of formaldehyde through 

 the reduction of water and carbon dioxide 

 has been the subject of numerous re- 

 searches. Maly^^ in 1865, and in more re- 

 cent time Lieben^^ (1895), attempted this 

 reduction by employing various amalgams 

 as reducing agents. Royer" in 1870 and 

 Coehn and Jahn^^ in 1904, on the other 

 hand, studied the effect of electrolytic 

 hydrogen on the carbonic acid. In all these 

 cases, however, the reduction resulted not 

 in the formation of formaldehyde, but of 

 formic acid. In 1893 Bach^° attempted to 

 carry out the reaction under conditions 

 closely approximating those existing in the 

 plant. As a substitute for the chlorophyll 

 in the plant Bach, relying upon the well- 

 known sensitiveness of uranium com- 

 pounds to light, used uranium acetate as a 

 chemical and photo-sensitizer. Carbon 

 dioxide was passed through flasks filled 



^- Annalen der Chem., 135, p. 119. 

 ^^Wien. Monats., 16, p. 211; 18, p. 582. 

 ^''Compt. rend., 70, p. 731. 

 "Ber. d. chem. Gesell, 37, p. 2836. 

 "Compt. rend., 116, pp. 1145, 1389. 



