Action of Light Hays on Organic Compounds. 175 



and not a provider of energy as in the synthesis of formaldehyde from carbon 

 dioxide and water, or in the synthesis of nitrites from nitrates. 



Hence it arises that very dilute solutions of formaldehyde do not yield 

 hexoses under the action of light, and that dilute solutions of sugars do not 

 condense to form disaccharides. Conversely, if dilute solutions of the higher 

 condensations, such as disaccharides or polysaccharides, be exposed to light, 

 they split up into simple sugars, and these invariably yield formaldehyde, as 

 will be shown in Section C. 



The first synthetic sugars were obtained by Butlerow,^ by Loew, and later 

 by Fischer and Passmore by acting upon concentrated solutions of form- 

 aldehyde or other organic substances with caustic alkalies. Thus Loew used 

 formaldehyde and milk of lime, and later freshly precipitated hydroxide of 

 lead, Butlerow dioxymethelen and caustic potash, Fischer and Passmore 

 acrolein bromide and baryta water. 



Such powerful reagents accomplish the condensations and give origin to 

 reducing sugars even in darkness and without need of external supply of 

 energy. In the absence of the alkali which acts as a catalyst, the reaction 

 towards equilibrium is held in check, or proceeds only at an infinitely slow 

 rate, so that a concentrated solution of formaldehyde can be kept in the dark 

 for an indefinite period without developing any reducing substances. 



In nature, no such strong hydroxyl-ion concentration is found in plant 

 tissues as that of the reagents used for synthesis of sugars i7i vitro as 

 mentioned above ; it is therefore interesting to obtain condensation with 

 light exposure in absence of any high alkalinity. 



At the time of our experiments we were unaware of any existing observa- 

 tions on the subject, but we have since discovered a paper by E. Pribram 

 and A. Franke,f in which condensation of formaldehyde and formation of 

 reducing substances was brought about by exposure of concentrated aqueous 

 solutions to ultra-violet light, also a paper by an Italian observer, 

 G. Inghilleri,J who exposed a mixture of concentrated aqueous formaldehyde 

 and 6 per cent, of oxalic acid in sealed glass tubes in sunlight for several 

 months, and obtained a hexose which he identified as the sugar sorbose 

 (inactive). In both these cases, although the authors do not comment upon 

 it, the law, stated above, of condensation in strong solutions holds. 



Formaldehyde itself reduces Fehling's solution in slight degree after long 



* Butlerow, ' Liebig's Ann.,' Bd. cxx, p. 295 ; 0. Loew, ' Berichte d. D. Chem. Gesellsch.,' 

 Bd. xix, p. 141 (1886) ; Bd. xx, pp. 141 and 3039 (1887) ; Bd. xxi, p. 278 (1888) ; Fischer 

 and Passmore, ' Berichte d. D. Chem. GesellscL.,' Bd. xxii, p. 3.59 (1889). 



t 'Berichte d. D. (Jhem. Gesellsch.,' Bd. xliv, p. 1035 (1911), and ' Monatsh. f. Chem.,' 

 Bd. xxxiii, p. 415 (1912). 



I 'Zeitsch. f. Physiol. Chem.,' Bd. Ixxi, p. 105 (1911), and Bd. Ixxiii, p. 44 (1911). 



p 2 



