Action of Light Rays on Organic Compounds. 181 



a reaction was obtained of about 2 parts of formaldehyde per 1,000,000, 

 showing an amount of about 1 part in 20,000 in the original emulsion. This 

 result was not, however, due to the combined action of chlorophyll and 

 colloidal ferric hydrate, for a similar intense result was obtained when an 

 exposure was made of an emulsion of chlorophyll extract alone in distilled 

 water and without any carbon dioxide. 



It follows that the formaldehyde must have originated either from the 

 chlorophyll or the other organic substances in the green leaves taken out by 

 the alcohol along with the chlorophyll. 



Additional experiments showed us that practically any complex organic 

 substance of biological origin yields formaldehyde when exposed to the action 

 of ultra-violet light, and also — though more slowly — when exposed to sun- 

 light. Solutions or emulsions were exposed of all the commoner sugars 

 (such as glucose, fructose, maltose, lactose, saccharose), of glycogen, starch, 

 glycerine, egg-albumen, milk, and various vegetable juices. After three to 

 four hours' exposure and subsequent filtration or distillation those all showed 

 the presence of formaldehyde in varying amount. The more transparent 

 solutions gave the more intense reactions, and amongst these the sugars were 

 most rapidly disrupted by the action of the light. The action appears to be 

 one of successive hydrolysis ; thus, for example, cane sugar is first inverted, 

 and after an hour or two gives a strong reduction with Benedict's solution. 

 The reaction takes place also with sterilised sugar solutions, in sealed glass 

 tubes, exposed to bright sunlight, but the speed of reaction is much less than 

 when a quartz container is used, and the exposure must be continued for 

 several days. 



The action of sunlight, and of ultra-violet light, on organic substances has 

 been studied by many observers* and on a vast number of substances. The 

 production of formaldehyde in a certain number of instances has been noted 

 by different experimenters, but no one appears hitherto to have noticed the 

 generality of the appearance of formaldehyde when any complex substance 

 of vegetable or animal origin is exposed to light vibrations of short wave- 

 length. This may be due to the employment by us of a more delicate 

 reagent, and to a systematic testing for the formaldehyde in all cases. 



Certain of the observers, such as C. Neumann, and D. Berthelot and 

 Gaudechon, appear to consider a catalyst as essential to the reaction, and for 



* The papers on the subject are too numerous to quote separately ; a key to the 

 literature will be found in the following : — Ciamician and Silber, ' Berichte d. Deut. Chem. 

 Gesellsch.,' from 1901 onward ; ' Atti Eeal. Accad. Lincei,' from 1901 ; C. Neumann and 

 Co-workers, 'Bio-Chem. Zeitsch.,' from 1908 onward ; Y. Henri and Co-workers, 

 ' Comptes Rendus Acad, des Sci.,' and ' Comptes Rendus Soc. de Biol.,' from 1910 onwards ; 

 and D. Berthelot and Gaudechon, 'Comptes Rendus Acad, des Sci.,' from 1910 onwards. 



