ON ORGANIC COMPOUNDS 93 



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 1 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 appear- 

 ance 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 here 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 this purpose have used salts of uranium. The 

 reactions of deduplication of these organic substances in dilute solu- 

 tions take place, however, quite readily without a chemical catalyst. 

 The reactions are exothermic, and the light itself acts as the catalyst. 



This production of formaldehyde has several important and 

 interesting relationships which may now be pointed out. 



In the first place, it has a practical bearing on all enquiries as to 

 the presence of formaldehyde in green leaves exposed to light, or of 

 chlorophyll solutions, or artificial schemata of various types, exposed 

 to light and afterwards tested for formaldehyde to elucidate the 

 functions of the chloroplast in the green leaf. Many observers 

 throughout the past generation have laboured at proving the pre- 

 sence of formaldehyde in green leaves exposed to light, but if it be 

 true that practically any organic substance of biochemical origin ex- 

 posed to light develops formaldehyde, then the presence of formalde- 

 hyde in green leaves furnishes no proof of its synthesis by sunlight 

 from carbon dioxide and water. The same holds for all the schemata, 

 for these always contain substances from which formaldehyde could 

 arise. But even although no other organic substance save chloro- 

 phyll, or any mixture of pure chlorophylls, were present and yet 



1 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. D. Chem. Gesellsch., from 1901 onward; Atti Real. Accad. Lined,' from 

 1901; C. Neumann and Co-workers, Biochem. Zeitsch., from 1908 onward; 

 V. Henri and Co-workers, Comptes Rendus Acad. des Sci., and Comptes Rendus 

 Soc. de Bid., from 1910 onwards; and D. Berthelot and Gaudechon, Comptes 

 Rendus Acad. de* Sci., from 1910 onwards. 



