136 



SCIENCE 



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



aniline, and (c) the formation of hexa- 

 methylene tetramine with ammonia and 

 bromine. Acting on the conclusion that 

 the production of formaldehyde in the 

 plant is not a vital process, these investi- 

 gators in a later article described a series 

 of experiments in which they attempted 

 to produce formaldehyde from water and 

 carbon dioxide in the laboratory by repro- 

 ducing the conditions existing in the plant. 

 Plates of glass were painted over . with 

 gelatine, which in turn was coated with a 

 thin film of chlorophyll. The plates so 

 prepared were placed in a moist atmos- 

 phere of carbon dioxide and exposed to the 

 sunlight. The chlorophyll was employed 

 to effect a reduction of the carbon dioxide 

 and water into formaldehyde by acting as 

 a photo-sensitizer, while the gelatine was 

 used in the hope that it would absorb all 

 formaldehyde as fast as formed, thus re- 

 moving it from the sphere of action. After 

 the exposure of the plate the gelatine was 

 removed and tested for formaldehyde by 

 the tests previously mentioned and in all 

 cases the aldehyde was found to be present. 



If the interpretation of these results, as 

 given by Usher and Priestley, is correct, 

 this work is of the very highest value, not 

 only in its relation to Baeyer's hypothesis, 

 but especially because the reduction of 

 carbon dioxide and water to formaldehyde 

 in plants is shown to be a laboratory and 

 not a vital process. It must be stated, how- 

 ever, that the conclusions reached have 

 been contradicted by Ewart,-'' who insists 

 that the gelatine used in the experiments 

 will give the test for formaldehyde just as 

 well before exposure to carbon dioxide and 

 light as after such exposure ; and that even 

 granting the generation of formaldehyde 

 under these conditions, it is, to say the 

 least, just as reasonable to conclude that it 



==" Proc. Royal Soc, B, 80, p. 30. 



is derived from the decomposition of the 

 chlorophyll in the presence of oxygen as it 

 is to conclude that it is formed from car- 

 bon dioxide and water. 



Some of the most interesting results in 

 this field of investigation have been ob- 

 tained by Lob,-* who attempted to gain 

 some insight into the changes taking place 

 in the plant by substituting the action of 

 the silent electric discharge for that of the 

 sunlight as well as of any catalytic agent 

 or enzyme present in the plant. In this 

 way it was shown that formaldehyde is a 

 direct reduction product of carbon dioxide 

 and water vapor. Lob claims, and with 

 justice, that his experiments bring the first 

 positive proof that formaldehyde is a 

 direct reaction product of moist carbon 

 dioxide. 



In 1907 Fenton-^ attempted the genera- 

 tion of formaldehyde directly from car- 

 bonic acid by passing a current of carbon 

 iioxide for a number of hours through 

 pure water in contact with several rods of 

 amalgamated magnesium. He concludes 

 that "the solution gives slight but unmis- 

 takable indications of formaldehyde" with 

 certain standard color tests. So far as I 

 know, these results have not been chal- 

 lenged. 



The most recent work, as well as prob- 

 ably the most significant, is that of Berthe- 

 lot and Gaudechon.^" By the action of 

 ultra-violet light on a mixture of carbon 

 dioxide and water vapor, these investiga- 

 tors have succeeded in obtaining formalde- 

 hyde together with carbon monoxide and 

 oxygen. Under the same conditions, car- 

 bon monoxide and water vapor gives rise 

 to formaldehyde, carbon dioxide and 

 hydrogen. 



^Zeit. f. Elektroohem., 12, p. 282. 

 »J. L. Chem. Soc, 91, p. 687. 

 " Compt. rend., 150, p. 1690. 



