THE CHEMISTRY OF PHOTOSYNTHESIS 291 



were unable to detect any formaldehyde in the distillate from the juice 

 of leaves by means of the phloroglucin reaction. 



Curtius and Franzen substantiated the fact that the reagent used l)y 

 Fincke gives only a temporary coloration with other aldehydes and that 

 the aldehydes now known to be present in leaves give no reaction. The 

 reagent is prepared by dissolving one gram of rosaniline hydrochloride 

 or acetate in 500 cc. of water and adding to this solution 25 grams sodium 

 sulfite and 15 cc. of hydrochloric acid (specific gravity 1.124) ; the 

 whole is then diluted to one liter. The solution is slowly decolorized 

 and can be used after a few hours. In pure solution formaldehyde can 

 be detected in concentration of 1 : 500,000, but in the colored extracts of 

 leaves 1 : 200,000 is the limit. The tests are carried out by adding 1 

 to 2 cc. of hydrochloric acid (specific gravity 1.124) to 10 cc. of the 

 solution to be tested and then 1 cc. of the rosaniline reagent. Formalde- 

 hyde produces a blue to red violet coloration. With dilute solutions sev- 

 eral hours are required for the development of the color, sometimes 

 not reaching maximum intensity until after 20 hours. Willstatter and 

 StoU "^ have studied the conditions essential for the detection of small 

 quantities of formaldehyde by means of the fuchsin test. They recom- 

 mend a 1 per cent solution of parafuchsine or fuchsine which is treated 

 with sulfur dioxide until 0.1 cc. of the solution when diluted to 10 cc. 

 does not develop a color. Care must be exercised in using this reagent, 

 for too great dilution, removal or neutralization of the sulfurous acid 

 cause the formation of a colored solution which may erroneously be 

 taken as a test for aldehyde. They employed the reagent by adding 

 two drops of concentrated hydrochloric acid to 10 cc. of the solution to 

 be tested and then 4 drops of the fuchsine reagent. The presence of 

 the hydrochloric acid greatly retards the rate of reaction, requiring often 

 a whole day, but the reagent is very sensitive. 



The tests for formaldehyde of Leach, Rimini, Schryver and Bono have 

 been subjected to a critical study by Salkowski.^- Fosse and Hieulle ^' 

 report that the color obtained by the Schryver test with formaldehyde 

 is also produced by glyoxylic acid. 



b. Other Intermediate Products. 



Glycollic aldehyde has been suggested by several authors as a possible 

 intermediate product in the reduction of carbon dioxide, but the evidence 

 of its presence in leaves is very limited. Maze '* distilled various kinds 

 of leaves under reduced pressure and reports obtaining glycollic alde- 

 hyde from the elder. He obtained no formaldehyde, and besides glycollic 

 aldehyde, ethyl alcohol and acetaldehyde, he reports the presence of sub- 



" Willstatter and Stoll, "Unters. ii. Assim. Kohlensaure," p. 387. 

 "Salkowski, Biochem. ZcU., 68, i?>7 (1915). 



"Fosse and Hieulle, Compt. rend., 179, 636 (1924). Larnal. BnU. acad. ro\. 

 Med. Belg., 27, 701 (1913). 



"Maze, Compt. rend., 171, 1391 (1920). 



