FORMALDEHYDE 67 



after five minutes adding 20 c.c. of hydrochloric acid (sp. gr. 

 i-i8). 



Kimpflin * tested for formaldehyde in the leaf of Agave 

 tnexicana by injecting into it, by means of a capillary tube, a 

 concentrated solution of sodium hydrogen sulphite, contain- 

 ing an excess of ^-methylamino-m-cresol. The presence of 

 formaldehyde was indicated by the formation of a red pre- 

 cipitate on exposure to light. The precipitate is best seen 

 by examining a section of the leaf which has been dipped in 

 absolute alcohol. Formaldehyde is the only aldehyde giving 

 a stable red colour with the above reagent, but other aldehydes 

 give unstable green, yellow, or reddish-brown colours. 



Occurrence in the Plant. — Since the work of Reinke, many 

 have reported the occurrence of formaldehyde in the plant, f 

 and its presence has been accepted as evidence of the truth 

 of Baeyer's hypothesis of photosynthesis. It has, however, 

 since been shown that this formaldehyde is a degradation 

 product of chlorophyll. 



Thus Warner % has found that formaldehyde is produced 

 when chlorophyll is exposed to sunlight or electric light in air ; 

 since this substance is produced both in the presence and in 

 the absence of carbon dioxide, it would appear that the latter 

 plays no part in the production of formaldehyde by photo- 

 synthesis outside the plant, and that the formaldehyde is in 

 reality an oxidation product of the chlorophyll. 



The above-mentioned investigations were carried out with 

 impure chlorophyll, Jorgensen and Kidd,§ on the other hand, 

 used chlorophyll a and h (see p. 313) in a state of purity which 

 satisfied Willstatter and StoU's criteria. They experimented 

 with a chlorophyll sol with water as the dispersion medium. 

 On exposing this sol, contained in glass vessels and in contact 



* Kimpflin : " Compt. rend.," 1907, 144, 148. 



t Curtius and Franzen : " Ber. deut. chem. Gesells.," 1912, 45, 1715 ; 

 Reinke : " Bar. deut. bot. Gesells.," 1883, i, 406 ; Curtius and Reinke : 

 " Ber. deut. chem. Gesells.," 1897, 30, 201 ; " Sitz. Heidelberger Akad. 

 Wiss. Math. Nat.," 1915, Abt. A. ; PoUacci : " Atti. Inst. Bot. Pavia.," 

 1900, 6, 1902 ; 1904, 8, 10 ; Usher and Priestley : " Proc. Roy. Soc, 

 Lond.," B., 1906, 77, 369. 



X Warner : id., 1914, 87, 378. 



§ Jorgensen and Kidd : id., 1916, 89, 342. 



5* 



