ON ORGANIC COMPOUNDS 91 



An attempt was made to remove the unchanged formaldehyde 

 by forming the addition compound with aniline, but unfortunately 

 the reducing substance also precipitated with the aniline. When 

 added to exposed formaldehyde solution aniline causes a white 

 precipitate as it does with unexposed formaldehyde, but the latter 

 precipitate remains white on heating, while that given by the exposed 

 solution turns a dark orange colour when heated. The filtrate 

 from the aniline precipitate no longer reduces Benedict's solution, 

 even when concentrated on the water-bath, neither does the aniline 

 precipitate reduce. It was not possible to separate from the pre- 

 cipitate anything but formaldehyde and aniline. 



Exposed formaldehyde solutions turn yellow when concentrated 

 by distillation either at atmospheric or reduced pressure, and leave 

 behind a yellow syrup with a bitter taste which strongly reduces 

 Benedict's solution; unexposed formaldehyde solutions leave a 

 smaller residue of white paraldehyde. 



Experiment IX. The condensing action of light is aided by 

 slight alkalinity. Three quartz test-tubes were taken: in the first 

 was placed a mixture of equal volumes of 4 per cent, formaldehyde 

 solution and water, in the second and third a mixture of equal 

 volumes of 4 per cent, formaldehyde solution and of a 1 per cent, 

 solution of sodium carbonate (Na 2 C0 3 ). The first and second were 

 exposed for three hours at a distance of 3 cms., while the third was 

 kept in darkness in an incubator at approximately the same tempera- 

 ture as that caused by the irradiation viz., about 50 C. At the 

 end of the period the unexposed solution gave no reduction with 

 Benedict's solution, and the tube contents exposed in presence of the 

 alkaline carbonate gave practically double the intensity of reduction 

 of those equally diluted with water. Tested again at the end of 

 fifteen hours the contents of the tube kept warm in darkness still 

 gave no reduction, while the other two now gave each a heavy reduc- 

 tion. Even after an additional period of three days in the incubator 

 the dilute formaldehyde and sodium carbonate solutions kept in 

 darkness gave no reduction with Benedict's solution. 



The General Formation of Formaldehyde by the Action of Light 

 upon Organic Substances of Biochemical Origin. The series of 

 experiments leading to the generalisation made in this section 

 were induced by an attempt to construct an emulsion of chlorophyll 

 in extractives from green leaves along with colloidal ferric hydrate 

 so as to produce an artificial system resembling that present in the 



