Action of Light Rays^ on Organic Compounds. 179 



It was evident to us that we were dealing with a complex mixture, and, 

 although there is a quite distinct effect with phenyl-hydrazine in acetic acid 

 solution, quite different from that of formaldehyde, and giving abundance of 

 coloured precipitate, we have not yet succeeded in isolating a crystalline 

 osazone, though we have on several occasions obtained crystals mixed with 

 amorphous smears. 



In order to prepare large quantities of material, four quartz flasks, each of 

 about 300 CO. capacity, were completely filled with a 4-per-cent. solution of 

 formaldehyde, and exposed at a distance of about 4 inches from the lamp for 

 several hours daily for a week. The result was disappointing, on account of 

 the slowness of action. The effect appears, like many effects of light, even 

 in clear solutions, to be all concentrated within a comparatively thin layer 

 lying next the incident surface. Accordingly, as in these larger vessels the 

 volume increases much more rapidly than the exposed surface, the con- 

 centration of reducing substance in the solution progresses at a corre- 

 spondingly slow rate. At the end of the week there was a fair amount of 

 reduction in all four flasks, but not more than would be obtained in a small 

 quartz test-tube with a single day's exposure. In continuation, four quartz 

 test-tubes, each of about 30 c.c. capacity, were filled with part of the 

 contents of one of the flasks, and exposed at 5 cm. distance for two days. 

 The contents were mixed and used for the following experiments : — 



Several attempts to obtain an osazone were made by heating with excess 

 of phenyl-hydrazine and acetic acid. The unchanged formaldehyde interfered, 

 and although attempts were made to overcome this by fractional precipitation, 

 the most that could be obtained was occasionally small microscopic tufts of 

 crystals, mixed with oily and amorphous material. 



Changes due to the exposure are evidenced by the deep orange colour and 

 orange precipitate obtained on boiling with the phenyl-hydrazine in the case 

 of the exposed solution, while similar treatment of the unexposed form- 

 aldehyde gave only a pale yellow colour in both solution and precipitate. 



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 precipitate anything but 

 formaldehyde and aniline. 



