226 BROOKS. 



Although formic acid has frequently been identified among the products 

 of oxidation in the sunlight of many organic substances, formaldehyde has 

 often been overlooked. As mentioned above, copal carefully freed from 

 terpenes yields a small amount of formaldehyde on aUtoxidation. I 

 have shown that formaldehyde is also formed during the autoxidation of 

 pinene. limonene, and linseed oil. In fact, the formic acid present may 

 have been formed from formaldehyde, since, according to Kastle and 

 Lovenhart, 25 the oxidation of formaldehyde is accelerated by sunlight. 



A sample of pinene boiling between 155° and 157° was carefully purified and 

 distilled over sodium. The oil was then exposed to moist air and sunlight for 

 three days, after which time the oil was shaken out with an equal volume of 

 water. Three drops of the aqueous solution were sufficient tp obtain a distinct 

 reaction for formaldehyde when tested by the milk and sulphuric acid reaction. 

 A sample of limonene treated in the same manner yielded formaldehyde. 



Linseed oil, which had been exposed to air and sunlight for three days, was 

 extracted with an equal volume of water and the extract tested for formaldehyde. 

 Positive tests were obtained although the concentration of the aldehyde solution 

 was much lower than in the previous eases. 



THE INFLUENCE OF SUNLIGHT ON THE ABSORPTION OP OXYGEN BY 



MANILA COPAL. 



• Sunlight, so far as it has been tested in this respect, has a marked 

 accelerating effect on autoxidation. 



Genthe 26 showed that light, particularly of the shorter wave lengths, greatly 

 accelerated the autoxidation of linseed oil. Light is also known to accelerate the 

 autoxidation of turpentine. Klason and Kohler 27 state, of the resin acids of the 

 Norway spruce which they studied, that "The sensibility of the resin acids to 

 oxidation is very different in winter and summer. It is almost impossible to work 

 with sapin acid from May to August. It is evidently not the temperature alone 

 which causes this. Either the light or a yet unknown cause is active here." 



Sunlight accelerates the oxidation of Manila copal by the air, as was 

 shown by a simple experiment in which equal portions of a powdered 

 sample were placed in two bottles of the same capacity and filled with 



Manometers were attached to the bottles. One bottle was covered with four 

 layers of tin foil and both were then exposed to direct sunlight. In five hours 

 the diminished pressure in the unprotected bottle was equivalent to 30 centimeters 

 of mercury while the manometer on the protected bottle showed a difference in 

 level of only 14 centimeters. The difference in the temperature in the two bottles 

 did not exceed three degrees. After four days both manometers showed a dif- 

 ference in level of about 43 centimeters. 



"-"Journ. Am. Ohem. Soc. (1899), 21, 268. 



20 Loc. cit. 



"Journ. f. prakt. Chem. (1906), N.F. 181, 337. 



