220 BROOKS. 



tion harden, 5 but there is no doubt that under natural conditions both oxidation 

 and evaporation accompany the hardening process, beginning as soon as the 

 fluid secretion is exposed to the air. 



The terpenes present in resins of this type also readily undergo oxidation by 

 the air, and their tendency to resinify is much affected by the presence of other 

 substances. 6 The changes during autoxidation will be discussed in another part 

 of this paper. 



The effect of atmospheric oxidation on the chemical constants of freshly pow- 

 dered samples of the more common varieties of copal was investigated by Wor- 

 stall, 7 who noted a marked increase in their acid numbers and a decrease in their 

 iodine absorption. The greatest change was noted in the case of Kauri, while 

 specimens of hard fossil Zanzibar resin did not change appreciably in four months. 

 The greatest increase observed by him in the acid number of Manila copal over 

 a period of four months was eleven units. 



I have found that the atmospheric oxidation of Manila copal is 

 accompanied by the formation of organic peroxides, an increase in the 

 Koettstorfer number and evolution of small quantities of carbon dioxide, 

 formaldehyde, formic acid, and hydrogen peroxide. The oxidation is 

 accelerated by sunlight. Under certain conditions the resin gives off 

 vapors which have the property of affecting a photographic plate. 



THE EVOLUTION OF CARBON DIOXIDE FROM MANILA COPAL. 



In a study of the distillation products s of this resin, it was noticed 

 that it was impossible to melt the resin without large quantities of 

 carbon dioxide being given off. At temperatures between 250° and 

 330° this gas is evolved in large quantities and is apparently derived 

 from the decomposition of a carboxyl group. Easterfield and Bagley ° 

 found that pure abietic acid gives off large quantities of carbon dioxide 

 when distilled in vacuo. However, small quantities of carbon dioxide 

 are given off by Manila copal during atmospheric oxidation even at 

 ordinary temperatures. 



Schwalbe I0 noted that colophony gave off carbon dioxide at about 120° and 

 suggested that the Koettstorfer number might be affected by this cause. He 

 regarded the gas as being derived from the decomposition of abietic acid. 



5 1 have recently had the opportunity of making a similar observation in the 

 case of the oleoresin secreted by the pines, Pinus insularis Endl., in the Province 

 of Benguet in northern Luzon. Samples of the clear, honey-yellow exudate were 

 poured into small vials and immediately sealed. In about one hour the contents 

 of the vials had solidified to a mass having the consistency of stiff lard. Stirring 

 the clear liquid greatly accelerated this hardening process which wa«s due to the 

 crystallization of the abietic acid, as shown by a subsequent examination of the 

 substance. 



6 Bacon, This journal, Sec. A (1909), 4, 93. 



7 Journ. Am, Chem. Soc. (1903), 25, 860. 

 "This Journal, Sec. A (1910), 5, 



"Journ. Chem. Soc. Loncl. (1904), 85, 1238. 

 10 Ztschr. f. ang. Chem. (1905), 18, 1852. 



