THE OXIDATION OF MANILA COPAL BY THE AIR. 



By Bexjamin T. Brooks. 



{From the Chemical Laboratory, Bureau of Science, Manila, P. I.) 



Since it is generally considered that the older copal resins are the 

 more valuable for varnish manufacture, it appeared desirable to investi- 

 gate the changes taking place in Manila copal during its oxidation in 

 the air. 



Little is known of the chemical structure of the compounds present 

 in fresh and old resins of the so-called copal type. -A brief review of 

 some of the properties of certain important constituents of the common 

 resins will be useful in understanding the behavior of Manila copal. 



A very common constituent of the resins of the Coniferce is abietic acid. 

 According to Frankforter 1 this acid, or one of its isomeric forms, is present in 

 nearly all natural resins. It is easily obtained in a crystalline form and has 

 been more thoroughly studied than any of the resin acids. 



One of the difficulties met with in the study of this and similar substances is 

 the ready absorption of oxygen from the air, which led to the discussion as to 

 whether its formula was C 19 H, 8 0, or C 20 H G0 O 2 . 2 According to Fahrion/ the absorp- 

 tion of oxygen is accompanied by the formation of peroxides. 



A large number of acids related to abietic acid, and in some cases 

 probably identical with it, have been found in many different resins. 

 It has not been isolated from Manila copal, but the behavior of this resin 

 on oxidation by the air is entirely similar to that of colophony or abietic 

 acid. The absorption of ox}fgen from the air appears to be a property 

 common to all complex resin acids, so far as they have been studied. 



Klason and Kohler 4 studied the resin acids secreted by the Norway spruce 

 and prepared them so as to avoid heating. The acids isolated by them absorbed 

 oxygen from the air with great rapidity, forming oxyacids which were quite 

 insoluble in turpentine and were particularly adapted to forming a protective 

 coating when the oleoresin exudes from the tree. The authors claim that it is 

 not necessary for oxidation or evaporation to take place in order that the secre- 



», Jo-urn. Am. Chem. Soo. (1909), 31, 563. 



2 Levy, Ztschr. f. ang. Chem. (1905), 18, 1739. 



3 Ztschr. f. ang. Chem. (1901), 14, 1197; (1907), 20, 356. 

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



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