222 BROOKS. 



peroxides in these substances causes the formation of carbon dioxide 

 and probably formic., acetic, and certain other acids also. According 

 to Engier's autoxidation theory the decomposition of an organic peroxide 

 may cause the oxidation of another substance, the "acceptor," which is 

 not autoxidizable. 



The air in several bottles containing powdered copal was washed through a 

 solution of barium hydroxide and an abundant precipitation of barium carbonate 

 was obtained. About 85 grams of powdered resin were placed in a tube and a 

 stopcock sealed into each end. The air was washed out with pure oxygen, and 

 on every day following about 200 cubic centimeters of moist oxygen were passed 

 through the tube, dried by passing through calcium chloride, and the carbon 

 dioxide absorbed in a potash bulb. The increase in weight averaged 0.017 gram 

 per day. 



The amount of carbon dioxide given off from Mania copal at 100° varies ac- 

 cording to the previous treatment of the specimen. A sample weighing 5 grams 

 was taken from the interior of a large lump, powdered, and heated to 100° in 

 a current of hydrogen, which was then passed through a solution of barium 

 hydroxide. Only a trace of carbon dioxide was detected after four hours heating. 

 About 3.0 grams of a powdered sample which had stood for several weeks in a 

 loosely stoppered bottle was treated in the same manner. The barium hydroxide 

 solution became cloudy in a few minutes, and after four hours' heating 0.0152 

 gram of barium carbonate was precipitated, equivalent to' about 0.1 per cent of 

 carbon dioxide. A portion of the powdered sample which gave no carbon dioxide 

 was tested for peroxides with a solution of potassium iodide and starch with a 

 negative result, while in the case of the specimen which yielded carbon dioxide 

 a marked liberation of iodine occurred. These experiments were duplicated quali- 

 tatively on several samples. 



The above phenomena could be caused by the terpenes in the copal, but 

 terpene-free resin obtained by heating to 300° also showed the same 

 behavior, which is consistent with the properties of colophony and 

 abietic acid. Copal, free from terpenes, was also prepared by extracting 

 an aqueous solution of the sodium salts of the resin acids four times 

 with ether. The solution Avas then half evaporated on a steam bath to 

 expel ether and the resin acids precipitated by dilute hydrochloric acid. 

 The dry, powdered acids were exposed to air and sunlight in a covered 

 crystallizing dish. All the changes noted as taking place in Manila 

 copal occurred in this case, but much more slowly. Positive tests for 

 formaldehyde and change of the photographic plate were easily obtained 

 after four days exposure to air and sunlight. 



Schwalbe 17 suggested that the evolution of carbon dioxide from a 

 carboxyl-group during the process of saponification might affect the so- 

 called "saponification" or Koettstorfer number. When phenolphthalein 

 is used as an indicator in titrating the alkaline solution, the splitting 

 off of carbon dioxide from a carboxyl-group should have no effect on 

 the Koettstorfer number obtained, since carbonic acid behaves as a 

 monobasic acid to this indicator and strong alkalies. If the alkaline 



" Log. cit. 



