OXIDATION OF MANILA COPAL BY THE AIR. 



223 



solution resulting from a determination of the Koettstorfer number is 

 acidified and the resin recovered, a second determination shows a decrease 

 in the Koettstorfer number only when the sample of resin gives off 

 carbon dioxide and shows a reaction for peroxides. 



Two series of Koettstorfer numbers were made on a portion of the sample which 



had been tested with negative results for the evolution of carbon dioxide and for 



peroxides. One series of determinations was made in small Erlenmeyer flasks 



with open-air- condensers. Another series was made in small Jena glass flasks 



of about 50 cubic centimeters capacity. A sample of resin weighing 2.00 grams, 



N 

 10 cubic centimeters of benzene, and 25 cubic centimeters of - alcoholic caustic 



potash were introduced into each of the Jena glass flasks, which were then sealed 

 and heated -in a bath of boiling alcohol in order that the temperature in the 

 sealed flasks would not be higher than in the open ones. The effect of prolonged 

 digestion is also brought out by these series. In determining the Koettstorfer 

 numbers of the recovered samples, the digestions lasted one-half hour each. 



Table I. — Koettstorfer numbers obtained under different conditions on a sample 



of Manila copal. 



Time. 



24 hours at 30° 



One-half hour boiling; . 



1 hour boiling 



2 hours boiling 



4 hours boiling 



6 hours boiling 



<S hours boiling 



Open. 



Sealed. 



1 



145.0 | 

 145. 

 153.8 j 

 160. 

 166.8 

 170.4 

 174.2 



144. 6 

 153. 5 

 162.9 

 166.3 

 170.6 

 174.0 



144.5 

 154.6 

 160. 2 

 166.8 



The recovered resins were dried in hydrogen to prevent oxidation. It 

 will be noticed that their Koettstorfer numbers are the same as for the 

 original samples. 



Powdered samples left exposed to the air for a few days show a 

 peroxide reaction when tested with potassium iodide and starch. Such 

 samples show a slight decrease in their Koettstorfer numbers after re- 

 covering the resin from the first determination. This is to be expected, 

 since part of the alkali is neutralized in the first determination by carbon 

 dioxide and small amounts of volatile acids. The sample weighing 3 

 grams, which yielded 0.1 per cent of carbon dioxide at 100°, also gave 

 up acids which were soluble in the water in contact with it, which 



required 5.5 cubic centimeters of _ caustic soda solution to make them 



neutral to phenolphthalein. The absence of these acids in the recovered 

 resin would cause a decrease in the Koettstorfer number of about- 10 units. 

 A powdered sample which had stood in a loosely stoppered bottle for 

 eight months showed a Koettstorfer number, after one-half hour's diges- 

 tion, of 210. The recovered resin, dried in hydrogen, showed a Koett- 



