ACTION OP ORGANIC PEROXIDES. 453 



In order to determine whether or not the resin acids in Manila coital 

 ■svoiild, like abietic acid, affect the photographic plate in the absence of 

 terpones, the following experiment was tried. 



About .50 grams of powdered copal were dissolved in cold dilute alkali 

 and the solution extracted four times with ether. The solution was then 

 evaporated to one-half its volume on the steam bath to expel the ether.. 

 The solution was diluted and the resin acids precipitated by dilute 

 hydrochloiic acid. Ten grams of the dried acids were exposed to sunlight 

 for one half day. A photographic plate was then placed over the sub- 

 stance and on developing the plate four days later a distinct lilack spot 

 was obtained. 



The above explanation of the action on the photographic plate of 

 certain organic substances was suggested by a study of the autoxidation 

 of Manila copal, but in view of the interest recently shown in this 

 peculiar phenomenon it is published at the present time while the work 

 on Manila copal will appear at a later date. 



