452 )'.u()(nvs. 



tension, is due to hydrogen jjcroxide formed \iy tlie (jxidulion of tlie metal in the 

 presence of moisture. 



Ehler " has recentl.y conliimed tliis view liy exposing certain metallic peroxides 

 in moist air to photographic plates. The efleet produced was the same as that 

 described by Russell and Saeland. 



Russell made no attempt to exjilain the formation of hydrogen peroxide by the 

 organic substances studied by him or to call attention to the fact that they are 

 capable of forming organic peroxides by autoxidation. The conditions under 

 which the activity is destroyed or increased are strongly suggestive i>f an intimate 

 connection M'ith organic peroxides. 



That organic peroxides are slowly hydrolyzed b.\' water with the formation of 

 hydrogen peroxide has been shown by Freer and Novy ° and by Clover and 

 Richmond.' This fact offers a plausible explanation of the formation of hydrogen 

 peroxide and the consequent change in the photographic plate produced by the 

 substances studied by Russell. 



In order further to test this theory benzoperacid, acetyl peroxide and 

 benzoylacetyl peroxide were tested and eaclt substance was found to 

 affect a pliotograj)hic plate. 



The experiment was carried out hj placing about 0.1 gram of the 

 substance- 6n a moist piece of fflter pajjer in a shallow crystallizing dish 

 and covering tlie dish with a photographic plate. In the case of acetyl 

 peroxide a distinct dark spot was obtained on developing the plate after 

 an exiDosure lasting twenty minutes. Benzoylacetyl peroxide gave a 

 distinct spot after about 45 minutes. If the plates were exposed too 

 long a reversal, or positive, was obtained. ^ 



In a study of Manila copal it was found that the substance rapidly 

 absorbed oxygen from the air and that the powdered resin aifected a 

 photogTaf)hic plate in the same way as colophony. Etissell stated that 

 amber was \'ery feebly active compared with colophony. In order to 

 ascertain if the older fossil resins coidd be differentiated in this way 

 from the more recent ones, several samples of Manila and other copal 

 resins were exposed to pliotographic plates. 



About 10 grams of each specimen of copal were pulverized and placed 

 in a shallow crystallizing dish. A photographic plate was tlten placed 

 with the film side down upon each dish. At the end of one week the 

 plates were developed in the usual manner and in all cases a round 

 dark spot sharply outlining the dish was obtained. Samples of recently 

 collected, semi fossil and partially distilled Manila copal gave very dark 

 spots. A specimen of kauri copal gave a much lilacker spot than Manila 

 copal, which pi'obably lias some connection with tlie fact noted by 

 Worstall ** that the oxidation of kauri is the faster of the two. Zanzil)ar 

 copal gave a fainter spot than kauri or Manila and a specimen of hard 

 l)rittle resin from Philippine coal showed the least activity of all. 



'■ Ztsfhr. f. aiigric. Chciii. (1!I0!I). 22, 205. 

 "Am. Chcm. Jour. (190-2). 27, Uil. 

 '.tm. Chem. Jour. (1903). 29, 179. 

 'Joiini. .()((. Clicm. Hoc. (190.S). 25, 8(53. 



