The Action of Metals, &c., on India-rubber, 267 



division, the file employed being first thoroughly cleansed, 

 and then washed with ether, to remove any oily or greasy 

 matters from it. Small pieces of 3 inches square were 

 ■cut from a large piece of the above-mentioned fine sheet 

 pure Para rubber, and thin layers of the filings of the 

 different metals were spread over about i^ inches square 

 of the centre. These were then placed together in an 

 incubator, kept constantly at a temperature of 140° Fah. 

 by means of a thermostat, night and day, on glass 

 shelves, and every day the positions of the pieces so treated 

 were altered, so that those in the middle were placed nearer 

 the sides, which we thought might possibly communicate 

 more heat than might be received in the middle. After 

 ten days the rubber on each square was tested in the manner 

 above indicated. This series of experiments was repeated, 

 and the following results were obtained : — 



One of the metals had a destructive effect on rubber 

 far beyond any of the others, and that was copper. As 

 compared with copper the following metals had a com- 

 paratively slight effect, although they exercised an injurious 

 influence. They are given in the order cf the injurious 

 influence they exercised : — 



1. Platinum. 



2. Palladium. 



3. Aluminium. 



4. Lead. 



The following metals were tried, and found to have no 

 -effect whatever : — 



Magnesium. 



Zinc. 



Cadmium. 



Cobalt. 



Nickel. 



Iron. 



Chromium. 



Tin. 



Arsenic. 



Antimony. 



Bismuth. 



Silver. 



Gold. 



