132 



Dr. J. Erskine-Murray. 



Table III. Potential of Metals covered with visible layer of 



Alcohol. 



Table IV. Change in Contact-potential of Zinc and Copper due to 

 Layers of Turpentine, Rosin Oil, and Indiarubber Solution. 



VJII. Films formed on Metals by Gases. 



54. The potential of a metal is usually altered by soaking the 

 plate in a gas other than air. If the gas be oxygen, this alteration 

 is as a rule only temporary, and apparently depends on the formation 

 of a surface film, or rather on a cjiange in the film which doubtless 

 already exists. It will be shown that the change of potential of zinc 



