Contact Potential Phenomena between Metals. 251 



as measured from time to time after polishing. Curves (1) 

 and (2) in fig. 4 illustrate this point in the case of lead- 

 brass. Curve (1) was taken several weeks after polishing 

 the lead plate, and curve (2) was taken eleven days later. 



Fig. 4. 



0-550- 



*— 0) 



195 aiOSfco/vos 



The following figures represent the type of decrease in the 

 total contact potential obtained after freshly polishing with 

 sandpaper in the case of zinc-brass, which is much more 

 constant. 



1 hour after polishing 



2 hours 



3 hours 



1 day 



2 days 



3 days 

 1 week 



5? 



J5 



0-596 volt. 



0-583 



0-575 



0-561 



0-550 



0-546 



0-543 



A repetition of such an experiment will involve variations 

 in the above values up to 002 volt, but the rate of change 

 remains approximately the same. As the surface of a metal 



S2 



