On Contact Electricity of Metals. 137 



with the standard copper. A short time later it gave 



+ 070 volt. 



It was now put into oxygen for 10 minutes, and after being taken 

 out gave 



Time. Contact-potential, 



Hrs. Mins. Volt. 



3 +0-80 



13 +078 



17 1 +074 



62. A tin plate was polished on clean glass-paper, and gave with 

 a copper plate 



+ 0-40 volt, 



tin being positive. Fifteen minutes later the potential of the plates 

 had not altered. I now put the tin into the bell-jar and turned on 

 the oxygen. After it had soaked for 47 minutes it was taken out and 

 compared with the same copper plate. It gave 



Time. Contact-potential. 



Hrs. Mins. Yolt. 



5 +0-32 



13 +0-32 



35 +0-35 



Thus the variation of tin appears to be in the negative direction, like 

 that of platinum. 



63. A silver plate, polished on glass-paper, gave with a standard 

 copper plate 



-0-04 volt, 



and remained constant during an hour. It was then put into oxygen 

 for 15 minutes, and when taken out its potential was found to be 



Thus by immersion in oxygen for 15 minutes it had risen O'OG 

 and had fallen to nearly its original value in an hour in air. 



64. Silver polished on clean "fine" glass-paper gave with a 

 standard copper 



0-095 volt. 



