554 Lord Kelvin on Contact Electricity of MetaU. [May 21, 



plate which had been made the positive pole in an electrolytic cell 

 with an electromotive force of one volt, tending to decompose water 

 acidulated with sulphuric acid ; the other pole being a piece of plati- 

 num wire. After the plate had been one hour under this influence 

 in the electrolytic cell he removed it, and dried it by lightly rubbing 

 it with a piece of linen cloth. He then placed it in the Volta- 

 condenser, and found it to be negative to a platinum plate in 

 ordinary condition ; the difference observed was * 27 of a volt. This 

 experiment was made on October 21 ; and on November 8 it was 

 found that the difference had fallen from '27 to '07, Mr. Eennie 

 also made similar experiments with the platinum disc made the 

 negative pole in an electrolytic cell, and found that this rendered 

 the platinum positive to undisturbed platinum to a degree equal 

 to about • 04 of a volt. The effect of soaking the platinum plate in 

 dry hydrogen gas, alluded to in my first postscript, which also was 

 observed by Mr. Eennie, was found to be about 'll of a volt. Thus 

 in the case of polarisation by hydrogen, as well as in the case of 

 polarisation by oxygen, the effect of exposure to the dry gas wa& 

 considerably greater than the effect of electro-plating the platinum 

 with the gas by the electromotive force of one volt. 



[K.1 



