Chemical Affinity in terms of Electromotive Force, 45 
as a more readily to a less readily oxidizable metal, this result 
being evidently brought about by the superior surface con- 
densing-power possessed by platinum, in virtue of which a 
greater proportion of the energy due to the transformation 
of the nascent into the final products of electrolysis evolved 
at the + electrode becomes adjuvant. For instance, the fol- 
lowing numbers were obtained with a pair of precisely similar 
cells containing the same copper-sulphate solution and copper 
— electrodes. 
Current- j 
density, mi- 
croamperes 
per square I - 
centimetre. , -(-Platinum 
Difference of potential 
between plates. 
+Gold. 
30 1-500 
7-0 1-534 
110 1-570 
1-555 
1-591 
1-630 
Difference. 
•055 
•057 
Even with the lowest current-density and with platinum as 
+ electrode the total amount of nonadjuvancy was here con- 
siderable ; for the E.M.F. corresponding with the net che- 
mical action i« only 1-234 volt (i[Cu, O, S0 3 aq] =27,980 
gramme-degrees = 1*234 volt); and the minimum difference of 
potential set up, after correction for the resistance of the cell 
(i. e. the counter E.M.F. set up, or the value of the term e in 
the expression E = 0+CR), exceeds 1*490, since the term CR 
in this case was much less than '010 volt. 
In just the same kind of way, when platinum and gold were 
respectively Trade the — electrodes in similar pairs of cells 
containing dilute sulphuric acid and a constant oxidizable 4- 
electrode, the superior surface condensing-power possessed by 
platinum caused a less degree of nonadjuvancy during the 
transformation of nascent into free hydrogen. Thus, for 
example, the following numbers were obtained with a copper 
+ electrode and acid containing 10 per cent, of H 2 S0 4 . 
Current- 
clensity.micro- 
amperes per 
square 
centimetre. 
Difference of potential 
between plates. 
Difference. 
—Platinum. 
-Gold. 
2-5 
5-0 
100 
•449 
•488 
•521 
•575 
•619 
•661 
•126 
131 
•140 
