Chemical Affinity in terms of Electromotive Force. 47 
charged with, solutions of acetates. It is noticeable that in 
such cases Volta's law of summation holds, the sum of the 
electromotive forces of two cells, one containing zinc and lead 
and the other lead and copper, being equal to the E.M.F. of a 
zinc-copper cell, the E.M.F. of the first cell being just as much 
below the amount calculated from the heat-development as 
that of the second is above the amount similarly calculated. 
This class of cells is now undergoing careful examination, 
and will be dealt with in a subsequent paper. Unfortunately, 
progress in this direction during the last fifteen months has 
been greatly retarded by the refusal of the Administrators of 
the Government Fund of £4000 to continue the grants by the 
aid of which the previous portions of these researches have 
mainly been made, on account of which circumstance nume- 
rous other points of interest that have cropped up have neces- 
sarily remained uninvestigated *. 
(3) When the electrolytic cell is not an electromotor, the 
counter E.M.F. set up (positive) always increases in amount 
with the current-density. When the -f- electrode is of such a 
nature as to combine with the products of electrolysis evolved 
thereat, other things being the same, the rate of increase is slower 
the greater the chemical affinity between the nascent products 
of electrolysis evolved at the + electrode and the material of 
which that electrode is composed; i. e. the greater the affinity, 
the less the degree of nonadjuvancy brought about at the + 
electrode. 
(4) Whether the cell be an electromotor or not, there is 
always (with currents not so small as to be practically infini- 
tesimal) a greater or less degree of nonadjuvancy brought 
about at the — electrode, owing to the development of heat in 
lieu of electricity during the transformation of nascent into 
ultimate permanent products of electrolysis. In many cases 
this source of nonadjuvancy decidedly predominates over that 
at the + electrode. 
(5 ) The particular extent to which the nonadjuvancy reaches 
at either electrode appears to be a complex function not only 
of the chemical nature of the electrode, the physical conditions 
of its surface, and the character of the nascent products of 
electrolysis evolved thereat, but also of the temperature, and 
the degree of concentration of the solution electrolyzed, and 
* Since tke presentation to the Physical Society of Part VI. of these 
researches, a paper has appeared hy F. Braun (Annalen der Phys. u. Chem. 
xvi. p. 561) ; in which the author shows that various combinations exa- 
mined by him give electromotive forces sensibly the same as those calcu- 
lated from thermochemical data, whilst others fall short of, and some 
exceed, the calculated values. 
