36 Messrs. Wright and Thompson on the Determination of 
Similarly the values -000439 and '000428 (mean =-000434) 
were obtained for x in the case of cell D simultaneously ex- 
amined. The following Table exhibits in brief these figures 
and those obtained in six other experiments with three other 
different cells: — 
1st experiment. 
2nd 
experiment. 
Mean. 
1st cell . 
. . -000358 
•000386 
•000372 
2nd „ . 
. . -000439 
•000428 
•000434 
3rd „ . 
. . -000480 
•000481 
•000481 
4th „ . 
. . -000436 
•000397 
•000417 
5th „ . 
. . -000364 
•000336 
•000350 
General average . . . "000411 
Hence, finally, it results that the E.M.F. of a Clark's cell 
set up with saturated zinc-sulphate solution is, at a tempera- 
ture t not more than 10° or 12° above or below 15°*5 C, 
1-457 {l-(*-15°-5)x 0-00041} volt; 
it being admitted that Clark's valuation is exact, viz. 1-457 
volt at 15°-5. 
On the Work done during Electrolysis. . 
140. The experiments described in the previous portions of 
these researches have shown that, when a current is passed 
through an electrolytic cell, the amount of energy expended 
(positively or negatively) during the passage in performing a 
given amount of chemical work (apart from that transformed 
into heat in consequence of the resistance proper of the cell in 
accordance with Joule's law) is not constant, but increases 
algebraically with the current-density r , in such wise that when 
the cell is an ordinary decomposing cell (e. g. a voltameter) 
the " counter electromotive force " of the cell increases in 
arithmetica 1 value with the current-density, whilst when the 
cells is an electromotor (i. e. such a cell as to yield a negative 
counter E.M.F. ), the arithmetical value of the negative counter 
E.M.F. (i. e. the direct E.M.F. of the cell) decreases with the 
current-density- The extra work done by a stronger current 
as compared with a weaker one in the former case, and the 
deficiency of work corresponding with the fall in direct E.M.F. 
in the latter case, make their appearance in the form of sen- 
sible heat in the cell. 
Experiments have been published by Favre (vide Part I. 
§§14 and 15) which appear to show that certain forms of 
electromotor-cells can generate currents capable of doing more 
work externally to the cell than corresponds with the net che- 
mical action taking place, this extra work being gained at 
