a 
ON ELECTROLYSIS. 749 
The properly calculated E.M.F. is then not simply 3 (Je0) but 
E=J (<9—II).! 
In a Daniell cell it happens that dH/dt, and therefore also XI, is very 
nearly 0, 
It is true that with voltameters a difficulty is often experienced, in 
reconciling the theoretical conclusion that a certain minimum E.M.F. is 
essential to the decomposition of a given substance, with the practical 
observation that any E.M.F., however small, can cause a constant leak 
through an electrolyte; but it has been pointed ont, at sufficient length 
already, how all this is capable of easy explanation by means of secondary 
chemical reactions. 
For remember that 6 is the thermal value of the reaction which actually 
goes on. Nowif the action is such as permits the ions to dissolve in 
the liquid, or to recombine indirectly with each other, less energy is 
expended, and less H.M.F. therefore required, than if they were really 
set free. We must not take 0 as measured for one kind of reaction and 
try to fit it to a case where an altogether different reaction is going on. 
Again it may happen (especially with intense currents such as are 
most easily applied by the use of small electrodes like the ends of Wol- 
laston wire) that ions are liberated in a condition of abnormal activity, 
as, for instance, oxygen as ozone, antimony in its explosive condition, &c. 
This necessarily means greater expenditure of energy, in proportion to the 
thermal value of such extra activity, and accordingly a greater E.M.F. is 
needed to effect decomposition under these circumstances ; .e., the polari- 
sation H.M.F’. rises in value, having been forced as high as 3°3 volts, in 
the case of dilute acid with platinum points, by Buff. 
If all these circumstances are properly taken into account, I am aware 
of no experimental reason which need cause us to doubt the general truth 
of the simple law, E = Je@— JIL} 
VY. Mecuanism or Enectrotytic Conpuction. 
Electrolytic conduction is, I suppose we may say certainly, a convec- 
tion of electricity by the atoms of matter; but concerning the mode in 
which the atoms make their way through the fluid there are several 
hypotheses : 
(1) The molecular chain of Grotthus; modified and accepted by 
Faraday and many others, modified further by Hittorf to explain migra- 
tion, 
1 The simplest mode of writing the complete law is 
1B 
Bi Jeo ee 
aot adv 
From this it follows that if heat of combination is independent of temperature, 
gE must be constant too; and generally, that 
dt 
_@E _d(Jeb) 
IL Pa ll 
Another way of writing it is 
H = — TJe [ 
ike 
Mr. Laurie (Proc. R.S.E., 1884-5) investigates the heat of combination of zinc 
and iodine by measuring the E and dE/d¢t of a zinc iodine cell. 
