Se, ee 
ON ELECTROLYSIS. 757 
where N’ is the total number of monad gramme-equivalents of the dis- 
solved substance in a cubic centimetre of solution. 
Our view, on the other hand, leads to the equation 
kn ss = N,u, + Naw, 
where N, + N, represents the (unknown) amount of actually conducting 
substance per c¢.c. of solution. 
Now it seems by experiment that &/N’ is an approximate constant,! 
at any rate for weak solutions ; so we must suppose the fact to mean that 
Nu, + Now, is, within limits, nearly proportional to N’. 
It is in no way surprising that the dissociation of both substances 
should proceed pari passu with, and be initially proportional to, the 
quantity of stuff added to the water; but there remains a further ques- 
tion, which, if I am able to discuss it, shall be considered elsewhere. 
Theory of von Helmholtz. 
Finally we come to the wide-reaching theory of Helmholtz. 
The root idea of this theory is that each kind of matter has a specific 
attraction for electricity, some kinds for positive, other kinds for negative ; 
that, accordingly, work must be done to separate an atom from its electrical 
charge, or to remove electricity from an atom of high specific attraction 
and give it to another lower in the scale. Further, that chemical affinity 
is mainly due to the electrical attraction of oppositely charged atoms, and 
that when such atoms combine into a compound molecule they do not 
discharge into each other, but retain their charge. 
Apply this principle to a Daniell cell. 
During the action of the cell a certain amount of positive electricity 
has to leave (deposited) Cu, a substance which attracts it feebly, and 
enter into union with (dissolved) Zn, a substance which attracts it much; 
hence is derived the energy or E.M.F. of the cell. 
Apply the same principle to a water voltameter. During the passage 
ofa current the charges are torn from hydrogen and oxygen atoms and 
given to the electrodes, which, if they are platinum, have no special 
attraction for either electricity ; hence arises the E.M.F. of polarisation, or 
the work needed to decompose the liquid. Work is done, according to 
this theory, not in tearing the atoms asunder, but in tearing their electric 
charges from them. If the ions are allowed to enter into combination 
with some available radicles, in such a way as to retain their charges, 
polarisation E.M.F.is much reduced. So long as the atoms have not given 
up their charges they cling to the electrodes and cannot be removed 
mechanically, say by exhaustion or the like; but if once their charges 
are given up and molecules of the single substance formed, it makes but 
little difference to polarisation whether that substance be allowed to 
dissolve in the liquid or be made to bubble up from it. 
But it is to be understood, I believe, that in estimating E.M.F., or 
effective energy of a cell per unit electricity conveyed, Helmholtz would 
take into account the energy of all secondary, as well as of all primary 
actions, ‘ minor attractions of solvents’ as well as affinities of ions. 
Helmholtz points out that the interior of an electrolyte can stand not 
the slightest electrostatic strain, and hence, in so far as a voltameter 
1 See, however, a previous footnote. 
