i tie 
ON ELECTROLYSIS. 755 
the corresponding amount of travelling matter is mn3udydz per second, 
so that the electrochemical equivalent of the substance is ¢ = m/q. 
By Ohm’s law the strength of current is & ae 
- dydz, where k is spe- 
cific conductivity of the solution; hence, since the current is also the 
quantity conveyed per second, 
i se dydz = qn udydz, 
je 
or 
- dV 
oF when, aN 
\) i ——— ae le >~e —- 
qn mn> de 
But mn’ is the number of grammes of the electrolysed or dissociated 
substance in a unit cube, and this we may write Nu, where N stands for 
the number of monad gramme-equivalents of the really electrolysed sub- 
stance per c.c., and yp is its molecular weight compared with hydrogen. 
Moreover “ is simply the electrochemical equivalent of hydrogen, i.e. a 
pL 
constant, say 7; so 
gk at, 
BL alu. O28 
We see then that for a given slope of potential « varies only with e P 
or, aS Kohlrausch would put it, with conductivity + concentration, 
which latter he has proved within certain limits to be nearly constant for 
many salt solutions.! 
But the question now arises, is N really simple concentration ? What 
is the substance really undergoing electrolysis? Kohlrausch considers 
that in weak saline or acid solutions it is the dissolved salt or acid only, 
and he appears to consider that every molecule of this is effective ; hence 
he would say N is at once determined by knowing how much stuff has 
been dissolved per litre. Take an example : 
A 5 per cent. solution of ammonic chloride contains about ‘001 
gramme equivalent of the salt per c.c. (i.e. say 53 grammes per litre) ; 
‘and it has a conductivity about 9 x 10-° that of mercury at 0°, or say 
10-'° absolute units. The H.C.E. of hydrogen is 10-*; so then we 
an easily calculate the sum of the ionic velocities for the AmCl mole- 
cule in such a solution, on the hypothesis that it is the sole effective com- 
pound present, and that the whole of it is effective— 
da tlne? dV 
= —— me SS = —. 
10-3 tre dz MY dz 
u 
’ Kohlrausch’s latest statements make z/N (understanding N in his sense pro tem.), 
a linear function of #N, i.e. of the distance between molecules; but the plotted 
lines showing this are after all very curved, and all that the facts really amount to 
is, I think, that 
k=a+ dN + cN? + &.; 
where a, being the conductivity of pure water, may be taken as zero. The N here in- 
terpreted in Kohlrausch’s sense, as representing the amount of dissolved salt, I call 
henceforth N’, 
3c 2 
