i ee 
ON ELECTROLYSIS. 753 
Circumstances affecting Conductivity. 
There are two ways of increasing conductivity ; increase of dissocia- 
tion would seem to be the main cause when a weak solution is made 
stronger; diminished viscosity is probably the main cause when a cold 
solution is made hotter. 
But whether the remarkable change in viscosity caused by rising 
temperature is essentially the same thing as what appears in electrolysis 
to be extra dissociation I am not able to conjecture. 
Cases where the conductivity reaches a maximum at a certain stage 
of concentration, and afterwards diminishes as the strength of solution 
still further increases, are easily explained on Wiedemann’s view of vis- 
cosity, combined with that of dissociation; for at first the percentage of 
dissociation may increase faster than does the viscosity, and so conduction 
be on the whole easier; while at last viscosity must increase fast enough 
to neutralise the advantage of whatever extra dissociation there may be. 
Indeed it is probable that dissociation itself may ultimately diminish, 
notably so for instance with nearly strong sulphuric acid, for it seems 
roughly to depend on heterogeneity of constitution. 
It may be plausibly argued that the experiments of Kohlrausch and 
Grotrian support the following view. Dissociation, and therefore also 
conductivity, falls to a minimum whenever the proportion of ingre- 
dients present are such as to make a very simple typical compound, such 
as (markedly) H,O, or H,SO,, or even H,SO,, H,O; but, with inter- 
mediate proportions, a certain number of semi-detached radicles are 
mixed along with these more stable compounds, and high conductivity is 
the result. 
Theory of Kohlrausch. 
The fundamental assumptions underlying the beautiful theory of 
Kohlrausch are the same as those adopted by Wiedemann. He considers 
electrolytic conduction performed by dissociated atoms, each of which 
carries the same numerical charge of electricity, one set positive the other 
set negative. He follows Quincke in considering their motion due and 
proportional to the slope of potential ie ; and he accounts for migration 
by unequal speed of travel. But—and this is the special Kohlrausch 
idea—every ion is supposed to have a specific velocity, in a given fluid, 
when urged by a given slope of potential; a velocity wholly independent 
of all other circumstances. Moreover, all very dilute solutions are found 
to behave similarly, so that an ion’s rate of travel is nearly independent 
of the nature of the dissolved substance so long as there is not sufficient 
of it to interfere with the general aqueous nature of the liquid. 
Kohlrausch has further shown how to calculate this specific ionic 
velocity in absolute measure, from conductivity, concentration, and mi- 
gration, data. And the following table, taken from Clerk Maxwell’s 
‘Elementary Electricity,’ embodies some of his results. 
1885. 3¢ 
