ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 143 
_ within the liquid. This seems so far untenable that it would appear that double the 
electric force would double both the polarisation and the motion of the molecules, 
and so should produce four times the electrolysis. The objection, however, assumes 
_ that we know the causes resisting the motion, and with proper, and not very impro- 
bable assumptions as to the resistance to motion depending on it and on the polarisa- 
tion, a linear relation between current and electromotive force, i.e. obedience to 
Ohm’s law, seems possible. A modification of Grotthus’ hypothesis in the direction 
of Clausius’ is, however, possible. Suppose that when polarised the molecules drew 
one another apart at a rate proportional to the polarisation. This at once makes the 
relation between electric force and the decomposition a linear one, and so satisfied 
_ Ohm's law in the case of small currents. It also so far agrees with Clausius’ hypothesis 
that it explains electrolysis and double decomposition as properties of the same kind. 
_ The molecules in a liquid will occasionally be arranged by accident in the proper 
_ polarised condition in a closed circuit for drawing one another apart; and if the 
circuit includes molecules of different kinds, there will result double decomposition. 
There seem to be very serious difficulties in supposing that uncombined atoms are 
for any finite time free in the liquid; and the supposition that it is a particular 
arrangement that is required before exchanges take place, and that with this arrange- 
ment exchanges take place of their own accord, seems to explain electrolysis and 
_ double decomposition without supposing free atoms to exist within the liquid. I 
_ have not assumed Professor Armstrong’s suggestion that the proper arrangement for 
double decomposition is a double molecule; but it seems a likely hypothesis, and one 
_ that should be investigated from the chemical rather than the physical side. 
There are some other phenomena that have been explained upon the supposition 
that free atoms are gadding about in a liqnid. Such are the lowering of the boiling 
and freezing points by solutions of salts, and their effect on osmotic pressure. If 
dissociated atoms are going about in a liquidas in a gas, it seems impossible but that 
they must diffuse at different rates; and that thisis not observed seems conclusive 
against the hypothesis, no matter what else the hypothesis may explain. Consider 
solution simply. Why does chloride of sodium dissolve in water? There must be 
some strong affinity between the two of a chemical or semi-chemical nature to break 
up the cohesion of the crystal; and it seems reasonable to assume that this same 
affinity keeps the molecules of NaCl moving about among the water molecules, so 
that they diffuse about. Now if the forces drawing them about be independent of 
the nature of the molecule, most of the phenomena explained by gaseous laws 
are explained. Pressure of a gas depends, at any temperature, on the number of 
molecules, and not on their kind. This is Avogadro’s law, by which molecular weights 
are calculated ; and if the forces drawing a molecule about in a liquid are independent 
of the kind of molecule, the very same law of pressure would hold, the pressure for- 
ward of molecules of different kinds would depend on their number only, and in the 
same way as Avogadro’s law would enable molecular weights to be calculated. In 
his connection it is well to state that some bodies may be much better able to pro- 
duce pressure than others, because of their being more easily polarised, i.e. turned 
into an effective direction. A molecule which could be easily turned into an effective 
direction would be about twice as effective as a molecule which went aboyt in a 
higgledy-piggledy way ; and one would consequently expect electrolytes to produce 
more, nearly double, the osmotic pressure that other bodies did. As to the changes 
f boiling and freezing points, they seem explicable by exactly the same hypothesis. 
he reduction of vapour pressure by molecular affinity of dissolved salt would depend 
nly on the number of molecules of salt if all salts have the same molecular affinity 
_ tor water ; and the same would apply to the change in freezing point. Hence ail 
these phenomena are explained without assuming free atoms, and they are all 
xplained by what can hardly avoid being a vera causa, namely, whatever affinities 
are that cause solution, which latter is an unexplained phenomenon on the 
sociation hypothesis. That it is reasonable to think that the forces keeping the 
molecules of salt moving about in the water are independent of the nature of the 
Salt appears from various considerations. In the first place, these forces are in all 
probability due to the residual affinities of the non-metallic elements. These same 
‘orces are probably the cause of crystallisation. These are old suggestions. That 
these residual affinities should be nearly the same for different combinations does not 
Seem at all unlikely. If a rather shaky argument in favour of its likelihood on 
mechanical grounds is desired, the following may deserve attention. 
Suppose a molecule of NaCl, for instance, at rest, or nearly so, in a crystal. 
Subject it to this affinity. Its velocity, after it has gone a distance, s, will be given 
