iy) 
NATURE 
[ DEcEMBER 17, 1896 
be great, when it comes to jostling their way for an appreciable 
distance in a definite direction through the surrounding crowd of 
solvent molecules, they will only be able to move very slowly. 
The migration of the ions is really a process of diffusion under 
the influence of electric forces, and will, of necessity, be very 
slow. I can assure Prof. Armstrong that no dissociation apologist 
will argue “that the charges act as brakes.” It is by reason 
of their charges that the ions are urged forward by the electric 
forces. Without them, the velocities would not reach even 
those present figures which appear so despicable, but would 
merely take the much smaller values given by ordinary liquid 
diffusion. By placing in contact a coloured and a colourless 
solution, containing one ion in common, and passing an electric 
current across the junction, Prof. Armstrong can actually watch 
the ions migrating, and check the accuracy of the ‘‘ conventional 
time-table.” W. C. D. WHETHAM. 
Trinity College, Cambridge, November 27. 
I FEEL sure that many readers, like myself, must have wel- 
comed the sentiments expressed by Prof. Armstrong, in his article 
on this subject which appeared in your issue of November 26. It 
seems to me a duty of teachers to protest against the growing 
tendency there seems tu be of putting forward the crude hy- 
potheses of the ionist school, as though they had the same claim 
to acceptance as well established scientific laws, about which 
no reasonable doubt exists. So far from this being the case, the 
arguments commonly advanced in support of this theory seem 
to consist mainly of the misapplication of physical laws to a 
few carefully selected cases, aided by plausible but misleading 
assertions. 
The objections that have from time to time been urged against 
both the views and the methods of argument have never re- 
ceived proper attention at the hands of the advocates of ionic 
dissociation. (Prof. G. F. Fitzgerald’s Helmholtz Lecture; a 
paper by Prof. S. U. Pickering, Journ. Phys. Soc., vol. xi., &c., 
remain unanswered.) Itis, therefore, with the object of drawing 
attention to certain further difficulties and, as I conceive, errors 
in the above theory, rather than of evoking a discussion, that I 
now write. 
In answer to the question—how is it that substances that are 
supposed to dissociate have ‘‘ abnormally” large values for 
osmotic pressure, lowering of freezing-point, and reduction of 
vapour pressure ?—we are told that the dissolved substance exerts 
the same pressure as if it were a gas and occupied the volume 
of the solvent, and that when dissociated it exerts a greater 
pressure on the solvent. Now, surely the term ‘‘osmotic pressure” 
in such a sense is misleading ; not only is there no evidence of 
the substance exerting fresswre on the solvent, but rather that 
by an attractive force it can allow water to pass into it, and 
hold it, up to a certain particular pressure, which, if exceeded, 
will cause water to pass out again through the semi- permeable 
wall. There is in this nothing at all comparable to gaseous 
pressure, which certainly never is the cause of another fluid 
entering it in a closed vessel; for I suppose it will hardly be 
imagined that in a gas diffusion-cell it is the pressure of the gas 
inside that causes another gas to pass by endosmosis into it. 
Similarly with regard to vapour pressure, an attraction between 
solvent and dissolved substance can account for a reduction of 
the vapour tension, but a pressure exerted on the solvent by the 
so-called gasified dissolved body cannot. 
In regard to the lowering of freezing-point, we are actually 
sometimes told that this is a direct effect of the pressure of the 
salt on the solvent, with a beautiful reference to the lowering of 
the freezing-point of water by pressure, but with a calm oblivion 
of the fact that an increase of pressure would raise the freezing- 
point of other solvents in common use, such as benzene, acetic 
acid, &c. The alleged fact that the vapour pressures of a solu- 
tion and of the solid solvent are the same at the temperature of 
the lowered freezing- point, may be true, but it affords no 
explanation of the way in which such depression of the freezing- 
point is brought about. 
Ostwald, in his ‘* Outlines of General Chemistry,” p- 139, 
suggests a cyclic change of frozen solvent cooled to T — A, melted 
by addition of the active substance, and raised to T again, but 
his data are fallacious in not taking into account the considerable 
difference in specific heat of the solid and liquid solvent, and the 
consequent variation of latent heat with temperature; so that 
NO. 1416, VOL. 55] 
the heat evolved on freezing and absorbed on melting are not 
the same as he assumes them to be. 
In that same Bible of the ionists a very curious representation 
of the action of a current on an electrolyte is given (p. 273), 
where Ostwald states that there is no place for any energy of the: 
current being expended in doing the work of dissociation, and. 
‘*that it has to perform no work in the matter at all.” So much 
for the researches of Favre, Joule, &c., let alone the most ele- 
mentary fact that the adverse E.M.F. of polarisation is roughly 
proportionate to the heat of combination of the electrolyte, and 
that EQ. units of work must be expended in the transference 
of Q. units of electricity through the electrolytic cell, quite apart 
from work done against ohmic resistance. Apparently this idea 
owes its origin to the observation of Helmholtz, that feeble 
E.M.F.s can send exceedingly small currents through an elec- 
trolyte ; but he points out in one of his papers, that if only one 
cubic centimetre of detonating gas were dissolved in the liquid, 
‘*its constituents need only migrate once in thirty-six days from 
the anode to the kathode in order to produce the observed cur- 
rent.” He also showed that under so smalla pressure as 10 m.m. 
an E.M.F. of 1°64 volt is necessary to separate visible gas, while 
the value calculated from the heat of combination of H, and O 
is 1°49 volt. 
In the same chapter (p. 275), Ostwald asks us to ‘‘ zmagine”’ 
two insulated vessels A and B, connecied by a syphon and filled 
with solution of potassium chloride. Let a negatively charged 
body be brought near A, remove the syphon and charged body, 
then A is left with a positive charge. Now, he says, in A there 
must be an excess of free potassium ions, and if the electricity 
be conducted away, the potassium assumes its ordinary form, 
and, acting on the water, develops hydrogen ‘‘ which can be 
collected 7n a suztable apparatus and tested.” Now I have cal- 
culated the electric capacity of such an arrangement, and sup- 
posing a very large beaker and an inductor placed close to it, to 
be used, the capacity of the condenser so formed could hardly be 
so large as ‘oooI microfarad. We can be generous and suppose 
that the vessel A is charged to a potential of 50,000 volts above 
the earth; with this potential the quantity would be 5x 10° 
coulomb, ‘which would yield approximately ‘ooo00005 milli- 
gramme of hydrogen! Did Ostwald repeat the charging by in- 
duction, removal of the syphon, and discharging 20 million 
times, and so obtain a milligramme of hydrogen which he 
‘collected’? and ‘‘tested.” Even if this be ‘‘ imagined,” it 
would evidently do just as well to leave out the potassium 
chloride altogether, as water, as pure as Kohlrausch ever ob- 
tained-it, would, with 50,000 volts, answer the purpose equally 
well. 
When from this experiment (?) he draws the conclusion that— 
“‘ The assumption that electrolytes contain free ions is not only 
possible but necessary,” one may form some opinion of the kind 
of evidence that ionists consider conclusive. 
In conclusion, I would like to ask ionists the following 
questions :— 
Why do not ions, if free to move under the influence of small 
external electric forces, attract each other with immense force if 
they be charged with such enormous quantities of + and — 
electricity ? 
Where did they get these charges from ? 
Does dissociation absorb or evolve heat ? 
Why does not an E.M.F., however small, liberate gas fron> 
dilute sulphuric acid ? 
Why does solid Ag,S conduct electrolytically ? 
ciated into ions” ? 
There are many other questions, but I should really like to 
know the answers to these first. I believe many of the points I 
have here raised have been brought forward by others before, so- 
I lay claim to no originality in their suggestion, but hope that 
their consideration may give pause to those who are at present 
only partly ‘‘ dissociated,” until, at least, some reasonably satis- 
factory explanations are forthcoming. E. F. HERROUN. 
Queen’s College, Harley-street, W., December 2 
“ 
Ts it ‘* disso- 
Responsibility in Science. 
My first letter (NATURE, October 15, p. 572) on this subject 
maintained that Prof. Poulton had no right to hold physicists 
as a body responsible for views presented by two or three 
of their number, however eminent. Prof. Poulton (NATURE, 
