78 
NATURE 
[ NoveMBER 26, 1896 
LETTERS TO THE EDITOR. 
(Zhe Editor does not hold himself responszble for opinions ex- 
pressed by hts correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for thzs or any other part of NATURE. 
No notice ts taken of anonymous communications. | 
Osmotic Pressure and Ionic Dissociation. 
No doubt there will be great joy in the camp of the ionists 
over the sinner that repenteth on seeing the letter of my friend 
Prof. Poynting, but I imagine that those who thought that he 
was about to break a lance on behalf of the opponent party will 
agree that he is but a fickle ally, if they do not go further and 
conclude that he has perhaps failed to understand the real 
question at issue. 
All are agreed that Arrhenius and van *t Hoff and their satel- 
lites have rendered inestimable service by their generalisations, 
and the consequent application they have made of them; 
certainly the world has shown its esteem of their work. More- 
over, there can be no doubt, asI stated not long ago in my 
presidential address to the Chemical Society, that in so far as 
weak solutions are concerned a law has been discovered which 
is broadly true 22 mathematical form: yet I have no hesitation 
in asserting that the fundamental premises on which it is based 
are destitute of common sense in the opinion of those who look 
at these matters without leaving chemical experience out of 
account; and I venture to think that this is not only their 
position, but also that of many physicists. Lord Rayleigh, in 
fact, in the course of his remarks on Prof. Fitzgerald’s Helm- 
holtz lecture at the Chemical Society in January last, actually 
said :—* It is to be hoped that chemists will take into grave 
consideration the emphatic warning that Prof. Fitzgerald has 
given, particularly as to the danger of supposing that there is 
any dynamical similarity between the condition of a gas and that 
of a dissolved substance in a liquid. . . 
risk of .pushing formal analogies too far, and of supposing that 
there isa real dynamical similarity, whereas perhaps there is 
only a similarity in mathematical law.” 
I for one require no better support than this, and shall con- 
tinue to be, as I have been from the outset, a determined 
opponent of what, I think, may fairly be termed the nonsensical 
hypothesis of ionic dissociation, for there is no other appro- 
priate term for a view which asserts that hydrogen chloride anda 
few other compounds are so loosely strung together that they 
fall to pieces when dissolved in water: out of sheer fright, it | 
| of the facts of electrolysis ? 
would seem, as no valid motive is suggested for such self- 
sacrifice ; and no such charge of unprincipled levity of conduct is 
brought against the vast majority of compounds other than a few 
acids and akalies ! I believe the view in question to be in entire 
opposition to the teachings of chemical experience ; inapplicable 
to the explanation of the greater number of facts. It is a sign 
of the times that such views can obtain the credence that has 
been accorded to them ; proof how little we care to criticise in 
these days when authority counts for so much—especially in 
Germany. On the other hand, the facts generally seem to be in 
entire accordance with an association hypothesis: and if Prof. 
Poynting would seriously devote himself to putting such an 
hypothesisinto mathematical form, he would be rendering the one 
great service that is required of physicists in this connection. 
All that is needed, I imagine, is to show that the equations 
deduced from the one hypothesis are equally compatible with 
another diametrically opposed to it—surelya small thing to ask 
of mathematicians. 
The dialectical skill of those who are seeking to impose on 
the scientific world the ionic dissociation hypothesis as the only 
true faith is very remarkable. They #zws/ be near relatives of 
Maxwell’s demons, judging from the adroitness with which they 
extricate themselves from seemingly hopeless positions—no 
matter at what sacrifice, and the infinite elasticity of their views— 
which, indeed, are often so elastic that it matters little which 
way the argument turns. For example, in a recent discussion 
on accumulators at a meeting of the German Electro-chemical 
Society, the possibility of lead peroxide ions existing in solution 
having been suggested, it was urged that the presence of a few 
such would not suffice: whereupon Prof. Nernst said that this 
was no diffieulty—it was only necessary to bear in mind the 
readiness with which silver was separated from cyanide solu- 
tions, in which the number of silver ions was inconceivably small. 
If so few will suffice, why not try to do without them altogether, 
NO: 1413, VOE. 55] 
there is possibly a ° 
one is tempted to say. As another instance, I may refer to Mr. 
Whetham’s diplomatic action in at once offering to conclude a 
treaty of peace with Prof. Poynting by conceding the willing- 
ness of the ions, if necessary, to bear the water molecules on 
their backs or be chained to them as galley-slaves: formerly we 
were assured that ionic dissociation was purely platonic suicide, 
and that there were no Rhine maidens in the stream to attract 
the ions apart and bear them away. Of course, in preferring 
these terms, the effect is carefully left out of account which such 
copulation would have on the mystic charges carried by the 
ions ; hypothetical burdens which place them on a level far 
superior to that of any commonplace independent molecule, 
serving to keep them in bounds, and which permit of subtle dis- 
tinctions being made between ordinary and ionic dissociation— 
making the latter not dissociation at all, in fact, for ionists 
certainly ask both to keep their cake and eat it. Again, Mr. 
Whetham, I note, refers to ionic velocities. To me it seems 
impossible to believe that the ions are the infinite sluggards 
indicated in conventional time-tables such as those issued under 
Lodgian editorship—apparently with his approval ; with all due 
deference to such authority, we must decline to accept so slow 
a service, the more if we are to believe that the gaseous and 
liquid states are in any way dynamically comparable. It may 
perhaps be argued that the charges act as brakes—but surely 
such an argument is double-edged, for if we are to suppose that 
the freedom of the ions be thus clogged, liberty can scarcely be 
theirs to act as ordinary gaseous molecules in effecting pressure. 
I am free to confess that my condition of belief as to the 
existence of ‘‘atomic charges”? and any form of ionic d7ssocéa- 
Zzon is purely agnostic—but this is clearly an attitude which is 
abhorrent to those who are now arrogating to themselves the 
position of superior persons to whom has been granted the 
mission and plenary powers to reform an ancient society long 
steeped in superstition : to wit, the chemists. But the chemists’ 
chief concern has been, and still is, to establish facts, and by so 
doing, they have probably got nearer to the inner workings of 
nature than any other class of investigators: for such, the new 
inquisition has no terrors. 
In a paper, of which the Physical Society—in a most 
aggravating and reprehensible manner—publish but the first 
two pages in the current number of their journal, Prof. Larmor 
tells us ‘‘that the facts of chemical physics point to electrification. 
being distributed in an atomic manner, so that an atom of elec- 
tricity, say an electron, has the same claims to separate and per- 
manent existence as an atom of matter.” But is not this view 
based on a particular—I venture to say, a narrow—interpretation 
Do the facts of chemistry point to- 
such a view? Those who cultivate chemical physics haye a way 
of putting chemistry altogether aside, as a mere unimportant 
detail. Does it not entirely leave out of account the difficulties 
which the existence of so-called molecular compounds intro- 
duces ? Do physicists—do chemists even—in any way appreciate 
these? I have already elsewhere contended that if there be an 
electron, it must be capable of acting piecemeal—no discussion of 
the question from this point of view has yet been attempted. 
The facts must not be left out of account! There are many 
gifted mathematicians and physicists at the present day who are 
showing willingness to take such matters into consideration, but 
they are too prone to accept their facts at second-hand—often 
from those who, although nominally chemists, are destitute of 
chemical feeing—an indefinable instinct which, however, has a 
very real existence : consequently two parties are arising with no 
common ground between them. A 
Surely there is no need to be in so great a hurry—it is no dis- 
grace to admit that we cannot yet explain all the mysteries of the 
universe. Lord Kelvin told us recently that he knew no more 
of electric and magnetic force, or of the relation between ether, 
electricity and ponderable matter, or of chemical affinity, than 
he knew and tried to teach his students of natural philosophy 
fifty years ago in his first session as professor. And it should 
also not be forgotten that one to whom all yield respect has 
written: ‘‘It is extremely improbable that when we come to: 
| understand the true nature of electrolysis we shall retain in any 
form the theory of molecular charges, for then we shall have ob- 
tained a secure basis on which to form a true theory of electric 
currents, and so become independent of these provisional 
theories.” (Clerk Maxwell, “ Electricity and Magnetism.”) 
Meanwhile, do not let us pervert the morals of our student 
youth by talking glibly of atomic dissociation, and using a dog- 
matic phraseology which leads them to believe that we have 
