758 REPORT—1 885. 
behaves as a condenser, it does so by reason of actions going on within 
the films or boundaries separating the liquid from the electrodes. From 
observations made with his air-free cell Helmholtz estimates the thickness. 
of these quasi-dielectric films as 10~§ centimetre—the customary mole- 
cular magnitude. 
It seems to me that Helmholtz accepts the possibility that ordinary 
electrostatic laws may be applied to the interactions of atoms and their 
charges, and to the attractions of atoms by the electrodes across this thin 
molecular film. And he points out that the reason so feeble an E.M.F. is. 
sufficient to effect decomposition is just because of the extreme thinness 
of the film—the slope of potential dV /dz being by no means insignificant. 
Helmholtz shows that the analogue between the pre-decomposition 
state of a voltameter and a condenser of constant capacity is accurately 
sustained by his air-free cell, charge being proportional to potential dowm 
to y,45p Volt or perhaps lower; and this fact he considers to prove that 
by far the greater part of the force binding atoms together, and probably 
the whole of it, is electrical; for ‘if any chemical force bound ions to- 
gether, requiring work to overcome it, an inferior limit ought to exist to 
such K.M.F.sas are able to attract ions to the electrodes and charge them 
as condensers. No indication of any such limit has yet been discovered.” 
But while he thus considers it proved that the mightiest chemical 
forces are really electrical, he by no means denies the existence of others. 
Atoms cling to electricity, and charged atoms cling to one another, but 
uncharged atoms may cling somewhat, and this may be the distinction 
between ‘typical compounds’ and ‘molecular aggregates.’ This distinc- 
tion had been forced upon me also independently, and so I quote it with 
full agreement. All electrolytes belong to the ‘ typical compound’ class, 
and it is by means of the charges in these atoms that they are so easily 
decomposable, notwithstanding their strong affinities. But combination 
can occur between elements of very weak affinity, which only with diffi- 
culty can be got to unite; and yet, once combined, they seem to cling 
with the most surprising tenacity. These bodies, I should suppose, are 
molecular aggregates held together by purely ‘ chemical,’ i.e. material or 
non-electrical, forces; and the reason of their apparent tenacity is, I 
would suggest, merely that they afford no handle to Jay hold of. They 
are quite unsusceptible to electrical influence, unless it be in the violent. 
and perhaps thermal form of the electric spark. IfI instance such bodies as. 
cyanogen andammonia it is only to indicate more suggestively what I mean. 
I do not feel sure whether Helmholtz would lend his name to the 
suggestion just made, for he hedges a little about these molecular modes 
of combination and says, ‘ But the fact that even elementary substances 
with few exceptions have molecules composed of two atoms makes it 
probable that even in these cases electric neutralisation is produced by 
combination of two atoms each fully charged, not by neutralisation of 
every single unit of affinity.’ I venture with great deference to suggest, 
as an objection to this view, the fact that charged (say hydrogen) atoms 
are unable to unite with each other, though they attack everything else 
with vigour, but that so soon as they are allowed to give up their charges 
to an electrode they at once unite and become molecules of gas. 
I need not stay to do more than remark that the notion of an attrac- 
tion between matter and electricity is made by Helmholtz to explain a 
great many other things—‘ contact E.M.F.,’ ‘thermo-electricity,’ ‘frictional 
electricity,’ and, in fact, all electrostatics and most of current electricity. 
