Sept. To, 1885 ] 
NATURE 
459 
(1) The salt only, 
(2) The water only, 
(3) Both the salt and the water, 
(4) A hydrate of the salt. 
(1) is to be held by those who regard the water as unchanged 
by the addition of salt 
(2) is to be held by those who suppose the water-molecules 
to be dissociated, or mechanically knocked asunder, by the 
massive salt-atoms 
(3) and (4) are mere modifications of one another, not easily 
to be distinguished. 
In deciding this question (4) we really decide what are the 
primary and what are the secondary products of electrolysis. 
Discussion of experimental evidence bearing on the point. 
Hittorf’s and Buff’s experiments on mixed Electrolytes. 
Magnus and others on the effect of current-intensity. (With 
intense currents you are more likely to get the real ions liberated 
because secondary actions have hardly time to occur). 
Direct experiment suggested by observing the place of appear- 
ance of free acid ; and preliminary reply in favour of (3) or (4). 
Valid objection suggested by Smee to regarding any of these 
experiments as crucial ; but possible means of evading the 
objection. 
Experiments of Hisinger, Berzelius and Davy on electrolytes 
in serie: sometimes throw light on the question, which are the 
real ions. 
Il. Questions about the ‘‘ migration of tons.” Do ions in salt- 
Solutions travel at different rates? And, in any case, at 
what rate do they travel ? 
Distinction between fused and dissolved compounds. 
There being simple experimental evidence that solutions often 
concentrate near anode and weaken near cathode, or perhaps 
occasionally vice versa : what is the explanation ? 
Several possible hypotheses : 
(1) Hittorf’s that the salt is primarily decomposed and that 
its ions travel at different speeds. 
(2) Hittorf’s resort in exceptional cases, that per-salts are 
electrolysed into sub-salts and radical. 
(3) Burgoin’s, that a hydrate of the salt is electrolysed and 
that the water travels mostly with the cation. 
(4) D’Almeida’s, that a free acid envelop is formed around 
anode and is electrolysed in series with the salt. 
(5) Quincke’s, that opposite ions have charges differing in 
magnitude as well as in sign, and are therefore urged with 
different forces. 
(6) Wiedemann’s, that the entire salt molecules electrify them- 
selves by comtact with the water and are thus urged bodily either 
with or against the current. 
(7) Kohlrausch’s, that every ion has its own definite rate of 
propagation in a given fluid when urged by a given force ; and 
that this rate is calculable from conductivity, concentration, and 
migration, data. 
(8) Suggested, that opposite corresponding ions’ must always 
travel at equal opposite rates, but that in solutions the water may 
conduct more or less of the current. 
- Mode in which this hypothesis (8) can explain migration ; and 
limitation to its explanation. 
Easy calculation of total or resultant velocity of ions, but 
difficulty in apportioning the right fraction of this velocity to each 
ion in accordance with Kohlrausch’s theory. 
Reasons for supposing it necessary that opposite ions must 
travel at the same pace. 
| Wiedemann’s, Quincke’s, and Helmholtz’s theories of electric 
Endosmose, and proof by Wiedemann that it is independent of 
“migration” phenomena, 
Bearing of experiments with electrolytes in series on the 
question of relative migration velocities ; and other suggested 
migration experiments. : 
IIL. Quantitative Laws of Electrolysis, 
(2) Ohm’s law of electrolytic conduction. 
(4) Faraday’s two laws, 
(1) The voltametric law. 
(2) The law of electro-chemical equivalence. 
And (c) dependence of decomposition EMF on chemical 
combination-energy. 
Nature of experimental evidence in favour of these laws. 
Question whether Ohm’s law will be exactly obeyed for 
violent currents. Very important consequences of the law, if 
exact for feeble currents. 
al 
Physical consequences of Faraday’s two laws; to be asserted 
of all substances for which they are accurately true. 7 
Law (1) asserts that no such electrolyte possesses a trace of 
metallic conduction ; ¢.e. that electrolytic conduction and chemical 
decomposition are precisely correlative. In Helmholtz’s words, 
““Through each section of an electrolytic conductor we have 
always equivalent electrical and chemical motion.” Or again, 
in other words, with a spice of natural hypothesis (first due 
perhaps to Ampére), Electrolysis is a kind of electrical convection 
rather than conduction, each atom carrying a charge with it; 
and the charge conveyed by every atom of a given substance is 
the same. 
Law (2) extends this last important statement to all electrolytes, 
and enables us to ccnclude that a definite quantity of electricity 
belongs to each unit of affinity of every atom of whatever kind, 
and that fractional portions of such atomic charges are, in 
electrolysis at least, unknown. 
This last is a most astounding statement, for it suggests that 
electricity may be ‘‘ atomic” as well as matter. 
Calculation of magnitude of this atomic charge ; enormous 
value of it in proportion to size of atoms (107! electrostatic units, 
probably, per monad atom). 
IV. Questions concerning Polarisation ; and the EMF needed to 
send a current through an electrolyte. 
The chemical changes which go on in a circuit wholly electro- 
lytic, or in any homogeneous portion of a circuit, are decom- 
position and identical recomposition, and consume no energy : 
accordingly no finite EMF is needed to send a current through 
an electrolyte when the force is really applied to it, and Ohm’s 
law is obeyed by electrolytes exactly as by metals. 
But at junctions of metals with electrolytes, or of electrolytes 
with one another, permanent chemical changes may occur, and 
at these places a finite EMF may be situated ; and this may be 
either negative, when it is called polarisation, or positive, when 
the whole arrangement is called a battery. 
Calculation of such EMF's from thermo-chemical data. 
Joule’s proof that the heat of chemical action is a secondary 
result—electric currents being the primary. The EMF (whether 
positive or negative) of any arrangement is obtained in volts, if 
the total heat produced by the chemical changes per dyad 
gramme-equivalent be divided by 46,000. 
Total polarisation may be regarded as the sum of two kinds : 
(z) Temporary polarisation, existing during continuance of 
current. 
(4) Residual polarisation, existing afterwards. 
(4) is caused by a more or less permanent alteration of the 
surface of the electrodes by the clinging or combined ions. 
(a) is caused, according to Helmholtz’s theory, by a Leyden 
jar action of the charged atoms straining across molecular dis- 
tance of the surface of each electrode, and unwilling to part 
with their charges. When the ions are able to combine with 
the electrode, or otherwise retain their charges, this (2) portion 
is very small. 
Effect of secondary actions in destroying polarisation, and 
rendering possible a permanent current even when apparently 
insufficiently propelled. Helmholtz’s air-free cell. 
Intense currents diminish the amount of secondary action ; 
and also modify maximum polarisation values, raising them 
above their customary amounts. 
V. Mechanism of Electrolytic Conduction. 
Electrolytic conduction is certainly a convection of Electricity 
by atoms of matter; but concerning the mode in which the 
atoms make their way through the fluid there are several 
hypotheses : 
(1) The molecular chain of Grotthus ; modified and accepted 
by Faraday and many others, modified further by Hittorf to 
explain migration. 
(2) The dissociation hypothesis of Clausius and Williamson ; 
virtually accepted by Maxwell, modified by Quincke to explain 
migration, and shewn by Kohlrausch to explain the facts of 
conductivity. 
(3) The electrostatic hypothesis of Helmholtz. 
Because Ohm’s law is obeyed, it is certain that no polarisation 
can exist inside a homogeneous electrolyte: in other words, 
there is no chemzcad cling of the atoms there, but only a frictional 
rub. Wiedemann’s view that conductivity is inversely propor- 
tional to ordinary viscosity. 
Probable independence of conductivity and tenacity of 
