(811.) 
Electro- 
chemical 
decomposi- 
tion, and 
theory of 
the pile. 
Definite 
character 
of decom- 
position— 
electrical 
equiva- 
lents. 
(812.) 
Inferences 
as to the 
identity of 
electrical 
and chemi- 
cal forces, 
978 
Currents and from Magnets, or the discovery of 
Magneto-Electricity. 
III. The influence of the Magnet on all bodies, 
and the consequent division of substances into two 
classes, Magnetics and Diamagnetics. 
IV. Optical changes induced by Magnetism. 
I. With regard to electro-chemical decomposition 
and the theory of the pile, the great extent and intri- 
cacy of the subject require us to restrict our analysis 
to a few of the leading conclusions. The most im- 
portant of these may be summed up in the following 
propositions :—Ist, The amount of a decomposable 
substance (or electrolyte) analysed into its elements 
by a current of electricity depends solely on the 
amount of electricity passing through it, and is in- 
dependent of the form of apparatus employed, the 
dimensions of the poles (or electrodes), the strength 
of the solution, or any other circumstance. It is 
thence inferred, with respect, for instance, to water, 
that the amount of it decomposed in a given time is 
an exact measure of the quantity of electricity set in 
motion in that time. 2d, When a substance is thus 
decomposed, it is a necessary, or at least a highly 
probable, consequence of Dalton’s laws, that the 
elements separated are in atomic proportions to one 
another. But Mr Faraday also found that when 
several decompositions are effected at the same time 
by interposing different electrolytes in intervals of 
the same circuit, the whole of the series of elements 
separated bear the atomic relations to one another. 
Thus, to take a single case; an electric current de- 
composes in the same time 0°497 grain of water 
and 3-2 grains of protochloride of tin. Now, these 
are exactly the proportions of the atomic weights of 
those bodies. From this and numerous other cases 
Mr Faraday infers, that universally the amount of 
electrical action required to dissolve a combination is 
in a constant proportion to the force of chemical affi- 
nity by which its elements are united. The corollary 
seems therefore highly probable that it is one and the 
same force which is exerted in either case. But the 
conclusion as to their identity becomes almost irre- 
sistible when we add to these propositions the follow- 
ing: 3dly, That the oxidation of one atom of zinc by 
the acid of the battery generates precisely so much 
electricity as would resolve one atom of water into 
its elements. Thus, 8°45 grains of zine dissolved 
occasioned the analysis of 2°35 grains of water ; but 
these numbers are in the ratio of 32-5 to9; the 
equivalents or atomic weights of zinc and water. 
From these strictly experimental laws, Dr Fara- 
day considers that he is entitled to draw these im- 
portant inferences: First, that the source of voltaic 
electricity in the pile is chemical action solely; 
Secondly, that the forces termed chemical affinity 
and electricity are one and the same.”! Itisneedlessto 
add that these conclusions, involving the very essence 
MATHEMATICAL AND PHYSICAL SCIENCE. 
(Wiss. VI. 
of the science of voltaic electricity, are supported by 
Mr Faraday by a great variety of collateral proofs ; 
and, on the whole, I cannot see that they admit of any 
reasonable doubt. The contact theory of Volta still, 
however, holds its ground in Germany, where the 
number of influential writers on electricity is con- 
siderable ; and so perseveringly is it maintained, that 
it is diffieult to perceive how it is ever to be dis- 
lodged. But on this wide and not very profitable 
controversy we cannot here enter, 
There are a great many other considerations 
(813.) 
connected with the action of the voltaic battery Dr Fara- 
which are independent of these primary ones, 
day on In- 
and duction 
which are scarcely less important. Dr Faraday ana Con- 
has entered into a most elaborate experimental duction. 
argument to show that induction always precedes 
both conduction and decomposition, and that de- 
composable bodies or electrolytes must be all more 
or less perfect conductors. His views may be thus 
concisely summed up in his own words ;—‘ The first 
effect”? of the electrifying influence, whether of frie- 
tional electricity or of voltaic electricity, upon bodies, 
is “ the production of a polarized state of their par- 
ticles which constitutes induction ; and this arises 
from its action upon the particles in immediate con- 
tact with” the excited body, “which again act upon 
those contiguous to them, and thus forces are trans- 
ferred to a distance. If the induction remain un- 
diminished, perfect insulation is the consequence ; 
if the contiguous particles” thus polarized “ have 
the power to communicate their forces, then con- 
duction occurs, conduction being a distinct act of 
discharge between neighbouring particles.” “In the 
inductive condition assumed by water” when about 
to be decomposed, “the discharge between particle 
and particle is not, as before, a mere interchange of 
their powers and forces, but an actual separation of 
them, the oxygen travelling in one direction and 
carrying with it its amount of force acquired during 
polarization, and the hydrogen doing the same thing 
in the other direction, until they each meet the next 
approaching particle, which is in the same electrical 
state with that they have left, and by association of 
their forces with it produce discharge. This action 
may be regarded as a carrying one performed by the 
constituent particles of the dielectric.”* Again, 
“the current is an indivisible thing; an aais of 
power, in every part of which both electric forces are 
present in equal amount.” 
These views respecting the molecular progress of 
conduction and decomposition, though perhaps never 
so categorically stated as by Dr Faraday, have been, 
I imagine, substantially held by a majority of those 
who have considered the subject since the time 
of Davy, who first gave them a partial expression. 
And when Davy and others speak of the electric 
forces in decomposition as if they emanated from the 
1 Researches, Art. 918, 
2 Ib., Arts, 1338, 1347, 
3 Ib., Art. 1642, 
————— 
(s14) 
