53. Now it is wonderful to observe how small a quantity of a compound body
is decomposed by a certain portion of electricity. Let us, for instance,
consider this and a few other points in relation to water. _One grain_ of
water, acidulated to facilitate conduction, will require an electric
current to be continued for three minutes and three quarters of time to
effect its decomposition, which current must be powerful enough to retain a
platina wire 1/104 of an inch in thickness[A], red-hot, in the air during
the whole time; and if interrupted anywhere by charcoal points, will
produce a very brilliant and constant star of light. If attention be paid
to the instantaneous discharge of electricity of tension, as illustrated in
the beautiful experiments of Mr. Wheatstone[B], and to what I have said
elsewhere on the relation of common and voltaic electricity (371. 375.), it
will not be too much to say that this necessary quantity of electricity is
equal to a very powerful flash of lightning. Yet we have it under perfect
command; can evolve, direct, and employ it at pleasure; and when it has
performed its full work of electrolyzation, it has only separated the
elements of _a single grain of water_.

[A] I have not stated the length of wire used, because I find by
experiment, as would be expected in theory, that it is indifferent.
The same quantity of electricity which, passed in a given time, can
heat an inch of platina wire of a certain diameter red-hot, can also
heat a hundred, a thousand, or any length of the same wire to the same
degree, provided the cooling circumstances are the same for every part
in all cases. This I have proved by the volta-electrometer. I found
that whether half an inch or eight inches were retained at one
constant temperature of dull redness, equal quantities of water were
decomposed in equal times. When the half-inch was used, only the
centre portion of wire was ignited. A fine wire may even be used as a
rough but ready regulator of a voltaic current; for if it be made part
of the circuit, and the larger wires communicating with it be shifted
nearer to or further apart, so as to keep the portion of wire in the
circuit sensibly at the same temperature, the current passing through
it will be nearly uniform.

[B] Literary Gazette, 1833, March 1 and 8. Philosophical Magazine,
1833, p. 201. L'Institut, 1833, p.261.

854. On the other hand, the relation between the cond