Origin of the Power of the Pile 185

rent is only another form of the forces of chemical affinity; that
its power is in proportion to the chemical affinities producing it;
that when it is deficient in force it may be helped by calling in
chemical aid,, the want in the former being made up by an
equivalent of the latter; that,, in other words, the fortes termed
chemical affinity and electricity are one and the same.

654. When the circumstances connected with the production
of electricity in the ordinary voltaic circuit are examined and
compared,, it appears that the source of that agent., always
meaning the electricity which circulates and completes the cur-
rent in the voltaic apparatus, and gives that apparatus power
and character (682, 732), exists in the chemical action which
takes place directly between the metal and the body with which
it combines, and not at all in the subsequent action of the sub-
stance so produced with the acid present.1 Thus, when zinc,,
platina, and dilute sulphuric acid are used, it is the union oi
the zinc with the oxygen of the water which determines the
current; and though the acid is essential to the removal of the
oxide so formed, in order that another portion of zinc may act
on another portion of water, it does not, by combination with
that oxide, produce any sensible portion of the current of
electricity which circulates; for the quantity of electricity is
dependent upon the quantity of zinc oxidised., and in definite
proportion to it: its intensity is in proportion to the intensity
of the chemical affinity of the zinc for the oxygen under the
circumstances, and is scarcely, if at all, affected by the use oi
either strong or weak acid (643).

655. Again, if zinc, platina, and muriatic acid are used, the
electricity appears to be dependent upon the affinity of the zinc
for the chlorine, and to be circulated in exact proportion to the
number of particles of zinc and chlorine which unite, being in
fact an equivalent to them.

656. But in considering this oxidation, or other direct action
upon the METAL itself, as the cause and source of the electric
current, it is of the utmost importance to observe that the
oxygen or other body must be in a peculiar condition, namely,
in the state of combination ; and not only so., but limited still
further to such a state of combination and in such proportions
as will constitute an electrolyte (558). A pair of zinc and platina
plates cannot be so arranged in oxygen gas as to produce a
current of electricity, or act as a voltaic circle, even though the

1 Wollaston, Philosophical Transactions, 1801, p. 427.ake, I find that the following bodies are electrolyticby a platina (or any other) wire for a second or two, and then