results, incomparably small in relation to the forces concerned,
and supplying no information of the way in which the particles are active
on each other, or in which their forces are finally arranged.

961. That such cases of chemical action produce no _current of
electricity_, is perfectly consistent with what we know of the voltaic
apparatus, in which it is essential that one of the combining elements
shall form part of, or be in direct relation with, an electrolytic
conductor (921. 923.). That such cases produce _no free electricity of
tension_, and that when they are converted into cases of voltaic action
they produce a current in which the opposite forces are so equal as to
neutralize each other, prove the equality of the forces in the opposed
acting particles of matter, and therefore the equality of electric power in
those quantities of matter which are called _electro-chemical equivalents_
(824). Hence another proof of the definite nature of electro-chemical
action (783. &c.), and that chemical affinity and electricity are forms of
the same power (917. &c.).

962. The direct reference of the effects produced by the voltaic pile at
the place of experimental decomposition to the chemical affinities active
at the place of excitation (891. 917.), gives a very simple and natural
view of the cause why the bodies (or _ions_) evolved pass in certain
directions; for it is only when they pass in those directions that their
forces can consist with and compensate (in direction at least) the superior
forces which are dominant at the place where the action of the whole is
determined. If, for instance, in a voltaic circuit, the activity of which
is determined, by the attraction of zinc for the oxygen of water, the zinc
move from right to left, then any other _cation_ included in the circuit,
being part of an electrolyte, or forming part of it at the moment, will
also move from right to left: and as the oxygen of the water, by its
natural affinity for the zinc, moves from left to right, so any other body
of the same class with it (i.e. any other _anion_), under its government
for the time, will move from left to right.

963. This I may illustrate by reference to fig. 83, the double circle of
which may represent a complete voltaic circuit, the direction of its forces
being determined by supposing for a moment the zinc _b_ and the platina _c_
as representing plates of those metals acting upon water, _d, e_, and other
substances,