Local and Current Chemical Force 195

me of more importance than the state of the metals and the
electrolytic conductor in a simple voltaic circuit before and at
the moment when metallic contact is first completed. If clearly
understood, T feel no doubt it would supply us with a direct
key to the laws under which the great variety of voltaic excite-
ments, direct and incidental, occur, and open out new fields of
: research for our investigation.

682. We seem to have the power of deciding to a certain
extent in numerous cases of chemical affinity (as of zinc with the
oxygen of water, etc., etc.) which of two modes of action of the
attractive power shall be exerted (732). In the one mode we can
transfer the power onwards, and make it produce elsewhere its
equivalent of action (602, 652); in the other, it is not trans-
ferred, but exerted wholly at the spot. The first is the case
of volta-electric excitation, the other ordinary chemical affinity:
but both are chemical actions and due to one force or principle.

683. The general circumstances of the former mode occur
in all instances of voltaic currents, but may be considered as in
their perfect condition, and then free from those of the second
mode, in some only of the cases; as in those of plates of zinc
and platina in solution of potassa, or of amalgamated zinc and
platina in dilute sulphuric acid.

684. Assuming it sufficiently proved, by the preceding ex:
periments and considerations, that the electro-motive action
depends, when zinc, platina, and dilute sulphuric acid are used,
upon the mutual affinity of the metal zinc and the oxygen of
the water (656, 659), it would appear that the metal, when
alone, has not power enough, under the circumstances, to take
the oxygen and expel the hydrogen from the water; for, in
fact, no such action takes place. But it would also appear that
it has power so far to act, by its attraction for the oxygen of the
particles in contact with it, as to place the similar forces already
active between these and the other particles of oxygea and the
particles of hydrogen in the water, in a peculiar state of tension
or polarity, and probably also at the same time to throw those
of its own particles which are in contact with the water into a
similar but opposed state. Whilst this state is retained, no
further change occurs; but when it is relieved, by completion
of the circuit, in which case the forces determined in opposite
directions, with respect to the zinc and the electrolyte, are
found exactly competent to neutralise each other, then a series
of decompositions and recompositions takes place amongst the
particles of oxygen and hydrogen constituting the water,,p. 398.oxidising or othernd then