an lead and a plate of platina were put into
_pure_ water. There was immediately a powerful current produced from the
lead through the fluid to the platina: it was even intense enough to
decompose solution of the iodide of potassium when introduced into the
circuit in the form of apparatus already described (880.), fig. 73. Here no
action of acid or alkali on the oxide formed from the lead could supply the
electricity: it was due solely to the oxidation of the metal.

* * * * *

946. There is no point in electrical science which seems to 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, I feel no doubt it would supply us
with a direct key to the laws under which the great variety of voltaic
excitements, direct and incidental, occur, and open out new fields of
research for our investigation[A].

[A] In connexion with this part of the subject refer now to Series XI.
1164, Series XII. 1343-1358, and Series XIII. 1621. &c.--_Dec. 1838._

947. 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, &c. &c.)
which of _two modes of action of the attractive power_ shall be exerted
(996.). In the one mode we can transfer the power onwards, and make it
produce elsewhere its equivalent of action (867. 917.); in the other, it is
not transferred, 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.

948. 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.

949. Assuming it sufficiently proved, by the preceding experiments 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 (921. 924.), it would appear that the
metal, when alone, has not power enough, under the circumstances, to take
the oxygen and expel the hydrogen fro