mposed by being fused and heated to dull
redness for a few minutes, and the whole reduced to protiodide, yet that is
not at all opposed to the possibility, that a little of that which is
formed in great excess of iodine at the _anode_, should be carried by the
rapid currents in the liquid into contact with the _cathode_.

803. This view of the result was strengthened by a third experiment, where
the space between the electrodes was increased to one third of an inch; for
now the interfering effects were much diminished, and the number of the
lead came out 89.04; and it was fully confirmed by the results obtained in
the cases of _transfer_ to be immediately described (818.).

The experiments on iodide of lead therefore offer no exception to the
_general law_ under consideration, but on the contrary may, from general
considerations, be admitted as included in it.

804. _Protiodide of tin._--This substance, when fused (402.), conducts and
is decomposed by the electric current, tin is evolved at the _anode_, and
periodide of tin as a secondary result (779. 790.) at the _cathode_. The
temperature required for its fusion is too high to allow of the production
of any results fit for weighing.

805. _Iodide of potassium_ was subjected to electrolytic action in a tube,
like that in fig. 68. (789.). The negative electrode was a globule of lead,
and I hoped in this way to retain the potassium, and obtain results that
could be weighed and compared with the volta-electrometer indication; but
the difficulties dependent upon the high temperature required, the action
upon the glass, the fusibility of the platina induced by the presence of
the lead, and other circumstances, prevented me from procuring such
results. The iodide was decomposed with the evolution of iodine at the
_anode_, and of potassium at the _cathode_, as in former cases.

806. In some of these experiments several substances were placed in
succession, and decomposed simultaneously by the same electric current:
thus, protochloride of tin, chloride of lead, and water, were thus acted on
at once. It is needless to say that the results were comparable, the tin,
lead, chlorine, oxygen, and hydrogen evolved being _definite in quantity_
and electro-chemical equivalents to each other.

* * * * *

807. Let us turn to another kind of proof of the _definite chemical action
of electricity_. If any circumstances could be supposed to exert an
influ