ight be looked upon
as the _determining_ cause of the current.

879. I thought it essential to decide this question by the simplest
possible forms of apparatus and experiment, that no fallacy might be
inadvertently admitted. The well-known difficulty of effecting
decomposition by a single pair of plates, except in the fluid exciting them
into action (863.), seemed to throw insurmountable obstruction in the way
of such experiments; but I remembered the easy decomposability of the
solution of iodide of potassium (316.), and seeing no theoretical reason,
if metallic contact was not _essential_, why true electro-decomposition
should not be obtained without it, even in a single circuit, I persevered
and succeeded.

880. A plate of zinc, about eight inches long and half an inch wide, was
cleaned and bent in the middle to a right angle, fig. 73 _a_, Plate VI. A
plate of platina, about three inches long and half an inch wide, was
fastened to a platina wire, and the latter bent as in the figure, _b_.
These two pieces of metal were arranged together as delineated, but as yet
without the vessel _c_, and its contents, which consisted of dilute
sulphuric acid mingled with a little nitric acid. At _x_ a piece of folded
bibulous paper, moistened in a solution of iodide of potassium, was placed
on the zinc, and was pressed upon by the end of the platina wire. When
under these circumstances the plates were dipped into the acid of the
vessel _c_, there was an immediate effect at _x_, the iodide being
decomposed, and iodine appearing at the _anode_ (663.), i.e. against the
end of the platina wire.

881. As long as the lower ends of the plates remained in the acid the
electric current continued, and the decomposition proceeded at _x_. On
removing the end of the wire from place to place on the paper, the effect
was evidently very powerful; and on placing a piece of turmeric paper
between the white paper and zinc, both papers being moistened with the
solution of iodide of potassium, alkali was evolved at the _cathode_ (663.)
against the zinc, in proportion to the evolution of iodine at the _anode_.
Hence the decomposition was perfectly polar, and decidedly dependent upon a
current of electricity passing from the zinc through the acid to the
platina in the vessel _c_, and back from the platina through the solution
to the zinc at the paper _x_.

882. That the decomposition at _x_ was a true electrolytic action, due to a
current determined