Electrolysation by a Pair of Plates 179

before (51, 52) with regard to the iodide of potassium, namely,
that bodies would differ in facility of decomposition by a given
electric current,, according to the condition and intensity of their
ordinary chemical affinities. This reason appeared in their
reaction upon the affinities tending to cause the current; and it
appeared probable that many substances might be found which
could be decomposed by the current of a single pair of zinc and
platina plates immersed in dilute sulphuric acid, although water
resisted its action. I soon found this to be the case, and as the
experiments offer new and beautiful proofs of the direct relation
and opposition of the chemical affinities concerned in producing
and in resisting the stream of electricity, I shall briefly describe
them.

634. The arrangement of the apparatus was as in fig. 37. The
vessel v contained dilute sulphuric acid; Z and P are the zinc
and platina plates; a, b, and c are platina wires;

the decompositions were effected at x, and
occasionally, indeed generally, a galvanometer
was introduced into the circuit at g: its place
only is here given, the circle at g having no refer-
ence to the size of the instrument. Various
arrangements were made at x, according to the
kind of decomposition to be effected. If a drop
of liquid was to be acted upon, the two ends
were merely dipped into it; if a solution con-
tained in the pores of paper was to be decom-
posed, one of the extremities was connected with a platina plate
supporting the paper, whilst the other extremity rested on the
paper, <?, fig. 44: or sometimes, as with sulphate of soda, a
plate of platina sustained two portions of paper, one of the ends
of the wires resting upon each piece, c, fig. 46. The darts
represent the direction of the electric current (403).

635. Solution of iodide of potassium, in moistened paper,
being placed at the interruption of the circuit at x, was readily
decomposed. Iodine was evolved at the anode, and alkali at
the cathode, of the decomposing body.

636. Protochloride of tin, when fused and placed at x, was
also readily decomposed, yielding perchloride of tin at the anode
(514), and tin at the cathode.

637. Fused chloride of silver, placed at x, was also easily
decomposed; chlorine was evolved at the anode, and brilliant
metallic silver, either in films upon the surface of the liquid, or
in crystals beneath, evolved at the cathode.

Fig. 37.ich has been sought for as a chemical test of the