pparatus was as in fig. 77. 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 reference 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 contained in the pores of paper was to be decomposed, one of the
extremities was connected with a platina plate supporting the paper, whilst
the other extremity rested on the paper, _e_, fig. 81: 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. 86. The
darts represent the direction of the electric current (667.).

900. 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.

901. _Protochloride of tin_, when fused and placed at _x_, was also readily
decomposed, yielding perchloride of tin at the _anode_ (779.), and tin at
the _cathode_.

902. 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_.

903. Water acidulated with sulphuric acid, solution of muriatic acid,
solution of sulphate of soda, fused nitre, and the fused chloride and
iodide of lead were not decomposed by this single pair of plates, excited
only by dilute sulphuric acid.

904. These experiments give abundant proofs that a single pair of plates
can electrolyze bodies and separate their elements. They also show in a
beautiful manner the direct relation and opposition of the chemical
affinities concerned at the two points of action. In those cases where the
sum of the opposing affinities at _x_ was sufficiently beneath the sum of
the acting affinities in _v_, decomposition took place; but in those cases
where they rose higher, decomposition was effectually resisted and the
current ceased to pass (891.).

905. It is however, evident, that t