spark discharge, or rather continuous
current, and involve little or no risk of deranging the magnetism of the
needles (294.).

309. iii. _Chemical decomposition._--The chemical action of voltaic
electricity is characteristic of that agent, but not more characteristic
than are the _laws_ under which the bodies evolved by decomposition arrange
themselves at the poles. Dr. Wollaston showed[A] that common electricity
resembled it in these effects, and "that they are both essentially the
same"; but he mingled with his proofs an experiment having a resemblance,
and nothing more, to a case of voltaic decomposition, which however he
himself partly distinguished; and this has been more frequently referred to
by some, on the one hand, to prove the occurrence of electro-chemical
decomposition, like that of the pile, and by others to throw doubt upon the
whole paper, than the more numerous and decisive experiments which he has
detailed.

[A] Philosophical Transactions, 1801, pp. 427, 434.

310. I take the liberty of describing briefly my results, and of thus
adding my testimony to that of Dr. Wollaston on the identity of voltaic and
common electricity as to chemical action, not only that I may facilitate
the repetition of the experiments, but also lead to some new consequences
respecting electrochemical decomposition (376. 377.).

311. I first repeated Wollaston's fourth experiment[A], in which the ends
of coated silver wires are immersed in a drop of sulphate of copper. By
passing the electricity of the machine through such an arrangement, that
end in the drop which received the electricity became coated with metallic
copper. One hundred turns of the machine produced an evident effect; two
hundred turns a very sensible one. The decomposing action was however very
feeble. Very little copper was precipitated, and no sensible trace of
silver from the other pole appeared in the solution.

[A] Philosophical Transactions, 1801, p. 429.

312. A much more convenient and effectual arrangement for chemical
decompositions by common electricity, is the following. Upon a glass plate,
fig. 43, placed over, but raised above a piece of white paper, so that
shadows may not interfere, put two pieces of tinfoil _a, b_; connect one of
these by an insulated wire _c_, or wire and string (301.) with the machine,
and the other _g_, with the discharging train (292.) or the negative
conductor; provide two pieces of fine platina wire, bent as in