composed by the current, the metals evolved at the _cathode_, though
elements, are _always_ secondary results, and not immediate consequences of
the decomposing power of the electric current.

[A] Annales de Chimie, 1801, tom. li. p. 167.

745. Many of these secondary results are extremely valuable; for instance,
all the interesting compounds which M. Becquerel has obtained by feeble
electric currents are of this nature; but they are essentially chemical,
and must, in the theory of electrolytic action, be carefully distinguished
from those which are directly due to the action of the electric current.

746. The nature of the substances evolved will often lead to a correct
judgement of their primary or secondary character, but is not sufficient
alone to establish that point. Thus, nitrogen is said to be attracted
sometimes by the positive and sometimes by the negative electrode,
according to the bodies with which it may be combined (554. 555.), and it
is on such occasions evidently viewed as a primary result[A]; but I think I
shall show, that, when it appears at the positive electrode, or rather at
the _anode_, it is a secondary result (748.). Thus, also, Sir Humphry
Davy[B], and with him the great body of chemical philosophers, (including
myself,) have given the appearance of copper, lead, tin, silver, gold, &c.,
at the negative electrode, when their aqueous solutions were acted upon by
the voltaic current, as proofs that the metals, as a class, were attracted
to that surface; thus assuming the metal, in each case, to be a primary
result. These, however, I expect to prove, are all secondary results; the
mere consequence of chemical action, and no proofs either of the attraction
or of the law announced respecting their places[C].

[A] Annales de Chimie, 1804, tom. li. p. 172.

[B] Elements of Chemical Philosophy, pp. 144. 161.

[C] It is remarkable that up to 1804 it was the received opinion that
the metals were reduced by the nascent hydrogen. At that date the
general opinion was reversed by Hisinger and Berzelius (Annales de
Chimie, 1804, tom. li. p. 174,), who stated that the metals were
evolved directly by the electricity: in which opinion it appears, from
that time, Davy coincided (Philosophical Transactions, 1826, p. 388).

747. But when we take to our assistance the law of _constant
electro-chemical action_ already proved with regard to water (732.), and
which I hope to extend satisfactorily