city, merely electricity from a most
abundant source, but having very small intensity.

824. Then, again, the substances into which these divide, under the
influence of the electric current, form an exceedingly important general
class. They are combining bodies; are directly associated with the
fundamental parts of the doctrine of chemical affinity; and have each a
definite proportion, in which they are always evolved during electrolytic
action. I have proposed to call these bodies generally _ions_, or
particularly _anions_ and _cations_, according as they appear at the
_anode_ or _cathode_ (665.); and the numbers representing the proportions
in which they are evolved _electro-chemical equivalents_. Thus hydrogen,
oxygen, chlorine, iodine, lead, tin are _ions_; the three former are
_anions_, the two metals are _cations_, and 1, 8, 3, 125, 104, 58, are
their _electro-chemical equivalents_ nearly.

825. A summary of certain points already ascertained respecting
_electrolytes, ions_, and _electro-chemical equivalents_, may be given in
the following general form of propositions, without, I hope, including any
serious error.

826. i. A single _ion_, i.e. one not in combination with another, will have
no tendency to pass to either of the electrodes, and will be perfectly
indifferent to the passing current, unless it be itself a compound of more
elementary _ions_, and so subject to actual decomposition. Upon this fact
is founded much of the proof adduced in favour of the new theory of
electro-chemical decomposition, which I put forth in a former series of
these Researches (518. &c.).

827. ii. If one _ion_ be combined in right proportions (697.) with another
strongly opposed to it in its ordinary chemical relations, i.e. if an
_anion_ be combined with a _cation_, then both will travel, the one to the
_anode_, the other to the _cathode_, of the decomposing body (530, 542.
547.).

828. iii. If, therefore, an _ion_ pass towards one of the electrodes,
another _ion_ must also be passing simultaneously to the other electrode,
although, from secondary action, it may not make its appearance (743.).

829. iv. A body decomposable directly by the electric current, i.e. an
_electrolyte_, must consist of two _ions_, and must also render them up
during the act of decomposition.

830. v. There is but one _electrolyte_ composed of the same two elementary
_ions_; at least such appears to be the fact (697.), dependent upon a law,
that