General Propositions	157
one class and another to the other class; but probably on the
proportions also (432). It is further remarkable, that with
very few, if any, exceptions (150, 426), these decomposable
bodies are exactly those governed by the remarkable law of
conduction I have before described (130); for that law does
not extend to the many compound fusible substances that are
excluded from this class. I propose to call bodies of this, the
decomposable class, Electrolytes (400).
 559.	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 pro-
posed to call these bodies generally ions, or particularly onions
and cations, according as they appear at the anode or cathode
(401); 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 anwns, the two metals are cations, and i, 8, 36, 125, 104, 58,
are their electro-chemical equivalents nearly.
 560.	A summary of certain points already ascertained respect-
ing electrolytes, ions, and electro-chemical equivalents, may be
given in the following general form of propositions, without, I
hope, including any serious error.
 561.	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 part of these
Researches (254, etc.).
 562.	ii. If one ion be combined in right proportions (432)
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 (266, 278, 283).
 563.	iii. If, therefore, an ion pass towards one of the elec-
trodes, another ion must also be passing simultaneously to the
other electrode, although, from secondary action, it may not
make its appearance (478).
 564.	iv. A body decomposable directly by the electric current,