be further arrange into groups of such substances as
either act with, or replace, each other. Thus, for instance, acids and
bases act in relation to each other; but they do not act in association
with oxygen, hydrogen, or elementary substances. There is indeed little or
no doubt that, when the electrical relations of the particles of matter
come to be closely examined, this division must be made. The simple
substances, with cyanogen, sulpho-cyanogen, and one or two other compound
bodies, will probably form the first group; and the acids and bases, with
such analogous compounds as may prove to be _ions_, the second group.
Whether these will include all _ions_, or whether a third class of more
complicated results will be required, must be decided by future
experiments.

849. It is _probable_ that all our present elementary bodies are _ions_,
but that is not as yet certain. There are some, such as carbon, phosphorus,
nitrogen, silicon, boron, alumium, the right of which to the title of _ion_
it is desirable to decide as soon as possible. There are also many compound
bodies, and amongst them alumina and silica, which it is desirable to class
immediately by unexceptionable experiments. It is also _possible_, that all
combinable bodies, compound as well as simple, may enter into the class of
_ions_; but at present it does not seem to me probable. Still the
experimental evidence I have is so small in proportion to what must
gradually accumulate around, and bear upon, this point, that I am afraid to
give a strong opinion upon it.

850. I think I cannot deceive myself in considering the doctrine of
definite electro-chemical action as of the utmost importance. It touches by
its facts more directly and closely than any former fact, or set of facts,
have done, upon the beautiful idea, that ordinary chemical affinity is a
mere consequence of the electrical attractions of the particles of
different kinds of matter; and it will probably lead us to the means by
which we may enlighten that which is at present so obscure, and either
fully demonstrate the truth of the idea, or develope that which ought to
replace it.

851. A very valuable use of electro-chemical equivalents will be to decide,
in cases of doubt, what is the true chemical equivalent, or definite
proportional, or atomic number of a body; for I have such conviction that
the power which governs electro-decomposition and ordinary chemical
attractions is the same; and such con