156	Faraday's Researches
conducting wires; for occasionally, and especially with those
which have been positive, they are cavernous, and contain
portions of the cloride or iodide used, which must be removed
before the final weight is ascertained. This is more usually
the case with lead than tin.
 556.	All these facts combine into, I think, an irresistible
mass of evidence, proving the truth of the important proposition
which I at first laid down, namely, that the chemical power of a
current of electricity is in direct proportion to the absolute quantity
of electricity which passes (113^ 518).   They prove, too, that this
is not merely true with one substance, as water, but generally
with  all  electrolytic  bodies;   and,  further, that the results
obtained with any one substance do not merely agree amongst
themselves, but also with those obtained from other substances.,
the whole combining together into one series of definite electro-
chemical actions (241).    I do not mean to say that no exceptions
will appear:  perhaps some may arise, especially amongst sub-
stances existing only by weak affinity; but I do not expect that
any will seriously disturb the result announced.    If, in the well
considered, well examined, and, I may surely say, well ascer-
tained doctrines of the definite nature of ordinary chemical
affinity, such exceptions occur, as they do in abundance, yet,
without being allowed to disturb our minds as to the general
conclusion, they ought also to be allowed if they should present
themselves at this, the opening of a new view of electro-chemical
action; not being held up as obstructions to those who may be
engaged in rendering that view more and more perfect, but laid
aside for a while, in hopes that their perfect and consistent
explanation will ultimately appear.
 557.	The doctrine of definite electro-chemical action just laid
down, and, I believe, established, leads to some new views of
the relations and classifications of bodies associated with or
subject to this action.    Some of these I shall proceed to consider.
 558.	In the first place, compound bodies may be separated
into two great classes, namely, those which are decomposable
by the electric current, and those which are not: of the latter,
some are conductors, others non-conductors, of voltaic elec-
tricity.1   The former do not depend for their decomposability
upon the nature of their elements only;  for, of the same two
elements, bodies may be formed of which one shall belong to
11 mean here by voltaic electricity, merely electricity from a most
abundant source, but having very small intensity.