I do not mean to say that no exceptions will appear:  perhaps some may arise, especially amongst substances 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-ascertained 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.

* * * * *

822.  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.

823.  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 electricity[A].  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 one class and another to the other class; but probably on the proportions also (697.).  It is further remarkable, that with very few, if any, exceptions (414. 691.), these decomposable bodies are exactly those governed by the remarkable law of conduction I have before described (694.); 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 (664.).

  [A] I mean here by voltaic electricity, 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.