848.  This Table might 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 confidence in the overruling influence of those natural laws which render the former definite, as to feel no hesitation in believing that the latter must submit to them also.  Such being the case, I can have, no doubt that, assuming hydrogen as 1, and dismissing small fractions for the simplicity of expression, the equivalent number or atomic weight of oxygen is 8, of chlorine 36, of bromine 78.4, of lead 103.5, of tin 59, &c., notwithstanding that a very high authority doubles several of these numbers.