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156 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 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.

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 electricity. 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