um; iodide of lead;
oxide of bismuth; oxide of lead: the electric current was in the same
direction as if acids had acted upon the metals. When any of the same
substances, or phosphate of soda, were made to act on platina and iron,
still more powerful voltaic combinations of the same kind were produced.
When either nitrate of silver or chloride of silver was the fluid substance
interposed, there was voltaic action, but the electric current was in the
reverse direction.

[A] Philosophical Transactions, 1826, p. 406.

iii. _Theory of Electro-chemical Decomposition._

477. The extreme beauty and value of electro-chemical decompositions have
given to that power which the voltaic pile possesses of causing their
occurrence an interest surpassing that of any other of its properties; for
the power is not only intimately connected with the continuance, if not
with the production, of the electrical phenomena, but it has furnished us
with the most beautiful demonstrations of the nature of many compound
bodies; has in the hands of Becquerel been employed in compounding
substances; has given us several new combinations, and sustains us with the
hope that when thoroughly understood it will produce many more.

478. What may be considered as the general facts of electrochemical
decomposition are agreed to by nearly all who have written on the subject.
They consist in the separation of the decomposable substance acted upon
into its proximate or sometimes ultimate principles, whenever both poles of
the pile are in contact with that substance in a proper condition; in the
evolution of these principles at distant points, i.e. at the poles of the
pile, where they are either finally set free or enter into union with the
substance of the poles; and in the constant determination of the evolved
elements or principles to particular poles according to certain
well-ascertained laws.

479. But the views of men of science vary much as to the nature of the
action by which these effects are produced; and as it is certain that we
shall be better able to apply the power when we really understand the
manner in which it operates, this difference of opinion is a strong
inducement to further inquiry. I have been led to hope that the following
investigations might be considered, not as an increase of that which is
doubtful, but a real addition to this branch of knowledge.

480. It will be needful that I briefly state the views of electro-chemical
dec