Secondary Results with Nitric Acid 137

results which might have been expected from the law usually
accepted respecting the final places of the elements.

485. If the salt in solution be an acetate of lead, then the
results at both electrodes are secondary., and cannot be used to
estimate or express the amount of electro-chemical action,
except by a circuitous process (578). In place of oxygen or
even the gases already described (484),, peroxide of lead now
appears at the positive, and lead itself at the negative electrode.
When other metallic solutions are used, containing, for instance,
peroxides, as that of copper, combined with this or any other
decomposable acid, still more complicated results will be ob-
tained; which, viewed as direct results of the electro-chemical
action, will, in their proportions, present nothing but con-
fusion, but will appear perfectly harmonious and simple if they
be considered as secondary results, and will accord in their
proportions with the oxygen and hydrogen evolved from water
by the action of a definite quantity of electricity.

486. I have experimented upon many bodies, with a view to
determine whether the results were primary or secondary. I
have been surprised to find how many of them, in ordinary
cases, are of the latter class, and how frequently water is the
only body electrolysed in instances where other substances have
been supposed to give way. Some of these results I will give
in as few words as possible.

487. Nitric acid.—When very strong, it conducted well, and
yielded oxygen at the positive electrode. No gas appeared at
the negative electrode; but nitrous acid, and apparently nitric
oxide, were formed there, which, dissolving, rendered the acid
yellow or red, and at last even effervescent, from the spon-
taneous separation of nitric oxide. Upon diluting the acid with
its bulk or more of water, gas appeared at the negative electrode.
Its quantity could be varied by variations, either in the strength
of the acid or of the voltaic current: for that acid from which
no gas separated at the cathode, with a weak voltaic battery,
did evolve gas there with a stronger; and that battery which
evolved no gas there with a strong acid, did cause its evolution
with an acid more dilute. The gas at the anode was always
oxygen; that at the cathode hydrogen. When the quantity of
products was examined by the volta-electrometer (442), the
oxygen, whether from strong or weak acid, proved to be in the
same proportion as from water. When the acid was diluted
to specific gravity 1.24, or less, the hydrogen also proved to be
the same in quantity as from water. Hence I conclude thathilosophical Transactions, 1826, p. 388).2.|