ction, but only in a feeble degree.

587. When a neutral solution of sulphate of soda, or of nitre, or of
chlorate of potassa, or of phosphate of potassa, or acetate of potassa, or
sulphate of copper, was used, the plates, rendered positive in them for
four minutes, and then washed in water, acted very readily and powerfully
on the mixed oxygen and hydrogen.

588. It became a very important point, in reference to the _cause_ of this
action of the platina, to determine whether the _positive_ pole _only_
could confer it (567.), or whether, notwithstanding the numerous contrary
cases, the _negative_ pole might not have the power when such circumstances
as could interfere with or prevent the action were avoided. Three plates
were therefore rendered negative, for four minutes in diluted sulphuric
acid of specific gravity 1.336, washed in distilled water, and put into
mixed oxygen and hydrogen. _All_ of them _acted_, though not so strongly as
they would have done if they had been rendered positive. Each combined
about a cubical inch and a quarter of the gases in twenty-five minutes. On
every repetition of the experiment the same result was obtained; and when
the plates were retained in distilled water for ten or twelve minutes,
before being introduced into the gas (582.), the action was very much
quickened.

589. But when there was any metallic or other substance present in the
acid, which could be precipitated on the negative plate, then that plate
ceased to act upon the mixed oxygen and hydrogen.

590. These experiments led to the expectation that the power of causing
oxygen and hydrogen to combine, which could be conferred upon any piece of
platina by making it the positive pole of a voltaic pile, was not
essentially dependent upon the action of the pile, or upon any structure or
arrangement of parts it might receive whilst in association with it, but
belonged to the platina _at all times_, and was _always effective_ when the
surface was _perfectly clean_. And though, when made the _positive_ pole of
the pile in acids, the circumstances might well be considered as those
which would cleanse the surface of the platina in the most effectual
manner, it did not seem impossible that ordinary operations should produce
the same result, although in a less eminent degree.

591. Accordingly, a platina plate (569.) was cleaned by being rubbed with a
cork, a little water, and some coal-fire ashes upon a glass plate: being
washed, i