e taken place.

576. Reverting to the action of the prepared plates on mixtures of oxygen
and hydrogen (570.), I found that the power, though gradually diminishing
in all cases, could still be retained for a period, varying in its length
with circumstances. When tubes containing plates (569.) were supplied with
fresh portions of mixed oxygen and hydrogen as the previous portions were
condensed, the action was found to continue for above thirty hours, and in
some cases slow combination could be observed even after eighty hours; but
the continuance of the action greatly depended upon the purity of the gases
used (638.).

577. Some plates (569.) were made positive for four minutes in dilute
sulphuric acid of specific gravity 1.336: they were rinsed in distilled
water, after which two were put into a small bottle and closed up, whilst
others were left exposed to the air. The plates preserved in the limited
portion of air were found to retain their power after eight days, but those
exposed to the atmosphere had lost their force almost entirely in twelve
hours, and in some situations, where currents existed, in a much shorter
time.

578. Plates were made positive for five minutes in sulphuric acid, specific
gravity 1.336. One of these was retained in similar acid for eight minutes
after separation from the battery: it then acted on mixed oxygen and
hydrogen with apparently undiminished vigour. Others were left in similar
acid for forty hours, and some even for eight days, after the
electrization, and then acted as well in combining oxygen and hydrogen gas
as those which were used immediately after electrization.

579. The effect of a solution of caustic potassa in preserving the platina
plates was tried in a similar manner. After being retained in such a
solution for forty hours, they acted exceedingly well on oxygen and
hydrogen, and one caused such rapid condensation of the gases, that the
plate became much heated, and I expected the temperature would have risen
to ignition.

580. When similarly prepared plates (569.) had been put into distilled
water for forty hours, and then introduced into mixed oxygen and hydrogen,
they were found to act but very slowly and feebly as compared with those
which had been preserved in acid or alkali. When, however, the quantity of
water was but small, the power was very little impaired after three or four
days. As the water had been retained in a wooden vessel, portions of it
were redi