88 Faraday's Researches

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.

314. Plates were made positive for five minutes in sulphuric
acid, specific gravity i .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 undimi-
nished vigour. Others were left in similar acid for forty hours,
and some even for eight days, after the electrisation, and then
acted as well in combining oxygen and hydrogen gas as those
which were used immediately after electrisation.

315. 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 exceed-
ingly 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.

316. When similarly prepared plates (305) 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
bu 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 redistilled in glass, and this was found to
preserve prepared plates for a great length of time. Prepared
plates were put into tubes with this water and closed up; some
of them, taken out at the end of twenty-four days, were found
very active on mixed oxygen and hydrogen; others, which were
left in the water for fifty-three days, were still found to cause
the combination of the gases. The tubes had been closed only
by corks.

317. The act of combination always seemed to diminish, or
apparently exhaust, the power of the platina plate. It is true,
that in most, if not all instances, the combination of the gases,
at first insensible, gradually increased in rapidity, and some-
times reached to explosion; but when the latter did not happen,
the rapidity of combination diminished; and although fresh
portions of gas were introduced into the tubes, the combination!xtent of decomposable matter in the direction of the current*ectly to