stilled 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.

581. 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 sometimes 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 went
on more and more slowly, and at last ceased altogether. The first effect of
an increase in the rapidity of combination depended in part upon the water
flowing off from the platina plate, and allowing a better contact with the
gas, and in part upon the heat evolved during the progress of the
combination (630.). But notwithstanding the effect of these causes,
diminution, and at last cessation of the power, always occurred. It must
not, however, be unnoticed, that the purer the gases subjected to the
action of the plate, the longer was its combining power retained. With the
mixture evolved at the poles of the voltaic pile, in pure dilute sulphuric
acid, it continued longest; and with oxygen and hydrogen, of perfect
purity, it probably would not be diminished at all.

582. Different modes of treatment applied to the platina plate, after it
had ceased to be the positive pole of the pile, affected its power very
curiously. A plate which had been a positive pole in diluted sulphuric acid
of specific gravity 1.336 for four or five minutes, if rinsed in water and
put into mixed oxygen and hydrogen, would act very well, and condense
perhaps one cubic inch and a half of gas in six or seven minutes; but if
that same plate, instead of being merely rinsed, had been left in distilled
water for twelve or fifteen minutes, or more, it would rarely fail, when
put into the oxygen and hydrogen, of becoming, in the course of a minute or
two, ignited, and would generally explode the gases. Occasionally the time
occupied in bringing on the action extended to eight or nine minutes, and
sometime