t was put into mixed oxygen and hydrogen, and was found to act at
first slowly, and then more rapidly. In an hour, a cubical inch and a half
had disappeared.

592. Other plates were cleaned with ordinary sand-paper and water; others
with chalk and water; others with emery and water; others, again, with
black oxide of manganese and water; and others with a piece of charcoal and
water. All of these acted in tubes of oxygen and hydrogen, causing
combination of the gases. The action was by no means so powerful as that
produced by plates having been in communication with the battery; but from
one to two cubical inches of the gases disappeared, in periods extending
from twenty-five to eighty or ninety minutes.

593. Upon cleaning the plates with a cork, ground emery, and dilute
sulphuric acid, they were found to act still better. In order to simplify
the conditions, the cork was dismissed, and a piece of platina foil used
instead; still the effect took place. Then the acid was dismissed, and a
solution of _potassa_ used, but the effect occurred as before.

594. These results are abundantly sufficient to show that the mere
mechanical cleansing of the surface of the platina is sufficient to enable
it to exert its combining power over oxygen and hydrogen at common
temperatures.

595. I now tried the effect of heat in conferring this property upon
platina (584.). Plates which had no action on the mixture of oxygen and
hydrogen were heated by the flame of a freshly trimmed spirit-lamp, urged
by a mouth blowpipe, and when cold were put into tubes of the mixed gases:
they acted slowly at first, but after two or three hours condensed nearly
all the gases.

596. A plate of platina, which was about one inch wide and two and
three-quarters in length, and which had not been used in any of the
preceding experiments, was curved a little so as to enter a tube, and left
in a mixture of oxygen and hydrogen for thirteen hours: not the slightest
action or combination of the gases occurred. It was withdrawn at the
pneumatic trough from the gas through the water, heated red-hot by the
spirit-lamp and blowpipe, and then returned when cold into the _same_
portion of gas. In the course of a few minutes diminution of the gases
could be observed, and in forty-five minutes about one cubical inch and a
quarter had disappeared. In many other experiments platina plates when
heated were found to acquire the power of combining oxygen and hydrogen.

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