d explosion of
the gas. This result was obtained several times, and when larger
proportions of olefiant gas were used, the action seemed still more
hopeless.

641. A mixture of forty-nine volumes oxygen and hydrogen (638.) with one
volume of olefiant gas had a well-prepared platina plate introduced. The
diminution of gas was scarcely sensible at the end of two hours, during
which it was watched; but on examination twenty-four hours afterwards, the
tube was found blown to pieces. The action, therefore, though it had been
very much retarded, had occurred at last, and risen to a maximum.

642. With a mixture of ninety-nine volumes of oxygen and hydrogen (638.)
with one of olefiant gas, a feeble action was evident at the end of fifty
minutes; it went on accelerating (630.) until the eighty-fifth minute, and
then became so intense that the gas exploded. Here also the retarding
effect of the olefiant gas was very beautifully illustrated.

643. Plates prepared by alkali and acid (605.) produced effects
corresponding to those just described.

644. It is perfectly clear from these experiments, that _olefiant gas_,
even in small quantities, has a very remarkable influence in preventing the
combination of oxygen and hydrogen under these circumstances, and yet
without at all injuring or affecting the power of the platina.

645. Another striking illustration of similar interference may be shown in
_carbonic oxide_; especially if contrasted with _carbonic acid_. A mixture
of one volume oxygen and hydrogen (638.) with four volumes of carbonic acid
was affected at once by a platina plate prepared with acid, &c. (605.); and
in one hour and a quarter nearly all the oxygen and hydrogen was gone.
Mixtures containing less carbonic acid were still more readily affected.

646. But when carbonic oxide was substituted for the carbonic acid, not the
slightest effect of combination was produced; and when the carbonic oxide
was only one-eighth of the whole volume, no action occurred in forty and
fifty hours. Yet the plates had not lost their power; for being taken out
and put into pure oxygen and hydrogen, they acted well and at once.

647. Two volumes of carbonic oxide and one of oxygen were mingled with nine
volumes of oxygen and hydrogen (638.). This mixture was not affected by a
plate which had been made positive in acid, though it remained in it
fifteen hours. But when to the same volumes of carbonic oxide and oxygen
were added thirty-t