Other tubes which
withstood the passage of the sparks from a Leyden jar, when submitted
to the discharge of the coil, exploded after a few seconds when the
platinum wires became red-hot. This I think may probably be attributed
to hydrogen, occluded by the platinum, being given off on heating, and
forming steam with the oxygen present.
For an easy and striking lecture experiment, I employ a tube open
at both ends and bent like a W. The two open arms are short and the
platinum wires are fixed at the highest bend. The tube is filled with
hot mercury--one of the ends being closed by a caoutchouc stopper for
the purpose--and a dry mixture of 5 volumes of air and 2 volumes of
carbonic oxide is introduced into the bent tube over the mercury. A
little phosphoric oxide is passed up one arm. After a few minutes the
gases may be submitted to the spark without exploding. A little water
may then be introduced through a pipette into the other arm; and if the
spark is passed directly the gases ignite in the wet and not in the dry
arm of the tube.
The admixture of the inert nitrogen renders a larger quantity of aqueous
vapor necessary for the explosion than when only carbonic oxide and
oxygen in proper proportion are present.
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