[Footnote 1: "Report of British Association," 1880, p. 503.]
For such a series of reactions a _comparatively_ few molecules of water
would suffice, and the change produced by their alternate reduction and
oxidation would come under the old term of "catalytic action," inasmuch
as the few water molecules present at the beginning are found in the
same state at the completion of the reaction.
The truth of this hypothesis has since been confirmed by experiments I
have made on the incomplete combustion of mixtures of carbonic oxide and
hydrogen; and on the velocity of explosion of carbonic oxide and oxygen
with varying proportions of aqueous vapor. I therefore thought a
description of the more convenient methods lately devised as lecture
experiments for showing the influence of water on the combustion of
carbonic oxide would not be uninteresting to the Section.
A glass tube from 18 inches to 2 feet long, closed at one end, and
provided with platinum wires, is bent near its open end so that the
shorter arm makes an angle of about 60° with the longer arm. The tube,
held by a clamp, is heated in a Bunsen flame, and is then filled with
mercury heated to about 130° C. The mixture of gases is then made to
displace a portion of the mercury by forcing it through a fine tube,
which is connected by a steel cap to the eudiometer of McLeod's gas
apparatus, and passes down through the mercury in the shorter arm of the
experimental tube. When a sufficient quantity of the gaseous mixture
has been collected in the longer arm, some dry phosphoric oxide is
introduced in the following way: A small glass tube is heated, packed
with the dry powder, and pushed down into the shorter arm of the
experimental tube. With a hot glass rod the phosphoric oxide is pushed
out at the bottom of the small tube, and passes up into the gaseous
mixture in the longer arm. After standing for a few hours in contact
with the phosphoric oxide, the gases may be submitted to strong sparks
from a Leyden jar without igniting. Care must be taken that none of the
oxide comes in contact with the platinum wires, for if any sticks to
the wires it becomes heated by the passage of the sparks, and gives off
enough water to determine the explosion. In this way I have prepared
several specimens of a non-explosive mixture of carbonic oxide and
oxygen in the proper proportions to form carbonic acid. Some of these
tubes have been submitted without explosion to sparks from a large
Leyden jar, to a continuous succession of sparks from a Holtz machine,
and to the discharge of a Ruhmkorff's coil, that heated the platinum
wires between which it passed to bright redness. 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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