By HAROLD B. DIXON, M.A.
[Abstract of a paper read before the Chemistry Section of the British
Association at Montreal.]
The author gave a _resume_ of the work he had done in continuation of
the researches of Bunsen, E. von Meyer, Horstmann, and other chemists,
on the division of oxygen when exploded with excess of hydrogen and
carbonic oxide. The following are the general conclusions arrived at:
1. No alteration _per saltum_ occurs in the ratio of the products
of combustion. The experiments made completely confirm Horstmann's
conclusion; Bunsen's earlier experiments being vitiated by the presence
of aqueous vapor in the eudiometer.
2. A dry mixture of carbonic oxide and oxygen does not explode when
an electric spark is passed through it. The union of carbonic oxide
is effected indirectly by steam. A mere trace of steam renders the
admixture of carbonic oxide and oxygen explosive. The steam undergoes
a series of alternate reductions and oxidations, acting as a "carrier
of oxygen" to the carbonic oxide. With a very small quantity of steam
the oxidation of carbonic oxide takes place slowly; as the quantity of
steam is increased, the rapidity of explosion increases.
3. When a mixture of dry carbonic oxide and hydrogen is exploded with
a quantity of oxygen insufficient for complete combustion, the ratio
of the carbonic acid to the steam formed depends upon the shape of the
vessel and the pressure under which the gases are fired. By continually
increasing the initial pressure, a point is reached where no further
increase in the pressure affects the products of the reaction. At and
above this critical pressure the result was found to be independent of
the length of the column of gases exploded. The larger the quantity of
oxygen used, the lower the "critical pressure" was found to be.
4. When dry mixtures of carbonic oxide and hydrogen in varying
proportions are exploded above their critical pressures with oxygen
insufficient for complete combustion, an equilibrium is established
between two opposite chemical changes represented by the equations:
(I.) CO + H_{2}O = CO_{2} + H_{2}.
(II.) CO_{2} + H_{2} = CO + H_{2}O.
At the end of the reaction the product of the carbonic oxide and steam
molecules is equal to the product of the carbonic acid and hydrogen
molecules multiplied by a coefficient of affinity. This result
agrees with Horstmann's conclusion. But Hortsmann considers that the
coefficient varies with the relative mass of oxygen taken.
5. A small difference in the initial temperature at which the gases are
fired makes a considerable difference in the products of the reaction.
This difference is due to the condensation of steam by the sides of the
vessel during the explosion, and its consequent removal from the sphere
of action during the chemical change. When the gases are exploded at an
initial temperature sufficiently high to prevent any condensation of
steam during the progress of the reaction, the coefficient of affinity
is found to be constant whatever the quantity of oxygen used--provided
only the quantity of hydrogen is more than double the quantity of
oxygen.
6. The presence of an inert gas, such as nitrogen, by diminishing the
intensity of the reaction, favors the formation of carbonic acid in
preference to steam. When the hydrogen taken is less than double the
oxygen, the excess of oxygen cannot react with any of the three other
gases present--carbonic oxide, carbonic acid, and steam--but has to
wait until an equal volume of steam is reduced to hydrogen by the
carbonic oxide. The excess of inert oxygen has the same effect as inert
nitrogen in favoring the formation of carbonic acid. The variations
in the coefficient of affinity found by Hortsmann with different
quantities of oxygen are due partly to this cause, but chiefly to the
varying amounts of steam condensed by the cold eudiometer during the
reaction taking place in different experiments.
7. As a general result of these experiments it is shown that, when a
mixture of dry carbonic oxide and hydrogen is exploded with oxygen
insufficient for complete combustion, at a temperature at which no
condensation of steam can take place during the reaction, and at a
temperature greater than the critical pressure, an equilibrium between
two opposite chemical changes is established, which is independent
of the mass of oxygen taken, so long as this quantity is less than
half the hydrogen. Within these limits the law of mass is completely
verified for the gaseous system composed of carbonic oxide, carbonic
acid, hydrogen, and steam at a high temperature.