674 
MR. H. B. DIXON ON CONDITIONS OF CHEMICAL CHANGE 
abscissae are parts of carbonic oxide in 1000 of the combustible gases, the ordinates are 
the coefficients found. 
The continuous curve is drawn through the coefficients given by the mixtures with 17'4 
parts of oxygen. The vertical line shows the point where the hydrogen is just twice the 
oxygen in the first series. The dotted curve is drawn through the coefficients given by the 
mixture with 12'4 parts of oxygen. The vertical line shows the point where the hydrogen 
is just twice the oxygen in the second series. 
General conclusions. 
1. Bunsen’s original experiments on the incomplete combustion of carbonic oxide 
and hydrogen are vitiated by the presence of aqueous vapour in the eudiometer. 
Both Horstmann’s experiments and my own show that no alteration jper saltum 
occurs in the ratio of the products of combustion. 
2. A mixture of dry carbonic oxide and oxygen does not explode when an electric 
spark is passed through it. The union of carbonic oxide and oxygen is effected 
indirectly by steam. A mere trace of steam renders a mixture of oxj'gen and 
carbonic oxide 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 the 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 steam formed, depends on 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 is independent of the shape of the 
vessel. The larger the quantity of oxygen used the lower the “ critical pressure " is 
found to be. 
4. When dry mixtures of carbonic oxide and hydrogen in varying proportions are 
exploded above the “ critical pressure ” with oxygen insufficient for complete com¬ 
bustion, an equilibrium is established between two opposite chemical changes 
represented by the equations 
