PROFESSOR H. B. DIXON OX THE RATE OF EXPLOSION IN GASES. 
1 
7 . It seems probable that in the explosion-wave— 
(1) The gases are heated at constant volume, and not at constant loressure; 
(2) Each layer of gas is raised in temperature before being burnt; 
(3) The wave is propagated not only by the movements of the burnt molecules. 
but also by those of the heated but yet unburnt molecules ; 
(4) When the permanent volume of the gases is changed in the chemical reaction 
an alteration of temperature is thereby caused which affects the velocity of 
the wave. 
8 . In a gas, of the mean density and temperature calculated on these assumptions, 
a sound-wave would travel at a velocity which nearly agrees with the observed rate of 
explosion in, those cases where the products of combustion are perfect gases. 
9. With mixtures in which steam is formed, the rate of explosion falls below the 
calculated rate of the sound-wave. But when such mixtures are largely diluted with 
an inert gas, the calculated and found velocities coincide. It seems reasonable to 
suppose that at the higher temperatures the lowering of the rate of explosion is brought 
about by the dissociation of the steam, or by an increase in its specific heat, or by 
both these causes. 
10 . The propagation of the explosion-wave in gases must be accompanied by a very 
high pressure lasting for a very short time. The experiments of MM. Mallard and 
Le Chatelier, as well as my own, show the presence of these fugitive pressures. It 
is possible that data for calculating the pressures produced may be derived from a 
knowledge of the densities of the unburnt gases and of their rates of explosion. 
Appendix. 
Received July 22, 1892. 
Part I .—The Preparation of the Gases. 
Hydrogen .—The hydrogen used in most of the experiments was prepared by the 
action of pure dilute sulphuric acid on re-distilled zinc, free from arsenic. The gas 
was washed with potash and silver nitrate solutions, and was then passed through a 
scrubbing tower and a series of bulbs filled with a strong solution of alkaline per¬ 
manganate. The gas so prepared had oidy the faintest odour. 
For a few experiments the gas was prepared by the electrolysis of pure dilute 
sulphuric acid with platinum electrodes. 
Marsh (ras. —The marsh gas was prepared by Gladstone and Tribe’s method,* in 
which pure methyl iodide is decomposed by the zinc-copper couple in presence of 
absolute alcohol. The “ scrubber,” packed with the zinc-copper couple, was kept 
moistened by alcohol dropping from a tap-funnel, and the gas was further washed 
* ‘ Chem. Soc. Jouni.,’ 1884, p. 1. 
