Gaseous combustion in electric discharges. Part II.—The ignition of electrolytic gas by direct current discharges

In Part I of the present series of researches an account was given of an investigation of the slow, non-self-propellant combustion of electrolytic gas in direct-current discharges. Owing to the limited output of the generator then available, it was not possible, except in a few isolated cases, to extend the investigation to the study of the ignition of electrolytic gas. Some time after the completion of the above-mentioned work, however, a larger high- tension direct-current generator, together with suitable smoothing chokes and condensers, became available, thus enabling us to carry out a systematic investigation of the conditions of ignition of electrolytic gas.Experimental . In the experiments to be described below, precautions were taken to eliminate as far as possible any conditions favourable to ignition, particularly heat and catalytic combustion at the electrodes, other than those due to ionisation of the gas; and then to study the effect of variations of the gas pressure upon the least-igniting current. We have been able to establish a gas pressure-least-igniting current relationship of such a nature that the conclusion may be drawn that ignition of electrolytic gas is determined, under the conditions of our experiments, by the attainment of a definite concentration of ions due to the passage of the electric current; and, further, it has been found that flame is propagated more rapidly in the gas when ionised by the electric discharge than otherwise.