Importance of gas in electrodes for the glow-to-arc transition

IN an earlier work¹ on the probability of glow-to-arc transitions in a low-pressure mercury-vapor discharge it was pointed out that these transitions occur in a completely random fashion and that the probability of a transition increases with an increase of pressure, cathode-current density, or glow voltage. In particular, cathode temperature was found to be very important, the transition probability being several times higher in a narrow temperature range near 425 degrees centigrade than it is at either lower or higher temperatures. The possible causes of these transitions were also investigated and the only explanation that seemed consistent with the experimental results obtained was that each transition was due to a burst of gas from the electrode surface. It was felt that even if the amount of gas given off in each burst was very small, the random appearance of these bursts from various parts of the electrode surface could explain the experimental results obtained.