Influence of Cathode Surface Layers on Minimum Sparking Potential of Air and Hydrogen

Oxide layers on the cathode produced marked irregularities in the Paschen curves for air and hydrogen, especially in the neighbourhood of the minimum V m . V m in hydrogen was measured at different stages during the removal of oxide layers from the cathode, and also during the deposition of one metal on another as base. Removal of the oxide layer produced smooth Paschen curves, while a thin film of one metal on a different metal as base gave values of V m which were not characteristic of either metal in bulk. The deposition of thin metallic films had considerable effect on cathode emission owing to the alteration of the work function