Results are given which show that the dielectric recovery after current zero, of short, stationary A.C.arcs between brass electrodes, is similar to that of cold-electrode arcs previously investigated and described. These results also show that the rate of recovery of dielectric strength of hot-electrode arcs after a current zero may be greatly increased by reducing, within limits, the electrode separation. A possible explanation on the basis of ionic diffusion to the electrode surfaces and the deionizing action of blasts of metal vapor from the boiling electrodes is mentioned.

The restriking after zero current of short stationary A.C. arcs with brass, copper, zinc, iron, tungsten and carbon electrodes, and of arcs moving rapidly over copper electrodes was investigated with a cathode-ray tube of the Braun type. The voltampere traces on the fluorescent screen showed clearly the voltage necessary to restrike the arc after current zero, and the effect of the electrode vapor on the magnitude and variation of the restriking voltage. The arcs with refractory electrodes, i.e. carbon and tungsten, showed traces differing from the arcs with the other metals in that no high voltage for restriking the arc appeared. This is believed to be due to the refractory electrodes being at a temperature high enough for thermionic emission. For the other electrode materials, re-ignition voltages of several hundred volts were observed, suggesting that re-ignition of the arc required breakdown of a gas layer by ionization by collision alone. The arcs which were rapidly moving over their electrodes usually restruck to a glow before breaking down to an arc. The magnitudes of the restriking voltage and the glow current depended upon the condition of the electrodes, magnitude of the driving magnetic field, and the transient characteristic of the circuit in which the arc was playing.