Arcs in Inert Gases. II

Abstract

Arcs in pure inert gases between electrodes of pure metals have been found impossible to maintain under ordinary conditions, whereas they are easy to maintain if the gas is slightly contaminated. (1) For highly purified iron in argon, helium and neon, and highly purified silver and zinc in argon, the arc discharge is inherently unstable. The cathode spot darts rapidly up and down the electrode, and finally goes out at values of open circuit voltage, short circuit current, pressure of the arc atmosphere, and electrode separation at which a stable arc is ordinarily obtained when slightly less pure elements are used. We conclude, therefore, that the degree of purity of the elements of metallic arcs in inert gases, and par-ticularly the degree of purity of the gas, determines the boundaries within which stable arcing may occur. Further, for elements of a high degree of purity the boundary values of the region of unstable operation are quite definite and readily determinable experimentally; beyond these boundaries much more stable arcs are encountered.(2) The extinction of an unstable arc is not characterized by any marked change in the current or voltage of the arc at the instant immediately preceding extinction. (3) Higher purity of the electrode material and of the inert atmosphere appears to move the voltage versus current curve in the direction of higher voltage.