The electric discharge in monatomic gases

Abstract

In a recent paper one of us has described the use of metallic calcium at high temperature for the production of high vacua, and in spectroscopic work as a very perfect chemical absorbent of all except the chemically inert gases. It was shown that helium and argon purified by calcium from traces of common gases or vapours, with which they are in practice invariably contaminated during manipulation, showed a great disinclination to conduct the discharge. In ordinary spectrum-tubes, helium offered a resistance equivalent to an alternative spark-gap of an inch in air, at a pressure of 0·05 mm., and argon at 0·02 mm. of mercury. This behaviour of the monatomic gases, together with the closely-allied phenomenon shown by spectrum-tubes filled with these gases of becoming non-conducting, or “running out,” under the action of the discharge, have now been investigated in detail. A great number of experiments have been performed and a short summary will be given in the present paper. The main object was to settle whether electric conduction in the monatomic gases is essentially different from that in other gases. The first results raised at least a presumption that perfectly pure helium might be unable to conduct the discharge at all, so that the running out of spectrum-tubes might be due to the absorption of the impurities only by the electrodes and not by the absorption of the inert gas itself. This view, however, proved to be untenable.