The Spectrum of the Arc in Hydrogen

Abstract

The spectrum of an arc-like discharge in ${\mathrm{H}}_{2}$ and HD of about 50 cm pressure at a current of about one ampere was photographed with a 15 ft. grating and compared with the spectrum of the ordinary vacuum discharge. The spectrum of the arc is very different in appearance but the differences can be easily understood if one takes into account the conditions under which the arc operates. The behavior of unclassified lines in the arc is very useful for their identification. The arc spectrum of hydrogen is very similar to the spectrum obtained in the presence of an excess of helium. An ordinary discharge operated at high pressures and current densities produces a spectrum which deviates from the spectrum of a discharge at low pressures and low currents in the direction of the arc spectrum.