Regularities in the arc spectrum of arsenic

Abstract

In the course of an investigation of the spectrum of arsenic under different conditions of excitation several regularities has been detected among the lines due to As I, and it is the purpose of the present paper to give an account of these. Besides the very early work of Kayser and Runge, previous investigations on the analysis of the arc spectrum of arsenic consist chiefly of two contributions. Ruark, Mohler, Foote and Chenault have made measurements of the critical potentials of As, and, with the aid of these and the recurring frequency differences pointed out by Kayser and Runge, have suggested an empirical scheme of terms with accounted for many of the more intense lines of the arc. But a large number of lines of wave-length below λ 2100 have not entered into the above scheme and remained unclassified. A study of the absorption by the normal vapour of arsenic failed to show any characteristic line absorption, for the vapour has been found to exhibit continuous absorption in the ultraviolet which spreads towards longer wave-lengths as the vapour pressure rises.