The replacement of air around a carbon arc by other gases has been shown to have several effects in the excitation of spectra, the most obvious being the elimination of cyanogen bands when the atmosphere surrounding the arc contains no nitrogen. Although the effects of controlled atmospheres have been applied in spectrographic analysis, work along these lines has been limited by the practical difficulties involved. These difficulties include delays in changing electrodes between samples, the need for flushing the chamber before excitation can be started, and clouding of chamber windows by deposits of sample and electrode vapors.
Marvin Margoshes and Bourdon F. Scribner, "Simple Arc Devices for Spectral Excitation in Controlled Atmospheres," Appl. Spectrosc. 18, 154-155 (1964)