Molecular Spectrum of Cadmium Vapour

Abstract

PROF. ROBERTSON'S observation¹ of a maximum at 2212 A. in the spectrum of an arc between cadmium electrodes which is much more intense than the cadmium band at 2125 is very interesting. This observation is surprising in view of the fact that no maximum at 2212 was observed by Cram² in fluorescence or Tesla discharge, while the 2125 band was easily observed both in fluorescence and discharge. The condensed copper spark giving more intensity near 2212 than 2125 when used as source for fluorescence excited 2125 with no emission maximum at 2212. These two bands have nearly the same intensity in absorption. The failure of an emission maximum at 2212 to appear along with the 2125 band of cadmium in fluorescence and discharge in pure cadmium vapour shows that the 2212 maximum is likely to be due to an impurity. The opportunity for observing spectra due to impurities (such as CdO, CdH, etc.) is always much greater in the arc in air than in a quartz tube containing only pure cadmium.