The vacuum arc spectra of sodium and potassium

Abstract

In connection with the investigation of spectral series, the need for more accurate measurements of the spectra of the alkali metals has long been felt, especially in the case of the diffuse series and the higher members of the sharp series. When it was found that the “sodium vapour lamp,” recently described by Lord Rayleigh, gave extremely narrow bright lines, such that the term diffuse as applied to one of the series becomes a misnomer, it seemed possible that the desired improvement in the measures of the wave-lengths might be attained by the use of this ideal vacuum arc as a source. Definite improvements in the measures for sodium, as proved by the constancy of the separations of pairs of lines, suggested that a potassium vapour lamp might also be used with probable success. The potassium lamp was much more troublesome than the sodium one, and the lines of the diffuse series were less sharply defined. The new measures of potassium lines, however, are probably more exact than before, and an interesting combination pair, indicating satellites to the diffuse series has been observed.