Comparison of Measurements of Critical Potentials of Mercury Vapor

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Abstract
The critical potentials of Hg vapor were examined with a tube constructed to permit use of a number of different methods. For detecting critical potentials other than those of ionization, the Hertz method proved much the most satisfactory. Of the 13 critical potentials found below ionization, 10 have definite spectroscopic interpretation and the remaining 3, which are probably due to mercury molecules, confirm similar values reported by Miss Messenger. The partial current method of Franck and Hertz showed less resolving power, but otherwise gave good agreement with the Hertz method. The Franck and Einsporn method gave peculiar results, suggesting that it detected only photoelectric effects and not metastable atoms, and that the failure to show the other critical potentials was due to features of tube design which eliminated inelastic impacts in the region around the filament where space charge acts to limit emission.