Heats of Condensation of Electrons and Positive Ions on Molybdenum in Gas Discharges

New method for measuring the electronic work function.---A new calorimetric method for measuring the electronic work function of a metal in a gas discharge, has been developed. A small molybdenum sphere was supported in a region of intense gas ionization by three fine wires, two of which formed a thermocouple to measure its temperature, while the third carried the current of the incoming ions. Space potential and mean electronic energies E_- were found by using the sphere as a Langmuir collector. Its rate of heating due to an increment Δj in the electron current reaching it against a small retarding field was measured and equated (with small corrections) to Δj(E_-+φ_-), whence the heat of electron condensation φ_- was found.Values of φ_- for molybdenum in argon, hydrogen and nitrogen.---The values of φ_- found by this method were: 4.76 volts in argon, 4.04 or 4.35 volts in hydrogen (mixed with argon), and 4.77 or 5.01 volts in nitrogen. The double values follow different treatments of the surface. Owing to uncertainty in the specific heat values of molybdenum these results may be a few percent too high, consequently all the information required for making any necessary corrections from more satisfactory specific heat values has been given.Measurement and theory of the heating effect on molybdenum due to the neutralization of an argon positive ion at its surface.---By a modification of the method, φ₊ for an argon positive ion neutralized at a molybdenum cathode was found to be about one volt. This low value indicates that a large part of the energy of neutralization at the cathode of a discharge tube is lost by the neutralized molecules, probably by radiation, before they make thermal contact with the metal.Confirmatory evidence for "secondary" electrons.---The presence in a low pressure gas discharge, of the high speed "secondary" electrons discussed by Langmuir, is shown by the good agreement between values of E_- obtained calorimetrically and values calculated from the $logj$-against-voltage lines of the two groups of electrons, as obtained by Langmuir's methods.