Low Voltage Arcs in Diatomic Gases. I. Hydrogen, Nitrogen, and Iodine

Abstract

Low-voltage Arcs in Hydrogen, Nitrogen, and Iodine Vapor.---After a general review of the previous experimental results and theoretical suggestions, (1) current-voltage curves obtained with a simple two-electrode tube are described. Precautions were taken to insure pure gases. The breaking potential was always the ionizing potential of the gas, 16.3, 16.2, and 14.6 volts, respectively, for the three gases. The striking potential was greater than the breaking one by an amount which increased with the pressure and with increasing cathode filament temperature. In dissociated hydrogen, maintained at a high temperature within a thin tungsten cylinder heated electrically, an arc was readily maintained at the ionizing potential of the atom, 13.7 volts, and under very favorable conditions, at the radiating potential, 10.0 volts. In dissociated iodine vapor, the arc was maintained at 12.1 volts and under certain conditions at the ionizing potential, 10.2 volts. Nitrogen was not appreciably dissociated in the furnace. The critical potentials given above agree with the best previous results within \ifmmode\pm\else\textpm\fi{} 0.2 volt as a rule. Those associated with the atom are experimentally distinguished from those associated with the molecule.Electric Furnace Spectra of Hydrogen, Nitrogen and Iodine to 2500\ifmmode^\circ\else\textdegree\fi{} C.---In hydrogen, the series lines flashed in when the arc was struck, even as low as 10.6 volts, but the bands did not appear. Evidently the series lines are due to the atom and the bands to the molecule. In nitrogen, a brilliant flare was produced at potentials which decreased from 70 to 40 volts as the temperature was increased. This flare shows both the positive and negative bands along with the spectrum of tungsten; it is probably due to the formation of active nitrogen. At 70 volts the first lines, 5006 and 5003 \AA{}., appeared, and at 90 volts only two more, 5680 and 5667 \AA{}. Reasons are given for assigning the positive bands to the neutral molecule, the negative bands to the ionized molecule and the lines to the atom. In iodine, the arc lines, particularly 4860 \AA{}., flashed in when the arc struck, the enhanced lines coming in at higher voltages. No band spectrum appeared.New negative bands of nitrogen were found at 5075, 5018 and 4961 \AA{}.