Excerpt from Ionization and Resonance Potentials of Some Nonmetallic Elements

A four-electrode vacuum tube of the same general form as described in Section II was used to study electron currents in nitrogen, oxygen, and hydrogen. The ionization chamber was made of platinum electrodes sealed in a glass tube about 3 cm in diameter. The grids were of fine platinum gauze supported on heavier strips, and the plate was a cylinder of platinum foil fitting tightly ih the tube. A' hot platinum. Strip coated with burned sealing wax served as a cathode. Connecting tubes to the pump and the gas reservoir were arranged so that gas could be streamed through the tube or kept stagnant while liquid-air traps on each side of the ionization chamber froze out any condensable impurities.

In the study of electron currents in these gases we are able to consider. Another effect of collision besides loss of electron velocity and ionization, namely, the effect of radiation, emitted above the resonance potential, on the outer electrodes, causing photo - electric emission from them. As the long wave-length limit of platinum is about As28oo A, this effect must be present whenever the resonance potential is above volts, but with our apparatus it has been too small to measure in all the elements prev10usly studied. The radiation effect has further interest in research on the gases, since in most of the considerable amount of work of other observers the resonance potentials have been observed by means of the radiation effects.

The Lenard method as used in Section II for the measurement of ionization potentials will Show this radiation effect at the resonance potential as a current in the same direction as the ionization current. Davis and Goucher 9 devised a method de scribed under method 3 for distinguishing effects of radiation and ionization. When precautions are taken to distinguish the two effects, we have a valuable means of measuring critical potentials, which is entirely distinct from the method of inelastic collisions here used. However, in all the work previous to the research of Davis and Goucher the simple Lenard method was applied with the assumption that the presence of a plate current was conclusive evidence of ionization. The uncertainty as to just what was meas ured accordingly vitiates nearly all this early work.

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