Atomic hydrogen II—surface effects in the discharge tube

Abstract

In the production of atomic hydrogen by means of the glow discharge, Wood (1921) found that a long discharge tube, e. g. 2m., was desirable, and that a trace of water vapour (or oxygen) in the hydrogen was necessary in order to obtain appreciable yields. Langmuir (Wood 1922) suggested that the effect of water vapour was to form on the walls of the tube a film very much less active than the glass surface as a catalyst for the recombination reaction H + H→H 2 . Wood also suggested that the beneficial effect of using a long tube was due to the removal of the catalytically active electrodes to a con­siderable distance from the point of emergence of the gas (usually near the middle of the tube). Bonhoeffer (1925) recommended a long preliminary discharge to “burn out” active areas of the glass surface. Wrede (1929) found that preliminary cleaning of the tube with chromic acid and hydrofluoric acid was desirable, v. Wartenberg and Schultze (1930) showed that a coating of meta-phosphoric acid inside the discharge tube, if used in conjunction with moist hydrogen, resulted in a great improvement in yield, presumably owing to the hygroscopic character of the acid. The latter workers also studied quantitatively the effect of increasing the amount of added water vapour, and showed that the atom output for a constant current rose rapidly from a very low value until about 2% of water vapour had been added, after which the yield was practically constant. It has been customary, therefore, to introduce about 2·5% of water vapour, and this is very easily done by bubbling the hydrogen through water at atmospheric temperature and pressure.