Atomic hydrogen - I—The calorimetry of hydrogen atoms

Abstract

Since the discovery of Wood (1920, 1921, 1922 a , b ) that hydrogen can be dissociated to a considerable extent into free atoms in the glow discharge, many workers have used this method of production of atomic hydrogen for the study of its chemistry. Few attempts have been made, however, to determine the optimum discharge conditions for large yields of atoms, although the consensus of opinion has favoured the use of long discharge tubes, operated with fairly heavy currents at gas pressures of about 0·3-1mm. The work described in this series of papers was undertaken to deter­mine and explain the factors controlling yield. Atomic hydrogen has been estimated by several different methods. The calorimetry of the heterogeneous catalysis reaction, H+H+ M → H 2 + Q + M ( Q being the dissociation energy of the hydrogen molecule, and M a suitable catalyst) has been the method employed by a number of workers. Bonhoeffer (I924) Bichowsky and Copeland (1928), v. Wartenberg and Schultze (1930), Dixon (1932), and Smallwood (1929) have all devised calorimeters based on this equation. But with none of these has it been possible to obtain a good degree of accuracy, coupled with reasonably rapid operation and the possibility of making consecutive readings. Probably the method of Small­ wood, also used by Amdur and Robinson (1933), is the best of those cited; but this involved corrections for conduction losses amounting to 40 or 45% of the observed rise of temperature; also about 20min. were required for each determination, and consecutive readings were not possible owing to the increasing temperature.