2820.     RIDEAL, E. K., AND TRAPNELL, B. M. W.  [Adsorption of Hydrogen by Tungsten, and the Mechanism of Para-Hydrogen Conversion at Tungsten Surfaces.]  Jour. chim. phys., vol. 47, 1950, pp. 126-138; Chem. Abs., vol. 44, 1950, p. 7118.

        The adsorption of H2 was measured over the temperature range -185 to 0 and pressure range 1.5X10-7 to 10-2 mm. on a film of W formed by evaporation of W atoms from a wire.  The equilibrium adsorption changed very slowly with temperature and pressure, increasing only 9% at 0 for a 104 pressure increase and only 14% on dropping the temperature from 0 to -183 at 10-2 mm.  If the surface area of the film is judged from the chemisorption of O2, the measurement represents coverages in the range 60%-90%.  The heats of adsorption calculated by the Clausius Clapeyron equations are 14, 11, 7, 3, and 2 kcal. per mole at coverages of 70, 75, 80, 85 and 90%, respectively.  The data fit a Freundlich isotherm.  quantitative analysis of the data leads to the conclusion that the observed fall in heat of adsorption with coverage cannot be accounted for on the basis of simple electrostatic dipole-dipole repulsions.  The data are consistent with the rate of interconversion of ortho-para H2 observed by Eley and Rideal (abs. 808) if it is assumed that this reaction is the result of alternate chemisorption and evaporation of H2 mol. from a surface that is so extensively covered with H2 as to have a low heat of desorption of H2 mol.