852a.    ---------------.  [EUCKEN, A.]  [Hydrogenation of Unsaturated Hydrocarbons on Nickel Contact Catalysts.  I.  Adsorption of Hydrogen on Nickel.]  Ztschr. Elektrochem., vol. 53, 1949, pp. 285-290; British Abs., 1951, I, A, p. 52.

       Adsorption of H2 on Ni powder is investigated at constant temperature and also at constant pressure.  The differential or intermediate heat of adsorption is determined calorimetrically.  The results agree with the assumption that H2 is dissociated and is adsorbed in the atomic state.  The adsorption velocity is determined.  There are 2 maxima in the adsorption velocity isobars, 1 at about 200 abs. and the other at about 270 abs.  At higher pressures the 1st maximum disappears.  This is not due to the presence of 2 regions of the surface with different activities.  It is more likely that changes take place in the whole surface on heating, and that the activity therefore alters.  The heat of adsorption decreases relatively strongly with increasing cover density.