2469.     ---------------.  [NIKITIN, N. I.]  [Hydrogen and Carbon Dioxide Absorption by Pyrophoric Iron, Nickel, and Cobalt.]  Ztschr. anorg. Chem., vol. 154, 1926, pp. 130-143; Chem. Abs., vol. 20, 1926, p. 3255.

        Experiments were carried out to determine the adsorption and solution of H₂ and CO₂ by pyrophoric Fe, Ni, and Co at different temperatures and pressures.  A specially constructed apparatus for this is illustrated and described.  Finely divided metals were obtained on slow reduction, in about 30 hr., of the respective carbonates with H₂, the reduction temperature being kept at 525° for Fe and at 350° for Ni and Co.  The following results were obtained:  For 5 gm. Fe the maximum H₂ adsorption at –185° and 667 mm. pressure was 8.3 cc.  At –80° and 16° there was virtually no adsorption, while at 380° and 500° there was again a larger adsorption.  The results obtained at different pressures exhibited in isotherms show an adsorption curve at –185°, following Freundlich’s equation:  a=βp^1/n, where β and ^1/n are determined constants.  A proof for the application of this equation is the straight line obtained on plotting log a against log p, the tangent to the angle between this end and X-axis being ^1/n.  That surface adsorption and not solution occurred at –185° was proved by the easy removal of the H₂ on evaluation, while the H₂ taken up at 400° could be removed only by heating strongly.  The results obtained with Ni and H₂ at –185°, 19° and 336° showed a maximum adsorption at 336°, which was 3.8 cm.³ for 5 gm. Ni at 714.9 mm. pressure.  The isotherm for 19° exhibits a straight line parallel to the X-axis and points to the formation of a superficial layer of Ni-H.  A similar formation is not present at –185° inasmuch as the isotherm stars at the O-point of the coordinate axis.  The isotherm for 336° starts below that of 19°, because the loose Ni-H compound dissociates at higher temperature and lower pressure.  Fe had a strong tendency to adsorb CO₂, 1 vol. Fe taking up 35 vol. CO₂ at ordinary temperature and pressure and 2 times as much at –80°.  Ni adsorbed virtually no CO₂ at 335°.  The application of Freundlich’s equation for the CO₂ adsorption by Ni at lower temperatures was not safe because of the small values obtained.  The results with Co and H₂ were all uncertain.  Adsorption values for CO₂ and Co were found between those for Fe and Ni.  5 gm. Co adsorbed 13 cm.³ CO₂ at 14° and 760 mm. pressure.