A Comprehensive Treatise on Inorganic and Theoretical Chemistry

144 INORGANIC AND THEORETICAL CHEMISTRY
F. P. Bowden and E. K. Rideal, F. W. Reynolds, and O. Erbacher studied
the active surface of platinum ; G. Kab, the influence of adsorbed gas on the
catalytic activity ; and J. C. Stimson, the electrical state of the metal.
O. Lioew and K. Aso 4 observed that when moist platinum black has been
exposed to air for some time, it contains nitric acid and traces of ammonia.
J. W. Ddbereiner, and T. J. Pelouze and E. Fremy showed that compact platinum
absorbs oxygen when heated to a high temp. Neither T. Graham, nor T. WiIm
detected any absorption of oxygen when platinum is heated in air. A. Sieverts
found a little oxygen is taken up by a platinum -wire heated in oxygen ;
G. Bodlander and K. Kdppen said that oxygen is absorbed between 700° and 900° ;
C. Ijanger and V. Meyer noted an absorption occurs at 1690° ; and E. Goldstein,
at a white-heat. The absorption of oxygen was also observed by A. Magnus,
E. F. Smith, V. A. Roiter and M. G. Leperson, J. C. Stimson, G. I. Finch and
J. C. Stimson, B. Neumann and E. Goebel, L. H. Reyerson and L. E. Swearingen,
H. Reischauer, and L. Holborn and F. J. Austin ; and E. Bose said that the
absorption is due to a process of solution, and not to the formation of a compound.
R. !Lucas said that purified platinum does not absorb oxygen, but platinum containing
iridium does not do so with activated oxygen. R. Schwarz and W. Kunzer
found that an oxide is formed. F. E. Carter said that the finely-divided metal,
in oxygen, begins to form black platinum monoxide at 450°, that this oxide at
500° forms platinum and its dioxide, and that the dioxide at 500° furnishes
platinum and oxygen. According to E. K. Rideal and O. H. W. Jones, the loss in
weight of a platinum wire heated electrically, to 1400° K. to 1900° K., in a glass
bulb immersed in liquid air, is greater in oxygen than in vacuo. This is in agreement
with the observations of R. Nahrwold, G. Owen, W. Stewart, and J. Elster
and H. Geitel. E. K. Rideal and O. H. W. Jones infer that two reactions are
involved : (i) a surface reaction between the platinum and oxygen at a rate which
is directly proportional to the press., pt of the oxygen ; and (ii) a reaction which
occurs simultaneously between the platinum vapour and the oxygen. The combined
effect is represented by the equation—dp/dt=a-\-bp, where a and b are constants.
Below 1700° K., and above that temp, when p is less than 5O bars, the second
reaction : Pt+O2=^ PtO2, predominates. I. Liangmuir suggested that the alteration
in the speed of the reaction at high press, and temp, is due to the concentration of
ozone, or of oxygen atoms, but E. K. Rideal and O. H. W. Jones consider this
to be less likely than the hypothesis of a surface reaction. H. H. Rowley and
K. F. Bonhoffer found the accommodation coeff. of oxygen to be 50 per cent,
higher than for hydrogen {q.v.). H. Damianovich and J. Piazza, studied the action
of hydrogen at a low press, under the influence of an electric discharge.
H. Damianovich observed that platinum with adsorbed gases dissolves at a lower
speed in aqua regia. R. Schwarz and W. Kunzer found that with activated
hydrogen some hydride is formed.
Li. Mond and co-workers found that although platinum foil at ordinary temp.,
or at a red-heat, does not absorb appreciable quantities of oxygen, yet two samples
of platinum sponge at a red-heat absorbed respectively 2-4, and 0-5 vol. of oxygen.
Platinum black was found to absorb relatively large proportions of oxygen—about
100 times its vol. The evolution of the absorbed oxygen is appreciable at 100°,
and between 300° and 400°, the rate of evolution is very great, but a red-heat is
necessary for its complete removal. Curves for four different specimens of platinum
black are indicated in Fig. 27. While hydrogen is given off when the metal is heated,
oxygen is absorbed at temp, below 300°, and given off at 360°. A. de Hemptinne
observed that platinum black always contains a considerable proportion of
absorbed oxygen. G. Neumann found that at 450°, platinum takes up 63 to 77 vols,
of oxygen ; JL. Wohler, that when platinum black is heated six weeks at 109° to
280° in air, it takes up 2-3 per cent, of oxygen ; H. S. Taylor and R. M. Burns
found that 1 vol. of platinum sponge absorbed 1*90, 2*80, and 4*30 vols, of oxygen,
respectively, at 25°, 110°, and 218° ; and platinum black, 26*50 and 26-10 vols.