A Comprehensive Treatise on Inorganic and Theoretical Chemistry

146 INORGANIC AND THEORETICAL, CHEMISTRY
The heat developed during the occlusion of oxygen by platinum was found by
L. Mond and co-workers to be ll-O cals. per gram of oxygen, and since this is almost
the same as the value given by J. Thomsen for the heat of formation of platinous
hydroxide, the two phenomena may be related, the necessary water being present
in platinum black dried in vacuo. They finally concluded that the occlusion of
oxygen by platinum or palladium is a true oxidation phenomenon. According
to Ja. Wohler, and C. Engler and L. Wohler, platinum black containing occluded
oxygen turns potassium iodide starch solution blue ; it is somewhat soluble in
dilute hydrochloric acid, the weight of platinum in solution is less than the weight
of platinum black dissolved, and if the difference be attributed to oxygen it is
found that the ratio of platinum to oxygen agrees well with PtO ; the amount of
oxide present in the platinum sponge depends on the state of division. It does not
easily amalgamate, and the amalgam formed becomes covered with a film of the
black oxide ; hydrogen dioxide does not reduce it in the cold, but on boiling, complete
reduction takes place, and it is also reduced by alcohol, ether, and other
organic substances ; in absence of air, it oxidizes arsenious to arsenic acid, and the
residue loses its spongy character and becomes granular. It is further shown that
the properties of active platinum sponge closely resemble those of platinous oxide,
in confirmation of the theory of A. de la Rive that in the catalysis by platinum
black, the intermediate active agent is this oxide. However, platinum sponge
free from oxide causes more active oxidation than does platinous oxide, and this
is explained by C. Engler and W. Wild's theory of the intermediate formation of
peroxide and secondary formation of oxide, which takes place more readily with
the finely-divided sponge than with the more compact platinous oxide.
R. Vondracek also inferred that platinum black contains a very labile compound
of platinum and oxygen ; and E. Goldstein, that in the electrical discharge in
oxygen with platinum electrodes, a compound of platinum and oxygen is formed,
that the absorption of oxygen is very rapid if the electrodes are at a high temp.,
and that the faculty of platinum to form these oxides is connected with its catalytic
activities. P. Lafntte and P. Grandadam found that platinum is oxidized when
heated between 300° and 500° at 50 to 200 kilogrms. per sq. cm. press. At the
optimum temp., 455°, spongy platinum at 4 atm. press, increased in weight
2-1 per cent. ; and at 150 atm. press., 7*37 per cent., and platinum black increased
13*96 per cent. The product is a mixture of platinum monoxide and dioxide.
F. C. Phillips also noted that the order of the oxidizability of the platinum
metals is connected with their faculty of burning hydrogen—namely, osmium,
palladium, platinum, and iridium.
Platinum black containing occluded oxygen was found by J. W. Ddbereiner 5
to exert an action on hydrogen and other combustible gases or vapours whereby
the metal may be heated to redness, and if air has access, the gases may be set
on fire. If air or oxygen has not access, the oxidation ceases as soon as the occluded
oxygen is consumed, but if air or oxygen has access, the platinum black takes up
more oxygen, and transfers it to the combustible body so that the process is continuous.
The subject was discussed by A. Adie, W. Artus, A. Baudrimont,
A. C. Becquerel, M. Berthelot, M. Bodenstein, R. Bottger, M. C. Boswell and
C. H. Bayley, C. Brunner, G. L. Cabot, H. Courcot and J. Meunier, W. Davies,
J. W. Dobereiner, F. P. DuIk, P. L,. Dulong and L.. T. Thenard, A. Fyfe,
L,. W. Gilbert, F. Gill, C. A. Gruel, G. F. Hanle, H. Karmarsch, W. Klinkerfues,
W. Knop, J. von Liebig, G. Merryweather, G. Merz, C. F. Mohr, F. Parmentier,
C. H. Pfaff, M. V. Poljakoff and co-workers, P. W. Schmidt, C. F. Schonbein,
J. S. C. Schweigger, H. A. von Vogel, A. Wagner, E. O. Wiig, and T. WiIm.
A. Osawa found that the arrangement of the atoms in the lattice of platinum black
is not changed by the adsorption of oxygen, but there is a linear expansion of
2-9 per cent. The inflammation of hydrogen was described by A. Garden,
C. G. Gmelin, W. Herapath, and A. Pleischl ; of alcohol, or ether vapour, by
S. F. Dana, K. Fuchs, H. B. Miller, and G. Schiibler ; and the self-ignition of coal