A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 141
by formaldehyde. The adsorption curve has the form ac=ap xln , or x—ap° 12 .
W. R. Ham, and G. Borelius gave more complicated expressions.
Observations showing the diffusion of hydrogen in platinum were made by
T. Graham, H. von Helmholtz, M. Bodenstein, H. Reischauer, V. Lombard,
E. Waldschmidt-Leitz and F. Seitz, G. C. Schmidt
and T. Lucke, W. W. Randall, V. Lombard,
R. Kohler, G. Borelius, A. IS. Freeman,
M. Thoma, A. L. Ferguson and G. Dubpernell,
F. H. Pollard, and W. Nernst and F. Lessing.
R. Jouan compared the rates of diffusion of H 1
and H 2 . A. Winkelmann observed that the rate
of diffusion increases after the platinum has
been heated some time, and that this is due not
to the expulsion of occluded air, but rather to
the crystalline structure assumed by the metal.
The diffusion of hydrogen through red-hot platinum
is not proportional to the press, of the gas ;
and it is probable that the diffusion is accompanied
by a dissociation of the molecules so
that only atoms of hydrogen diffuse in the metal.
Analogous results were obtained with palladium.
O. W. Richardson and co-workers found
that the rate of diffusion is proportional to the
square root of the press., and they also assume
that it is atomic hydrogen which diffuses in the
metals. W. C. Heraeus and W. Geibel studied
the diffusion of hydrogen through red-hot platinum
crucibles ; the hydrogen present in the
inner zone of the Bunsen flame diffuses through
the hot platinum into the interior of a platinum
crucible heated in this part of the flame. This
200 400 600
Pressure in millimetres
FlO. 25. Tho Kffoft. of Pressure on
the Adsorption of Hydrogen.
hydrogen can reduce very energetically ; thus, ferric oxide is partially reduced to
iron, magnesium sulphate to sulphide, sodium sulphate to sulphite, etc. Consequently,
a platinum crucible containing anything which on reduction would yield
a substance capable of attacking platinum may be destroyed if heated in the inner
zone of a Bunsen flame.
M. Traube assumed that a platinum hydride is formed when platinum is used
as a catalyst in hydrogenation reactions ; and similarly with T. Graham, L. Troost
and P. Hautefeuille, and M. Berthelot. J. H. Gladstone and A. Tribe also suggested
that part of the hydrogen occluded in platinum is chemically combined, and
L. Wohler came to a similar conclusion. F. Winteler found that when a film of
platinum on glass in hydrochloric acid is touched with a piece of zinc, a dark film
with a metallic lustre immediately forms on the surface of the acid, and he regarded
this as a platinum-hydrogen alloy. R. Engel showed that when platinum hypophosphite,
suspended in water, is treated with copper sulphate, some platinum
passes into soln. and some platinum hydride, as well as copper hydride, is formed.
H. A. Wilson suggested that a platinum hydride, stable at a high temp., is formed
when an electrical discharge is sent through hot platinum electrodes in hydrogen.
F. Mohr, H. Moissan, and G. F. Hiittig studied the subject. The discontinuity in
the temp, of an electrically heated wire and the absorption of heat was attributed
by A. Farkas and H. H. Rowley to the formation or decomposition of hydrides.
M. Berthelot showed that spongy platinum absorbs several times its vol. of
hydrogen, forming a hydride which is not decomposed at 200°, only 1 vol. of
gas being expelled at that temp. When oxygen in the cold is passed into the
evacuated globe containing the hydride, water is formed, with evolution of 50 CaIs.
per 16 grms. oxygen, from which it may be deduced that 1 grm. of hydrogen