A Comprehensive Treatise on Inorganic and Theoretical Chemistry

76 INORGANIC AND THEORETICAL CHEMISTRY
eliminated with continuous heating, and they are produced by the evolution of
the gases occluded by the wires. The properties of the nuclei are as follow :—
They are emitted by the wire at comparatively low temp. The minimum temp,
required to produce them is lower the less the press, of the surrounding gas. They alter
in size and disappear very soon after their liberation, but last longer if water-vapour has
been caused to condense upon them. The ability of the wire to emit them is temporarily
lost after an omission, but is slowly regained after the lapse of time. The wire immediately
regains the ability to produce them when hydrogen is brought into contact with it ; air,
oxygon, and nitrogen do not produce this effect. If the wire has been kept at a white-heat
in a vacuum for a very long time, the admission and withdrawal of pure hydrogen does not
revive the power to emit nuclei in a vacuum.
The second set is dependent on the presence of oxygen about the heated wire,—
these nuclei are never obtained below a certain temperature, and about this temp,
they are always formed in the presence, but never in the absence of oxygen. The
properties of the second set of nuclei indicate that an unstable, endothermal, and
volatile platinum oxide is formed as indicated above, and this is in agreement with
the following observations :
The second sot of nuclei aro not formed in nitrogen, hydrogen, or a vacuum, but pnly
in the presence of oxygen. The rate of loss of weight of the metal is zero in nitrogen,
hydrogen, or a vacuum. For platinum and rhodium the rate of disintegration at a given
temperature is roughly proportional to the oxygen pressure ; for iridium, which is very
oxidizablo, the rate of disintegration increases much more rapidly than the oxygen pressure.
The disintegration of palladium is of a different nature and will be considered later. At
low pressures of oxygen the nuclei aro very small. The nuclei begin to be formed (that
is, the disintegration begins) at a fairly definite temperature. The nuclei are very persistent
and do not alter in size ; thoy are unaffected by light or by an electric field.
I. Ijangmuir and G. M. J. MacKay, and W. R. Mott estimated the boiling point
to be 3907° ; H. A. Jones and co-workers gave 4527° ; and F. E. Carter, 3910°.
G. A. Hulett estimated that the vapour pressure of platinum at 200° is O0626 mm.
I. Langmuir and G. M. J. MacKay calculated the vap. press, of platinum, p mm. at
different temp., on the absolute scale, T 0 K., and found log 2>=14-09 —27800X-*
—1-26 log Tt or :
? 7 ° K. . 1000° 1250° 1500° 17/50° 2000° 4180°
jy . 324x10-2» 891OxIO- 16 3160xlO~ 12 13OO XlO" 9 49-5xlO-« 76O mm.
J. A. M. van Liiempt studied the vap. press, curves.
According to L. Arons, 6 when a bead of platinum is fused, and cooled, as the
metal solidifies it emits a momentary glow owing to the liberation of the heat of
fusion. J. Violle gave 27-18 CaIs. per gram or 5-3 CaIs. per gram-atom for the
latent heat of fusion ; G. Pionchon gave 27-17 CaIs. ; and J. W. Richards computed
27-8 cals. per gram, J. A. M. van Liempt calculated 530O cals. per gram-atom.
N. F. Mott studied the relation between the latent heat, the m.p., and the electrical
conductivity. N. von Raschevsky, and N. F. Deerr made some observations on the
relation between the m.p. and the heat of fusion. I. Langmuir and G. M. J. MacKay
represented the latent heat of vaporization by (128,000—2-5T) cals. per gram-atom.
F. S. Mortimer also studied the vapour pressure. A. Jouniaux said that Trouton's
rule did not apply to platinum. C. M. Guldberg estimated the critical temperature
of platinum to be 7000° when that of mercury is 1000°. J. J. van Laar, and
M. Thiesen discussed the equation of state of platinum. J. Thomsen studied
the thermochemistry of the platinum compounds. G. N. Lewis and co-workers,
R. C. Tolman, and E. C. Eastman gave 10-0 for the entropy of platinum at 25° ;
W. M. Latimer gave 0-41 for the change of entropy between 200° and 900°. The
internal energy and entropy were studied by K. K. Kelley, R. D. Kleeman, W. Herz,
B. Bruzs, R. von D. Wegener, and E. Kordes. E. D. Eastman and co-workers
discussed the thermal energy of the electrons in platinum.