A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 139
Fig. 18. A. Sieverts and H. Bruning's curve for the speed of absorption of hydrogen
by platinum black prepared by the reducing action of magnesium is shown in
Fig. 19, for 25° and also for —20°. E. B. Maxted and N. Hassid observed that
with 12 grms. of platinum the rates of absorption
with different initial concentrations
of hydrogen decrease as the absorption
concentration at which the gas is added
increases. A. F. Benton's curves for the rates
of approach to equilibrium at different temp,
and pressure, with 4-269 grms. of platinum
at 737*7 mm. and at 774*3 mm., are shown
in Fig. 20. T. WiIm noted the evolution of
heat during the absorption of hydrogen by
platinum black, and P. A. Favre observed
that the heat developed in the early stages
of the absorption is 23*075 cals. per eq. of
hydrogen, and in the later stages, 13-528
Cals. Li. Mond and co-workers could not confirm this result. The decrease in the
values is connected with the union of the hydrogen with the oxygen already
occluded by the metal. They gave 68-8 Cals. per gram of hydrogen, or 137-6 Cals.
per mol of hydrogen. According to E. B. Maxted, the differential heat of adsorption
rises from a low value to a maximum, and finally decreases with further
adsorption. The results for two specimens are summarized in Fig. 19. II. S. Taylor
I
22\
S
~%>20
g 18 I—
M ,7
—
_-
P*
"_'- nf
— — -_
—
— J
S
40.000
30.000
20,000
)c~~
70,000 Y/ 6
Hydrogen absorbed in c.c.
Fio. 18. The Heat of Absorption of
Hydrogen by Platinum Klack.
20 40 6O 80
Time in minutes
8 10
Temp. 0~ 7 Fio. 19. Rates of Absorption of Fio. 2O.
x JOO
Rates of Approach
18
to
Hydrogen.
E qui I i br ium.
and IX. M. Burns obtained curves which exhibited no maximum, but gradually
decreased with an increase in the adsorption concentration ; and E. 13. Maxted
and N. Hassid found that the differential heat of adsorption on platinum is
nearly constant between 13,300 and 17,50O cals. ; the heat of desorption also was
nearly constant between —15,0OO and —19,1OO cals. G. B. Taylor and co-workers
gave 20,(XX) cals. (approx.) for the heat of adsorption of hydrogen. The subject
was studied by E. W. Flosdorf and G. B. Kistiakowsky, P. A. Favre, and
A. Montier.
A. de Hemptinne found that platinum black absorbs less hydrogen at —78°
than it does at 15°, and if the absorption tube at —78° be allowed to regain a higher
temp., a marked absorption of gas occurs at about —40°. Freshly-prepared
platinum black has a great absorptive power even at the temp, of liquid air—it
can induce the union of hydrogen and oxygen at —190°. A. Gutbier observed a
small maximum in the absorption curve at 0°. E. Harbeck and G. Lunge said
that when platinum black saturated with hydrogen is cooled from 250°, it takes
up the same amount of hydrogen as was given off in raising the temp. H. Baerwald
found platinized asbestos absorbs more hydrogen at the temp, of liquid air than it
does at room temp. F. H. Pollard also made some observations on the absorptive
power of platinized asbestos. The gas molecules which bombard the metal are
partly absorbed and partly reflected. The molecules which make non-elastic
790\