A Comprehensive Treatise on Inorganic and Theoretical Chemistry

228 INORGANIC AND THEORETICAL. CHEMISTRY
The ductility data show that with increasing iridium content, higher annealing
temp, are required. The hard-worked alloys do not show a very marked difference
in ductility until over 20 per cent, is attained, when there is a decrease. F. Korn,
and N. S. Kurnakoff studied the subject.
A. E. Tutton measured the coeff. of thermal expansion of a platinum-iridium
alloy. W. A. Nemiloff measured the sp. electrical resistance, R9 of some alloys
at 25°, and 100°, and obtained :
Iridium
0-25
11-948
14-838
1
14-894
17-590
2
14-792
17-605
The results at 25°, and the temp, coeff. of the binary alloys between 25° and 100°
are indicated in Fig. 77. L. Guillet and M. Ballay observed a slight increase in
the resistance when the alloy is cold-worked and annealed at 950°. J. Obata
studied the effect of a magnetic field, and J. L. R. Morgan and co-workers, the
^30-
Ca
40-^
#20-
Ct:
\ ?
-
"^l
0 004
0 003 §=
0 002
R
22-773
25-376
I
oooi Ji
IO
20 40
I
60 80 100
Per cent of Iridium
Fia. 77.—The Electrical "Resistance
Iridium Alloys.
of the Platinum -
10
24-349
26-705
20 per cent.
30-685
32-710
°0° 200° 400° 600° 800 6 1000*1200°
FIG. 78. The Thermoelectric
Force of the Platinum-iridium
Alloys.
reproducibility of quinhydrone electrodes with platinum-iridium electrodes.
W. Geibel, R. von D. Wegner, W. Broniewsky, W. H. Keesom and J. N. van Ende,
and J. W. Schmidt measured the thermoelectric force of the alloys. The results
are summarized in Fig. 78. B. Brenner, C. W. Waidner and Gr. K. Burgess,
H. Ie Chatelier, and C. Barus made some observations on the subject. J. Luke
and R. Fricke studied the action of the alloy on nitrous oxide. P. G. Tait gave
dE/d0—7-9O-+-O'OO620 microvolts per degree for lead against alloys with 15 per cent,
of iridium, 5-90—001330 for alloys with 10 per cent, iridium, and 6-15+O-OO550
for alloys with 5 per cent, iridium ; and the corresponding neutral points are
respectively —1274°, 444°, and —1118°. F. Haber found that the alloy with
10 per cent, iridium is scarcely attacked when used as anode in the electrolysis of
hydrochloric acid, and the alloy with 20 per cent, is not attacked at all. G. R. Levi
observed that the presence of 10 per cent, of iridium decreased the catalytic activity
of platinum on hydrogen dioxide. M. Delepine noted the dissolution of the
platinum-iridium alloy in sulphuric acid at the rate of 0*10 grm. per hour per
sq. dm. at 265°.
H. St. C. Deville and H. Debray discussed the platinum-iridium-rhodium
alloy which occurs as " a triple alloy of an invariable composition " ; and they
prepared the quaternary platinum-iridium-rhodium-tin alloy. F. E. Carter said
that the platinum-iridium-rhodium alloys are used for radio tubes. The platinumiridium-osmium
alloys are used for sparking plugs. C. O. Bannister and E. A. du
Vergier discussed the analyses of the platinum-iridium alloys.