A Comprehensive Treatise on Inorganic and Theoretical Chemistry

222 INORGANIC AND THEORETICAL, CHEMISTRY
summarized in Fig. 67, and their hardness, in the same diagram. W. A. Nemiloff
and N. M. Voronoff found the Brinell's hardness of the alloy to be :
Rhodium
0 7O 20 40 60 80 90 100 at. per cent.
Hardness
2800 56-87 67-73 71-41 75-83 47-60 73-47 54-91
Rhodium is sometimes added to platinum for hardening platinum, and such
alloys retain their hardness even after long exposure at a high temp.—vide Table IV.
An alloy with 20 per cent, of rhodium has been recommended as wire for high
temp, resistance furnaces. The alloys have a lower rate of volatilization than
platinum, and they do not crystallize so readily. They are therefore preferred to
platinum alone for crucible and some thermoelectric work. An alloy with 3£ per
I
wo\-
80
=* 60
40
Rochwnll
^*^
•
——
—- -1
J
25
20 IL
20 40 60 80 100
20 Per cent, (by weicjht) of Rhodium
Fio. 67.—Tho -Density and Hardness of
the Rhodium-Platinum Alloys.
CJ
I
0-005r
20 40 60 80 100
Per cent, (by weight) of Rhodium
Fio. 68.—Tho Electrical .Resistance arid
its Temperature Coefficient of the
Rhodium-Platinum Alloys.
cent, of rhodium is in use. E. R. Thews, and I. E. Adaduroff discussed some uses
of the alloys. F. E. Carter observed that alloys with up to 50 per cent, of rhodium
can be worked, but those with higher percentages work with difficulty. Rhodium
does not harden platinum so much as ruthenium, or iridium, but it hardens the
metal more than palladium. The Brinell's hardness, U, the tensile strength in
kgrms. per sq. mm., the resistance R ohms per million ft., and the temp, coeff.
a per degree between 0° and 1200°, are :
Rhodium
Hardness
Annealed J1 2Q0°
R . r
a
3-5
107
—
6k
103
0-00195
10
165
9O
HO
0-00135
2O
211
169
107
125
O-00120
5O per cent
323
254
138
134
T. Barratt and R. M. Winter found the thermal conductivity of an alloy with
10 per cent, rhodium to be 0-072 CaI. per cm. per sec. per degree at 17°, and
0-073 at 100°. The electrical resistance, and the temp, coeff. of the resistance of
the alloys observed by J. S. Acken, are indicated in Fig. 69. W. A. Nemiloff and
N. M. Voronoff found the sp. resistance, UxIO 6 , to be, at 25° and 100° :
Rhodium
Temp, coeff.
0 IO 20 30 40 50 60
10-88 16-97 19-69 20-40 19-83 17-95 16-35
13-79 19-64 2203 22-42 22-07 19-70 18-09
000392 0-00221 0-00165 O OO 1.3 6 0-00156 0-00134 0-00147
1OO at. %
602
J. Ii. R. Morgan and O. M. Lammert studied electrodes made of this alloy in
electrometric titrations. J. L. R. Morgan and co-workers studied the reproducibility
of the quinhydrone electrode with platinum-rhodium. R. JB. Sosman,