A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 217
soln. are formed. E. Isaac and G. Tammann observed that the two metals at a
high temp, form a continuous series of solid soln., Fig. 56, but as the temp, falls, this
decomposes into two other series of solid soln. extending from 0 to 50 per cent, plati­
num, and from 60 to 100 per cent, platinum.
W. A. NemilofFs values for the temp, coeff. of
the resistance of the annealed and quenched
alloys, and the singular points, have some
analogies with the hardness curves. There
are breaks in the cooling curves of alloys with
0 to 4O per cent, of platinum and with from
70 to 90 per cent, of platinum—owing to a
modification in the crystals of the solid soln.
rich in platinum. Alloys with up to 10 per
cent, of platinum have two breaks corresponding
with the transitions from y- to )8-iron, and
from £- to a-iron, respectively. There is only
the change from y- to ci-iron in alloys having
10 to 40 per cent, of platinum. All the alloys
from O to 9O per cent, of platinum are magnetic,
and this property appears to diminish
in the same ratio as the iron, from 80 to 20
per cent, of that metal. The alloys from 10
to 50 per cent, of platinum lose their magnetic
power on heating at temperatures varying
from 800° to 650°, and this property returns
on cooling at much lower temperatures ; the
curve of temperature at which the magnetic
power reappears practically coincides with
that representing the transformation y- to
a-iron referred to above. On the other hand,
the temperatures at which the alloys contain­
18OO
1600
1400 — t -
ing 60 to 9O per cent, of platinum regain their magnetic power are much lower than
the breaks in the cooling curve in this region. P. Oberhoffer, L. Graf and A. Kussmann,
F. Wever, and W. Guertler also made observations on these alloys.
According to E. Isaac and G. Tammann, the colour of the alloys becomes paler
as the proportion of platinum increases. The structure of the alloys with about
88 per cent, of platinum is very similar to that of native ferroplatinum.
G. H. Billings added that the fracture of alloys with 1 per cent, of platinum is not
essentially different from that of iron, but the grain is rather finer, resembling
more or less closely the fracture of a 0-3 per cent, carbon steel. W. A. Nemiloff
discussed the microstructure of the alloys. The sp. gr. of an alloy with 0-82 per
cent, of platinum, and 008 per cent, of carbon is 7-861. W. Lewis gave for the
sp. gr. of the platinum-iron alloys :
Iron . 56-4 76-9 83-7 90-9 92-3 1OO per oent.
Sp. gr. . 9-9Ol 8-7OO 8-202 7-862 7-800 7-1OO
E. Isaac and G. Tammann said that the hardness of the alloys decreases with a
proportion of platinum up to 5 per cent., and the hardness then gradually rises as
the proportion of platinum increases up to 40 per cent, of platinum ; beyond that
point up to 9O per cent, platinum, the hardness remains constant. The brittleness
of the alloys reaches a maximum at 50 per cent, platinum. W. A. Nemiloff observed
BrinelFs hardness for the annealed (A) and quenched (Q) alloys and obtained for
alloys with :
Pt
0
O
•{
Bri
»{Q ZIl
8-94
2-71
118-48
100-81
27-74
9-89
148-34
146-65
48-87
21-42
197-84
137-78
61-83
31-67
203-38
1200
WOO
800
600
400
200
67-53
37-30
251-39
109-62
20 40 60 80 100
Per cent, of platinum
Fio. 56. Freezing-point Curves of the
Plrttinum-lron Alloys.
70-68
40-82
268-56
118-01
77-60
49-78
161-68
14708
90-41
72 95
110- 64
94-94
96-32% wt.
88-22% at.
65-69
59-28