PLATINUM AND ALLIED METALS. 779
metal intermediate in color between silver and tin. Its specific
ravity is 22.421
(Deville and Debray), and its fusion point is very high—2150° to 2250°
C. At 1100° C. iridium begins to oxidize to a Eurple oxide. Tungsten
has a higher melting point than iridium, ut oxidizes readily. Under
ordinary conditions iridium is not attacked by any acid.
to its unique qualities iridium finds an extensive use. Most of the
metal produced is probably used for the purpose of hardening platinum,
the percentage of iridium in the alloys ranging from 5 to 20 per cent.
Up to 10 per cent the alloys are ductile and malleable; those
containing from 10 to 20 per cent of iridium are hard and difficult to
work; where the alloy contains 30 per cent of iridium it is no longer
attacked by aqua regia.1 Iridium is further used for various
scientific and technical purposes, such as standard weights, pivots,
contact points, and fountain-pen points. For certain high-temperature
experiments (above 1600° C.) iridium is rolled in sheets and welded
into tubes. Pure iridium is difficult to work on account of its
brittleness. Iridium black, an oxide of the metal, is highly valued as
a pigment for decorating chinaware.
Production, import, and prices.—A
few ounces of iridium are probably obtained from domestic crude
platinum, but figures showing the quantity are not available. According
to the Bureau of Statistics, 3,028 troy ounces of iridium and iridium
in native combinations with platinum metals, valued at $140,232, or
about $46.33 per troy ounce, were imported in 1910 into the United
States. The price of iridium has been increasing rapidly. In 1909 the
average price was about $35 per troy ounce; in 1910 the price rose
still higher, and in October, 1910, iridium was quoted at $60 per
ounce. The supply is evidently very limited.
is a hard and brittle bluish-gray metal, which, as stated above,
generally occurs in combination with iridium. Its melting point is very
high and its specific gravity is 22.48 (Joly and Vezes). Thus far
little use has been found for it, except for certain kinds of
incandescent lamps. In 1910, according to the Bureau of Statistics, 939
ounces of osmium, valued at $32,647, or about $33.70 per ounce troy,
were imported into the United States. As in the case of iridium there
is little present probability of obtaining a supply of osmium from
is a white metal intermediate in color between platinum and silver. It
is malleable, has about the hardness of platinum, and has a low
specific gravity—11.97 (Violle). It has a lower melting point than any
other of the platinum metals—about 1,549° C.
finds a fairly large use in technology. Circles of astronomical
instruments are made of it, and it is also employed in watchmaking.
Its most extensive use is probably for certain alloys in dental work.
It is also employed for soldering platinum metals. The demand for this
metal is considerably greater than the supply.
' Molssan, H., op. cit., p. 899.