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For fountain pen points.
(Gr. osme, a smell) Discovered in 1803 by Tennant in the residue left when crude
platinum is dissolved by aqua regia.
Osmium occurs in iridosule and in platinum-bearing river sands of the Urals, North
America, and South America. It is also found in the nickel-bearing ores of Sudbury,
Ontario region along with other platinum metals. While the quantity of platinum metals in
these ores is very small, the large tonnages of nickel ores processed make commercial
The metal is lustrous, bluish white, extremely hard, and brittle even at high
temperatures. It has the highest melting point and the lowest vapor pressure of the
platinum group. The metal is very difficult to fabricate, but the powdered or spongy metal
slowly gives off osmium tetroxide, which as a powerful oxidizing agent and has a strong
smell. The tetroxide is highly toxic, and boils at 130oC.
The measured densities of iridium and osmium seem to indicate that osmium is slightly
more dense than iridium, so osmium has generally been credited with being the heaviest
known element. Calculations of the density from the space lattice which may be more
reliable for these elements than actual measurements, however, give a density of 22.65 for
iridium compared to 22.661 for osmium. At present, therefore, we know either iridium or
osmium is the heaviest element, but the data do not allow selection between the two.
Concentrations in air as low as 107
g/m3 can cause lung
congestion, skin damage, or eye damage. Exposure to osmium tetroxide should not exceed
0.0016 mg/m3 (8-hour time
weighted average - 40-hour work week).
The tetroxide has been used to detect fingerprints and to stain fatty tissue for
miscroscope slides. The metal is almost entirely used to produce very hard alloys, with
other metals of the platinum group, for fountain pen tips, instrument pivots, phonograph
needles, and electrical contacts.
The price of 99% pure osmium powder - the form usually supplied commercially - is about
$100/g, depending on quantity and supplier.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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