Osmium
Osmium, a hard, bluish-white metallic chemical element. Osmium is one of the heaviest elements known; it is twice as heavy as lead and 22 times as heavy as water. It is also the least compressible material known. Osmium is a member of the platinum family of metals and is found in ores containing platinum. It is insoluble in most acids.
Osmium is used in small amounts as a hardening agent in various alloys. An osmium-iridium alloy is used to make pen points, electrical contacts, and phonograph needles. Osmium tetroxide, the most important osmium compound, is a powerful oxidizing agent. It is used to harden and stain microscope slides of biological specimens, and plays an important role in the synthesis of certain organic compounds, including cortisone.
Osmium was discovered in 1804 by Smithson Tennant, a British chemist. Osmium metal remained as a residue when he dissolved crude platinum in aqua regia (a mixture of nitric and hydrochloric acids). The name osmium is derived from osme, the Greek word for smell, in recognition of the strong, chlorinelike odor of osmium tetroxide.
Symbol: Os. Atomic number: 76. Atomic weight: 190.2. Specific gravity: 22.57. Hardness: 7.0. Melting point: about 5,520 F. (3,050 C.). Boiling point: about 9,000 F. (5,000 C.). Osmium has seven stable isotopes: Os-184, Os-186 through 190, and Os-192. It belongs to Group VIII of the Periodic Table, and its principal valences are +3, +4, +6, and +8.