Atomic number: 77
Year discovered: 1803
Discovered by: Smithson Tennant (1761-1815), a British chemist, Antoine-François de Comte Fourcroy (1755-1809), a French chemist, Louis Vanquelin, and Hippolyte Collet-Descotils.
- Osmium was discovered in 1803 by Smithson Tennant in the dark colored residue left when crude platinum is dissolved by aqua regia (a mixture of hydrochloric and nitric acid). This dark residue contains both osmium and iridium.
- The name iridium is appropriate, for its salts are highly colored.
- Iridium is white, similar to platinum, but with a slight yellowish cast.
- It is very hard and brittle, making it very difficult to machine, form, or work.
- It is the most corrosion resistant metal known, and was used in making the standard meter bar of Paris, which is a 90% platinum and 10% iridium alloy. This meter bar has since been replaced as a fundamental unit of length.
- Iridium is not damaged by any of the acids nor by aqua regia which dissolves gold and platinum; but it is affected by molten salts.
- Because of difficulties in preparation and fabrication, the pure metal does not have important applications by itself.
- The element’s principal use is in the preparation of platinum alloys.
- Pure platinum is a soft metal and unsatisfactory for many uses.
- Alloyed with from 5% to 10% iridium, platinum forms a readily worked metal, much harder and stiffer and more resistant to chemical attack.
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Information about other elements may be seen at this Chemical Elements List.
A special unit about words that include chemo-, chem- may be seen here.