A bead of high-purity arc-melted osmium. Image copyright: smart-elements.com.
Osmium (Os) is a hard, silver-gray element in the platinum group; also a transition element. Discovered by Smithson Tennant in London in 1803, osmium is the densest of the elements (twice as dense as lead) and as rare as gold; the chief source is a by-product of smelting nickel. It is slowly oxidized in air. The most common isotope is 192Os (41.0%).
Osmium tetroxide is a colorless or faintly yellowish compound used to stain fats or as a fixative in the preparation of tissues for study by microscope. Osmium tetroxide evaporates readily, the vapor having a toxic action on the eyes, skin, and respiratory tract.
|relative atomic mass||190.2|
|melting point||3.045°C (5,513°F)|
|boiling point||5,027°C (9,081°F)|