Osmium tetroxide (also called osmium tetraoxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite the rarity of osmium. It also has a number of interesting properties, one being that the solid is volatile. The compound is colourless, but most samples appear yellow.
Read more about Osmium Tetroxide: Physical Properties, Structure and Electron Configuration, Synthesis, Safety Considerations