Uranium was discovered in 1789 by Martin Heinrich Klaproth. He was studying the mineral pitchblende and upon mixing with nitric acid and potash discovered a yellow precipitate. He named it Uranium, after the planet Uranus. It was not until 1841 that Eugene-Melchior Peligot isolated uranium metal. Uranium oxides have been used for many years as pigments due to their intense yellow colour. Uranium is a highly reactive and radioactive metal and is very popular in thermonuclear reactors due to its ability to undergo nuclear decay and release heat energy. It is also used in nuclear weapons. Uranium occurs in the earths crust as an ore and is not free elementally. Whilst uranium is dangerous it emits alpha particles which cannot penetrate skin, however it is still highly toxic and easily ignites as a powder. It is a solid metal at room temperature and it has a melting point of 1132°c and a boiling point of 4131°c.