Caesium was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff whilst analysing the contents of mineral water using spectroscopy. They discovered some lines in one spectrum that did not correspond to any known previously. Like other Alkali metals Caesium has a violent reaction with water and oxygen so must be kept in oil or an inert environment. Caesium’s main use is in atomic clocks for accuracy in timing. It is also used as a catalyst in the hydrogenation of organic compounds. It is a solid metal at room temperature with a melting point of 28.4°c and a boiling point of 670°c. Caesium if found in minerals pollucite and lepidolite in the earth’s crust and is not found naturally.
Gustov Kirchoff, Robert Bunsen