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What the name means: The name Caesium (sometimes spelt cesium) is derived from the Latin word caesius, meaning “blue (as the sky)”.

Who identified caesium? Caesium was detected in 1860 by Robert Bunsen and Gustav Robert Kirchhoff. The two German scientists were analysing a sample of mineral water from Dürkheim, in Germany. They used a spectroscope on the sample and recognised the spectra from lithium, sodium and potassium. However, there were two vivid blue lines that did not correspond to any known element at that time. Bunsen and Kirchhoff concluded that they had identified a new element that they named caesium because of its emission spectrum. Twenty years after caesium had been identified, Carl Setterberg obtained a sample of the metal by electrolysis.

About caesium: Caesium metal is normally liquid at room temperature since its melting point is 28°C. Like all group 1 metals it will react with oxygen in the air and it has a violent reaction with water. It is a soft, silvery-white metal that has an important function in atomic clocks.