Caesium: historical information
Caesium (cesium in USA) was discovered spectroscopically by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff in 1860 in samples of mineral water from Durkheim. Their identification was based upon two bright blue lines in the spectrum. The name caesium (from the Latin "caesius" - heavenly blue) was coined for its bright blue spectroscopic lines.
Caesium salts were isolated by Bunsen by precipitation from these spring waters - along with salts of other Group 1 elements. He was able to separate them and isolated the chloride and the carbonate. He was unable to isolate caesium metal, this wasachieved by Setterberg.