Cesium(Cs) Description: Cs rapidly combines with oxygen and is used as a getter, a material that combines with and removes trace of gases from the vacuum tube. Cesium was discovered by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, German chemists, in 1860 through the spectroscopic analysis of Durkheim mineral water. They named cesium after the blue lines they observed in its spectrum. Heidelberg, Germany is where they discovered cesium. To obtain pure cesium, cesium and rubidium ores are crushed and heated with sodium metal to 650°C, forming an alloy that can then be separated with a process known as fractional distillation.