The Element Cesium Cesium was discovered in 1860 by R. Bunsen using the process of spectroanalysis ( spectroanalysis is the chemical analysis of a mixture of substances or of a complex substance by study of a spectra). Cesium is the heaviest of all alkali metals because of it’s atomic weight. Cesium’s description, however, seemingly contradicts this statement because it is described as, “ A soft, light, very low-melting metal, and is the most reactive of all the elements” (Sittig p. 446). Before 1958, little was known about Cesium because of it’s relative unavailability in the chemical market; Cesium compounds were very expen