CAESIUM, se'zi-um, a metallic element dis covered in 1860 by Bunsen and Kirchhoff, in the form of the chloride, in a mineral spring at Diarkheim, Bavaria. It has the historic dis tinction of being the first element discovered by the agency of the spectroscope. The metal is widely disseminated, but is seldom found in any considerable quantity. It never occurs in the metallic state, but usually as the chloride or oxide, and commonly associated with the rare element rubidium. Cesium is found in the ashes of many seaweeds, in tea and tobacco and in several mineral springs. It is also a common constituent of the drainage water of mines. Its most important source is the mineral pollucite (q.v.), or pollux, which is found on the island of Elba and in the vicinity of Hebron, Me., and which contains as much as 36 per cent of cesium oxide, with no rubidium. Caesium forms stable salts, and strongly re sembles potassium in its chemical properties. It may be separated from this metal by taking advantage of the fact that cesium platinochlor ide is much less soluble in water than the cor responding potassium compound. Metallic
cesium cannot he obtained by reducing the oxide will carbon, but is best prepared by the electrolysis of a fused mixture of four parts of the cyanide of cesium and one part of the cyanide of barium, using aluminum electrodes. It may also be obtained by heating cesium chloride with metallic calcium. It is a silvery white metal, quite soft and ductile, and oxidiz ing rapidly upon exposure to the air. It also decomposes water with the production of suffi cient heat to ignite the liberated hydrogen. Cesium has a specific gravity of 1.88, and melts at about 80° F. Its chemical symbol is Cs, and its atomic weight is 133 (0=16). Its oxalate and nitrate are used to a limited extent in medicine. The spectrum of cesium is char acterized by two blue lines, from which circum stance the element takes its name (ccesius, bluish-gray). Cesium stands first in rank among the electro-positive elements.