Caesium n. (Chem.) A rare alkaline metal found in mineral water; so called from the two characteristic blue lines in its spectrum. It was the first element discovered by spectrum analysis, and is the most strongly basic and electro-positive substance known. Symbol Cs. Atomic number 55. Atomic weight 132.6.
...caesium, caesia (Cs{2}O), is found associated with lithia in lepidolite, &c., and, together with rubidium, in many mineral waters. The mineral pollux is essentially a silicate of alumina and caesia; it contains 34.0 per cent. of ... — A Textbook of Assaying: For the Use of Those Connected with Mines. • Cornelius Beringer and John Jacob Beringer
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