CAESIUM.
The oxide of 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 the latter oxide.
Caesium is best detected by the spectroscope, its spectrum being
characterised by two lines in the blue and one in the red; the latter is
about midway between the lithium and sodium lines.
If not detected by the spectroscope, or specially looked for, caesia
would, in the ordinary course of work, be separated with the potash and
weighed as potassium platino-chloride.
Caesia is separated from all the other alkalies by adding to the acid
solution of the mixed chlorides a strongly acid cold solution of
antimonious chloride. The acid used must be hydrochloric. The caesium is
precipitated as a white crystalline precipitate (CsCl.SbCl_{3}), which
is filtered off, and washed, when cold, with strong hydrochloric acid;
since it is decomposed by water or on warming. The precipitate is washed
into a beaker, and treated with sulphuretted hydrogen; after filtering
off the sulphide of antimony, the solution leaves, on evaporation, the
caesium as chloride.
RUBIDIUM.
Rubidium occurs widely diffused in nature, but in very small quantities.
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