SIUM

~Occurrence in nature.~ Potassium is a constituent of many common rocks
and minerals, and is therefore a rather abundant element, though not so
abundant as sodium. Feldspar, which occurs both by itself and as a
constituent of granite, contains considerable potassium. The element is
a constituent of all clay and of mica and also occurs in very large
deposits at Stassfurt, Germany, in the form of the chloride and
sulphate, associated with compounds of sodium and magnesium. In small
quantities it is found as nitrate and in many other forms.

The natural decomposition of rocks containing potassium gives rise to
various compounds of the element in all fertile soils. Its soluble
compounds are absorbed by growing plants and built up into complex
vegetable substances; when these are burned the potassium remains in the
ash in the form of the carbonate. Crude carbonate obtained from wood
ashes was formerly the chief source of potassium compounds; they are now
mostly prepared from the salts of the Stassfurt deposits.

~Stassfurt salts.~ These salts form very extensive deposits in
middle and north Germany, the most noted locality for working
them being at Stassfurt. The deposits are very thick and rest
upon an enormous layer of common salt. They are in the form of
a series of strata, each consisting largely of a single mineral
salt. A cross section of these deposits is shown in Fig. 78.
While these strata are salts from a chemical standpoint, they
are as solid and hard as many kinds of stone, and are mined as
stone or coal would be. Since the strata differ in general
appearance, each can be mined separately, and the various
minerals can be worked up by methods adapted to each particular
case. The chief minerals of commercial importance in these
deposits are the following:

Sylvine KCl.
Anhydrite CaSO_{4}.
Carnallite KCl.MgCl_{2}.6H_{2}O.
Kainite K_{2}SO_{4}.MgSO_{4}.MgCl_{2}.6H_{2}O.
Polyhalite K_{2}SO_{4}.MgSO_{4}.2CaSO_{4}.2H_{2}O.
Kieserite MgSO_{4}.H_{2}O.
Schoenite K_{2}SO_{4}.MgSO_{4}.6H_{2}O.

~Preparation and properties.~ The metal is prepared by the same method
used in the preparation of sodium. In most respects it is very similar
to sodium, the chief difference being that it is even more energetic in
its action upon other substances. The freshly cut, bright su