tion by the waters of occasional rains to
shallow basins, which become covered with temporary thin sheets of water
or "playa lakes." Evaporation of these lakes leaves broad flats covered
with the white salts. These may subsequently be covered with drifting
sands and capillary action may cause the borates to work up through the
sands, becoming mixed with them and efflorescing at the surface. One of
the largest of the California deposits of this general class is that at
Searles Lake, from which it has been proposed to recover borax along
with the potash (pp. 113-114).

The deposits which at present constitute the principal source of
domestic borax are not the playa deposits just described, but are masses
of colemanite in Tertiary clays and limestones with interbedded basaltic
flows. The principal deposits are in Death Valley and adjacent parts of
California. The colemanite occurs in irregular milky-white layers or
nodules, mingled with more or less gypsum. The deposits are believed to
be of the replacement type, rather than ones formed contemporaneously
with the sediments. Whether they are due to magmatic solutions carrying
boric acid from the associated flows, or to surface waters carrying
materials leached from other sediments, is not clear. The crude
colemanite as mined carries an average of about 25 per cent B_2O_3; it
is treated with soda in the manufacture of borax, or with sulphuric acid
in making boric acid.

Boron is present in minute quantities in sea water. When such water
evaporates, it becomes concentrated, along with the magnesium and
potassium salts, in the "mother liquor"; and upon complete evaporation,
it crystallizes out as boracite and other rarer minerals. Thus the
Stassfurt salts of Germany (p. 113) contain borates of this type in the
carnallite zone of the upper part of the deposits. This is the only
important case known of borate deposits of marine origin.

BROMINE

ECONOMIC FEATURES

Bromine finds a considerable use in chemistry as an oxidizing agent, in
separating gold from other metals, and in manufacturing disinfectants,
bromine salts, and aniline colors. The best known and most widely used
bromine salts are the silver bromide, used in photography, and the
potassium bromide, used in medicine to depress the nervous system.
During the war, large quantities of bromine were used in asphyxiating
and lachrymating gases.

The chief center of the bromine industry in Europe prior to 1914 was