name from the Greek [Greek: barus] (heavy) on account of its presence
in barytes or heavy spar which was first investigated in 1602 by V.
Casciorolus, a shoemaker of Bologna, who found that after ignition with
combustible substances it became phosphorescent, and on this account it was
frequently called Bolognian phosphorus. In 1774 K. W. Scheele, in examining
a specimen of pyrolusite, found a new substance to be present in the
mineral, for on treatment with sulphuric acid it gave an insoluble salt
which was afterwards shown to be identical with that contained in heavy
spar. Barium occurs chiefly in the form of barytes or heavy spar, BaSO_4,
and witherite, BaCO_3, and to a less extent in baryto-calcite,
baryto-celestine, and various complex silicates. The metal is difficult to
isolate, and until recently it may be doubted whether the pure metal had
been obtained. Sir H. Davy tried to electrolyse baryta, but was
unsuccessful; later attempts were made by him using barium chloride in the
presence of mercury. In this way he obtained an amalgam, from which on
distilling off the mercury the barium was obtained as a silver white
residue. R. Bunsen in 1854 electrolysed a thick paste of barium chloride
and dilute hydrochloric acid in the presence of mercury, at 100deg C.,
obtaining a barium amalgam, from which the mercury was separated by a
process of distillation. A. N. Guntz (_Comptes rendus_, 1901, 133, p. 872)
electrolyses a saturated solution of barium chloride using a mercury
cathode and obtains a 3% barium amalgam; this amalgam is transferred to an
iron boat in a wide porcelain tube and the tube slowly heated electrically,
a good yield of pure barium being obtained at about 1000deg C. The metal
when freshly cut possesses a silver white lustre, is a little harder than
lead, and is extremely easily oxidized on exposure; it is soluble in liquid
ammonia, and readily attacks both water and alcohol.

Three oxides of barium are known, namely, the monoxide, BaO, the dioxide,
BaO_2, and a suboxide, obtained by heating BaO with magnesium in a vacuum
to 1100deg (Guntz, _loc. cit._, 1906, p. 359). The monoxide is formed when
the metal burns in air, but is usually prepared by the ignition of the
nitrate, oxygen and oxides of nitrogen being liberated. It can also be
obtained by the ignition of an intimate mixture of the carbonate and
carbon, and in small quantities by the ignition of the iodate. It is a
greyish coloured solid, which comb