ines very energetically with water to
form the hydroxide, much heat being evolved during the combination; on
heating to redness in a current of oxygen it combines with the oxygen to
form the dioxide, which at higher temperatures breaks up again into the
monoxide and oxygen.

Barium hydroxide, Ba(OH)_2, is a white powder that can be obtained by
slaking the monoxide with the requisite quantity of water, but it is
usually made on the large scale by heating heavy spar with small coal
whereby a crude barium sulphide is obtained. This sulphide is then heated
in a current of moist carbon dioxide, barium carbonate being formed, BaS +
H_2O + CO_2 = BaCO_3 + H_2S, and finally the carbonate is decomposed by a
current of superheated steam, BaCO_3 + H_2O = Ba(OH)_2 + CO_2, leaving a
residue of the hydroxide. It is a white powder moderately soluble in cold
water, readily soluble in hot water, the solution possessing an alkaline
reaction and absorbing carbon dioxide readily. The solution, known as
_baryta-water_, finds an extensive application in practical chemistry,
being used in gas-analysis for the determination of the amount of carbon
dioxide in the atmosphere; and also being used in organic chemistry as a
hydrolysing agent for the decomposition of complex ureides and substituted
aceto-acetic esters, while E. Fischer has used it as a condensing agent in
the preparation of [alpha]- and [beta]-acrose from acrolein dibromide. A
saturated solution of the hydroxide deposits on cooling a hydrated form
Ba(OH)_2 . 8H_2O, as colourless quadratic prisms, which on exposure to air
lose seven molecules of water of crystallization.

Barium dioxide, BaO_2, can be prepared as shown above, or in the hydrated
condition by the addition of excess of baryta-water to hydrogen peroxide
solution, when it is precipitated in the crystalline condition as BaO_2 .
8H_2O. These crystals on heating to 130deg C. lose the water of
crystallization and leave a residue of the anhydrous peroxide. In the Brin
process for the manufacture of oxygen, barium dioxide is obtained as an
intermediate product by heating barium monoxide with air under pressure. It
is a grey coloured powder which is readily decomposed by dilute acids with
the production of hydrogen peroxide.

Barium chloride, BaCl_2 . 2H_2O, can be obtained by dissolving witherite in
dilute hydrochloric acid, and also from heavy spar by ignition in a
reverberatory furnace with a mixture of coal, limestone and c