, AND
MAGNESIA.

In the pure state, the alkaline earths are caustic, cause red litmus
paper to become blue, and are more or less soluble in water. Their
sulphides are also soluble. The carbonates and phosphates of the
alkaline earths are insoluble in water. By igniting the carbonates,
their carbonic acid is expelled, and the alkaline earths are left in
the caustic state. The alkaline earths are not volatile, and their
organic salts are converted, by ignition, into carbonates.

(_a._) _Baryta._ (BaO).--This alkaline earth does not occur free in
nature, but combined with acids, particularly with carbonic and
sulphuric acids. In the pure state, baryta is of a greyish-white
color, presents an earthy appearance, and is easily powdered. When
sparingly moistened with water, it slakes, becomes heated, and forms a
dry, white powder. With still more water it forms a crystalline mass,
the hydrate of baryta, which is completely soluble in hot water. Pure
baryta is infusible; the hydrate fuses at a red heat, without the loss
of its hydratic water; if caustic baryta is exposed for too great a
length of time to the flame, it absorbs water, originated by the
combustion, and becomes a hydrate, when it will melt. Salts of baryta,
formed with most acids, are insoluble in water; for instance, the
salts with sulphuric, carbonic, arsenic, phosphoric, and boracic
acids. The salts of baryta, soluble in water, are decomposed by
ignition, except the chloride.

Carbonate of baryta loses its carbonic acid at a red heat, becomes
caustic, and colors red litmus paper blue.

By exposing baryta or its compounds upon a platinum wire, or a
splinter of the substance held with the platinum tongs, to the point
of the blue flame, a pale apple-green color is communicated to the
external flame. This color appears at first very pale, but soon
becomes more intense. This color is most visible if the substance is
operated with in small quantities. The chloride of barium produces the
deepest color. This color is less intense if the carbonate or sulphate
is used. The presence of strontia, lime, or magnesia, does not
suppress the reaction of the baryta, unless they greatly predominate.

When alcohol is poured over baryta or its salts, and inflamed, a
feeble green color is communicated to the flame, but this color should
not be considered a characteristic of the salt.

Baryta and its compounds give, when fused with carbonate of soda upon
platinum foil, a clear