w, when placed in contact with the air. When heated in the
oxidation flame, it is converted into the sesquioxide, and then is
changed into light brick-red color. In the oxidation flame it is
dissolved by borax into a clear bead, which appears of an orange or
red while hot, but becomes yellow upon cooling. When highly saturated
with the metal, or when heated with a fluctuating flame, the bead
appears enamelled as when cold. In the reduction flame it is dissolved
by borax to a clear yellow bead, which is colorless when cold. If too
much of the metal exists in the bead, it then appears enamelled when
cooled.

Microcosmic salt dissolves it, in the oxidation flame, to a clear
bead, which is colored dark yellow or orange, but loses its color when
cold. In the reduction flame the bead is colorless when either hot or
cold. Even if highly saturated with the metal, the bead remains
colorless when cold. By fusing it with carbonate of soda upon charcoal
in the reduction flame, the soda is absorbed by the charcoal, while
the protoxide of the metal remains as a light grey powder.

(_B._) _Sesquioxide of Cerium_ (Ce^{2}O^{3}).--This oxide, in the pure
state, is a red powder. When heated with hydrochloric acid, it
produces chlorine gas, and is dissolved to a salt of the protoxide. It
is not affected by either the flame of oxidation or of reduction; when
fused with borax or microcosmic salt, it acts like the protoxide. It
does not fuse with soda upon charcoal. In the reduction flame it is
reduced to the protoxide, which remains of a light grey color, while
the soda is absorbed by the charcoal.

(_b._) _Lanthanium_ (La.)--This metal is invariably associated with
cerium. It presents, in its metallic state, a dark grey powder, which
by compression acquires the metallic lustre.

The _oxide of lanthanium_ (LaO) is white, and its salts are colorless.
Heated upon charcoal, it does not change either in the oxidation flame
or that of reduction. With borax, in the flame of oxidation or
reduction, it gives a clear colorless bead. This bead, if saturated,
and when hot, presents a yellow appearance, but is clouded or
enamelled when cold. With microcosmic salt the same appearance is
indicated. It does not fuse with carbonate of soda, but the soda is
absorbed by the charcoal, while the oxide remains of a grey color.

(_c._) _Didymium_ (D).--This metal occurs only in combination with the
preceding ones, and it is therefore, like them, a rare one.