e. Borax and microcosmic salt dissolve glucina
and its compounds to a colorless bead which, when overcharged with
glucina, or heated with the intermittent flame appears, after cooling,
turbid or milk-white. Glucina yields, by ignition with nitrate of
cobalt, a black, or dark grey infusible mass.

(_c._) _Yttria_ (YO) occurs only in a few rare minerals, and usually
in company with terbium and erbium. Its reactions before the blowpipe
are similar to the preceding, but for its detection in compounds it
will be necessary to resort to analysis in the wet way.

(_d._) _Zirconia_ (Zr^{2}O^{3}).--This substance resembles alumina in
appearance, though it occurs only in a few rare minerals. It is in the
pure state infusible, and at a red heat produces such a splendid and
vivid white light that the eyes can scarcely endure it. Its other
reactions before the blowpipe are analogous to glucina. Microcosmic
salt does not dissolve so much zirconia as glucina, and is more prone
to give a turbid bead. Zirconia yields with nitrate of cobalt, when
ignited, an infusible black mass. To recognize zirconia in compounds
we must resort to fluid analysis.

(_e._) _Thorina_ (ThO).--This is the rarest among the rare minerals.
In the pure state it is white and infusible, and will not melt with
the carbonate of soda. Borax dissolves thorina slowly to a colorless,
transparent bead, which will remain so when heated with the
intermittent flame. If overcharged with the thorina, the bead
presents, on cooling, a milky hue. Microcosmic salt dissolves the
thorina very tardily. By ignition with nitrate of cobalt, thorina is
converted into an infusible black mass,

CLASS II.

FOURTH GROUP. CERIUM, LANTHANIUM, DIDYMIUM, COLUMBIUM, NIOBIUM,
PELOPIUM, TITANIUM, URANIUM, VANADIUM, CHROMIUM, MANGANESE.

The substances of this group cannot be reduced to the metallic state,
neither by heating them _per se_, nor by fusing them with reagents.
They give by fusion with borax or microcosmic salt, colored beads,
while the preceding groups give colorless beads.

(_a._) _Cerium_ (Ce).--This metal occurs in the oxidated state in a
few rare minerals, and is associated with lanthanium and didymium,
combined with fluorine, phosphoric acid, carbonic acid, silica, etc.
When reduced artificially, it forms a grey metallic powder.

(_a._) _Protoxide of Cerium_ (CeO).--It exists in the pure state as
the hydrate, and is of a white color. It soon oxidizes and becomes
yello