istened is brought
within the orifice of the tube; an infusible residue is left in the
tube.

The greater part of the alumina compounds give off water with heat;
the most of them are also infusible, except a few phosphates and
silicates.

Pure alumina does not fuse with carbonate of soda. The sulphates, when
exposed upon charcoal with soda to the reducing flame, leave a hepatic
residue. The phosphates melt with a little soda, with a hissing noise,
to a semi-transparent mass, but they are infusible with the addition
of soda, and give only a tough mass. This is the case, likewise, with
the silicates of alumina. Fluoride of aluminium melts with carbonate
of soda to a clear bead, spreads by cooling, and appears then
milk-white. Borax dissolves the alumina compounds slowly in the
oxidizing and reducing flames to a clear bead, which is also clear
when cold, or heated intermittingly with a vacillating flame. The bead
is turbid, as well in the heat as the cold, when an excess of alumina
is present. When the alumina compound is added to excess in the
powdered form, the bead appears crystalline upon cooling, and melts
again with great difficulty.

Alumina and its compounds are slowly dissolved in the microcosmic salt
to a bead, clear in both flames, and when hot or cold. When alumina is
added to excess, the undissolved portion appears semi-transparent.
Alumina melts with bisulphate of potash into a mass soluble in water.
When the powdered alumina compounds are strongly ignited in the
oxidizing flame, then moistened with nitrate of cobalt, and re-ignited
in the oxidizing flame, an infusible mass is left, which appears, when
cooled, of an intense blue color. The presence of colored metallic
oxides, in considerable quantity, will alter or suppress this
reaction. The silicates of the alkalies produce, in a very strong
heat, or continued heat, with nitrate of cobalt, a pale blue color.
The blue color produced by alumina is only distinctly visible by
daylight; by candle-light it appears of a dirty violet color.

(_b._) _Glucina._ (G^{2}O^{3}).--Glucina only occurs in a few rare
minerals, in combination with silica and alumina. It is white and
insoluble in the pure state, and its properties generally are similar
to those of alumina. The most of its compounds are infusible, and
yield water by distillation. Carbonate of soda does not dissolve
glucina by ignition. Silicate of glucina melts with carbonate of soda
to a colorless globul