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 globule.  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.