Gallium sesqui-oxide, Ga₂O₃

Gallium sesqui-oxide, Ga₂O₃, which may be prepared by igniting the hydroxide or nitrate, is a white mass, infusible at a red heat. Its specific heat (0° to 100°) is 0.1062. The strongly ignited oxide resembles ignited alumina in its resistance to acids and alkalies, and requires to be fused with potassium hydrogen sulphate in order to be brought into solution. At a red heat, hydrogen reduces the sesqui-oxide to a greyish-blue mass, probably a suboxide (GaO ?), which dissolves in dilute mineral acids to form solutions which instantly reduce potassium permanganate. At a bright red heat, reduction to the metal can be effected. Gallium sesqui-oxide is also reduced to gallium when heated with magnesium.

The oxides of samarium, dysprosium, terbium, and chromium act as phosphorogens when diluted with gallium sesqui-oxide and submitted to the action of cathode rays. The phosphorescence is a beautiful red when the quantity of chromium sesqui-oxide equals 0.1 per cent.