Gallium trichloride, GaCl₃

Gallium trichloride, GaCl₃, obtained by heating gallium in chlorine or hydrogen chloride, forms long, white needles, melting at 75.5° and boiling at 215° to 220°. The vapour has a density of 6.13 (air = 1) between 440° and 606°, the simple formula GaCl₃ corresponding to 6.08. At 1000° the vapour density indicates that dissociation has occurred, while at low temperatures the results obtained by the method of Dumas point to the existence, over the range 237° to 378°, of gaseous Ga₂Cl₆, the molecules of which gradually undergo dissociation into GaCl₃ with further rise of temperature.

Molten gallium trichloride has a density of 2.36 at 80°, readily absorbs gases, but evolves them on solidification. The crystalline chloride is very deliquescent and dissolves in water with the evolution of considerable heat, producing a colourless solution from which oxychlorides are slowly precipitated. The aqueous solution loses hydrochloric acid when evaporated, leaving an amorphous residue which absorbs water and becomes gelatinous. An acid solution of the trichloride is obtained by dissolving gallium in aqua regia.

The bromides of gallium closely resemble the chlorides. They are, however, less fusible and less volatile, and do not seem to have been analysed.

The iodides of gallium, like the bromides, require further study. Two appear to exist, a colourless tri-iodide and a yellow di-iodide.