Gallium. Ga; at. wt. 69.72; at. no. 31; valence 3-2-1. Discovered by Boisbaudran: Compt. rend. 81, 493, 1100 (1875); 82, 163, 1036 (1876); isolated pure by Boisbaudran and Jungfleisch: Bull. Sec. Chim. [2] 31, 50 (1879). The best source of it is the mineral gernianite, a copper sulfide ore; occurs in very small quantities in zinc blendes, in aluminum clays, found in ores of iron, chromium, manganese; constitutes 5 X 10^–4% of the crust of the earth. Isoln. from rhenium-rich copper schist: Feit, Angew. Chem. 46, 216 (1933). Spectra: Boisbaudran, etc., cited by Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry 5, 378 (1929).

Grayish metal; possesses a greenish-blue reflection; tin- or silver-like when molten; bar a crystalline orthorhombic texture; m. 30.15°; shows a tendency to remain in supercooled state; (Ref.) d^24.45_24.45 solid 5.935; d^24.7 liquid 6.07 (Boisbaudran); contracts on melting. Stable in dry air; tarnishes in moist air or oxygen. Soluble in alkalies with evolution of hydrogen; soluble in cold conc. hydrochloric acid; rendered passive by hot nitric acid; readily attacked by halogens.

Sesquioxide, Ga₂O₃; obtained by thermal decompn. of the salts; exists in many crystalline modifications; on heating with magnesium is violently reduced to the metallic state.

Suboxide, Ga₂O; brown powder; obtained by heating at 700° the sesquioxide and the metal; stable in dry air; decomposes above 800°; converted to the trivalent state by nitric acid or bromine.

Hydroxide, Ga(OH)₃, a gelatinous precipitate; obtained by the action of ammonia or alkali hydroxide on a solli. of a gallic salt.

Chloride, GaCl₃, colorless needles, m. 78°; prepd. by the action of chlorine or hydrogen chloride on the metal.

Dichloride, GaCl₂, white crystals; m. 164°; prepd. by heating the trichloride with the metal.

Sulfate, Ga₂(SO₄)₃ • 16H₂0; octahedral crystals; formed by dissolving the sesquioxide or the hydroxide in sulfuric acid and precipitating with ether or alcohol; soluble in water or 60% alcohol.

Nitrate, Ga(NO₃)₃ • 8H₂O, obtained by dissolving the metal or the oxide in conc. nitric acid.