Gallium

Collier's New Encyclopedia (1921)

a metallic element, symbol Ga, atomic weight 69.9. Gallium is triad element. Specific heat 0.079. It by a French chemist, was discovered by Lecoq de Boisbaudram, in zinc blende. The metal is obtained by dissolving the blende in sulphuric acid and placing in the solution plates of zinc till the disengagement of hydrogen becomes slow, but is still perceptible, by which means the greater portion of the copper, lead, cadmium, iridium, thallium, silver, mercury, selenium, arsenic, etc., contained in the ore is precipitated; the clear filtered liquid is then heated with a large excess of zinc, the resulting gelatinous precipitate, consisting chiefly of alumina, basic salts of zinc, and gallium, is redissolved in hydrochloric acid, and again heated with zinc, which gives a precipitate in which the gallium is more concentrated. This precipitate is redissolved in hydrochloric acid, the solution is treated with hydrogen sulphide, and the filtered liquid, after expulsion of the H₂S, is fractionally precipitated with ammonium carbonate till the solution of the resulting precipitate in hydrochloric acid no longer gives any indication of the presence of gallium when examined by the spectroscope. The precipitates are collected and dissolved in sulphuric acid, and cautiously evaporated till the free sulphuric acid is expelled; the residue when cold is digested with water till it is dissolved, the nearly neutral solution is boiled, the basic gallium sulphate is precipitated and filtered while hot, and then dissolved in a small quantity of sulphuric acid, treated with excess of potash till the precipitate is redissolved and then precipitated by a stream of CO2. Finally the gallium oxide is redissolved in the smallest quantity of sulphuric acid, the solution mixed with excess of slightly acid ammonium acetate, then H₂S gas is passed through the liquid; the filtered acetic solution is diluted with water, and heated to boiling, whereby the greater part of the gallium is precipitated as oxide; this precipitate is filtered off hot, washed with boiling water, and redissolved in sulphuric acid, and the solution mixed with a slight excess of potash, and filtered, whereby a pure alkaline solution of gallium is obtained. Metallic gallium is obtained by the electrolysis of this alkaline solution, platinum electrodes being used, and the positive electrode being larger than the negative on which the metallic gallium is precipitated, which is detached by dipping the platinum plate in warm water and bending it backward and forward. Gallium is a silver-white metal, which melts at 30°, but remains liquid for weeks at 0°. Cooled to 15° it crystallizes. Gallium is a hard metal, very slightly malleable, and leaves a bluish-gray trace on paper; when melted it does tarnish in their specific gravity is 5.95. it adheres to glass; It gives a brilliant violet line in the spectrum.