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GALLIUM (symbol Ga; atomic weight 69.9)

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Originally appearing in Volume V11, Page 421 of the 1911 Encyclopedia Britannica.
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GALLIUM (See also:symbol Ga; atomic See also:weight 69.9) , one of the metallic chemical elements. It was discovered in 1875 through its spectrum, in a specimen of See also:zinc See also:blende by Lecoq de Boisbaudran (Comptes rendus, 1895, 81, p. 493, and following years). The See also:chief chemical and See also:physical properties of gallium had been predicted many years before by D. Mendeleeff (c. 1869) from a See also:consideration of the properties of See also:aluminium, See also:indium and zinc (see See also:ELEMENT). The See also:metal is obtained from zinc blende (which only contains it in very small quantity) by dissolving the See also:mineral in an See also:acid, andprecipitating the gallium by metallic zinc. The precipitate is dissolved in hydrochloric acid and See also:foreign metals are removed by sulphuretted See also:hydrogen; the residual liquid being then fraction-ally precipitated by See also:sodium carbonate, which throws out the gallium before the zinc. This precipitate is converted into gallium sulphate and finally into a pure specimen of the See also:oxide, from which the metal is obtained by the See also:electrolysis of an alkaline See also:solution. Gallium crystallizes in greyish-See also:white octahedra which melt at 30.1'5° C. to a silvery-white liquid. It is very hard and but slightly malleable and flexible, although in thin plates it may be See also:bent several times without breaking. The specific gravity of the solid See also:form is 5.956 (24.50 C.), of the liquid 6•o69, whilst the specific heats of the two varieties are, for the solid form o•079 (12-23° C.) and for the liquid 0•082 (106-119°) [M.

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Berthelot, Comptes rendus, 1878, 86, p. 786]. It is not appreciably volatilized at a red See also:heat. See also:Chlorine acts on it readily in the See also:cold, See also:bromine not so easily, and See also:iodine only when the mixture is heated. The atomic weight of gallium has been determined by Lecoq de Boisbaudran by ignition of gallium ammonium See also:alum, and also by L. See also:Meyer and K. Seubert. Gallium oxide Ga203 is obtained when the nitrate is heated, or by solution of the metal in nitric acid and ignition of the nitrate. It forms a white friable See also:mass which after ignition is insoluble in acids. On See also:heating to redness in a stream of hydrogen it forms a bluish mass which is probably a See also:lower oxide of See also:composition See also:GaO. Gallium forms colourless salts, which in neutral dilute aqueous solutions are converted on heating into basic salts. The gallium salts are precipitated by alkaline See also:carbonates and by See also:barium carbonate, but not by sulphuretted hydrogen unless in acetic acid solution.

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Potassium ferrocyanide gives a precipitate even in very dilute solution. In neutral solutions, zinc gives a precipitate of gallium oxide. By heating gallium in a regulated stream of chlorine the dichloride GaCl2 is obtained as a crystalline mass, which melts at 164° C. and readily decomposes on exposure to moist See also:air. The tichloride GaCla is similarly formed when the metal is heated in a rapid stream of chlorine, and may be purified by See also:distillation in an See also:atmosphere of See also:nitrogen. It forms very deliquescent See also:long white needles melting at 75.5 C. and boiling at 215-220° C. The bromide, iodide and sulphate are known, as is also gallium ammonium alum. Gallium is best detected by means of its spark spectrum, which gives two See also:violet lines of See also:wave length 4171 and 4031.

End of Article: GALLIUM (symbol Ga; atomic weight 69.9)

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