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(symbol Ge, atomic weight 72.5); one of the metallic elements included in the same natural family as carbon, silicon, tin and lead. It was discovered in 1886 by C. Winkler in argyrodite, a mineral found at Freiberg in Saxony. On examination of the metal and its salts it was shown to be identical with the hypothetical element ekasilicon, whose properties had been predicted by D. Mendeleeff many years previously. The element is of extremely rare occurrence, being met with only in argyrodite and, to a very small extent, in euxenite. It may be obtained from argyrodite by heating the mineral in a current of hydrogen; or by heating the dioxide to redness with carbon. It forms grey coloured octahedra of specific gravity 5.49 6 at 20° C., melting at 900° C.; it burns at a red heat, is insoluble in hydrochloric acid, but dissolves in aqua regia, and is also soluble in molten alkalis. Two oxides of germanium are known, the dioxide, GeO₂, being obtained by roasting the sulphide and treatment with nitric acid. It is a white powder, very slightly soluble in water, and possesses acid properties. By heating with a small quantity of magnesium it is converted into germanious oxide, GeO. By heating the metal with chlorine, germanic chloride, GeCl₄, is obtained as a colourless fuming liquid boiling at 86-87° C., it is decomposed by water forming a hydrated germanium dioxide. Germanium dichloride, GeCl₂, and germanium chloroform, GeHCl₃, have also been described.

Germanium compounds on fusion with alkaline carbonates and sulphur form salts known as thiogermanates. If excess of a mineral acid be added to a solution of an alkaline thiogermanate a white precipitate of germanium disulphide, GeS₂, is obtained. It can also be obtained by passing sulphuretted hydrogen through a solution of the dioxide in hydrochloric acid. It is appreciably soluble in water, and also in solutions of the caustic alkalis and alkaline sulphides. By heating the disulphide in a current of hydrogen, germanious sulphide, GeS, is formed. It sublimes in thin plates of a dark colour and metallic lustre, and is soluble in solutions of the caustic alkalis. Alkyl compounds of germanium such as germanium tetra-ethyl, Ge(C₂H₅)₄, a liquid boiling at C., have been obtained. The germanium salts are most readily recognized by the white precipitate of the disulphide, formed in acid solutions, on passing sulphuretted hydrogen. The atomic weight of the element was determined by C. Winkler by analysis of the pure chloride GeCl₄, the value obtained being 72.32, whilst Lecoq de Boisbaudran (Comptes rend us, 1886, 103, 45 2), by a comparison of the lines in the spark spectrum of the element, deduced the value 72.3.