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Germanium

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GERMANIUM, a chemical element included in the same natural family as tin and lead (see PERIODIC LAW) , was discovered in 1886 by C. Winkler in the argyrodite (a silver thiogermanate) of Freiburg in Saxony. (Symbol Ge, atomic number 32, atomic weight 72.6.) The properties of this element and its compounds indicated that it was identical with the hypothetical element, ekasilicon, the properties of which had been predicted by D. Mendeleeff in 1871. It is still a very rare metal, although a promising source has been found in the concentrate from certain residues obtained in the smelting of American zinc ores, G. H. Buchanan having reported that such residues contain 0. 2 5 % of germanium dioxide. This source has been exploited by L. M. Dennis and his collaborators in Cornell university, U.S.A., who have thereby increased very considerably our knowledge of germanium and its compounds. The following data are largely collected from these researches.

Germanium is separated from other metals by fractional dis tillation of its volatile tetrachloride and is isolated in the metallic state by reduction of its dioxide with aluminium, carbon or hydrogen.

Germanium is a greyish-white metal of crystalline structure and so brittle that it cannot be drilled ; it has the specific gravity C, melts at C, and is not volatile at 1,25o° C. When heated in oxygen at 73o° C it is partially oxidized to dioxide, a dense white powder (specific gravity 4.7o at 18°) . When acted on by the halogens, germanium yields the corresponding tetrahalides, GeX,. The tetrachloride is a colourless liquid boiling at 83° C (melting point C). The tetrabromide is a colourless crystalline solid (octahedra) melting at 26.1 ° C and boiling at 186.5° C. The tetraiodide is an orange powder or coral-red solid; it melts at 144° C and has specific gravity 4.3215 at C. A germanium-magnesium alloy when decomposed by di lute hydrochloric acid yielded a mixture of germanium hydrides from which the following were isolated :—monogermane or ger manomethane, a gas with nauseating odour, melting point, —165° C, boiling point — 9o° C; digermane or germanoethane, a colourless volatile liquid boiling at 29° C and melting at — 109° C; and trigermane or germanopropane, a colourless liquid boiling at 110.5° C with melting point —105.6° C.

Germanium resembles silicon and tin in forming organic deriva tives :—germanium tetramethyl, Ge and tetraethyl, are colourless liquids boiling respectively at 43.4 and 163.5° C. Tetraphenylgermane, Ge and hexaphenyldiger mane, are crystalline solids melting at 235° C and C respectively (G. T. Morgan and H. D. K. Drew, 1925; C. A. Kraus and L. S. Foster, 1927), and homologous alkyl and aryl derivatives of germanium have been prepared in the Cornell laboratories. Just as carbon and silicon give respectively chloro form, and silicochlorof orm, so germanium fur nishes germanochloroform, a liquid boiling at 75° (melt ing point —71° C). Germano-bromoform and -iodoform are also known. The three compounds are prepared by adding the halogen hydride to the corresponding germanium dihalide: GeX,+HX = The three germanium dihalides are solids the fusibility of which diminishes with increase in the atomic weight of the halogen; they possess strong reducing power similar to that of the stannous halides (F. M. Brewer, 1927). Germanium compounds when fused with alkaline carbonates and sulphur form thiogermanates which on decomposition with acid give white ger manium disulphide. This substance, which is useful in the ana lytical separation of germanium, is also formed by passing hydro gen into acid solutions of germanium dioxide. In its general chemical reactions, germanium disulphide resembles stan nic sulphide.

When silica is replaced by germanium dioxide in flint and crown glasses, an increase in refractive index is observed. Ger manium compounds have been suggested in treating anaemia.

A further analogy between germanium and tin is seen in the interactions of their tetrachlorides or tetrabromides with acetyl acetone. The products, germanium bisacetylacetone dichloride, and dibromide, are non-ionized metallic complexes corresponding closely with the similar tin bisacetyl acetone dihalides. When, however, germanium tetrahalides are condensed with copper acetylacetone, the final products are ger manium trisacetylacetone cuprohalides, In this respect germanium shows its relationship to silicon which gives rise to similar complex salts (Morgan and Drew, 1924).

BIBLIOGRAPHY.-J.

W. Mellor, A Comprehensive Treatise on InorBibliography.-J. W. Mellor, A Comprehensive Treatise on Inor- ganic Chemistry (vol. vii., 1927) ; L. M. Dennis and others, Journal of the American Chemical Society (1921 et seq.) ; Journal of Physical Chemistry (1926 et seq.). (G. T. M.)

boiling, melting, compounds, dioxide, colourless, ger and tin