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 1455.    HOFMANN, U.  [Deposition of Carbon From Carbon Monoxide and Benzine in the Presence of Iron.  I.]  Ber. Deut. Chem. Gesell., vol. 61, B, 1928, pp. 1180-1195; Chem. Abs., vol. 22, 1928, p. 4289.

       Continuation of the study of block C crystals.  In previous work on thermal decompositions of hydrocarbons, temperatures under 700° could not be employed.  With an Fe catalyst C separates from CO at 400°-700°, and from benzine at 700°-900°.  The form or previous history of the Fe is without influence.  The C samples so obtained were distinctly crystalline by X-ray analysis, the grain size increasing with temperature of deposition.  Numerous density, chemical, and activity tests also depend on temperature.  The fact that crystals of C can be obtained at so low a temperature indicates formations of a carbide with the Fe with subsequent decomposition.  The formation of Fe3C is not proved by X-ray analysis.  However, at 400° with CO and at 700° with benzine diffraction lines appear for an unknown substance, which is called X-carbide, richer in C than Fe3C.