2718.     PODGURSKI, H. H., KUMMER, J. T., DEWITT, T. W., AND EMMETT, P. H.  Preparation, Stability, and Adsorptive Properties of the Carbides of Iron.  Jour. Am. Chem. Soc., vol. 72, 1950, pp. 5382-5388.

        Hägg Fe₂C can be formed by carbiding finely divided Fe catalysts with a hydrocarbon such as propane, butane, or pentane equally as well as carbiding with CO.  The carbiding process using a hydrocarbon is not accompanied by a lay-down of free C or by any strong exothermicity.  The samples of Fe₂C formed by using butane as a carbiding gas still contain a little residual Fe after the carbiding reaction at 300° apparently comes to an end.  Only about 7.5% C seems capable of being incorporated by this procedure in the catalyst employed.  It is possible to form hexagonal Fe₂C by carefully carbiding an Fe synthetic NH₃ catalyst at about 215° with CO, even though the catalyst does not contain Cu.  CO is still chemisorbed by a partly carbided Fe catalyst at –195°, -78.5°, and –46°, indicating that the carbiding proceeds through the formation of nuclei of carbide rather than by the formation of a smooth layer of carbide over the catalyst surface.  The formation of carbide eliminates most of the chemisorption of CO at 100° and 200°.  It also eliminates the chemisorption of H₂ in the temperature range –78.5° to 0°.  On the other hand, it has little effect on the higher temperature type of H₂ adsorption occurring at and above 100° until the catalyst samples are almost completely converted to Fe₂C.  The energy of activation for carbiding Fe with CO to form Fe₂C is about 32.5 kg.-cal. per mol.

        PODUROVSKAYA, O. M.  See abs. 1653.]

        POLL, A.  See abs. 642.

        POLLCHIK, M.  See abs. 2100, 2101, 2103a.

        POLLEY, M. H.  See abs. 1771.

        POLOZHINTSEVA, E.  See abs. 2775.