168.    BAUR, E., AND GLAESSNER, A.  [Equilibrium Between Iron Oxides and Carbon Monoxide and Dioxide.]  Ztschr. physik. Chem., vol. 43, 1903, pp. 354-368; Jour. Chem. Soc., vol. 84, 1903, (2) p. 423.

                  Equilibria, which may be established by passing CO or CO₂ over Fe, are represented by the equations:  Fe+CO=FeO+C; FeO+CO=Fe+CO₂; and C+CO₂=2CO.  The reaction Fe₃O₄+CO=3FeO+CO₂ is also one of equilibrium.  The equilibrium relationships were determined by heating the solid in an atmosphere of CO or CO₂ in a boat contained in a porcelain tube connected with a gas burette.  After equilibrium had been established the gas was drawn off and analyzed.  The solids examined were ferrosoferric oxide and ferrous oxide and ferrous oxide and Fe.  The equilibrium curve in the 1^st case exhibits a maximum at 490°, when the gas phase contains 47% CO. This indicates the temperature at which ferrosoferric oxide is reduced most difficultly.  In the 2d case, the curve shows a minimum point at 680° when 59% CO is present; this corresponds to the temperature at which ferrous oxide is most easily reduced to Fe.  The results are plotted along with Boudouard’s values for the equilibrium between C and CO₂, and from points where the curves cut, it is deduced that at atmospheric pressure, CO, CO₂, ferrous oxide, ferrosoferric oxide, and C can exist side by side at 647°, and the 3 solids are in equilibrium at 685°.  Above 685°, C and Fe can exist together, and below 647°, C and ferrosoferric oxide.  When applied to the blast furnace, the results show that the reductions of ferrosoferric oxide and ferrous oxide must take place at different zones, which are characterized by different contents of CO.  Fe in contact with a gas rich in CO at temperatures below 647° is oxidized and C is deposited, but no C can be deposited from the gas at a temperature higher than 680°.  The heat of formation of ferrosoferric oxide at 490° under constant pressure is calculated to be 267,380 cal., and that of ferrous oxide at 680° is 67,350 cal.