The activity of iron in liquid iron-carbon solutions has been determined in the whole range of carbon concentration up to its saturation at 1 550° and 1 630° by measuring the rate of effusion of iron vapor through the orifice of alumina cells. It is found that the rate of effusion of iron through the orifice per unit time and unit orifice area at a constant temperature is constant independent of the orifice area.
The logarithm of activity coefficient of iron expressed in atom fraction unit is proportional to the square of atom ratio of carbon to iron at each temperature.
The activity coefficient of carbon is calculated from the value of that of iron by integrating the Gibbs-Duhem equation. The interaction parameters of carbon in liquid iron-carbon solutions have been expressed as a function of temperature and the concentration of carbon either in atom fraction or in weight percentage unit in the whole range of carbon up to its saturation.
Partial molar enthalpy and entropy of mixing of carbon in iron-carbon solutions are calculated as the function of atom fraction of carbon.
The obtained thermodynamic values are compared with those of other authors.