From the Cd vapor pressures measured over the samples in the
four two-phase fields (see above) the corresponding activity
values were calculated. They are plotted as ln aCd versus reciprocal
temperature in Fig. 3. Assuming straight phase boundaries, i.e. no
variation of the solubilities with temperature for the different
compounds, one can apply an adapted Gibbs–Helmholtz equation
to estimate partial molar enthalpies of mixing of Cd in these
two-phase fields