Psg°i s the vapor pressure of pure mercury at the temperature, T, under study. Png is the mercury vapor pressure at the temperature, T, under study. The variations of the activity coefficient with the temperature are within the range of the precision of the measurements: ~1_2%)X "Hg / The values of 7Hg are indicated in Table II. For the solid liquid phase, we used the liquidus curve given by Ito et al. ( 5). The activity coefficient of mercury in the presence of indium can be considered as independent of the temperature in the range of temperature studied. On the other hand, the dependence as regards the concentration of indium is important and the mercury-indium amalgams deviate negatively from ideality.