<Original Papers>Thermodynamic Studies of the Liquid Lead-Arsenic System

The liquid, lead-arsenic system has been investigated by the isopiestic method over the temperature range, 737 to 855 K, and the concentration range, N_=0.1 to 0.5. Based on a standard state of solid arsenic, the activity, excess molar free energy, heat of mixing and excess molar entropy were calculated from the experimentally determined vapor pressures. Utilizing the standard free energy of fusion, these thermodynamic quantities were converted to a liquid arsenic standard state. The activity of arsenic exhibited a slight, positive deviation from Raoultian behavior when N_ was less than 0.15. Conversely, a negative deviation was observed over the high concentration range. The value of the activity coefficient at infinite dilution was 1.2 at 855 K. Based on the activity coefficient data determined in this work, the elimination of arsenic from crude lead by oxidation and vaporization processes was discussed