Results of the experimental thermodynamic investigations of the system Bi-Au2Bi obtained by using Oelsen calorimetry are presented in this paper. Activities, activity coefficients and partial molar quantities
for bismuth in the temperature interval 600-1000 K are determined. Based on the values of the thermodynamic parameters, negative
deviation from Raoult law was obtained for the investigated system. Also, bismuth activities and activity coefficients dependence
on composition and temperature is calculated by the nonlinear programming using gradient method.