The molalities m of (m(1)LiBr + m(2)CaBr(2))(aq) have been investigated in saturated solutions at the temperature T = 298.15 K by the physico-chemical analysis methods. The crystallization of a new double salt LiBr . CaBr2 . 5H(2)O has been established. The solutions (m(1)LiCl + m(2)CaCl(2))(aq), and (m(1)LiBr + m(2)CaBr(2))(aq) have been simulated thermodynamically at T = 298.15 K on the basis of the Pitzer model. The necessary thermodynamic functions (binary and ternary ion-interaction parameters, thermodynamic solubility products) have been calculated and the theoretical solubility isotherms plotted. The calculated data are in very good agreement with the literature data as well as our experimental data. The standard molar Gibbs free energies of reaction Delta (r)G(m)(o) of the synthesis of the double salts LiCl . CaCl2 . 5H(2)O, and LiBr . CaBr2 . 5H(2)O from the corresponding simple salts and their standard molar Gibbs free energies of formation Delta (f)G(m)(o) have been determined. (C) 2000 Academic Press.