An experimental study on metastable equilibria at 288 K in the quaternary system Li+, Na+ //So(4)(2-), B4O72-- H2O was done by isothermal evaporation method. Metastable equilibrium solubilities and physico-chemical properties such as density, conductivity, pH, refractive index and viscosity of the solution were determined. The results show that the double salt (Na2SO4Li2SO4)-Li-. forms in the quaternary system Li+, Na+ // SO42-, B4O72- - H2O at 288 K. According to the experimental data, the metastable equilibrium phase diagram and the physico-chemical composition diagram were plotted. In the metastable phase diagram, the quaternary system has three invariant points, seven univariant curves, five fields of crystallization (Li2SO4 (.) H2O, Na2SO4, Li2B4O7 (.) 3H(2)O, Na2B4O7 (.) 10H(2)O, Na2SO4. Li2SO4). The double salt (Na2SO4 (.) Li2SO4) and Li2SO4 (.) H2O have smaller crystallization fields, but borates (Li2B4O7. 3H(2)O and Na(2)B(4)O(7)(.)10H(2)O) have larger crystallization fields. The crystallization field of Na(2)SO(4)(.)10H(2)O was not found in the metastable equilibria.
