Abstract: In accordance with the coexistence theory of slag structure and by means of regression analysis, the presence of MnSiO₃ and Mn₂SiO₄ in the slag system MnO-SiO₂(and that both of them take part in the reaction of this system) has been determined, therefore the structural units of this system can be expressed as simple ions Mn²⁺ O^2- and molecules SiO₂, MnMnSiO₃, Mn₂SiO₄ and the calculating model of mass action concentrations can also be written.
At 1600℃ the calculated values of N_MnO are identical with the measured α_MnO, but the differences; between them at high concentrations of MnO and ower temperatures are due to the coexistence of liquid and solid in the slag system MnO-SiO₂, which makes it departure from equilibrium.