The density and surface tension of melts of the systems CaO-FeO-Fe2O3 MgO at the temperature 1623 K, CaO-FeO-Fe2O3-ZnO at 1573 K, and CaO-Fe2O3-Cu2O at 1573 K were determined using the maximum bubble pressure method. The molar volume, the excess molar volume, and the excess surface tension were calculated on the basis of the obtained data. From these properties information on the interactions of components and possible chemical reactions between them was obtained. Due to the absence of silica and the low concentration of other network-forming oxides, only isolated FeO45− tetrahedra and the CaO·FeO ionic pairs are formed in these basic melts, the donor of the oxygen atoms being either CaO, FeO, or both CaO+FeO oxides. Even the observed ternary interactions may be attributed to the formation of the anions FeO45− only.