A strict scientific analysis of thermodynamics, kinetics, and mechanism of oxide melts, as well as metal and gas phase interaction, cannot be possible without studying the effect of wire former quantities and nature on the ionic composition and physicochemical properties of those melts. Quantitative evaluation of the ionic composition and thermodynamic properties of silicate systems can be based on the polymer theory. This paper concerns the methods of calculating components' activity and ionic compositions in silicate melts, as based on the anion volume ratio. The design and experimental data on component activity in binary silicate melts are provided.