In a previous paper, the existence of octahedral coordinate Al³⁺ ion in the range of molar ratio of Al₂O₃/MO<1 was inferred from the effect of Al₂O₃ on the viscosities of Na₂O, PbO, CaO and MnO silicate melts. In the present study, the viscosities of K₂O, Li₂O, BaO, ZnO, SrO and MgO systems were measured in order to confirm the previous result, and the viscosity data of each alumino-silicate melt were arranged using a parameter P corresponding to the ratio, n_O⁻⁄n_Si, in the binary silicate.
The parameter P is expressed by
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\ oindentwhere Z_M is the electric charge of M ion, and n_M, n_Si and n_Al are the ion fractions, and X is the ratio of the number of tetrahedral coordinate Al³⁺ ions to that of the total Al³⁺ ions.
Satisfactory results were obtained by the arrangement described above, and calculated values of X were 0.95(K₂O), 0.90(Na₂O, BaO), 0.78(SrO), 0.74(PbO), 0.73(Li₂O, CaO), 0.60(MnO), 0.51(MgO) and 0.50(ZnO). Plot of X against the polarizing power Z⁄r_i² was linear, and X decreased with the basicity of MO.