The optical basicity (Λ; Pb
2+ as probe ion) of various oxide glass systems has been measured to establish the new basicity scale of oxyacid salt melts. Best conditions of glassy fragments to measure Λ were determined. Problems in establishing the new basicity scale using Λ-values are discussed, and also relation between Λ and Fe
2+–Fe
3+ redox equation is discussed in terms of Fe
3+-constitution. Λ has the posibility of showing the Lewis and new scale of basicity in these melts.
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