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Abstract

Boron oxide in the Na₂O.P₂O₅-x B₂O₃ system behaves as a Lux base. Its addition to Na₂O.P₂O₅ brings about transformation of a Co(II) indicator from octahedral to tetrahedral configuration, increase in the optical basicity Λ_Pb(II), increase in the relative basicity of the melt as determined by means of a galvanic cell, and depolymerization reactions releasing PO₄^3- ions. In the Na₂O-B₂O₃ system free of P₂O₅, boron oxide behaves as a Lux acid. The amphoretic nature of B₂O₃ is explained in terms of Lux's acid-base theory extended in analogy with the protolysis theory. The theoretical optical basicity values do not indicate the amphoretic behaviour of B₂O₃ because in this approach boron oxide is a priori regarded as more acidic than Na₂O.P₂O₅.