Fused is reduced electrolytically first to nitrite and oxide. This process, however, is mixed as exact correspondence is not obtained between the nitrite produced and the coulombs passed. On further reduction of there is an increasing contribution from various other cathodic processes including the production of colored species containing oxidized cathode metal. Reduction of and also gives rise to mixed electrode processes and the formation of colored species in the cathode compartment. Ag+/Ag is shown to be a suitable reference couple for fused .