Fig. 1. (a) Nitrate reduction to NH₄⁺ and NO₂^– by FeO(s) at a constant pH 6.45. The small inset shows NO₂^– reduction by FeO(s) in a separate experiment over a 4-h interval under similar conditions. (b) Production of NH₄⁺ vs. consumption of NO₃^– for the reaction of NO₃^– with FeO(s) at a constant pH 6.45. The solid line represents a linear least square regression fit of the data. Error bars indicate ±range of duplicate runs; bars not visible are smaller than the symbols.