The anodic dissolution of gold in concentrated phosphoric acid was investigated at 145–200°C. Gold dissolves in a narrow potential region (150 mV) about 300 mV positive to the oxygen potential in the same electrolyte. At higher potentials it passivates. At very high overvoltages dissolution, which increased rapidly with temperature, was also observed in the transpassive region. The product of the dissolution is finely divided gold, probably formed by immediate decomposition of the oxydation product. At 200°C, at which temperature pyrophosphoric acid is formed, the gold dissolution also yields a clear yellow solution of gold pyrophosphate