The characteristic potential obtained just before decay of passivity (Flade potential) was measured for iron passivated by ferrates, nitrites, chromates, molybdates, tungstates, conc. , and by anodic polarization in . The Flade potential is linear with , of slope 0.059 up to approximately 4.5. Above this value up to 11.5, the potentials tend to follow an extension of the data in acids in the case of iron passivated by chromates and nitrites, but reach a constant value for iron passivated anodically or by conc. . The standard Flade potential () for various passivators is increasingly noble in the order: nitrite (−0.50 v) ; chromate, ferrate, molybdate (−0.54 v); tungstate (−0.61 v); and anodic polarization or conc. (−0.64 v). The average of these values is in reasonable accord with previously reported values and only small observed deviations from the average indicate that the structure and composition of the passive film on iron is largely independent of the passivation process.