The dynamics of the BrO3--SCN- reaction in an HClO4 medium has been st
udied using the stopped-flow method. Production of bromine in the syst
em follows a sigmoidal course with two induction periods (low acidity
conditions). Under conditions of higher acidity the bromine concentrat
ion passes through a maximum, while the first induction period (lag ph
ase) is preserved, though it becomes very short. The effect of H+ and
SCN- ions on the lag phase was quantitatively investigated. A simple k
inetic model based on four component processes is proposed. Simulation
s are in good agreement with experiments. The dynamics of the BrO3--SC
N- reaction under conditions of a closed reactor may be understood as
clock behavior.