The reaction of bromate, sulfite, and ferrocyanide ions in a continuous stirred tank reactor (CSTR) exhibits sustained oscillations at temperatures of 20, 30, and 40 OC. The oscillations, the behavior in a closed (batch) system, and the observed bistability in a CSTR are all in excellent agreement with simulations using a nine-step mechanism in which the reaction of BrO,- with Fe(CN)6& plays a key role. The relationship between the present system and the 'mixed Landolt oscillator, in which bromate is replaced by iodate, is discussed. Here we investigate the reaction of bromate, sulfite, and fer- rocyanide ions. The present system is derived from the iodate- sulfite-ferrocyanide oscillator recently discovered by Edblom, OrbBn, and Epstein (EOE)6 by replacing the iodate ion of that mixed Landolt reaction by bromate. As anticipated, we do indeed obtain oscillatory behavior in a continuous stirred tank reactor (CSTR), though that behavior differs from that of the iodate system in several unforeseen ways. We have also studied the mechanism for this system and find that it must depart sig- nificantly from that propo~ed~.~ for the analogous iodate reaction in order to simulate our experimental results. Experimental Section A thermally regulated CSTR9 was used for all flow experiments. Both batch and flow experiments were carried out at 20, 30, and 40 OC. The reaction temperature was kept constant to fO.l C. Reactant solutions were pumped into the reactor through four inlet tubes by means of a Sage 375A peristaltic pump. During all flow experiments reservoir concentrations were fixed while the inlet flow rate was changed. This pumping rate was varied in both directions in order to observe any hysteresis behavior. Sufficient time was allowed at each flow rate for the system to reach either an oscillatory or a stationary steady state. Analytical grade KBr03 and K4Fe(CN)6.3H20 produced by Fisher Co. and Reanal (Hungary) were used without further purification. All solutions were made with distilled water. The concentrations of sulfite and bromate solutions were determined by using iodometric titration methods while the ferrocyanide concentration was checked with a Ce(S04)2 titration. The po- tentiometric progress of the reaction was monitored by a platinum redox electrode with a Hg(Hg,S041K2S04 reference electrode. The pH was followed with a combined glass electrode. Some mea- surements were made using a bromide ion sensitive electrode (Orion). Results Batch. Br03- + SO?-. In a closed system, the reaction between bromate and sulfite is less dramatic than its iodate counterpart. In both systems, large amounts of H+ are produced, resulting in a significant pH drop as the sulfite is depleted. In the iodate-sulfite reaction, the pH rises again later owing to reaction between iodide formed in the initial stages of the reaction and previously unreacted