Among other bactericidal agents used in treating water, bromine is sometimes mentioned. Although there are no known applications of bromine to public water supplies, it is finding occasional and increasing use in swimming' pools and industrial water supplies. Because the chemical is used in water conditioning, it was considered desirable to explore its reactions with ammonium compounds to determine if there is a "breakpoint" analogous to the chlorine reactions. Tests were conducted in the usual manner. To an ammonium hydroxide solution containing 0.5 ppm. ammonia nitrogen, there were added varying quantities of bromine water to give the desired bromine application. The solutions were buffered with disodium phosphate or monopotassium phosphate. The mixtures were stirred for 30 minutes, and the resulting bromine and ammonia nitrogen residuals were determined. The bromine residual was determined with orthotolidine using a Taylor bromine slide comparator. It was not possible to distinguish between the 7 1 i ! ' i ' i i / я (Л) pH