Many studies of the reaction of bromine with aliphatic acids and with acyl derivatives have been recorded (1). The inconsistencies of data reported, and the conflicting conclusions drawn, however, indicate that a complete qualitative knowledge of factors governing bromination of these substances has not yet been attained. The nature and magnitude of the effects of recognized catalysts are inadequately known, in that some investigations have employed such relatively high2 "catalyst" concentrations as to suggest that the supposed catalysts might actually be primary reactants, and further in that the effects of light and oxygen (shown by previous studies in this laboratory (2) to be highly significant in other bromination reactions) have been neglected. The present study was designed to supplement existing knowledge of the effects of catalysts, with special attention to oxygen, and of the effect of light, and to test incidentally Watson's hypothesis that certain acid brominations take place through the intermediate acyl bromides. The authors hope that the data recorded may contribute towards a sounder basis for future quantitative studies.