A detailed procedure is given for the detection or determination of sulfur in ancient brass. Sulfur was not detected by this method in typical Roman brass coins of the first century A.D., but was found to be usually present in those of the second century. The proportion ranged from 0.08% in the earliest coin to 0. 33% in the latest. These findings indicate that only oxidized ores of zinc were used in the first century, and that a sulfide ore, probably sphalerite, was admixed with oxidized ores in increasing proportion during the second century. One reason why Roman coinage in brass ceased by the end of the second century would appear to be the exhaustion of the known zinc ore deposits or the exhaustion of the type of ore that could be successfully used for brass manufacture. -- AATA