By MARTHA COOLEY

Sulfur: odor of rotten eggs, matchhead, volcanoes, gunpowder, and Lucifer down there in Hell’s fire and brimstone.

Also the smell that pervades thermal spas. Along with minerals such as sodium chloride, iodine, and calcium, sulfur is a key component of many therapeutic waters. Linked as it is with fire and corrosion, sulfur also has a storied association with the healing of numerous ailments, particularly respiratory and skin-related ones.