Sulfur

Sulfur is one of a handful of elements known in the free state since antiquity, scraped in yellow crusts from volcanic vents and burnt as a fumigant by Homer's time. Two inventions made it industrial. Charles Goodyear stumbled on vulcanisation in 1839 when he dropped a rubber and sulfur mixture on a hot stove and found the result stayed elastic instead of melting in summer and cracking in winter — the crosslinks are sulfur bridges. And sulfuric acid, produced in greater tonnage than any other chemical, has been used since the nineteenth century as a proxy for a nation's industrial output. Hydrogen sulfide is the other face: it smells of rotten eggs at parts per billion, and above roughly 100 ppm it paralyses the sense of smell entirely, which is what makes it a routine killer in sewers and sour gas wells.