Fluorine is so reactive that its isolation defeated chemists for most of a century and injured or killed several who tried; it was finally obtained in 1886 by the French chemist Henri Moissan, by low-temperature electrolysis of hydrogen fluoride, work for which he received the Nobel Prize in 1906. Its name comes from fluorspar, the mineral fluorite, from the Latin fluere, to flow, because the mineral was used as a flux to make ores melt and flow more freely. Fluorine is a pale yellow gas, the most electronegative and aggressive of all elements. Despite its danger in the free state, fluorine's compounds pervade modern life: the fluoride added to toothpaste and drinking water to strengthen teeth, the non-stick polymer PTFE, and the refrigerants, propellants and etching gases of industry all depend on the element.
Fluoridation of public water supplies, adopted widely in the mid twentieth century to reduce tooth decay, also became one of the most durable targets of American conspiracy theory: from the 1950s onward, groups including the John Birch Society claimed it was a communist plot to poison or control the population, a fear later satirised in the film Dr. Strangelove and one that persists in various forms among fringe health movements today. The episode makes fluorine's most everyday compound a genuine case study in how a public-health measure can acquire an entirely unfounded esoteric mythology of its own.