Well, it's both! Unbelievably dangerous in one form, but indispensable in another? But first, the startling history of fluorine. Fluorine was suspected for centuries before Henri Moissan isolated it in 1886. In 1529, Georgius Agricola (the Latinized version of the German Georg Bauer George the Farmer wrote his classic mining and metallurgical treatise "De Re Metallica" that fluorspar (fluorite, CaF2) was used as a flux (from the Latin fluere = to flow) in furnaces to bring down the melting temperature of metals, making them easier to work with, and to flow away undesirable impurities from the smelt. By the way, that great treatise was translated by Lou Hoover, the multi-talented wife of Herbert Hoover, America's first great mining engineer, whose classic textbook grew out of his professorship at Stanford, long before he got into politics.
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