Molybdenum

Molybdenum was recognised in 1778 by Carl Wilhelm Scheele, who showed that the mineral molybdenite was not a lead ore as had been assumed, and the metal was isolated in 1781 by Peter Jacob Hjelm. The name records the very confusion Scheele dispelled: it comes from the Greek molybdos, meaning lead. Molybdenum is a hard, silvery, extremely high-melting metal, valued for strengthening steel and as an essential trace element in living enzymes. Its high melting point makes molybdenum valuable in steels and superalloys for engines, tools and furnaces and as a catalyst in refining petroleum, while as a trace nutrient it sits at the active centre of enzymes in plants, animals and bacteria, including those that fix nitrogen.

Hjelm produced the first metallic molybdenum in 1781 by reducing molybdic acid with linseed oil and carbon in a sealed crucible, a method Scheele himself had specifically asked him to try, lacking a furnace that could reach the necessary temperature. The metal found unexpected strategic importance in the First World War, when Germany, cut off by blockade from adequate tungsten supplies, substituted molybdenum in artillery and armour steel and found it performed comparably at a fraction of the weight, a wartime discovery that permanently established molybdenum as a standard alloying element in high-strength steels rather than a mere tungsten substitute.

Molybdenum's name is a fossil of an old error. Its chief ore, molybdenite, is soft, grey and greasy to the touch, and it so resembled both galena, the lead ore, and graphite that all three were lumped together under names derived from molybdos, the Greek word for lead, and used interchangeably as marking materials. Only when Scheele analysed molybdenite did it become clear that it contained neither lead nor carbon but a distinct new metal, which nonetheless kept the misleading name. Molybdenum has no alchemical or symbolic tradition of its own; its story is one of disentangling substances that looked alike, and its name is a lasting reminder of the pre-modern difficulty of telling one grey mineral from another.

The confusion molybdenum's name preserves has a curious counterpart in biology: the enzyme nitrogenase, which lets certain bacteria fix atmospheric nitrogen into a usable form without any industrial Haber-Bosch plant, depends on a molybdenum-containing cofactor at its reactive centre, so the element chemists once mistook for lead turns out to be indispensable to the natural nitrogen cycle that sustains most of the planet's soil fertility. Graphite, molybdenite's other historical look-alike, was itself long called black lead or plumbago for the same reason, and only careful nineteenth-century chemistry finally separated the three greasy, grey, superficially similar minerals into carbon, molybdenum and true lead.