alumen

The Romans knew alumen, a bitter mineral salt used for dyeing cloth and tanning leather. The word probably traces to the Greek root alud-, meaning bitter, though some scholars connect it to alum's astringent taste directly. For eighteen centuries, alum was just a useful chemical compound. Nobody imagined a metal hiding inside it.

In 1808, Humphry Davy at the Royal Institution in London isolated the metallic element from alumina — the oxide of alum — and called it alumium. He revised this to aluminum in 1812, following the pattern of platinum and tantalum. The name lasted exactly long enough to cross the Atlantic before British chemists objected. They wanted aluminium, matching sodium and potassium. The Americans, having already printed aluminum in textbooks, refused to change.

Charles Martin Hall in Oberlin, Ohio, and Paul Héroult in Gentilly, France, independently discovered the electrolytic process for extracting aluminum in 1886 — the same year, the same method, an ocean apart. The Hall-Héroult process dropped the price from more than gold to cheaper than iron within a decade. Napoleon III had served state dinners on aluminum plates to impress guests; by 1900, people were wrapping sandwiches in it.

The International Union of Pure and Applied Chemistry recognized aluminium as the standard spelling in 1990 but accepted aluminum as a legitimate variant. Neither side conceded. The two-letter difference between aluminum and aluminium remains the most famous spelling dispute in the history of science, a permanent monument to the fact that Humphry Davy changed his mind one too many times.