What It Actually Is

Oil of Vitriol is sulfuric acid, H2SO4, in a concentrated form, one of the cleanest and least contested identifications among all the named alchemical liquors; John Emsley and other historians of chemistry treat it as effectively synonymous with its modern name once the color qualified vitriols themselves are understood, since oil of vitriol is simply what a vitriol's acid spirit becomes when fully concentrated by heat. Its recognition as a distinct, powerful acid, rather than merely one variety of generic corrosive water, is usually credited to the medieval Latin alchemical tradition and to writers working in the orbit of Jabir ibn Hayyan's school, though the exact chain of transmission from Arabic sources to the European recipe that survives is debated by historians and cannot be traced to a single named discoverer with confidence.

What is not in doubt is the substance's importance afterward: sulfuric acid manufacture became, from the eighteenth century onward, a benchmark by which historians of industry measure a nation's chemical capacity, precisely because the alchemical process of distilling vitriol scaled so cleanly into an industrial one. Later economic historians have gone so far as to track a nation's industrial development partly by its annual sulfuric acid output, a modern echo of how central this one distilled vitriol became to chemistry far beyond the workshop that first isolated it.