Sulfur, as gathered and used by pre-modern chymists, is simply the chemical element sulfur, S, one of the comparatively few substances in this entire table that alchemists could obtain in an essentially pure, naturally occurring elemental form without any refining or reduction, which is part of why it played such a central role in laboratory work: its behavior could be studied directly rather than inferred from a compound.
The identification carries no scholarly ambiguity at all for the mineral itself; the genuine complexity lies in keeping the mined yellow element clearly separated from the Paracelsian alchemical principle that shares its name, Sulphur, one of the tria prima alongside Mercury and Salt, which names an abstract active, combustible quality attributed to substances generally rather than the specific chemical element. This atlas treats the two as related but distinct entries precisely because conflating them, treating every mention of alchemical Sulphur as a reference to the mined mineral, would misread a philosophical category as a chemical claim, exactly the kind of category error this atlas works throughout to avoid. Sicily's sulfur mines remained a major world source into the nineteenth century, and the same island's near-monopoly on supply briefly became a matter of international diplomatic tension in the 1830s, a reminder that even the most chemically simple substance in this atlas had a real, sometimes contentious, economic history.