The alchemists were sure that the intention of nature regarding metals was that they should become gold, for gold was considered to be the most perfect metal, and nature, they said, evidently strains after perfection. The alchemist found that metals were worn away, eaten through, broken, and finally caused to disappear, by many acid and acrid liquids which he prepared from mineral substances. But gold resisted the attacks of these liquids; it was not changed by heat, nor was it affected by sulphur, a substance which changed limpid, running mercury into an inert, black solid.