- vitriol: Vitriol (sulfuric acid) was widely considered the most important alchemical substance, intended to be used as a philosopher's stone. Highly purified vitriol was used as a medium to react substances in. This was largely because the acid does not react with gold, often the final aim of alchemical processes. The importance of vitriol to alchemy is highlighted in the alchemical motto, Visita Interiora Terrae Rectificando Invenies Occultum Lapidem ('Visit the interior of the earth and rectifying (i.e. purifying) you will find the hidden/secret stone'), found in L'Azoth des Philosophes by the 15th Century alchemist Basilius Valentinus.
It is possible for a Promethean to claim another's Vitriol by performing a lacuna on them. This is a horrendous sin, on par with vampiric diablerie, and automatically costs the reaper a point of Humanity. Pandorans can also utilize Vitriol by stealing it from a Promethean as they feed upon them, using it to fuel bodily transformations.