“'It's alkahest,' she announced. 'The universal solvent. It can only be stored in a bubble of itself because it dissolves everything else. Wood. Steel. Flesh.'”
Alkahest, a universal solvent, is the second most difficult material for an alchemist to make. According to Lady Galvin, it can dissolve anything except itself, including wood, steel, and flesh. In order to contain it, alkahest is stored in a bubble of itself, in which it hovers above a ring of fire on the floor. It appeared to be a milky liquid that danced within flames in Keeper of the Lost Cities.