Athanor or 'Slow Harry', a self-feeding furnace maintaining a constant temperature. This plate displays the Athanor and side chambers (5,5) for reagents in separate parts. One of the uses of the furnace was the production of nitric acid (also known as Aqua Fortis or Parting Acid) which was used in the refining and assaying of metals. From 1683 English edition of Beschreibung allerfurnemisten mineralischen Ertzt, Lazarus Ercker, (Prague, 1574). Copperplate engraving.