Figure 6 from Lambsprinck's De Lapide Philosophico [On the Philosophers' Stone] (1678). "Mercury rightly precipitated or sublimated in its own water, dissolved and again coagulated." A serpent or dragon bites its tail, symbolizing mercury. The ouroborous is one of the oldest alchemical symbols. Allegorical descriptions that required decoding by the practitioner had always been part of alchemical communication. Medieval alchemy in the West added visual imagery to that long tradition.