Alchemical Sulfur
The Combustible Principle
In 1531 Paracelsus distinguished many sulphurs: blood, flesh and organs each have their own, rather than sharing one universal combustible substance.
Paracelsus, Opus Paramirum (1531), book II, chapter I, in Andrew Weeks, Essential Theoretical Writings (Brill, 2008), p. 413; introduction, pp. 3–6, on dating.
An alchemical sign for sulphur: a triangle above a cross.
More context
Sulphur is one of the three substances in Paracelsus's Opus Paramirum of 1531. In his demonstration with burning wood, sulphur is what burns, mercury appears as smoke, and salt remains as ash. His bodily theory recognises many sulphurs: blood, flesh, organs and marrow differ from one another. He also distinguishes volatile sulphur from the fixed sulphur of bones. These are constituents to be investigated by separation, within a medical account of bodies. The principles explain how matter is constituted and how its components respond to fire in the physician's investigation.
Light
Paracelsus uses sulphur to distinguish bodily constituents: blood, flesh, organs and marrow each have their own.
Shadow
In Paracelsus's wood-burning demonstration, sulphur is consumed by fire; its visible action also destroys the material in which it appears.