Alchemical Mercury
The Volatile Principle
In 1531 Paracelsus identified the smoke from burning wood as mercury: this principle was not confined to metallic quicksilver.
Paracelsus, Opus Paramirum (1531), book I, chapter II, in Andrew Weeks, Essential Theoretical Writings (Brill, 2008), pp. 319–321; introduction, pp. 3–6, on dating.
An alchemical sign for mercury, or quicksilver.
More context
Mercury names both quicksilver and one of the three substances in Paracelsus's Opus Paramirum of 1531. His demonstration begins with wood: burning reveals sulphur, smoke reveals mercury, and ash reveals salt. The same substances belong to the human body, where he describes mercury as its liquid constituent. In this account, mercury escapes rather than burns in the fire. Its role is therefore broader than the metallic substance. Paracelsus presents these distinctions as foundations for recognising bodily constituents and investigating disease.
Light
In Paracelsus's account, fire reveals mercury as smoke, allowing the physician to recognise one constituent of bodies.
Shadow
Paracelsus's mercury escapes the fire: the constituent sought in a body can become volatile during its separation.