menstruum

Menstruum is a historical term used in alchemy and early chemistry to denote a solvent—something capable of dissolving other substances. In practice, a menstruum is chosen to extract or separate constituents from a material, whether plant, mineral, or animal.

The word comes from Latin menstruum, literally meaning a solvent or that which dissolves. In medieval and early modern laboratories, writers spoke of a substance’s dissolving power as a menstruum and described resources as “vegetable menstruums” or “mineral menstruums” according to their source material. The concept emphasized the role of a liquid in transforming a material’s components through dissolution and extraction.

In herbalism and pharmacognosy, a “vegetable menstruum” denotes the solvent used to prepare tinctures and plant extracts. Common menstruums include water, alcohol (spirit of wine), vinegar, glycerin, or mixtures thereof. The choice of menstruum influences which constituents are dissolved and retained in the final preparation.

In mineral and alchemical contexts, various reagents were described as menstruums, categorized by their dissolving power rather than by composition alone. Aqua regia, for example, is often cited as a potent mineral menstruum capable of dissolving noble metals, illustrating how solvents were associated with their ability to break down substances rather than with a fixed chemical identity.

Decline and legacy: With the rise of modern chemistry and standardized terminology for solvents, the term menstruum largely fell from everyday scientific usage. It remains encountered in historical texts and in discussions of alchemical and traditional pharmacognostic practices.