The Menstrua

n. pl. men·stru·ums or men·stru·a (-str-)
A solvent, especially one used in extracting compounds from plant and animal tissues and preparing drugs.

In Alchemy, Menstrua are the liquids which have the power to dissolve or extract the elements of various materials.
In general, the Mercury proper to a realm is an excellent menstruum for that realm.
Very often, the word ALKAHEST designates a menstruum with limited power: sometimes it acts only on one of the principles of Sulfur or Mercury, or in other cases it acts on only one part of its realm. For example, there is an ALKAHEST which is semimetallic and satisfactory in the mineral realm but not in the metallic realm.

The Menstruum is generally obtained or liberated through fermentation or putrefaction and
it is separated by means of distillation. In the vegetable realm, the Mercury is vegetable
alcohol. For your information, the following sequence:
Grapes + fermentation = fermented juice + distillation = Alcohol or Mercury
This is valid for all the volatile substances of the vegetable realm.

If we undertake a second fermentation we have:
Fermented juice or Alcohol + fermentation = vinegar or acetic acid.
Acetic acid is a "fixing menstruum according to the alchemical concept.

Fermentation, distillation, purification and sharpening of the menstruum are necessary operations, it is also useful to know that:
-a menstruum is a living being, that is to say the more pure it is the more sensitive it is to
psychic influences.
- a menstruum is contaminated by disharmonious sounds, negative words, selfish or malevolent thoughts. The closer the menstruum gets to perfection the more vigilant the operator must be with his (her) acts, words and thoughts.

In Alchemy, we often speak of a universal solvent, that is to say a menstruum that can act in all realms and on all things. This prompted negative minds to comment that this is impossible because this solvent would then dissolve its own container. In fact, this menstruum separates living compounds but the glass is a dead body, it is not a living compound and so resists the menstruum.