A hypothetical substance in alchemy, the universal solvent - it was believed to dissolve anything (in some versions, only compounded substances, not the elements themselves). The alkahest was one of several substances (along with the elixir of life, philosopher's stone, etc.) that alchemists wished to discover how to make. In some alchemical traditions, creation of the alkahest was one of the necessary steps in the great work of alchemy - usually the project to create the Elixir of Life and live forever. Where classical elements are considered (and they usually will be with alchemists about), the alkahest is either the great work of the element of fire or water1.
In the 16th Century, Paracelsus believed it could be made from caustic lime (presumably quicklime), potash (potassium carbonate), and alcohol. Paracelsus may have been the one to name Alkahest as well, either deriving it from Latin for "it is alkaline", or just giving it a made-up vaguely arabic-sounding name.
In the 17th Century, Jan Baptist van Helmont claimed to have successfully made Alkahest from a formula similar to Paracelsus', and in the process he also discovered the process for making glycerol (which he called "sweet oil") 300 years before DuPont patented it. One of the interesting things about Alchemy is the way it blurs the line between magical occultism and chemistry, which has caused a number of old alchemist's breakthroughs to be ignored until independently rediscovered by modern science.
Hydrofluoric acid was also - briefly - a contender for the alkahest secret identity, due to its ability to dissolve things like glass that tended to resist other acids. It too turned out to be just another mineral acid.
Game and Story Use
- In a fantasy game, vials of Alkahest could be used as a weapon (projected from siphons and grenades like Greek fire).
- The potential use of alkahest as a weapon could lead to intrigues, with different kingdoms trying to co-opt alchemical research into it, bribe or kidnap the alchemists, etc.
- An alchemist working secretly in the city the PCs are based out of has managed to create Alkahest. It immediately starts dissolving everything it touches, melting a hole straight down towards the center of the earth.
- On the way, it creates a shaft that opens into the local sewers, and some vast caverns beneath the city, effectively opening up a new dungeon right below the PCs home town. Perhaps horrible things start crawling out at night.
- Rather than monsters, this could lead to ecological disaster. The local river might drain down the hole. The Alkahest might trigger or destabilize a fault line, and/or lava might come bubbling up from deep in the ground. Perhaps the whole just slowly grows wider like a sinkhole, threatening to swallow the entire city if the PCs don't find a way to neutralize or stabilize the Alkahest.
- If a bottle of Alkahest is included in a treasure haul, it may effectively be two treasures in one. There's not just the universal solvent, there's also a magical flask] or bottle resilient enough to hold it. Even once the Alkahest is all used up, the bottle that held it might be repurposed in some clever way… perhaps it's a fitting prison for a genie or demon?
- Or, to invert that, perhaps the only way to capture a rampaging genie is by use of a particular type of magic bottle. The only such bottle the PCs know of is currently full of Alkahest. They can't take care of the genie unless they first find a place where it's safe to dump out the Alkahest (without causing ecological disaster or opening up a cavern of monsters worse than the genie, as mentioned above).
- The GM has a lot of leeway in determining exactly what it does, and how Alkahest works in the campaign. It could work as any of the following:
- An extremely potent acid, which melts and burns everything it touches.
- A chemical reagent which transforms or reacts to a wide variety of other substances, rather than destroying them.
- "Super Water" that can make solutions that have the same properties as whatever solid is suspended within it. Allowing you to turn magic dust or green rocks into potions.
- A purifying oil, which benignly separates various substances into their truest forms, and removes impurities and blemishes.
- The liquid version of wild magic, unleashing different seemingly-random magical effects depending on what elements are dissolved in it. It releases the magic within the matter, so to speak.
- In a more modern setting, the glycerol-DuPont link could suggest that some large chemical and pharmaceutical companies also have secret alchemy laboratories, where magic and chemistry are explored side-by-side.