This thread just keeps spinning its wheels with boring arguments over science versus magic.
I'm with NW_Kohaku here, lets get this thing back on track and try and discuss what Alchemy should actually do.
Here's my take on what would make for an interesting new component to the game.
Firstly, the settings include two new important things:
1. A setting on whether Alchemical reactions should be procedurally* generated by the game during worldgen.
2. A list of valid Alchemical reactions, which provides the only valid reactions for the Alchemists shop if procedural generation is off.
"Science only" players can just list all the reactions that they want in the raws and turn off procedural generation. Players that are interested in generating a magical or strange world that doesn't operate like ours can opt for the route that procedurally generates reactions and has no preexisting reactions. Other players could opt for a combination of both known and new reactions, by leaving generation on but adding some known reactions.
In either case, reactions will be unknown to the player and must be discovered; unless the player entered the reactions in the raws manually, or uses a mod which provides reactions that they're familiar with, in which case obviously they'll know what they are.
General rules of Alchemy:
Alchemy should be the combination of two or more substances, with the result generally being of a type of one of the substances used.
Some possible examples that could be generated:
A blood barrel combined with milk might result in a barrel of blood wine.
A vinegar barrel, water barrel, and animal hide could produce a gelatin barrel.
A bar of aluminum, a barrel of cockroach ichor, and a barrel of longland beer might produce a bar of gold.
The furnaces have already assumed the role of creating most metal alloys, but perhaps exotic alloys and electroplating could be possible at the alchemists shop.
In addition, this would be a great place for players to be able to create intriguing substances like greek fire, gunpowder, poisons, and the like. (Commonly suggested stuff that doesn't fit elsewhere)
*In this case procedurally meaning "randomly with certain constraints".