RM2 Spell Law included the Alchemist as a core profession. The "Liquid-Gas Skills" list is for making potions. The general guidelines for item creation in Spell Law Stock #1200, Copyright 1981, 1984, exact printing unlisted, for which a "Terry K. Amthor" has credits under "Design" and "Graphics" begin on p.17, section 9.92 "Alchemical Research".
Alchemy Companion had further options.
For RMSS/FRP, see the Treasure Companion.
Drinking potions is standard, though there isn't much on usage. I think % activity and second-by-second round options included quaffing times, but I might be wrong. The spell item chart lists potion use as "ingested". Certainly, this is the traditional concept of a potion. By Alchemy Companion, however, there was the Gaseous Potion option, which releases a magical cloud of the embedded spell.