OK.
So I have an idea of combining an elixir drinking alchemist with an elementalist alchemist.
Basically, at 1st level, you choose an element (air, earth, fire, or water) as your specialty.
You gain Brew Elixir and Alchemical Formulas at 1st level.
Elixirs are based on the 4 humors (black bile (earth), yellow bile (fire), blood (air), and phlegm (water)). There are 7 levels of them, based on the 7 alchemical planets and metals (Saturn & Lead, Jupiter & Tin, Mars & Iron, Venus & Copper, Mercury & Quicksilver, Moon & Silver, and Sun & Gold).
You can use elixirs based on the humor of your specialty element and any non-opposed elements. You would not be able to use elixirs based on the humor of your opposed element.
Elixirs would work somewhat like binder vestiges, giving the alchemist a suite of thematically related abilities based on the humor and planet/metal of the elixir. Eventually, the alchemist will be able to brew elixirs that non-alchemists can survive imbibing.
Brewing an elixir would require 1 hour and access to an alchemist's kit similar to a healer's kit) or alchemist's laboratory. A successful Craft alchemy check would be needed to successfully create an elixir. Imbibing an elixir would require a successful Fortitude save to avoid a negative side-effect.
Alchemical Formulas will be spell-like abilities that focus on the creation and manipulation of the classical elements (air, earth, fire, and water), combining them to make different substances and energies (base metals, noble metals, electricity, acid, etc.), and altering the elements in some way (transforming air into fire (fireball!), animating elements (like quasi-elementals), dismissing elementals (quenching fires, drawing the air from an opponent's lungs, etc. etc.),
The first Alchemical Formulas an alchemist would learn would involve creating one of the classical elements (Create Air, Create Earth, Create Fire, Create Water). Later, the alchemist would learn how to combine 2 or more elements (Create Acid, Create Electricity, Create Metal, etc.) and/or modify the elements in some way (Create Wall of Fire, Create of Gust of Wind, Create Cone of Cold, Transmute Steel to Alchemical Silver (Transmute Metal to Metal), etc.).
Using an Alchemical Formula would require a successful Craft alchemy check to cast, the DC dependent on the number of modifiers added to the base Create Element Alchemical Formula. Also, using the same Alchemical Formula more than once a day increases the DC by 2 each time it is successful. The Alchemist would learn 1 Alchemical Formula per level.
There would be certain pathways that would need to be followed to learn higher level Alchemical Formula Modifiers.
The Alchemist would also have some class-related powers dealing with actual alchemical items.
I'm sure there would also be Alchemist-related feats that allow an Alchemist to learn additional Elixirs and Alchemical Formulas.