Alchemists already add their Intelligence modifier to damage with bombs and the Underground Chemist archetype's 2nd level ability dues the same with all splash weapons.
I am assuming i get to add Int to damage twice, is there something that says otherwise?
Also, if I use alchemist's fire, is my Int mod added to the damage in subsequent rounds from the Underground Chemist's Ability? (Like the Immolation bomb Discovery does for alchemists.)