SRD:Acid

Acid
Corrosive acids deals 1d6 points of damage per round of exposure except in the case of total immersion (such as into a vat of acid), which deals 10d6 points of damage per round. An attack with acid, such as from a hurled vial or a monster's spittle, counts as a round of exposure. The fumes from most acids are inhaled poisons. Those who come close enough to a large body of acid to dunk a creature in it must make a DC 13 Fortitude save or take 1 point of Constitution damage. All such characters must make a second save 1 minute later or take another 1d4 points of Constitution damage.

Creatures immune to acid's caustic properties might still drown in it if they are totally immersed.

Flask of Acid
You can throw a flask of acid as a splash weapon. Treat this attack as a ranged touch attack with a range increment of 10 feet. A direct hit deals 1d6 points of acid damage. Every creature within 5 feet of the point where the acid hits takes 1 point of acid damage from the splash.