Iron doors should be able to take water damage and become rusty. Once rusty, it should be possible to break an iron door like a normal wooden one.

Alternatively, iron doors should be corrodable by throwing or smashing acid on them, with it taking 2-3 potions to weaken a door to the point of destroyability.

Monsters carrying a potion of acid as well as some other potion that they would normally drink may accidentally drink the acid by mistake.

You can apply or otherwise dump a potion of acid into a sink to flush out the black pudding in the pipes, if the sink hasn’t yet produced one.

When a thrown potion of acid hits a creature, it may corrode some corrodable armor of that creature.

Dipping a unicorn horn in acid dissolves and destroys the horn, producing a potion of healing.

Potions of acid and oil are immune to freezing and shattering.

When acid breaks on someone’s head and spills on them, it actually does more damage than quaffing it, because it is spread out over more surface area.

The “weakest” beatitude of the potion of acid (usually blessed in vanilla, but if #1918 is implemented it will be cursed) may not cure stoning.

Swap the blessed and cursed effects of the potion of acid, which means that blessed acid is more powerful acid, while cursed acid is kind of cruddy.

Potions of acid have a splash radius effect when broken (could probably be implemented as an acid explosion).

Whenever a diluted potion of acid would be created (i.e. by wishing or polypiling) it immediately explodes in an alchemic blast.

F corpses can be dipped into potions to make different potions: juice + violet fungus = booze, juice + yellow mold = sickness, water + green mold = acid. (Note the existence of the Brewing Patch, which dissolves most F in juice to produce confusion, hallucination, booze, sleeping, and healing.)

Later suggested recipes which involve dipping a corpse in acid to dissolve it:

• Wraith corpse → potion of gain level. (Does not always succeed, to compensate for the fact that a wraith corpse doesn’t always grant a level. Maybe it even has a lower success rate than getting a level from a corpse.)
• Newt corpse → potion of gain energy.
• Floating eye corpse → potion of levitation or possibly monster detection.

You can dip fruits (slime molds) in a potion of acid (or potion of water?) to turn it into a potion of fruit juice (consuming the fruit).

Add a silvery potion, either as a random appearance or a dedicated potion like dNetHack’s potion of silver starlight, which will silver ammunition dipped into it, perhaps temporarily. It might also silver other weapons (spears, daggers) or other items. Random appearances have the possible problems of the potion potentially having a defined dip effect already (polymorph, for example), and it potentially not appearing in the game if there are extra random appearances.

Dipping fragile silver items, like silver arrows, into a potion of acid could create a silvery potion.