Acid Pool

The pool filled with Hollywood Acid is the go-to Death Trap for any Mad Scientist that doesn't have access to a Lava Pit - usually bubbling a sickly green color, it will melt the flesh of your bones and leave nothing but a bleached skeleton, if that. Can be used both for moats near precarious bridges and lowering heroes into. Acid pools are generally treated as green variants of the Lava Pit and used in a similar manner as obstacles or execution methods.

Highly impractical in Real Life due to the nature of acid, particularly if bubbling. Acid is often produced when highly caustic negative ions are dissolved in water, and they are quite capable of escaping, particularly if in high enough concentrations as to remove flesh from the bone. These remain caustic and are quite likely to damage anyone nearby (almost like a chemical version of Convection, Schmonvection).

Strong acid is also extremely poisonous to breathe, so the air would be fatal long before its first victim could fall into it, unless it was from a substantial height; and even then it would have a substantial stench even from a great distance, which would drive anyone away if they had a choice.

The counterpart on the opposite end of the pH scale is the pool of lye, which shows up typically in industrial vat form.

May overlap in video games with Grimy Water. See also Shark Pool.

Comic Books

 * One of the many Booby Traps Scrooge McDuck has to protect his money bin is an acid pool.

Fanfic

 * In And If That Don't Work, Matarael (the acid dripping, a-joke-in-canon Angel) actually got to the pilot's entry plug and turned it into an acid bath.

Film

 * That weird black goo at the end of the second Tomb Raider movie.
 * Shows up in the Transformers: The Movie.
 * In the Vincent Price movie House on Haunted Hill, the house had an acid pit in the basement. (But it was OK because there was a lid on it.)

Literature

 * Nomads of Gor had a pool that was alive, and digested its victims.
 * One of the Drizzt novels includes an acid pool just sitting around in the Underdark. Because the Underdark is just nasty that way.

Live Action TV

 * The Wild Wild West actually had a pool of lye in an episode.
 * Subverted in an episode of Kung Fu, where young Kwai-Chang is ordered by Master Po to cross a plank over an acid-pit full of human skeletons, and blind Master Po demonstrates by walking across it himself. Kwai-Chang obeys and walks across the plank, but falls into the pit halfway across -- only to find that it's only full of warm water, and the skeletons were made of paper; the "test" was simply a lesson to teach him that "fear is like a magnet" that pulls a man in its direction.
 * Showed up in the "Look at the Princess" Trilogy in Farscape.
 * In The Vampire Diaries a vampire-specific one is created by simply scattering vervain into the water. Any vampire that entered it would have their powers drained, then their skin burn.

Real Life

 * John George Haigh, the "Acid Bath Killer", disposed of his victims' bodies by dumping them into acid. He also makes an appearance in Clock Tower 3.
 * Large scale livestock farms often have large bodies of liquid known as waste lagoons, which are used to store animal excrement. These lagoons are extremely toxic, and falling in one is pretty much instant death.

Tabletop RPG

 * Dungeons and Dragons adventures have had a lot of these over the years. For example, WG5 Mordenkainen's Fantastic Adventure had an Acid Pool so concentrated that anyone jumping in would be instantly killed.
 * Also, D&D third edition averts the "harmless fumes" - if you approach a large vat of acid, you can suffer constitution damage from inhaling the toxic mist.

Toys

 * Bionicle had a villain (a Makuta named Gorast) who had the title "Queen of the Acid Falls," so apparently there was an entire river of acid running through her domain.

Video Games

 * Appears instead of lava pools in some particularly nasty places in Severance: Blade of Darkness.
 * The liquid pits in several areas in Portal.
 * Several of the areas in Metroid (for example, Brinstar in the original game) have acid pools which only damage Samus should she fall in. Perhaps justified because of her Powered Armor.
 * All over the place in Doom and Quake, in addition to lava.
 * The Dead Pool in the Mortal Kombat series, which you can knock your opponent into at the end of a match, or to end a round by Ring Out in Deception.
 * The fourth Commander Keen game, Secret of the Oracle, has two vats of this in the first level, and they show up sporadically throughout. Glowing green goo variety.
 * The cave in Space Quest 1 has a pool of acid with a few stupid actions you can take that result in Roger's death. Fortunately, messing around with this pool is entirely optional.
 * In Space Quest II, there's a Death Trap in Vohaul's Space Base where the door locks and the floor slowly retracts to drop you into an acid pit.
 * the second Metal Gear for the MSX had acid pools that could be neutralized with chocolate.
 * In Monkey Island 2: LeChuck's Revenge, Guybrush and Wally are unwillingly suspended above a pool of acid while caught in Lechuck's Death Trap.
 * Knights of the Old Republic has one just before the goal in the Sith academy exam.
 * Heavy Rain - Norman Jayden can investigate one and find a skeleton floating in it.
 * Acid pools appear in World 2 fortress in Purple.
 * The Sorceress from Spyro: Year of the Dragon is killed when she falls into a pit of purple acid.

Web Comics

 * The Order of the Stick had that little incident with O-chul getting dunked into an acid pool with spikes at the bottom and an acid-breathing shark swimming in it.
 * Interestingly, the D&D 3.5 supplement Dungeon Scape actually includes rules for an acid-breathing shark.
 * Early in Eight Bit Theater, Garland and Evil Princess Sara capture the Light Warriors and attempt to dunk them in a vat of acid.

Western Animation

 * The Joker lowers Sid the Squid into one in Batman the Animated Series.
 * In another episode Batgirl and Catwoman are captured by a mob boss and taken near acid vats. One of them asks if they'll suspend them above the acid so the vapors will kill them, but he replies he'll just shoot them and get rid of their bodies in the vats.
 * The episode "Cop Out" of The Powerpuff Girls involved a corrupt cop had the girls getting dunked into one after the good cops weren't quite able to rescue them..