Acid was a type of chemical compound that was caustic in nature.
Natural occurrences Edit
Acid, sometimes in large bodies, could be found on many planets. The seas of Marinus, (TV: The Keys of Marinus) 16 Alpha Leonis One (PROSE: Eternity Weeps) and Endpoint were all composed of acid. (PROSE: Hope) The planet Vortis also had pools of acid on its surface. (TV: The Web Planet) Skaro had a river of acid, where the Dalek Emperor attempted to kill Zeg. (COMIC: Duel of the Daleks) Lake Mono on the Gyre was composed of acid, where the humans put criminals to death by immersing them in it. (PROSE: Night of the Humans)
Offensive purposes Edit
Some species used acid as a method of killing. This could include regular weaponry or an impromptu defence.
Eldrad developed an acid that neutralised the molecular bond in silicon-based lifeforms. When he returned to Kastria after his execution, Eldrad triggered a booby trap that fired a missile containing the acid upon him. Knowing there to be no antidote, he was forced to use the regenerator chamber. (TV: The Hand of Fear) An Eldrad known as "the Watcher", who had been restored from the original's eye, was killed with an acid filled dart by the Eldrad who was restored from the original's hand. In turn, this Eldrad was killed with the same dart by Mulkris. (AUDIO: Eldrad Must Die!)
The calcium-based bodies of Raxacoricofallapatorians were vulnerable to acetic acid. (TV: World War Three) On Raxacoricofallapatorius, criminals were executed by being dissolved in a vat of acetic acid while still alive. (TV: Boom Town)