MIDDLE DUNGEONS LEVEL FOUR 152 GRAY ROOM.

152 GRAY ROOM. The ceiling in this room is not illuminated, but instead is dark gray stone. A stone bowl on a small pedestal is in the center of the room. It holds a potent acid that resembles water. It is colorless and odorless. There is about one gallons worth.

This can be weaponized, if the characters have suitable containers (see page 64 of the Dungeon Master's Guide).