The Vial of Acid is a tube containing green acid with orange/yellow caps on both ends. It is used in the Uprinsing level to remove graffiti. It must be thrown at the graffiti, where it will burst and release a green splatter. The acid will then slowly disappear, as it dissolves the graffiti paint. Once sufficiently dissolved, the paint can be removed with the Mop.
Some graffiti requires 2 (or more) vials of acid to dissolve enough to be removed with the mop.
The vial of acid may leave a burn mark on the wall or ceiling where it bursts. This mark must be removed with the Laser Welder. The burn mark should only appear if there is no paint present while the acid splat remains. If the player breaks a vial on a surface without paint nearby, a burn mark can be prevented by mopping up the acid quickly, before it starts eating away at the wall or ceiling.
A few vials of acid are included at the start of the level, but more can be obtained from the Vendor.