The vial of liquid is a quest item used only in Recruitment Drive. A set of three vials and an individual vial can be found in two separate bookcases in Miss Cheevers's trial.
It is used on the stone door when the metal spade is inserted into the hole after already used cupric sulfate on it to expand the spade to use it as a door handle. It is also used on the gypsum tin to make a hardening tin. If combined incorrectly with other chemicals, it may result in ??? mixture or a strange tin.
After leaving the room, all copies in the inventory are deleted.