Cupric sulphate is one of the chemicals that is obtained by examining cupboards during the Miss Cheevers challenge as part of the Recruitment Drive quest. The cupric sulphate is used on the metal spade (head) after it is stuck into the door. When used with a vial of liquid it will react and heat up, causing the metal spade to expand. If used incorrectly with the other ingredients, it may become one of the ??? mixtures, or produce the strange tin.
Cupric sulphate is a salt better known as copper(II) sulphate, with the chemical formula CuSO4. It is a white powder that is often used as a reagent to detect water, since its colour changes from white to blue after coming in contact.