What are they?

Mercury is a dense, silvery metal element that is liquid at room temperature. It has a high thermal expansion giving it excellent properties for measurement devices. It is electrically conductive. It forms into spherical beads making it highly mobile when poured or spilled on non-porous surfaces.

Commonly encountered compounds of mercury in collections include mercury sulphide (cinnabar and the pigment vermilion), mercuric chloride (corrosive sublimate) and mercurous chloride (calomel).