What is mercury?
Mercury (Hg) is the only pure metal that is liquid at room temperature.
Mercury has a low boiling point, which means that considerable evaporation takes place at room temperature. It also means that mercury in vapour form can spread over thousands of kilometres from the discharge source and thus low concentrations of mercury vapour are present in the atmosphere.
As a result of being the only liquid metal and many other technically advantageous properties, mercury has been used by mankind for an enormous variety of purposes for thousands of years.