Mercury has several unique and useful properties that have led to widespread use. It is the only metal that, in its pure form, is a liquid at room temperature. Liquid mercury is volatile, meaning that it easily evaporates to form a poisonous vapor. Mercury conducts electricity and expands at a constant rate in response to changes in pressure or temperature. Electrical switches, barometers and thermometers take advantage of these properties. In its vapor state, mercury can combine with other gases to form more complex molecules that emit light when charged with electricity, hence the use of mercury in fluorescent and neon lights.
Mercury combines easily with most metals to form malleable alloys, such as dental filling amalgam. This particular property of attaching to other metals, together with the ease of separating and distilling the amalgams, led to mercury’s widespread use in gold mining. Mercury continues to be widely used in household products, as well as commercial, medical and industrial applications.