Mercury has a number of unique and fascinating properties. It is the only metal that, in its pure form, is a liquid at room temperature. Liquid mercury is volatile, meaning that it evaporates easily to form a poisonous vapour. 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 vapour 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
