Mercury

Discovered by: Mercury was found in Egyptian tombs that date from 1500 BC.

What is it? A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure.

Why is it important? Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, although concerns about the element's toxicity have led the phase out of such mercury-containing instruments.