Mercury (Element)

Mercury's atomic number is 80 and its atomic weight is 200.59. It has a boiling point of 674°F (356.7°C) and a melting point of -38°F (-38.89°C). Mercury is stable (it does not react) in air and water, as well as in acids and alkalis. The surface tension of mercury is six times higher than that of water. Because of this, even when mercury is in liquid form, it does not wet the surfaces it contacts.

Like some other metals, mercury exhibits unusual behavior at extremely low temperatures. In 1911, Dutch physicist Heike Kamerlingh Onnes discovered the phenomenon of superconductivity by freezing mercury to only a few degrees above absolute zero. At that temperature, mercury loses all of its natural resistance to the flow of electricity and becomes superconductive.

Mercury is uniquely suited for measuring temperatures. When heated or cooled, mercury expands or contracts at a rate that is more constant than most other substances. Also, it has a wide range of temperatures between its boiling and freezing points. In 1714, German-Dutch physicist Gabriel Daniel Fahrenheit developed the mercury thermometer. (Previous fluid thermometers had used alcohol or alcohol-water mixtures.) With mercury as the measuring fluid, temperatures could be recorded well above water's boiling point and below its freezing point. Using mercury also allowed the degrees to be marked more accurately in finer subdivisions.