II.

Properties and Occurrence

At ordinary temperatures mercury is a shining, mobile liquid, silvery-white in color. Slightly volatile at room temperature, mercury becomes solid when subjected to a pressure of 7,640 atmospheres (7.7 million millibars), and this pressure is used as a standard in measuring extremely high pressures. The metal dissolves in nitric or concentrated sulfuric acid but is resistant to alkalis. When cooled to sufficiently low temperatures, mercury exhibits superconductivity (the ability to conduct electrical currents with zero resistance). Mercury has a freezing point of about -39°C (about -38°F), a boiling point of about 357°C (about 674°F), and a density of 13.55 grams per cu cm. The atomic weight of mercury is 200.59.

Mercury ranks about 67th in natural abundance among the elements in crustal rocks. It occurs in its pure form or combined with silver in small amounts but is found most often in the ore cinnabar, a mineral consisting of mercuric sulfide (HgS). The metal is obtained from cinnabar by heating the ore in air until the mercuric sulfide breaks down, yielding pure mercury metal.