Characteristics | Found | Uses

Mercury, a metal and one of the few elements that is liquid at room temperature, is the densest element in Group IIB. Other members of the group are zinc (Zn) and cadmium (Cd).

Quicksilver, as it is often called, is about as abundant in the earth's crust as silver.

Its principal ore is cinnabar or natural vermilion, the common names of mercury(II) sulfide, HgS. Since cinnabar is an obvious red mineral that occurs in concentrated deposits, it is one of the oldest elements known.

Prehistoric people mixed powdered vermilion with a little water and used it as a pigment to draw on the walls of caves. Ancient peoples also found that heating the red rock in a fire gave liquid quicksilver,

HgS(s) + O2(g) Hg(liq) + SO2(g)

and this is still the way to release the element from its ore. Samples of the metal have been found in graves of the 16th century BC and Aristotle, in the 4th century BC, was the first to call it "liquid silver".

The ability of mercury to form amalgams (alloys) with other metals such as gold and silver has been known for centuries. If a liquid amalgam of gold and mercury is rubbed onto a copper object, the object becomes covered with gold. Since mercury is volatile, heating drives away the mercury and leaves a gold coating. The same idea has been used to extract gold from natural sources.

Mixing gold-bearing soil with mercury gives a liquid amalgam that is easily separated from the dirt. Heating this amalgam then drives off the mercury and leaves gold behind. It was for this reason that, in the 16th century, the Spanish fleet carried casks of mercury to the New World and returned with silver and gold. It is a method still used in places such as Brazil, and is the reason that its rivers are polluted with mercury.

There may be as many as 3000 uses for the metal in our modern society. Dentists use an amalgam with silver and tin to fill cavities in teeth; a drop of mercury goes into every fluorescent light; and the liquid metal is used in thermometers and barometers, in gauges and gas-handling apparatus, and in electrical equipment of many kinds.

Compounds of mercury also find many uses. Mercury oxide, for example, is used in batteries as an oxidizing agent. Many mercury compounds are antiseptics, inhibiting the growth of bacteria and mildew.

But mercury and its salts have a darker side, and none has expressed it better than Alfred Stock, a German chemist. Stock said that "mercury is a strong poison, particularly dangerous because of its liquid form and noticeable volatility at room temperature . . . . [I] found from personal experience . . . that a protracted stay in an atmosphere charged with only 1/100 of the amount of mercury required for its saturation [can] induce chronic mercury poisoning. [It] reveals itself [first] as an affection of the nerves, causing headaches, numbness, mental lassitude, depression, and the loss of memory."

A well-known example of mercury poisoning is "hatter's disease". Years ago felt was made by dipping furs into vats containing mercury(II) nitrate. Workers in these ill-ventilated shops breathed mercury-laden fumes and developed tremors, lost teeth, had difficulty in walking, and lost mental ability. Legend has it that the Mad Hatter in Lewis Carroll's Alice in Wonderland was patterned after a victim of this affliction.

Finally, a verse found in the "Discovery of the Elements" by M.E. Weeks and H. M. Leicester (Journal of Chemical Education, 7th edition, 1968, page 46) illustrates the properties of mercury. "It is a fluid but does not moisten, and runs about, though it has no feet."