Named for the changeable messenger of the Greek and Roman gods, mercury is one of the world’s strangest metals, not least because it is molten at room temperature, and is only solid at temperatures of -38°Fahrenheit or below. Only four other metallic elements – specifically, francium, gallium, caesium, and rubidium – are also liquid under these conditions, but they are much rarer and seldom encountered by most people in their various applications.
Mercury is a heavy liquid at the temperatures when it is usually seen, dense enough so that small objects placed on it – even other metals – will tend to float rather than sink. This strange metal boils at a relatively low temperature, as well, giving it a very narrow band of temperatures at which it is liquid compared to iron, gold, silver, and so on. These unusual properties are due to all of the subshells of its microscopic structure being filled with electrons. This also results in the fact that mercury can form an amalgam with almost every other common metal except iron.
Iron resists amalgamation with mercury totally, and for this reason, iron flasks and other iron containers have typically been employed to hold the substance. Mercury is frequently amalgamated with other metals for various applications, especially tooth fillings. Ironically, given its dangerous and sometime deadly toxicity, mercury has been widely used as an internally-ingested medicine through the centuries, even having been used as a teething powder for infants in the early twentieth century.
Two of mercury’s most intriguing uses both involve its tendency to amalgamate with other metals – in gold mining and in wartime sabotage during World War II. Gold mining through hydraulic means is assisted by using mercury, although this is actually a fairly dangerous procedure, since it puts the miners at risk from their close exposure to the mercury.
If a metal pan or plate is coated with mercury, then as water containing gold particles washes over it, the gold will tend to become trapped in the mercury, through a combination of the mercury’s surface tension (which is considerable, since it is a very thick liquid) and the fact that the mercury immediately begins to amalgamate with the gold. This gives the mercury a strong ‘grip’ on the gold, trapping minute flecks that would otherwise escape. The gold must be retrieved quickly, before it becomes entirely amalgamated with the mercury. This method is used mostly for illegal mining currently, but in the past, it was very common, resulting in the major gold mining areas of the United States and Canada being contaminated with tens of thousands of tons of mercury.
The other interesting use of mercury’s amalgamating tendencies comes from the fact that when it amalgamates with aluminum, mercury also tends to destroy this metal. Since combat aircraft (and, indeed, all aircraft) have used aluminum in their construction for a long time, the Allies in World War II employed saboteurs who would paint a thin layer of mercury onto crucial parts of German aircraft, causing rapid corrosion and weakening of their structure. It is currently illegal to bring mercury onto aircraft in liquid form, because of the risk of damage to the airplane’s structure if the metal escapes.
Mercury’s main applications today include mercury-vapor lighting and some neon lighting, as well as various chemical processing techniques designed to produce industrial chemicals. The biggest mercury market is the European Union, where use of compact fluorescent bulbs has been mandated by law, encouraging nations across the world to reopen their cinnabar mines, since mercury can be extracted from cinnabar.
