Mercury, (HG) is a most unusual metal. It is the only common metal that occurs as a liquid at room temperature. This bright silvery, dense liquid- formerly known as quicksilver- has long held the fascination of people. Children sometimes play with the mercury from a broken thermometer, often with tragic results. Mercury vapor is hazardous. An open container or a few droplets spilled on the floor can put enough mercury vapor into the air to exceed the established maximum safety level by a factor of 200. Mercury presents a hazard to those who work with it. Dentists use it to make analgams for filling teeth. Laboratory workers use mercury and it's compounds in a variety of ways. Farmers use seeds treated with compounds of mercury. Since mercury is a cumulative poison, chronic poisoning is a real threat to those continually exposed. It takes the body about 70 days to rid itself of half a given dose. Fortunately, there are antidotes available for mercury poisoning. British scientists, searching for an antidote for the arsenic-containing war gas Lewisite, came up with a compound effective for heavy metal poisoning as well. The compound, a derivative of glycerol came to be known a BAL (British Anti-Lewisite). BAL acts by chelating the metal ion. Thus tied up, the mercury cannot attack vital enzymes. The symptoms of mercury poisoning may not show up for several weeks. Bye the time the symptoms (loss of equilibrium, sight, feeling, hearing) are recognizable, extensive damage has already been done to the brain and the nervous system. Such damage is largely irreversible. The BAL antidote is effective only when a person knows that he or she has been poisoned and seeks treatment right away. Metallic mercury seems not to be very toxic when ingested. Most of it passes through the system unchanged. Indeed, there are numerous reports of mercury being given orally in the eighteenth and nineteenth centuries as a remedy for obstruction of the bowels.