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Arsenic
by Jonathan Buhalis

History

realgar and orpiment, arsenic minerals, A. Jonathan BuhalisArsenic has a reputation best embodied in its nickname, "the king of poisons" or alternatively "the poison of kings". Arsenic is indeed poisonous, but its compounds have been used since antiquity. Reddish realgar (right, with orpiment), which is an arsenic sulfide, was recommended by Hippocrates for treating ulcers. Yellow orpiment, another sulfide of arsenic, was used in eastern Asia as a depilatory. In fact, medical uses of arsenic are legion and continue through the Middle Ages and Victorian England to the present day.

Arsenic hardens bronze, a use employed in tools and weapons from ancient Iran and elsewhere. Since arsenic occurs naturally in copper ore (bronze is copper plus tin), the arsenic may have been a fortuitous addition, but it most likely arises from arsenic ore deliberately added during smelting. Arsenic bronze is found in northern Italy, northwest China, and west central South America among other places.

Arsenic became one of the tools of the alchemists. At some time during the Middle Ages, the element was first isolated. Albertus Magnus was possibly the first in the 13th century. Certainly, the famous alchemists Paracelsus describes elemental arsenic three centuries later. A Chinese encyclopedia from about 1590 details the uses of arsenic in medicine and poisoning.

By the Victorian years of the 19th century, arsenic was readily available in the form of arsenic trioxide (ArO3, called white arsenic). Women ate this with vinegar to whiten their skins. Merck & Company's 1899 pharmacology includes a long list of uses for potassium arsenic and other such compounds to be taken internally to treat "malarial fever, skin disease, chorea, neuralgia, gastralgia, uterine disorders" and so on.

In the century just past, by far the largest use of arsenic in the United States was in manufacturing pressure-treated wood. Chromated copper arsenate (CCA) was invented in 1933. The combination of elements protects wood against both fungus and insects, and it also gives the wood a characteristic green tint. CCA is still used world-wide but was voluntarily discontinued by American manufacturers in 2003 because of arsenic's toxicity. (Australia and the EU quickly followed.) Arsenic joins lead and mercury as elements that were once much more widespread, at least in the developed world, but whose use is tapering off for environmental reasons.

Mining and Production

Arsenic is reasonably abundant. It occurs naturally in ores such as realgar. Commercial arsenic, however, is produced as a byproduct of smelting copper, lead, and gold. It is normally supplied in the form of arsenic trioxide. 46,000 tons of ArO3 were produced in 2014. China was the largest producer at 54%, followed by Chile (22%) and Morocco (17%).

Properties and Uses

Arsenic is a metalloid and in some forms a semiconductor. Like carbon and phosphorus in its chemical vicinity, it takes a few different forms. Gray arsenic is the most common and stable metalloid. Black arsenic is a hard brittle solid. Yellow arsenic is soft and pliable. When heated sufficiently (about 600°C), arsenic vaporizes rather than melts.

Arsenic is fairly reactive. It will combine with most of the metals. It will also combine with the more reactive elements to its right on the periodic table, particularly oxygen and sulfur.

The element is still used as a alloy, notably with lead. Arsenic is added to the terminals and plates in a lead-acid battery to strengthen them. Lead shot contains arsenic. Arsenic is also added to bronze and brass.

Feast of the Gods, by Giovanni Bellini; A. Jonathan BuhalisIn past times, the minerals realgar and orpiment were used as pigments (as in the reds and oranges of Giovanni's Feast of the Gods). The copper-arsenic compound known as Paris Green (sometimes Emerald Green) is a much more recent pigment. All three are poisonous.

A recent and high-tech application of the element is in gallium arsenide. Gallium arsenide is a semiconductor capable of higher speed electronics than traditional silicon, although at a higher cost. Related semiconductors include indium arsenide and gallium-indium-arsenide. Arsenic is also a trace impurity added to (doping) silicon to adjust the degree of semiconductor behavior.

Environmental and Poison

arsenic trioxide tablets, A. Jonathan BuhalisArsenic is a lethal poison, although the symptoms leading to death are very nonspecific. Chemist James Marsh developed a test for arsenic inthe body in 1836. For centuries prior to this discovery, however, arsenic was a favorite choice of poisoners because the chance of discovery was very low.

Roman Emperor Nero is known to have poisoned Britannicus, son of former Emperor Claudius, in 55 AD. Arsenic poisoning has not always been deliberate, however. King George III of England suffered episodes of disabling illness. In 2004, a sample of his hair was discovered to contain arsenic, quite possibly from medicines he was given.

In France, arsenic was nicknamed "inheritance powder" (poudre de succession) because of how often it brought about a transfer of title. Several poisonings are documented from the 17th century. France is where, in 1840, Marsh's test first conclusively led to a murder conviction, thus ending a long tradition. Arsenic is also a favorite poison in literature. Mystery writer Agatha Christie, a former pharmacy worker, incorporated arsenic into many of her novels. The title of the 1941 play, "Arsenic and Old Lace", speaks for itself.

Moving away from human subjects, arsenic has been used as a pesticide. The Chinese used it to kill insects. Victorians used it as a rat poison. Paris Green is an insecticide as well as a pigment, used as such as early as 1867. Lead arsenate, a double health threat, was widely sprayed on trees in the early 20th century, as was a substitute, calcium arsenate, during World War I. CCA was and is injected into wood precisely because it kills fungus and insects.

All of this history of arsenic poisoning makes clear that the element can be an environmental threat. In many places, running water passes over arsenic minerals and is then incorporated into drinking water. The health risk in this context is generally cancer, rather than overt poisoning. Pressure-treated wood is another danger in the cases where it is burned as firewood, for the fumes are quite toxic.

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Content by Jonathan Buhalis
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