Bismuth
Bismuth is an elemental metal which has an atomic number of 83, an atomic weight of 208.98 and is designated by the atomic symbol Bi. The element's original name-- weissemasse, or " white mass"--comes from its physical appearance. It is a white, brittle, crystalline material with a faint pinkish cast. It melts at 520.5°F (271.4°C) and boils at 2,847.2 ± 9°F (1,564 ± 5°C).
Many early scholars believed that metals grew inside the Earth, under the influence of the planets and stars. The least developed form of metal, they thought, was lead. The most highly developed were gold and silver. Because of this belief, scholars often confused metals with each other, thinking that all were somehow related to each other.
Bismuth was one metal about which such confusion existed. Scholars thought that tin was a more developed form of lead, and bismuth and even more highly developed form of tin. In fact, when miners found bismuth buried on top of silver veins in the Earth, they believed the bismuth was "on its way" to becoming silver. They referred to bismuth as the "roof of silver."
Some scholars argued that bismuth was a distinct metal. Georgius Agricola (1494-1555) made that point in the sixteenth century. But not until 1753 was the metal generally recognized as a distinct element. In that year, Claude-François Geoffrey completed a thorough study of bismuth and showed that it was not a form of lead, but was a metal in its own right.
Bismuth occurs in nature both as an element and in compounds. Bismite (bismuth (III) oxide; Bi 2O 3) and bismuthinite (bismuth (III) sulfide; Bi 2S 3) are the two most common ores of the element. In addition to its ores, the element is obtained as a by-product during the smelting of gold, silver, copper, and lead.
The most important uses of bismuth depend on an unusual physical property: it expands as it cools. Thus, any alloy that contains bismuth will expand and fill up a form into which it is poured as a hot liquid. One of the first industries to make use of this property was the printing industry. As early as 1450, a method was developed to make type metal from a bismuth alloy. Letters, numbers, and figures made from this alloy had sharp, clear edges.
Bismuth is also mixed with other metals to make low-melting point alloys. Wood 's metal, for example, is an alloy of bismuth (50%), cadmium (10%), tin (13%), and lead (27%) that melts at 158°F (70°C). This temperature is 392°F (200°C) below the melting point of bismuth itself. One use for low melting point alloys like Wood's metal is in automatic sprinkler systems. Heat from a fire is sufficient to melt a Wood 's metal seal and turn on the sprinkler system.
At one time, bismuth compounds were widely used in medicines, especially in the treatment of sexually transmitted diseases. Today they have been largely replaced by antibiotics. One familiar product still in wide use is bismuth subsalicylate, or Pepto-Bismol.
Other bismuth compounds are used in cosmetics, paints and dyes, and in the electronics industry. Bismuth oxychloride, for example, is a fine white powder used in face and body powders.
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