bismuth ► bivalve I 225
Annexed by Germany in 1884, it was named for Otto von Bismarck. Occu¬ pied by Australia in 1914, it was made a mandated territory of Australia in 1920. The group became part of the UN Trust Territory of New Guinea after World War 11 and part of Papua New Guinea when it attained inde¬ pendence in 1975.
bismuth \'biz-math \ Semimetallic to metallic chemical element, chemi¬ cal symbol Bi, atomic number 83. Hard, brittle, and lustrous, it has a dis¬ tinctive gray-white colour with a reddish tinge. It is often found free in nature and also occurs in compounds and in mixed ores. Bismuth alloys are used (because of their low melting points) in making metal castings, special solders, automatic sprinkler heads, fuses, and many fire-detection devices. Bismuth phosphomolybdate is a catalyst in the production of acrylonitrile, an important raw material for fibres and plastics. Salts of bismuth are used in making soothing agents for digestive disorders (espe¬ cially bismuth subsalicylate), in treating skin infections and injuries, and in lipstick, nail polish, and eye shadow, to which they impart a pearles- cent quality.
bison Vbl-s 3 n, 'bl-z 3 n\ Either species (genus Bison ) of oxlike bovid with a convex forehead and a pronounced shoulder hump. Its dark brown, coarse hair is especially long on the head, which is held low, and on the neck and shoulders. Both sexes bear heavy, curved horns. A mature bull stands about 6.5 ft (2 m) at the shoul¬ der and weighs more than 1,980 lb (900 kg). Bison live in herds. The American bison ( B. bison), com¬ monly called buffalo, was abundant over most of North America when Europeans arrived. Uncontrolled hunting drove it nearly to extinction by 1900, but it has since recovered. The European bison ( B. bonasus ) is similar and survives only in a few managed herds.
Bissau \bis-'au\ Seaport (pop., 1999 est.: 274,000), capital of Guinea- Bissau. Lying on an estuary of the Geba River where it flows into the Atlantic Ocean, the port originated in 1687 as a Portuguese fortified post. In 1941 it replaced Bolama as the country’s capital and has since devel¬ oped as an excellent roadstead for large vessels.
bit in full binary digit In communication and information theory, a unit of information equivalent to the result of a choice between only two possible alternatives, such as 1 and 0 in the binary code generally used in digital computers. It is also applied to a unit of memory corresponding to the ability to store the result of a choice between two alternatives. A byte consists of a string of eight consecutive bits and makes up the basic infor¬ mation processing unit of a computer. Because a byte includes only an amount of information equivalent to one letter or one symbol (e.g., a comma), the processing and storage capacities of computer hardware are usually given in kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and even gigabytes (about 1 billion bytes) and terabytes (1 trillion bytes).
bit-map Method by which a display space (such as a graphics image file) is defined, including the colour of each of its pixels (or bits). In effect, a bit-map is an array of binary data representing the values of pixels in an image or display. A GIF is an example of a graphics image file that has a bit-map. When the GIF is displayed on a computer monitor, the com¬ puter reads the bit-map to determine which colours to use to “paint” the screen. In a bit-mapped font, each character is defined as a pattern of dots in a bit-map.
Bithynia \ba-'thin-e-a\ Ancient country, northwestern Anatolia. Bounded by the Sea of Marmara, the Bosporus, and the Black Sea, it was settled by Thracians in the late 2nd millennium bc. They never submitted to Alexander the Great, and by the 3rd century bc a powerful Hellenistic kingship had been established in the area. There followed a century of inept leadership and rapid decline. Bithynia’s last king, Nicomedes IV, bequeathed his kingdom to the Romans in 74 bc.
bittern Any of 12 species of solitary marsh birds (family Ardeidae), related to herons but having a shorter neck and a stouter body. Most bit¬ terns bear a camouflage pattern (streaks of variegated brown and buff) that enables them to hide by standing upright with bill pointed upward, imitating the reeds and grasses of their habitat. They feed on fish, frogs,
(genus Bison ) of oxlike bovid with
American bison, or plains buffalo (Bison bison).
ALAN G. NELSON/ROOT RESOURCES
crayfish, and other small swamp and marsh animals, which they spear with their sharp-pointed bills. Bitterns are found almost worldwide. The largest species grow to 30 in. (75 cm), the smallest to about 12-16 in. (30^10 cm).
Bitterroot Range Segment of the northern Rocky Mountains, U.S. Extending north-south 300 mi (480 km) along the Idaho-Montana border, its peaks average about 9,000 ft (2,700 m); Idaho’s Scott Peak is the high¬ est, at 11,393 ft (3,473 m). Owing to the mountains’ inaccessibility from the east, the Lewis and Clark Expedition (1805) had to travel north more than 100 mi (160 km) to find a route through the range. Bitterroot National Forest extends across the centre of the range.
bittersweet Any of several vines with colourful fruit. The genus Celas- trus (family Celastraceae) includes American bittersweet, or staff vine (C. scandens ), and Oriental bittersweet (C. orbiculatus), woody vines grown as ornamentals. Oriental bittersweet is a more vigorous climber than the American species. Both types climb by twining around supports. Another bittersweet, Solanum dulcamara, belongs to the nightshade family.
bitumen \ba-'tyu-man\ Mixture of tarlike hydrocarbons derived from petroleum. Black or brown, it varies from viscous to solid; the solid form is usually called asphalt. Bitumen occurs in nearly every part of the world and in nearly the whole range of geologic strata. The term may also refer to synthetic hydrocarbon compounds.
bituminous Vba-'tyii-ma-nasN coal or soft coal Most abundant form of coal. It is dark brown to black and has a relatively high heat value. Widely abundant and with the broadest range of commercial uses, it has long been used for steam generation in electric power plants and indus¬ trial boiler plants. Certain varieties are also used to make coke, a hard substance of almost pure carbon that is important for smelting iron ore. One major problem is that burning large quantities of bituminous coal that has a medium to high sulfur content contributes to air pollution and produces acid rain. See also subbituminous coal.
bituminous sand See tar sand
bivalve Any member of the mollusk class Bivalvia, or Pelecypoda, char¬ acterized by having a two-halved (valved) shell. Clams, cockles, mussels, oysters, scallops, and shipworms are bivalves. Most are completely enclosed by the shell, the two valves of which are joined by an elastic ligament,
posterior
adductor
muscle
anterior adductor digestive gland muscle
foot
ganglion
intestine
mantle
excurrent
siphon
incurrent
siphon
Internal structure of a clam. A ligament hinges the shell's two halves (valves) open, and the beating motion of cilia on the gills causes water to enter through the incur¬ rent siphon. As water moves over the gills, oxygen diffuses into the blood, and food particles become trapped in mucus and are moved to the mouth. A pair of adductor muscles can hold the shell tightly closed. A fold of tissue (mantle) encloses the body's organs and releases the material that forms the shell. A large muscular foot allows the clam to creep and burrow. The circulatory system consists of a heart and blood vessels, and kidneys remove wastes from the blood. Deoxygenated blood and wastes are removed in the water that exits through the excurrent siphon.
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226 I Biwa ► black-figure pottery
and by two sheets of tissue called the mantle. Bivalves have no head. They feed on phytoplankton by pumping water across the gills and trapping food particles that are then moved to the mouth. Bivalves are found in most parts of the ocean from the intertidal zone to abyssal depths.