Potala Palace Vpo-to-loV Religious and administrative complex, near Lhasa, Tibet, China. It covers 5 sq mi (13 sq km) atop a hill 425 ft (130 m) above the Lhasa River valley. Potrang Karpo (the White Palace, com¬ pleted 1648) once served as the seat of the Tibetan government and the main residence of the Daai Lama; from the mid-18th century it was used as a winter palace. Potrang Marpo (the Red Palace, 1694) houses several chapels, sacred statues, and the tombs of eight Dalai Lamas; it remains a major pilgrimage site for Tibetan Buddhists. The complex, which has a total of 1,000 rooms, was declared a world heritage site in 1994.
potash \'pat-,ash\ Name used for various inorganic compounds of potas¬ sium, chiefly the carbonate (K 2 C0 3 ), a white crystalline material formerly obtained from wood ashes. They are used to make special types of glass, potassium silicate (a dehydrating agent), pigments, printing inks, and soft soaps; for washing raw wool; and as a lab reagent and general-purpose food additive. Potassium hydroxide is frequently called caustic potash, and in the fertilizer industry, potassium oxide is called potash.
potash mica See muscovite
potassium Chemical element, one of the alkali metals, chemical symbol K, atomic number 19. It is a soft, silvery white metal, not found free in nature and rarely used as the metal (except as a chemical reagent) because of its extreme reactivity. Potassium is essential for life and is present in all soils. Potassium ions (K + ) and sodium ions act at cell membranes in electrochemical impulse transmission and in transport. Potassium in com¬ pounds has valence 1. The chloride is used as a fertilizer and a raw mate¬ rial for producing other compounds, and the hydroxide for making liquid soaps and detergents and in preparing various salts. The iodide is added to table salt to protect against iodine deficiency. The nitrate is also called saltpetre, and the carbonate is called potash.
potassium-argon dating Method for determining the age of igne¬ ous rocks based on the amount of argon-40 in the rock. Radioactive potassium-40 decays to argon-40 with a half-life of about 1.3 billion years, making this method useful for dating rocks that are billions of years old. A more sophisticated method, called argon-argon dating, provides a more accurate estimate of the original potassium-40 content by means of the ratio of argon-40 to argon-39 in the rock, thus yielding a more accurate age determination. See also dating.
potato Herbaceous annual (Solatium One of the world’s main food crops, the potato differs from other food crops in that the edible portion is a tuber. Highly digestible, potatoes are prepared for eating in many ways and are a major source of starch as well as amino acids, protein, vitamin C, and B vitamins. The stem grows 20^10 in. (50-100 cm) tall, sprouting spi¬ rally arranged compound leaves.
Underground, stems extend as sto¬ lons, the ends of which enlarge into 1-20 tubers of variable shape and size. The tubers have spirally arranged buds (eyes) that may remain dormant after the tuber is fully grown for up to 10 weeks or more; they grow into plants identical to the par¬
ent plant. A native of the Andes, the potato (also known as the common potato, white potato, or Irish potato) was carried by Spaniards into Europe during the 16th century. A century later, it had become the major food crop in Ireland; disastrous damage to the crop by a fungal blight caused the Irish potato famine in the mid-1800s. See also sweet potato.
potato beetle Destructive species (Lema trilineata) of leaf beetle (fam¬ ily Chrysomelidae). Less than 0.25 in. (6 mm) long, it is yellow and has three black stripes on its wing covers. Eggs are laid on the underside of a potato leaf, on which both larvae and adults feed. The larvae are cam¬ ouflaged by excrement the beetles pile on their back. Two generations are produced each year; the second overwinters in the ground in the pupal stage. See also Colorado potato beetle.
potato bug See Colorado potato beetle
Potemkin \p9-'tyem-kin\, Grigory (Aleksandrovich) (b. Sept. 24, 1739, Chizovo, Russia—d. Oct.
16, 1791, near Ia§i, Moldavia) Rus¬ sian army officer. He entered the horseguards (1755) and helped bring Catherine II to power (1762). He fought with distinction in the Russo- Turkish War (1768-74), then became Catherine’s lover (1774-76) and was made governor-general of “New Russia” (southern Ukraine). In 1783 she made him prince of Tauris. As a field marshal from 1784, he intro¬ duced reforms in the army, built the harbour of Sevastopol, and con¬ structed a fleet in the Black Sea. He attempted to colonize the Ukrainian steppes, but he underestimated the costs, leaving many projects half- complete; his successful disguising of the weak points of his adminis¬ tration led to the claim that he erected mere facades—“Potemkin villages”—to show Catherine on her tour of the region. He commanded the Russian army in the second Russo- Turkish War.
potential, electric See electric potential
potential energy Energy stored by an object by virtue of its position. For example, an object raised above the ground acquires potential energy equal to the work done against the force of gravity; the energy is released as kinetic energy when it falls back to the ground. Similarly, a stretched spring has stored potential energy that is released when the spring is returned to its unstretched state. Other forms of potential energy include electrical potential energy, chemical energy, and nuclear energy.
Potenza \po-'tent-sa\ ancient Potentia City (pop., 2001 prelim.: 69,295), capital of the Basilicata region, southern Italy. Located at 2,684 ft (819 m) above sea level in the Apennines, the Roman city Potentia was founded in the 2nd century bc and became an important road junction and flourishing community. In medieval times it had a succession of feudal overlords. In 1860 it was the first town in southern Italy to expel the Bourbon rulers of the Kingdom of the Two Sicilies. The town has been rebuilt several times after earthquake damage. It is an agricultural centre and ships fruit and vegetables.
potestas patria See patria potestas
potlatch Ceremonial distribution of property and gifts practiced among the American Indians of the Northwest Pacific coast, particularly the Kwakiutl. A potlatch is given by an heir or successor to assert and vali¬ date his newly assumed social position. Ceremonial formalities are observed in inviting guests, in speech making, and in distributing goods according to the social rank of the recipients. Great feasts and generous hospitality accompany the potlatch. The ceremony has been much stud¬ ied by anthropologists for the light it sheds on the nature of property, wealth, prestige, and social status. See also gift exchange.
Potok \'po-tak\, Chaim orig. Herman Harold Potok (b. Feb. 17, 1929, New York, N.Y., U.S.—d. July 23, 2002, Merion, Pa.) U.S. rabbi and novelist. The son of Polish immigrants, he was reared in an Ortho-
tuberosum ) in the nightshade family.
Potato (Solanum tuberosum).
GRANT HEILMAN
Grigory Potemkin, engraving by James Walker, 1789, after a portrait by Johann Baptist Lampi.
REPRODUCED BY COURTESY OF THE TRUSTEES OF THE BRITISH MUSEUM; PHOTOGRAPH, J.R. FREEMAN & CO., LTD.
© 2006 Encyclopaedia Britannica, Inc.
1536 I Potomac River ► Pound
dox Jewish home and was ordained a Conservative rabbi. He taught until he began a career as an editor and writer of scholarly and popular articles and reviews in the 1960s. His novels, which have introduced to Ameri¬ can fiction the spiritual and cultural life of Orthodox Jews, include The Chosen (1967; film, 1981), The Promise (1969), and My Name Is Asher Lev (1972). Three connected novellas, Old Men at Midnight, appeared in 2001. Notable among Potok’s nonfiction writings are Wanderings: Chaim Potok’s History of the Jews (1978), in which the author combines impres¬ sive scholarship with dramatic narrative, and The Gates of November (1996), a chronicle of a Soviet Jewish family and the rise and fall of the Soviet Union.