plating Coating a metal or other material, such as plastic or china, with a hard, nonporous metallic surface to improve durability and beauty. Early plated goods (“old Sheffield plate”) are made by the process invented by Thomas Boulsover, and consist of a sandwich of copper between two lay¬ ers of silver. Today surfaces such as gold, silver, stainless steel, palladium, copper, and nickel are applied by dipping an object into a solution con¬ taining the desired surface material, which is deposited by chemical or electrochemical action (see electroplating). Much plating is done for deco¬ rative purposes, but still more is done to increase the durability and cor¬ rosion resistance of softer materials. Most automotive parts, appliances, housewares and flatware, hardware, plumbing and electronic equipment, wire goods, aircraft and aerospace products, and machine tools are plated for durability. See also galvanizing, ternepiate, tinplating.
platinum Metallic chemical element, one of the transition elements, chemical symbol Pt, atomic number 78. A very heavy, silvery white pre¬ cious metal, it is soft and ductile, with a high melting point (3,216 °F [1,769 °C]) and good resistance to corrosion and chemical attack. Small amounts of iridium are commonly added for a harder, stronger alloy that retains platinum’s advantages. Platinum is found usually as alloys of 80-90% purity in placer deposits or more rarely combined with arsenic or sulfur. It is indispensable in high-temperature laboratory work for elec¬ trodes, dishes, and electrical contacts that resist chemical attack even when very hot. Platinum is used in dental alloys and surgical pins; alloys typically containing 90-95% platinum are used in expensive jewelry. The international primary standard for the kilogram is made of 90% platinum, 10% iridium. Platinum has valence 2 or 4 in its compounds, which include many coordination complexes. It and some compounds are useful cata¬ lysts, particularly for hydrogenation and in catalytic converters for reduc¬ ing automobile emissions.
Plato \'pla-to\ orig. Aristocles (b. 428/427, Athens, or Aegina, Greece—d. 348/347 bc, Athens) Greek philosopher, who with his teacher Socrates and his student Aristotle laid the philosophical foundations of Western culture. His family was highly distinguished; his father claimed descent from the last king of Athens, and his mother was related to Cri- tias and Charmides, extremist leaders of the oligarchic terror of 404. Plato (whose acquired name refers to his broad forehead, and thus his range of
knowledge) must have known Socrates from boyhood. After Socrates was put to death in 401, Plato fled Athens for Megara, then spent the next 12 years in travel. Upon his return, he founded the Academy, an institute of scientific and philosophical research, where Aristotle was one of his stu¬ dents. Building on but also departing from Socrates’ thought, he devel¬ oped a profound and wide-ranging philosophical system, subsequently known as Platonism. His thought has logical, epistemological, and meta¬ physical aspects, but much of its underlying motivation is ethical. It is presented in his many dialogues, in most of which Socrates plays a lead¬ ing role. See also Neoplatonism.
Platonic solid also known as regular polyhedron Geometric solid all of whose faces are identical regular polygons and all of whose angles are equal. There are only five such polyhedrons. The cube is constructed from the square, the dodecahedron from the regular pentagon, and the tetrahedron, octahedron, and icosahedron (with 20 faces) from the equi¬ lateral triangle. They are known as the Platonic solids because of Plato’s attempt to relate each to one of the five elements that he believed formed the world.
Platonism Vpla-ta-.ni-zsmV Any philosophy that embodies some major idea of Plato’s, especially in taking abstract forms as metaphysically more basic than material things. Though there was in antiquity a tradition about Plato’s “unwritten doctrines,” Platonism then and later was based primar¬ ily on a reading of the dialogues. It is characterized by an intense con¬ cern for the quality of human life—always ethical, often religious, and sometimes political, based on a belief in unchanging and eternal realities (the Platonic Forms), independent of the changing things of the physical world perceived by the senses. This belief in absolute values rooted in an eternal world distinguishes Platonism from the philosophies of Plato’s immediate predecessors and successors and from later philosophies inspired by them. See also Neoplatonism.
platoon Principal subdivision of a military company, battery, or troop. Usually commanded by a lieutenant, it consists of 25-50 soldiers orga¬ nized into two or more squads led by noncommissioned officers. The term was first used in the 17th century to refer to a small body of musketeers who fired together in a volley alternately with another platoon. It has been used in U.S. military manuals since 1779, and throughout the 19th cen¬ tury it meant half a company. It was reintroduced into the British army in 1913. See also military unit.
Platt, Orville Hitchcock (b. July 19, 1827, Washington, Conn., U.S.——d. April 21, 1905, Washington) U.S. politician. He served in the Connecticut legislature (1861-62, 1864, 1869) and later in the U.S. Sen¬ ate (1879-1905), where he sponsored legislation concerning patents and copyrights. He was chairman of the committee on territories (1887-93), which recommended admission of six new western states. He is remem¬ bered for sponsoring the Platt Amendment (1901), which became the basis for the withdrawal of U.S. troops from Cuba following the Spanish- American War of 1898.
Platt Amendment (1901) Rider appended to a U.S. Army appropria¬ tions bill stipulating conditions for withdrawing of U.S. troops remaining in Cuba after the Spanish-American War. The amendment, which was added to the Cuban constitution of 1901, affected Cuba’s rights to nego¬ tiate treaties and permitted the U.S. to maintain its naval base at Guantanamo Bay and to intervene in Cuban affairs “for the preservation of Cuban independence.” In 1934 Pres. Franklin Roosevelt supported abro¬ gation of the amendment’s provisions except for U.S. rights to the naval base. See also Good Neighbor Policy.
Platte River River, central Nebraska, U.S. Formed by the confluence of the North Platte and South Platte rivers, it is 310 mi (500 km) long. It flows southeast into a big bend at Kearney, Neb., then empties into the Missouri River at Plattsmouth, south of Omaha. It is too shallow for navi¬ gation and is almost dry for much of the year. Its waters are used for irri¬ gation and municipal water systems.
Plattsburgh City (pop., 2000: 18,816), northeastern New York, U.S. Situated on the western shore of Lake Champlain, south of the Canadian border, Plattsburgh was founded by Zephaniah Platt in 1784. It was the scene of an important U.S. victory during the War of 1812 on Lake Champlain that saved New York from British invasion via the Hudson River valley. Incorporated as a city in 1902, it became the centre of the Lake Champlain resort area.
platyhelminth See flatworm
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1512 I platypus ► Plekhanov
platypus or duckbill Monotreme amphibious mammal ( Ornithorhyn - chus anatinus ) of lakes and streams in eastern Australia and Tasmania. About 23 in. (60 cm) long, the squat-bodied platypus has a ducklike snout, short legs, webbed feet, and a beaverlike tail. Each day it eats nearly its own weight in crustaceans, fishes, frogs, mollusks, tadpoles, and earth¬ worms; lacking teeth, it crushes its food with ridges in the bill. The female lays one to three eggs in a nest in a long twisting passage above the waterline. The young are weaned about four months after hatching. The male’s heel bears a spur connected to a poison-secreting gland. Large fishes and perhaps snakes prey on platypuses. Formerly trapped for their dense, soft fur, they are now protected by law.