Achelous River V.a-ko-'lo-osX Longest river in Greece. It rises in the Pindus Mountains and flows south 140 mi (220 km) to the Ionian Sea. Hydroelectric dams harness its waters at Kastraki and Kremasta. In ancient mythology, Achelous was a protean river god, who was van¬ quished by Hercules.
Acheson Va-cho-sonN, Dean (Gooderham) (b. April 11, 1893, Mid¬ dletown, Conn., U.S.—d. Oct. 12, 1971, Sandy Spring, Md.) U.S. secre¬ tary of state (1949-53). After graduating from Yale University and Harvard Law School, he practiced law in Washington, D.C. In 1941 he joined the State Department, where he later served as undersecretary (1945-47). In 1947 he helped design the Truman Doctrine and the Mar¬ shall Plan. As secretary of state under Harry S. Truman, he promoted the formation of NATO and was a principal creator of U.S. foreign policy in the early years of the Cold War. During congressional hearings held by Sen. Joseph McCarthy, Acheson refused to fire any alleged subversives in the State Department, including Alger Hiss. He established the policies of nonrecognition of China and aid to the regime of Chiang Kai-shek in Tai¬ wan, and he supported U.S. aid to the French colonial regime in Indo-
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Acheson ► acorn I 11
china. After leaving office, he continued to advise successive presidents. His memoir Present at the Creation won a 1970 Pulitzer Prize.
Acheson, Edward Goodrich (b. March 9, 1856, Washington, Pa., U.S.—d. July 6, 1931, New York, N.Y.) U.S. inventor. He helped develop the incandescent lamp and in 1881 installed the first electric lights for Tho¬ mas Alva Edison in Italy, Belgium, and France. Attempting to produce artificial diamonds, he created instead the highly effective abrasive mate¬ rial Carborundum. He later found that the silicon vaporizes from Carbo¬ rundum at 7,500 °F (4,150 °C), leaving graphitic carbon, and patented his GRAPHiTE-making process in 1896.
Acheulean Vo-'shii-le-onX industry Stone-tool industry of the Lower Paleolithic Period characterized by bifacial stone tools with round cutting edges and typified especially by an almond-shaped (amygdaloid) flint hand ax measuring 8-10 in. (20-25 cm) in length and flaked over its entire surface. Other implements include cleavers, borers, knives, and choppers. The name derives from the site near St.-Acheul, in northern France, where such tools were first discovered. Acheulean industry was extremely long- lived (1,500,000-110,000 years ago) and is associated with both Homo erectus and archaic Homo sapiens.
Achilles \a -'ki-lez\ In Greek mythology, the bravest and strongest of the Greek warriors in the Trojan War. Because his mother dipped him into the River Styx, he was invulnerable except at the heel by which she held him. During the war against Troy Achilles took 12 nearby cities, but after a quarrel with Agamemnon he refused further service. He allowed his beloved cousin Patroclus to fight in his armor, and when Hector slew Patroclus, Achilles returned to battle, killed Hector, and dragged his body around the walls of Troy. Homer mentions Achilles’ funeral but not the circumstances of his death; the later poet Arctinus relates that Paris killed Achilles with an arrow guided by Apollo.
Achilles Painter (fl. 5th century bc) Greek vase painter, named for an amphora decorated with a painting of Achilles and Briseis attributed to him. He was active in Athens in the time of Pericles and was a contem¬ porary of Phidias. His Achilles vase (c. 450 bc) is among the finest sur¬ viving examples of red-figure pottery from the Classical period. He is also known for his lekythoi (funerary vases with coloured figures on a white background), which are regarded as the most reliable documentation of monumental Greek paintings. Over 200 extant vase paintings are attrib¬ uted to him.
Achinese X.a-cho-'nezX One of the main ethnic groups on the island of Sumatra, Indon. In the 13th century the Achinese became the first people in the archipelago to adopt Islam. After expelling the Portuguese in the 17th century, the sultanate of Acheh was dominant in northern Sumatra until it was conquered by the Dutch in 1904 (see Achinese War). Now part of the Indonesian republic, the Achinese are restive and are administered within a special district. They trace their descent through both maternal and paternal lines. Women have a high social position, and they do not wear veils. The group numbers roughly 2.1 million.
Achinese War (1873 -1904) Armed conflict between The Netherlands and the Muslim sultanate of Acheh in northern Sumatra. The Dutch con¬ sidered the sultanate to be within their northern Sumatran sphere of influ¬ ence and invaded it. Although the sultan capitulated, the Achinese people engaged the Dutch in a prolonged and costly guerrilla war, which the Dutch were able to win only by researching the area and devising a new “castle strategy” that relied on fortified bases.
acid Any substance that in water solution tastes sour, changes the colour of acid-base indicators (e.g., litmus), reacts with some metals (e.g., iron) to yield hydrogen gas, reacts with bases to form salts, and promotes cer¬ tain chemical reactions (e.g., acid catalysis). Acids contain one or more hydrogen atoms that, in solution, dissociate as positively charged hydro¬ gen ions. Inorganic, or mineral, acids include sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. Organic acids include carboxylic acids, phenols, and sulfonic acids. Broader definitions of acids cover situ¬ ations in which water is not present. See also acid-base theory.
acid and basic rocks Division of igneous rocks on the basis of their silicate mineral content, these minerals usually being the most abundant in such rocks. Rocks are described as acid, intermediate, basic, and ultraba- sic, in order of decreasing silica content, because it was earlier thought that silica is present in rock magmas in the form of silicic acid. In mod¬
em usage the terms do not refer to acidity in the chemical sense. In gen¬ eral, the gradation from acid to basic corresponds to an increase in colour (i.e., light to dark).
acid-base theory Any of several theories that give rise to alternative definitions of acids and bases. The original theory was based on Svante Arrhenius’s electrolytic theory of solutions and involved the dissociation of water into hydrogen and hydroxide ions. To explain the behaviour of a chemical, particularly if water is not present, two other theories were developed. The most widely accepted and useful is the Brpnsted-Lowry definition (1923): An acid is a chemical that tends to lose a proton (H + ), and a base is a chemical that tends to gain a proton. Another is the Lewis definition (also 1923): An acid (see electrophile) is a chemical that can accept an electron pair from a base (see nucleophile), which they share to form a covalent bond. The three theories have superficial similarities but subtle and important differences for certain applications.
acid rain Any precipitation, including snow, that contains a heavy con¬ centration of sulfuric and nitric acids. This form of pollution is a serious environmental problem in the large urban and industrial areas of North America, Europe, and Asia. Automobiles, certain industrial operations, and electric power plants that burn fossil fuels emit the gases sulfur diox¬ ide and nitrogen oxide into the atmosphere, where they combine with water vapour in clouds to form sulfuric and nitric acids. The highly acidic precipitation from these clouds may contaminate lakes and streams, dam¬ aging fish and other aquatic species; damage vegetation, including agri¬ cultural crops and trees; and corrode the outsides of buildings and other structures (historic monuments are especially vulnerable). Though usu¬ ally most severe around large urban and industrial areas, acid precipita¬ tion may also occur at great distances from the source of the pollutants.