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334 I Carboniferous Period ► Cardin
Carboniferous Period Interval of geologic time 354-290 million years ago, marked by great changes in world geography. All the land- masses drew closer together as a result of tectonic plate movements. The supercontinent Gondwana occupied much of the Southern Hemisphere. By the end of the period, present-day North America, Greenland, and northern Europe were also part of Gondwana. Siberia and China (includ¬ ing Southeast Asia) remained individual continents located at high lati¬ tudes in the Northern Hemisphere. During this period, swamp forests became widespread, and enormous coal deposits formed. Plants made great advances in the complex forests, and vertebrates were undergoing extensive evolution. Amphibians became widespread and diverse, and reptiles appeared for the first time and rapidly adapted to many habitats.
carbonyl chloride See phosgene
Carborundum V.kar-bo-'ron-domV Trademark name of silicon carbide, an inorganic compound discovered in the 1880s by E.G. Acheson. Car¬ borundum has a crystal structure like that of diamond and is almost as hard. It is used as an abrasive for cutting, grinding, and polishing, as an antislip additive, and as a refractory.
carboxylic acid \,kar-bak-'si-lik\ Any organic compound with the gen¬ eral chemical formula —COOH in which a carbon (C) atom is bonded to an oxygen (O) atom by a double bond to make a carbonyl group (—C=0; see functional group) and to a hydroxyl group (—OH) by a single bond (see bonding). The fourth bond on the carbon links it to a hydrogen (H) atom (for formic acid), a methyl (—CH 3 ) group (for acetic acid), or another natural or synthetic monovalent group. Carboxylic acids occur widely in nature. In fatty acids, the fourth group is a hydrocarbon chain. In aromatic acids (see aromatic compound), it is a ring-structured hydrocarbon. In amino acids, it contains a nitrogen atom. Carboxylic acids participate in chemical reactions as acids, usually fairly weak. Many car¬ boxylic acids (acetic acid, citric acid, lactic acid) are intermediates in metabolism and can be found in natural products; others (e.g., salicylic acid) are used as solvents and to prepare many chemical compounds. Important carboxylic-acid derivatives include esters, anhydrides, amides, halides (see halogen), and salts (see soap).
carburetor \'kar-b3-,ra-t3r\ Device for supplying a spark-ignition engine with a mixture of fuel and air. Carburetors are used in small gaso¬ line engines, such as lawn mowers and chainsaws. Once an essential com¬ ponent in all gasoline engines, automobile carburetors were displaced by electronic fuel injection systems from the late 1970s through 1990. Car¬ buretors for automobile engines usually contained a storage chamber for liquid fuel, a choke, an idling jet, a main jet, an airflow restriction, and an accelerator pump. The quantity of fuel in the storage chamber was controlled by a valve actuated by a float. The choke, a butterfly valve, reduced the intake of air so that a fuel-rich charge was drawn into the cylinders when a cold engine was started. As the engine warmed up, the choke was gradually opened. Reduced pressure near the partially closed throttle valve caused the fuel to flow from the idling jet into the intake air. Further opening the throttle valve activated the main fuel jet. Then the venturi-shaped airflow restriction created reduced pressure, drawing fuel from the main jet into the airstream at a rate related to the airflow so that a nearly constant fuel-air ratio was obtained. The accelerator pump injected fuel into the inlet air when the throttle was opened suddenly. See also GASOLINE ENGINE; VENTURI TUBE.
carburizing Oldest method for surface-hardening steel, by heat or mechanical means to increase the hardness of the outer surface while leaving the core relatively soft. The combination of hard surface and soft interior withstands very high stress and fatigue, and also offers low cost and superior flexibility in manufacturing. To carburize, the steel parts are placed in a carbonaceous environment (with charcoal, coke, and carbon¬ ates, or with carbon dioxide, carbon monoxide, methane, or propane) at a high temperature for several hours. The carbon diffuses into the surface of the steel, altering the crystal structure of the metal. Gears, ball and roller bearings, and piston pins are often carburized.
Carcassonne \,kar-ka-'s6n\ ancient Carcaso City (pop., 1999: 43,950), southwestern France. Situated on the Aude River, it was occupied by the Iberians in the 5th century bc and later by Gallo-Romans. Muslims took it in ad 728. The French soldier Simon de Montfort captured it c. 1209, and in 1247 it was united with the French crown. It was burned by Edward the Black Prince in 1355 when he failed to take the citadel. A 13th- century church and cathedral survive, as do remains of medieval fortifi¬
cations, the last of which were designated a World Heritage site in 1997. The city’s main economic activities are tourism and retailing.
Carchemish Vkar-ko-.mishX Ancient city-state, western bank of the Euphrates River. Its remains lay southeast of Gaziantep, Tur., near the Syr¬ ian border. It was a city of the Mitanni kingdom in the 2nd millennium bc and later a chief Hittite city. Probably subjugated by Sea Peoples after c. 1200 bc, it gradually came under Assyrian rule, finally capitulating in 717 bc. In a battle at Carchemish in 605 bc, Babylonian king Nebucha¬ drezzar II expelled the Egyptians from Syria. The ruins were excavated in
1911-20.
carcinogen Vkar-'si-no-jonX Agent that can cause cancer. Exposure to one or more carcinogens, including certain chemicals, radiation, and cer¬ tain viruses, can initiate cancer under conditions not completely under¬ stood. Some people have a genetic tendency to develop cancer when exposed to a specific carcinogen or combination of carcinogens. Repeated local injury or irritation to a part of the body can be carcinogenic. Iden¬ tifying and eliminating carcinogens in time can reduce the incidence of cancer.
cardamom Vkar-do-moirA Spice consisting of whole or ground dried fruit, or seeds, of Elettaria cardamomum, a perennial herb of the ginger family. The flavour is warm, slightly pungent, and highly aromatic. Car¬ damom is a popular seasoning. Native to moist forests of southern India, the fruit may be collected from wild plants, but most is cultivated. The whole fruit is a green, three-sided oval capsule containing 15-20 dark, hard, angular seeds.
Cardenas, Bartolome de See Bartolome Bermejo
Cardenas \'kar-d 3 n-,as\ (del Rio), Lazaro (b. May 21, 1895, Jiquil- pan, Mex.—d. Oct. 19, 1970, Mexico City) President of Mexico (1934- 40). Of Indian descent, he joined the armed struggle against the dictatorial Victoriano Huerta, rising through the ranks of the revolutionary forces. His faction triumphed, and Cardenas was made a general in the Mexican army in 1920. In 1928 he became governor of Michoacan, and in 1934 he became president. Noted for his efforts to carry out the social and eco¬ nomic aims of the revolution, he distributed a record amount of land to peasants, made loans available to them, organized workers’ and peasants’ confederations, and nationalized the oil industry, the principal railways, and other foreign-owned industries. He opposed U.S. influence in Mexico and later supported Fidel Castro. For many Mexicans he remains the fore¬ most symbol of the political left. His son Cuauhtemoc, a prominent leader of the opposition to Mexico’s ruling party, is widely believed to have been denied victory in the 1988 presidential elections by fraud; he has since served as mayor of Mexico City. See also Indigenismo.
Cardiff City and county (pop., 2001: 305,340), capital of Wales. It is located on the Bristol Channel in southeastern Wales. The Romans built a fort there c. ad 75. The town itself was established with the arrival of the Normans in the 11th century. Its population was small into the early 19th century, but by the early 20th century Cardiff had become the largest coal-exporting port in the world. The coal trade ceased in the 1960s, but Cardiff remains the largest city and the principal commercial centre of Wales.