indicators, acid-base, organic compounds that, in aqueous solution, exhibit color changes indicative of the acidity or basicity of the solution. Common indicators include p-nitrophenol, which is colorless from pH 1 to 5 and yellow from pH 5 to 9; methyl orange, yellow in basic and neutral solutions and reddish below pH 3.7; phenolphthalein, colorless in acid and neutral solutions, pink at about pH 8.5, and purplish at pH 10; and litmus. Most indicators are also used in large amounts for dyeing; small quantities are nonetheless invaluable for use as indicators in chemical laboratories.

base line: see geodesy.

base: see acids and bases.

acid-base indicators: see indicators, acid-base.

Wright-Patterson Air Force Base, U.S. military installation, 8,023 acres (3,247 hectares), W Ohio, NE of Dayton; est. 1917. One of the largest airport installations in the world, it is the air force's main research and development base, and the headquarters of the Air Force Logistics Command (national center for defense activities). The Aerospace Medical Laboratory and the Air Force Museum are also on the base.

Vandenberg Air Force Base, U.S. military installation, 3,456 acres (1,399 hectares), SW Calif., near Lompoc; chief Pacific coast launch site for military satellites. Commercial satellites are launched from the base as well, and it is also a site for test-firing intercontinental ballistic missiles.

Offutt Air Force Base, U.S. military installation, 1,907 acres (772 hectares), E Neb., S of Omaha; est. 1896 as Fort Crook, an army base. Converted to an airbase in the early 1900s and renamed in 1924, it is the headquarters of the Strategic Command, the successor to the Strategic Air Command. The Nebraska Museum of Aerospace History is on the base.

Malmstrom Air Force Base, U.S. military installation, 3,573 acres (1,446 hectares), W central Mont., E of Great Falls; est. 1942. During World War II, it was the takeoff point for Soviet-bound lend-lease materiel; after the war it was a training base for crews in the Berlin Airlift. The now-dissolved Strategic Air Command (SAC) assumed command in 1954; SAC's first Minuteman missile wing was established there in 1961. The missile complex adjoining the base is one of the largest in the world.

Langley Air Force Base, U.S. military installation, 3,195 acres (1,293 hectares), SE Va., N of Hampton; est. 1917 and named for aviation pioneer Samuel P. Langley. The facility, the oldest continuously active air force base in the United States, is the headquarters of the Air Combat Command and has air-defense missile units. NASA's Langley Research Center is adjacent.

Lackland Air Force Base, U.S. military installation, c.6,835 acres (2,766 hectares), S Tex., W of San Antonio; est. 1941. It is a major air force training center.

Edwards Air Force Base, U.S. military installation, 301,000 acres (121,805 hectares), S Calif., NE of Lancaster; est. 1933. It is one of the largest air force bases in the United States and has the world's longest runway. The base houses the Air Force Flight Test Center, which researches and develops aerospace weapons and rocket-propulsion systems, and the National Aeronautical and Space Administration's Flight Research Center. The base is also the proving ground for military aircraft. It has been the landing point for a number of space shuttle missions; on Sept. 5, 1983, the Challenger made the first nighttime landing of a spacecraft there.

Andrews Air Force Base, U.S. military installation, 4,279 acres (1,732 hectares), central Md., est. 1943. It is the chief military airport of Washington, D.C., as well as the headquarters for the air force's high-priority airlift command.

Collection of data or information organized for rapid search and retrieval, especially by a computer. Databases are structured to facilitate storage, retrieval, modification, and deletion of data in conjunction with various data-processing operations. A database consists of a file or set of files that can be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage. Users retrieve database information primarily through queries. Using keywords and sorting commands, users can rapidly search, rearrange, group, and select the field in many records to retrieve or create reports on particular aggregates of data according to the rules of the database management system being used.

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In chemistry, any substance that in water solution is slippery to the touch, tastes bitter, changes the colour of acid-base indicators (e.g., litmus paper), reacts with acids to form salts, and promotes certain chemical reactions (e.g., base catalysis). Examples of bases are the hydroxides of the alkali metals and alkaline earth metals (sodium, calcium, etc.; see caustic soda) and the water solutions of ammonia or its derivatives (amines). Such substances produce hydroxide ions (OH⁻) in water solutions. Broader definitions of bases cover situations in which water is not present. Seealso acid-base theory; alkali; nucleophile.

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