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nonmetal
(Encyclopedia)nonmetal, chemical element possessing certain properties by which it is distinguished from a metal. In general, this distinction is drawn on the basis that a nonmetal tends to accept electrons and for...plumbing
(Encyclopedia)plumbing, piping systems inside buildings for water supply and sewage. The Romans had a highly developed plumbing system; water was brought to Rome by aqueducts and distributed to homes in lead pipes...compound
(Encyclopedia)compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound...Montreal Protocol
(Encyclopedia)Montreal Protocol, officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 197 nations are now parties to the accord. The protoc...methane
(Encyclopedia)methane mĕthˈān [key], CH4, colorless, odorless, gaseous saturated hydrocarbon; the simplest alkane. It is less dense than air, melts at −184℃, and boils at −161.4℃. It is combustible and c...mineral, dietary
(Encyclopedia)mineral, dietary, any of a group of inorganic elements that are essential to humans and animals for normal body function. In nutrition, minerals are those elements for which the body's requirement is ...magnesium
(Encyclopedia)magnesium măgnēˈzēəm, –zhəm [key], metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.3050; m.p. about 648.8℃; b.p. about 1,090℃; sp. gr. 1.738 at 20℃; valence +2. In 1808, Sir...neutrino astronomy
(Encyclopedia)neutrino astronomy, study of stars by means of their emission of neutrinos, fundamental particles that result from nuclear reactions and are emitted by stars along with light. Approximately 100 billio...tungsten
(Encyclopedia)tungsten tŭngˈstən [key] [Swed.,=heavy stone], metallic chemical element; symbol W; at. no. 74; at. wt. 183.84; m.p. about 3,410℃; b.p. 5,660℃; sp. gr. 19.3 at 20℃; valence +2, +3, +4, +5, or...stratosphere
(Encyclopedia)stratosphere strătˈəsfēr [key], second lowest layer of the earth's atmosphere. The level from which it extends outward varies with latitude; it begins c.51⁄2 mi (9 km) above the poles, c.6 or 7 ...Browse by Subject
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