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pitchblende

(Encyclopedia)pitchblende pĭchˈblĕndˌ [key], dark, lustrous, heavy mineral, a source of radium and uranium. Largely natural uranium oxides, triuranium octaoxide (U3O8) and uranium dioxide (UO2), it usually cont...

hydrogenation

(Encyclopedia)hydrogenation hīdrôjˈənāˌshən, hīˌdrəjənāˈshən [key], chemical reaction of a substance with molecular hydrogen, usually in the presence of a catalyst. A common hydrogenation is the harde...

phosgene

(Encyclopedia)phosgene fŏsˈjēn [key], colorless poison gas, first used during World War I by the Germans (1915). When dispersed in air, the gas has the odor of new-mowed hay. The gas is highly toxic; when inhale...

Avogadro's number

(Encyclopedia)Avogadro's number ävōgäˈdrō [key] [for Amedeo Avogadro], number of particles contained in one mole of any substance; it is equal to 602,252,000,000,000,000,000,000, or in scientific notation, 6.0...

tree

(Encyclopedia)CE5 Types of trees tree, perennial woody plant with a single main stem (the trunk, or bole) from which branches and twigs extend to form a characteristic crown of foliage. In general, a tree diffe...

vapor pressure

(Encyclopedia)vapor pressure, pressure exerted by a vapor that is in equilibrium with its liquid. A liquid standing in a sealed beaker is actually a dynamic system: some molecules of the liquid are evaporating to f...

carboloy

(Encyclopedia)carboloy kärˈbəloi [key] [portmanteau word from carbon and alloy], an alloy containing cobalt, tungsten, and carbon. This alloy is extremely hard, harder than steel; it is used to cut steel, porcel...

cigar and cigarette

(Encyclopedia)cigar and cigarette, tubular rolls of tobacco designed for smoking. Cigars consist of filler leaves held together by binder leaves and covered with a wrapper leaf, which is rolled spirally around the ...

mass extinction

(Encyclopedia)mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were thos...

resistor

(Encyclopedia)resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of the...