Columbia Encyclopedia

(Encyclopedia) tracer, an identifiable substance used to follow the course of a physical, chemical, or biological process. In chemistry the ideal tracer has the same chemical properties as the molecule it replaces a...

(Encyclopedia) ruthenium ro͞othēˈnēəm [key], metallic chemical element; symbol Ru; at. no. 44; at. wt. 101.07; m.p. about 2,310℃; b.p. about 3,900℃; sp. gr. 12.41 at 20℃; valence commonly +2, +3, +4, +6, ...

(Encyclopedia) actinium ăktĭnˈēəm [key] [Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; mass number of most stable isotope 227; m.p. about 1,050℃; b.p. 3,200℃±300℃; sp. gr. 10.07;...

(Encyclopedia) fungicide fŭnˈjəsīdˌ, fŭngˈgə– [key], any substance used to destroy fungi. Some fungi are extremely damaging to crops (see diseases of plants), and others cause diseases in humans and other ...

(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...

(Encyclopedia) photochemistry, study of chemical processes that are accompanied by or catalyzed by the emission or absorption of visible light or ultraviolet radiation. A molecule in its ground (unexcited) state can...

(Encyclopedia) mortar, in building, mixture of lime or cement with sand and water, used as a bedding and adhesive between adjacent pieces of stone, brick, or other material in masonry construction. Lime mortar, a co...

(Encyclopedia) carboxyl group kärbŏkˈsĭl [key], in chemistry, functional group that consists of a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond. Carboxylic a...

(Encyclopedia) aquarium, name for any supervised exhibit of aquatic animals and plants. Aquariums are known to have been constructed in ancient Rome, Egypt, and Asia. Goldfish have been bred in China for several hun...

(Encyclopedia) protactinium prōˌtăktĭnˈēəm [key], radioactive chemical element; symbol Pa; at. no. 91; mass number of most stable isotope 231; m.p. greater than 1,600℃; b.p. 4,026℃; sp. gr. 15.37 (calcula...