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tar and pitch

(Encyclopedia)tar and pitch, viscous, dark-brown to black substances obtained by the destructive distillation of coal, wood, petroleum, peat, and certain other organic materials. The heating or partial burning of w...

bedbug

(Encyclopedia)bedbug, any of the small, blood-sucking bugs of the family Cimicidae, which includes about 30 species distributed throughout the world. Bedbugs are flat-bodied, oval, reddish brown, and about 1⁄4 in...

xerography

(Encyclopedia)xerography zərŏgˈrəfēˌ [key], also called electrophotography, method of dry photocopying in which the image is transferred by using the attractive forces of electric charges. A beam of light, us...

silica

(Encyclopedia)silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. It occurs in sev...

nickel

(Encyclopedia)nickel, metallic chemical element; symbol Ni; at. no. 28; at. wt. 58.6934; m.p. about 1,453℃; b.p. about 2,732℃; sp. gr. 8.902 at 25℃; valence 0, +1, +2, +3, or +4. Nickel is a hard, malleable, ...

Precambrian

(Encyclopedia)Precambrian, name of a major division of geologic time (see Geologic Timescale, tablegeologic timescale, table), from c.5 billion to 570 million years ago. It is now usually divided into the Archean a...

copper, chemical element

(Encyclopedia)copper, metallic chemical element; symbol Cu [Lat. cuprum=copper]; at. no. 29; at. wt. 63.546; m.p. 1,083.4℃; b.p. 2,567℃; sp. gr. 8.96 at 20℃; valence +1 or +2. Copper and some of its alloys ha...

fire

(Encyclopedia)fire, the phenomenon of combustion as seen in light, flame, and heat. One of the basic tools of human culture, its use is extremely ancient, predating the existence of Homo sapiens by several hundred ...

evaporation

(Encyclopedia)evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at ...

iridium

(Encyclopedia)iridium ĭrĭdˈēəm [key], metallic chemical element; symbol Ir; at. no. 77; at. wt. 192.217; m.p. about 2,410℃; b.p. about 4,130℃; sp. gr. 22.55 at 20℃; valence +3 or +4. Iridium is a very ha...