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white lead

(Encyclopedia)white lead, heavy, white substance, poisonous, insoluble in water, extensively used as a white pigment and base in paints. It is one of the oldest paint pigments used by humans. Chemically, it is basi...

diffusion

(Encyclopedia)diffusion, in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life process...

exobiology

(Encyclopedia)exobiology or astrobiology, search for extraterrestrial life within the solar system and throughout the universe. Philosophical speculation that there might be other worlds similar to ours dates back ...

silver

(Encyclopedia)silver, metallic chemical element; symbol Ag [Lat. argentum]; at. no. 47; at. wt. 107.8682; m.p. 961.93℃; b.p. 2,212℃; sp. gr. 10.5 at 20℃; valence +1 or +2. Pure silver is nearly white, lustrou...

star

(Encyclopedia)star, hot incandescent sphere of gas, held together by its own gravitation, and emitting light and other forms of electromagnetic radiation whose ultimate source is nuclear energy. The universe co...

tellurium

(Encyclopedia)tellurium tĕlo͝orˈēəm [key] [Lat.,=earth], semimetallic chemical element; symbol Te; at. no. 52; at. wt. 127.60; m.p. 450℃; b.p. 990℃; sp. gr. 6.24 at 20℃; valence −2, +4, or +6. Telluriu...

cresol

(Encyclopedia)cresol krēˈsōl [key], CH3C6H4OH, any one of three aromatic alcohols present in coal tar. The three compounds are structural isomers; they may be thought of as hydroxy derivatives of toluene or as m...

xylene

(Encyclopedia)xylene dīˌmĕthəlbĕnˈzēn [key], C6H4(CH3)2, colorless, oily, liquid aromatic hydrocarbon, used extensively as a solvent, obtained from coal tar, wood tar, and sometimes from petroleum. It is a m...

promethium

(Encyclopedia)promethium prōmēˈthēəm [key], artificially produced radioactive chemical element; symbol Pm; at. no. 61; mass no. of most stable isotope 145; m.p. 1,042℃; b.p. 3,000℃ (estimated); sp. gr. unk...

liquid air

(Encyclopedia)liquid air, ordinary air that has been liquefied by compression and cooling to extremely low temperatures (see liquefaction). Its commercial preparation involves purification by washing to remove solu...