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Helwan
(Encyclopedia)Helwan wänˈ [key], town (1989 est. pop. 230,000), N Egypt, on the Nile River, opposite the ruins of Memphis; a suburb of Cairo. Manufactures include iron and steel, cement, and textiles; there is a ...club moss
(Encyclopedia)club moss, name generally used for the living species of the class Lycopodiopsida, a primitive subdivision of vascular plants. The Lycopodiopsida were a dominant plant group in the Carboniferous perio...Narbonne
(Encyclopedia)Narbonne närbônˈ [key], city (1990 pop. 47,086), Aude dept., S France, near the Mediterranean coast. It is the commercial center of a wine-growing region and an industrial city producing sulfur, co...ammonia
(Encyclopedia)ammonia, chemical compound, NH3, colorless gas that is about one half as dense as air at ordinary temperatures and pressures. It has a characteristic pungent, penetrating odor. Ammonia forms a minute ...gas
(Encyclopedia)gas, in physics, one of the three commonly recognized states of matter, the other two being solid and liquid. A substance in the gaseous state has neither definite shape nor definite volume. Like liqu...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...asthma
(Encyclopedia)asthma ăzˈmə, ăsˈ– [key], chronic inflammatory respiratory disease characterized by periodic attacks of wheezing, shortness of breath, and a tight feeling in the chest. A cough producing sticky...membrane
(Encyclopedia)membrane, structure composed mostly of lipid and protein that forms the external boundary of cells and of major structures within cells. Membrane organization is based on a sheet two molecules thick...snowball earth
(Encyclopedia)snowball earth, hypothesized condition in which the earth was covered completely by ice during several periods in the Proterozoic. The hypothesis was originally developed to explain evidence of the co...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...Browse by Subject
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