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sand dollar

(Encyclopedia)sand dollar, common name for a marine animal in the same phylum as the starfish (see sea star). The sand dollar has a rigid, flattened, disk-shaped test, or shell, made of firmly united plates lying j...

gopher

(Encyclopedia)gopher or pocket gopher, name for the burrowing rodents of the family Geomyidae, found in North America and Central America. The gopher is gray, buff, or dark brown. Its combined head and body length ...

Wöhler, Friedrich

(Encyclopedia)Wöhler, Friedrich frēˈdrĭkh vöˈlər [key], 1800–1882, German chemist. He studied under the German chemist Leopold Gmelin and J. J. Berzelius, a Swedish chemist, and in 1836 was appointed profe...

Berthelot, Pierre Eugène Marcelin

(Encyclopedia)Berthelot, Pierre Eugène Marcelin pyĕr ûzhĕnˈ märsəlăNˈ bĕrtəlōˈ [key], 1827–1907, French chemist. He was professor at the École Supérieure de Pharmacie (1859) and at the Collège de ...

DDT

(Encyclopedia)DDT or 2,2-bis(p-chlorophenyl)-1,1,1,-trichloroethane, chlorinated hydrocarbon compound used as an insecticide. First introduced during the 1940s, it killed insects that spread disease and fed on crop...

Grignard reagent

(Encyclopedia)Grignard reagent grēnyärdˈ rēāˈjənt [key], any of an important class of extremely reactive chemical compounds used in the synthesis of hydrocarbons, alcohols, carboxylic acids, and other compou...

Gerhardt, Charles Frédéric

(Encyclopedia)Gerhardt, Charles Frédéric shärl frādārēkˈ zhārärˈ [key], 1816–56, French chemist, b. Strasbourg. He revived the theory of acid radicals, which he called the theory of residues, and did va...

Liebig, Justus, Baron von

(Encyclopedia)Liebig, Justus, Baron von yo͝osˈto͝os bärônˈ fən lēˈbĭkh [key], 1803–73, German chemist. As professor at Giessen (1824–52), he was among the first to establish a chemical teaching labora...

chelating agents

(Encyclopedia)chelating agents kēˈlātĭng [key]. Certain organic compounds are capable of forming coordinate bonds (see chemical bond) with metals through two or more atoms of the organic compound; such organic ...

speech defect

(Encyclopedia)speech defect, any condition that interferes with the mental formation of words or their physical production. Speech defects in children generally become apparent in the early school years. Speech pro...