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Parkinson's disease

(Encyclopedia)Parkinson's disease or Parkinsonism, degenerative brain disorder first described by the English surgeon James Parkinson in 1817. When there is no known cause, the disease usually appears after age 40 ...

hafnium

(Encyclopedia)hafnium hăfˈnēəm [key], metallic chemical element; symbol Hf; at. no. 72; at. wt. 178.49; m.p. about 2,227℃; b.p. 4,602℃; sp. gr. 13.31 at 20℃; valence +4. Hafnium is a lustrous, ductile, si...

peptide

(Encyclopedia)peptide, organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) o...

lighting

(Encyclopedia)CE5 Incandescent lamp CE5 Basic fluorescent lamp lighting, light produced by artificial means to allow visibility in enclosures and at night. For stage lighting, see scene design and stage ligh...

tin

(Encyclopedia)tin, metallic chemical element; symbol Sn [Lat. stannum]; at. no. 50; at. wt. 118.710; m.p. 231.9681℃; b.p. 2,270℃; sp. gr. 5.75 (gray), 7.3 (white); valence +2 or +4. Tin exhibits allotropy; abov...

mineral

(Encyclopedia)mineral, inorganic substance occurring in nature, having a characteristic and homogeneous chemical composition, definite physical properties, and, usually, a definite crystalline form. A few of the mi...

Montreal Protocol

(Encyclopedia)Montreal Protocol, officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 197 nations are now parties to the accord. The protoc...

tracer

(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...

rhenium

(Encyclopedia)rhenium rēˈnēəm [key], metallic chemical element; symbol Re; at. no. 75; at. wt. 186.207; m.p. about 3,180℃; b.p. about 5,625℃; sp. gr. 21.02 at 20℃; valence −1, +2, +3, +4, +5, +6, or +7....

praseodymium

(Encyclopedia)praseodymium prāˌzēōdĭmˈēəm, –sēō– [key] [Gr., =green twin], metallic chemical element; symbol Pr; at. no. 59; at. wt. 140.90765; m.p. 931℃; b.p. 3,512℃; sp. gr. about 6.8; valence +...