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aerogel

(Encyclopedia)aerogel, any of a group of extremely light and porous solid materials; the lightest is less than four times as dense as dry air. Aerogels are produced from certain gels (see colloid) by heating the ge...

halogen

(Encyclopedia)halogen hălˈəjĕn [key] [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromin...

steel

(Encyclopedia)steel, alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese; steelmaking involves the removal of these imp...

soap

(Encyclopedia)soap, a cleansing agent. It cleanses by lowering the surface tension of water, by emulsifying grease, and by absorbing dirt into the foam. Ancient peoples are believed to have employed wood ashes and ...

phonetics

(Encyclopedia)phonetics fōnĕtˈĭks, fə– [key], study of the sounds of languages from three basic points of view. Phonetics studies speech sounds according to their production in the vocal organs (articulatory...

color

(Encyclopedia)color, effect produced on the eye and its associated nerves by light waves of different wavelength or frequency. Light transmitted from an object to the eye stimulates the different color cones of the...

topology

(Encyclopedia)CE5 Möbius strip: On the ordinary flat loop (A), an ant walking along the middle of the strip will pass only around the outside of the strip. If the strip is cut along the dotted line, twisted onc...

acids and bases

(Encyclopedia)acids and bases, two related classes of chemicals; the members of each class have a number of common properties when dissolved in a solvent, usually water. Another theory that provides a very broad ...

methanol

(Encyclopedia)methanol, methyl alcohol, or wood alcohol, CH3OH, a colorless, flammable liquid that is miscible with water in all proportions. Methanol is a monohydric alcohol. It melts at −97.8℃ and boils at 6...

Macy, Anne Sullivan

(Encyclopedia)Macy, Anne Sullivan, 1866–1936, American educator, friend and teacher of Helen Keller, b. Feeding Hills, Mass. Placed in Tewksbury almshouse (1876), she was later admitted (1880) to Perkins Institut...