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hydroponics

(Encyclopedia)hydroponics, growing of plants without soil in water to which nutrients have been added. Hydroponics has been used for over a century as a research technique, but not until 1929 were experiments condu...

Amu Darya

(Encyclopedia)Amu Darya or Amudarya both: ämo͞oˈ däryäˈ, äˈmo͞o därˈyə [key], river, c.1,600 mi (2,580 km) long, formed by the junction of the Vakhsh and Pandj rivers, which rise in the Pamir Mts. of ce...

boiler

(Encyclopedia)boiler, device for generating steam. It consists of two principal parts: the furnace, which provides heat, usually by burning a fuel, and the boiler proper, a device in which the heat changes water in...

liposome

(Encyclopedia)liposome līˈpəsōmˌ, lĭpˈə– [key], microscopic, fluid-filled pouch whose walls are made of layers of phospholipids identical to the phospholipids that make up cell membranes. Liposomes are us...

well

(Encyclopedia)well, aperture in the earth's surface through which substances in a natural underground reservoir, such as water, gas, oil, salt, and sulfur, can flow or be pumped to the surface. In the United States...

snorkel

(Encyclopedia)snorkel, tube through which a submarine or diver can draw air while underwater. When in use, the top of the snorkel tube extends above the water surface into the air. The first snorkels were probably ...

molecular weight

(Encyclopedia)molecular weight, weight of a molecule of a substance expressed in atomic mass units (amu). The molecular weight may be calculated from the molecular formula of the substance; it is the sum of the ato...

Dehn, Adolf Arthur

(Encyclopedia)Dehn, Adolf Arthur dān [key], 1895–1968, American painter and illustrator, b. Waterville, Minn. During the 1920s, Dehn became known as a forceful satiric illustrator. Later he concentrated primaril...

lead acetate

(Encyclopedia)lead acetate, chemical compound, a white crystalline substance with a sweetish taste. Like other lead compounds, it is very poisonous. Lead acetate is soluble in water and glycerin. With water it form...

perfluoroalkyl and polyfluoroalkyl substances

(Encyclopedia)perfluoroalkyl and polyfluoroalkyl substances (PFAS), a group of several thousand synthetic organic chemical compounds made up of a chain of carbon atoms bonded to fluorine atoms. PFAS, which resist w...