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  • hydrogasification process

    coal utilization: Gasification systems: Hydrogasification processes use hydrogen to produce a gas (mainly methane, CH4) of high calorific value (37 to 41 megajoules per cubic metre, or 980 to 1,080 British thermal units per cubic foot).

  • hydrogen (chemical element)

    Hydrogen (H), a colourless, odourless, tasteless, flammable gaseous substance that is the simplest member of the family of chemical elements. The hydrogen atom has a nucleus consisting of a proton bearing one unit of positive electrical charge; an electron, bearing one unit of negative electrical

  • hydrogen bomb (fusion device)

    Thermonuclear bomb, weapon whose enormous explosive power results from an uncontrolled self-sustaining chain reaction in which isotopes of hydrogen combine under extremely high temperatures to form helium in a process known as nuclear fusion. The high temperatures that are required for the reaction

  • hydrogen bonding (chemistry)

    Hydrogen bonding, interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons; such a bond is weaker than an ionic bond or covalent bond but stronger than van der Waals forces. Hydrogen bonds can exist between atoms in different molecules or in

  • hydrogen bridge (chemistry)

    Hydrogen bonding, interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons; such a bond is weaker than an ionic bond or covalent bond but stronger than van der Waals forces. Hydrogen bonds can exist between atoms in different molecules or in

  • hydrogen bromide (chemical compound)

    bromine: Production and use: …bromine compounds of significance include hydrogen bromide (HBr), a colourless gas used as a reducing agent and a catalyst in organic reactions. A solution of the gas in water is called hydrobromic acid, a strong acid that resembles hydrochloric acid in its activity toward metals and their oxides and hydroxides.

  • hydrogen carbonate (chemical compound)

    oxyacid: Carbonate and hydrogen carbonate salts: These salts can be prepared by the reaction of carbon dioxide with metal oxides and metal hydroxides, respectively. CO2 + O2 → CO32− CO2 + OH− → HCO3− For example, when an aqueous solution of sodium hydroxide (NaOH) is saturated with carbon…

  • hydrogen chloride (chemical compound)

    Hydrogen chloride, (HCl), a compound of the elements hydrogen and chlorine, a gas at room temperature and pressure. A solution of the gas in water is called hydrochloric acid. Hydrogen chloride may be formed by the direct combination of chlorine (Cl2) gas and hydrogen (H2) gas; the reaction is

  • hydrogen clock (measurement instrument)

    time: Other atomic clocks: Clocks regulated by hydrogen masers have been developed at Harvard University. The frequency of some masers has been kept stable within about one part in 1014 for intervals of a few hours. The uncertainty in the fundamental frequency, however, is greater than the stability of the clock; this…

  • hydrogen cloud (astronomy)

    Hydrogen cloud, interstellar matter in which hydrogen is mostly neutral, rather than ionized or molecular. Most of the matter between the stars in the Milky Way Galaxy, as well as in other spiral galaxies, occurs in the form of relatively cold neutral hydrogen gas. Neutral hydrogen clouds are

  • hydrogen cyanide (chemical compound)

    Hydrogen cyanide, a highly volatile, colourless, and extremely poisonous liquid (boiling point 26° C [79° F], freezing point -14° C [7° F]). A solution of hydrogen cyanide in water is called hydrocyanic acid, or prussic acid. It was discovered in 1782 by a Swedish chemist, Carl Wilhelm Scheele, who

  • hydrogen electrode (chemistry)

    acid–base reaction: Dissociation constants in aqueous solution: For example, a hydrogen electrode (or more commonly a glass electrode, which responds in the same way) together with a reference electrode, commonly the calomel electrode, serves to measure the actual hydrogen ion concentration, or the pH, of the solution. If E is the electromotive force (in volts)…

  • hydrogen fluoride (chemical compound)

    Edmond Frémy: …isolate free fluorine and discovered hydrogen fluoride and a series of its salts. He studied the colouring matters of leaves and flowers and the composition of animal substances. He contributed to the technology of iron, steel, sulfuric acid, glass, paper, and, in particular, the saponification of fats. He sought to…

  • hydrogen fuel cell (energy cell)

    fuel cell: …the development and use of hydrogen fuel cells in transportation and other applications. While the technology has proven to be workable, efforts to make it commercially competitive have been less successful because of concern with the explosive power of hydrogen, the relatively low energy density of hydrogen, and the high…

  • hydrogen halide (chemical compound)

    halogen: Relative reactivity: …form compounds with hydrogen, the hydrogen halides. The energy of the hydrogen-halogen bond increases strongly from iodide to fluoride. Hydrogen fluoride in the crystalline state consists of infinite zigzag chains, as shown in the diagram,

  • hydrogen ion (chemistry)

    Hydrogen ion, strictly, the nucleus of a hydrogen atom separated from its accompanying electron. The hydrogen nucleus is made up of a particle carrying a unit positive electric charge, called a proton. The isolated hydrogen ion, represented by the symbol H+, is therefore customarily used to

  • hydrogen ion concentration (chemistry)

    PH, quantitative measure of the acidity or basicity of aqueous or other liquid solutions. The term, widely used in chemistry, biology, and agronomy, translates the values of the concentration of the hydrogen ion—which ordinarily ranges between about 1 and 10−14 gram-equivalents per litre—into

  • hydrogen line

    21-centimetre radiation, electromagnetic radiation of radio wavelength emitted by cold, neutral, interstellar hydrogen atoms. The hydrogen atom is composed of a positively charged particle, the proton, and a negatively charged particle, the electron. These particles have some intrinsic angular

  • hydrogen maser (device)

    maser: Gas masers: In the hydrogen maser, hydrogen atoms are produced in a discharge and, like the molecules of the ammonia maser, are formed into a beam from which those in excited states are selected and admitted to a resonator. To improve the accuracy, the resonance of each atom is…

  • hydrogen peroxide (chemical compound)

    Hydrogen peroxide, (H2O2), a colourless liquid usually produced as aqueous solutions of various strengths, used principally for bleaching cotton and other textiles and wood pulp, in the manufacture of other chemicals, as a rocket propellant, and for cosmetic and medicinal purposes. Solutions

  • hydrogen phosphide (chemical compound)

    Phosphine (PH3), a colourless, flammable, extremely toxic gas with a disagreeable garliclike odour. Phosphine is formed by the action of a strong base or hot water on white phosphorus or by the reaction of water with calcium phosphide (Ca3P2). Phosphine is structurally similar to ammonia (NH3), but

  • hydrogen selenide (chemical compound)

    selenium: Compounds: …directly with hydrogen, resulting in hydrogen selenide, H2Se, a colourless, foul-smelling gas that is a cumulative poison. It also forms selenides with most metals (e.g., aluminum selenide, cadmium selenide, and sodium selenide).

  • hydrogen sulfate (chemical compound)

    Sulfuric acid, dense, colourless, oily, corrosive liquid; one of the most important of all chemicals, prepared industrially by the reaction of water with sulfur trioxide (see sulfur oxide), which in turn is made by chemical combination of sulfur dioxide and oxygen either by the contact process or

  • hydrogen sulfide (chemical compound)

    Hydrogen sulfide, colourless, extremely poisonous, gaseous compound formed by sulfur with hydrogen (see

  • hydrogen-3 (chemical isotope)

    Tritium, (T, or 3H), the isotope of hydrogen with atomic weight of approximately 3. Its nucleus, consisting of one proton and two neutrons, has triple the mass of the nucleus of ordinary hydrogen. Tritium is a radioactive species having a half-life of 12.32 years; it occurs in natural water with an

  • hydrogen-metal exchange (chemistry)

    metalation: …commonly the process involving a hydrogen–metal exchange. An example is the metalation of benzene (C6H6) by reaction with ethylsodium (C2H5Na), forming phenylsodium (C6H5Na) and ethane (C2H6). Metalation by means of hydrogen–metal exchange is a very powerful method of removing a hydrogen atom (in the form of its cation, H+) from…

  • hydrogenated amorphous silicon (chemistry)

    amorphous solid: Amorphous semiconductors in electronics: …in what is now called hydrogenated amorphous silicon, emerged in a scientific puzzle that took years to solve. Stated briefly, hydrogen eliminates the electronic defects that are intrinsic to pure amorphous silicon.

  • hydrogenated FAD (chemical compound)

    cell: Formation of the electron donors NADH and FADH2: …dinucleotide (FAD), yielding NADH and FADH2. It is the subsequent oxidation of these hydrogen acceptors that leads eventually to the production of ATP.

  • hydrogenated NAD (chemical compound)

    alcohol consumption: Processing in the liver: …NAD is thus changed to NADH and becomes available again for the same reaction only after its own further oxidation. While adequate ADH seems always present for the first step of alcohol metabolism, the temporary reduction of the available NAD apparently acts as a limit on the rate at which…

  • hydrogenated NBR (chemical compound)

    major industrial polymers: Nitrile rubber (nitrile-butadiene rubber, NBR): A hydrogenated version, abbreviated as HNBR, is also highly resistant to thermal and oxidative deterioration and remains flexible at lower temperatures.

  • hydrogenation (chemical reaction)

    Hydrogenation, chemical reaction between molecular hydrogen and an element or compound, ordinarily in the presence of a catalyst. The reaction may be one in which hydrogen simply adds to a double or triple bond connecting two atoms in the structure of the molecule or one in which the addition of

  • hydrogenolysis (chemical reaction)

    hydrogenation: …up) of the molecule (called hydrogenolysis, or destructive hydrogenation). Typical hydrogenation reactions include the reaction of hydrogen and nitrogen to form ammonia and the reaction of hydrogen and carbon monoxide to form methanol or hydrocarbons, depending on the choice of catalyst.

  • hydrogenosome (biology)

    Hydrogenosome, membrane-bound organelle found in the cytoplasm of eukaryotic cells (cells with clearly defined nuclei) that is so named because it releases molecular hydrogen (H2) as a by-product of energy generation under anaerobic (oxygen-deficient) conditions. The term hydrogenosome was

  • Hydrogéologie (work by Lamarck)

    Jean-Baptiste Lamarck: Professorship at the National Museum of Natural History: …publish under the title of Hydrogéologie (1802). In his physico-chemical writings, he advanced an old-fashioned, four-element theory that was self-consciously at odds with the revolutionary advances of the emerging pneumatic chemistry of Antoine-Laurent Lavoisier. His colleagues at the Institute of France (the successor to the Academy of Sciences) saw Lamarck’s…

  • hydrographic charting (cartography)

    Hydrography, the art and science of compiling and producing charts, or maps, of water-covered areas of Earth’s surface. A brief treatment of hydrography follows. For full treatment, see map and surveying: Hydrography. The terms hydrography and hydrographer are based on an analogy with geography and

  • hydrography (cartography)

    Hydrography, the art and science of compiling and producing charts, or maps, of water-covered areas of Earth’s surface. A brief treatment of hydrography follows. For full treatment, see map and surveying: Hydrography. The terms hydrography and hydrographer are based on an analogy with geography and

  • hydroid (cnidarian class)

    Hydroid, any member of the invertebrate class Hydrozoa (phylum Cnidaria). Most hydroids inhabit marine environments, but some have invaded freshwater habitats. Hydroids may be either solitary or colonial, and there are about 3,700 known species. Hydroids have three basic life-cycle stages: (1) a

  • hydroid (bryophyte anatomy)

    bryophyte: Form and function: …cylinder of water-conducting cells (the hydroids) surrounded by layers of living cells (leptoids) that conduct the sugars and other organic substances manufactured by the gametophore. This conducting system is analogous to that of the vascular plants, except that it lacks lignin (a carbohydrate polymer), and it closely resembles that found…

  • Hydroida (cnidarian order)

    cnidarian: Size range and diversity of structure: …phase in groups such as hydroids and hydrocorals. Hydromedusae are smaller and more delicate than scyphomedusae or cubomedusae; they may be completely absent from the life cycle of some hydrozoan species. Some other species produce medusae, but the medusae never separate themselves from the polyps. Cubozoans have medusae commonly known…

  • Hydroides (polychaete genus)

    annelid: Annotated classification: Serpula, Hydroides. Order Archiannelida Minute, primitive, with ciliated epidermis; prostomium small, with or without appendages; parapodia absent; septa reduced or absent; size, minute. Contains 4 groups of poorly known species considered separate orders by some (Nerillida, Dinophilida, Polygordiida

  • hydroiodic acid (chemical compound)

    ether: Cleavage: …give alkyl bromides or by hydroiodic acid (HI) to give alkyl iodides.

  • hydroisocyanic acid (acid)

    molecular cloud: Composition: …the interstellar molecule HNC (hydroisocyanic acid) and its isomer HCN (hydrocyanic acid); in ordinary terrestrial conditions there is plenty of energy to allow the nitrogen and carbon atoms in HNC to exchange positions and produce HCN, by far the preferred species for equilibrium chemistry. In the cold clouds, however,…

  • hydrokinetics (science)

    ship construction: …century, it was inevitable that hydrokinetics (the study of fluids in motion), hydrostatics (the study of fluids at rest), and the science of materials and structures should augment the shipbuilder’s skill. The consequence of this was a rapid increase in the size, speed, commercial value, and safety of ships.

  • hydrolaccolith (geology)

    permafrost: Pingos: A hydrolaccolith (water mound) forms and freezes, heaving the overlying frozen and unfrozen ground to produce a mound.

  • hydrolase (class of enzymes)

    Hydrolase, any one of a class of more than 200 enzymes that catalyze the hydrolysis of several types of compounds. Esterases include lipases, which break ester bonds (between a carboxylic acid and an alcohol) in lipids, and phosphatases, which act analogously upon phosphates; a narrower category

  • hydrologic cycle

    Water cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle

  • hydrologic sciences

    Hydrologic sciences, the fields of study concerned with the waters of Earth. Included are the sciences of hydrology, oceanography, limnology, and glaciology. In its widest sense, hydrology encompasses the study of the occurrence, movement, and physical and chemical characteristics of water in all

  • hydrological map (cartography)

    Hydrological map, chart showing such hydrologic features as rivers and streams; the purpose and content of these maps vary according to the country of their origin. Some maps are used as supplements to a detailed written text, whereas others, such as the USGS Hydrologic Investigations Atlases

  • hydrology (science)

    Hydrology, scientific discipline concerned with the waters of the Earth, including their occurrence, distribution, and circulation via the hydrologic cycle and interactions with living things. It also deals with the chemical and physical properties of water in all its phases. A brief treatment of

  • hydrology, chemical

    Chemical hydrology, subdivision of hydrology that deals with the chemical characteristics of the water on and beneath the surface of the Earth. Water in all forms and modes of occurrence is affected chemically by the materials with which it comes into contact. Often called the universal solvent, w

  • hydrolysis (chemical reaction)

    Hydrolysis, in chemistry and physiology, a double decomposition reaction with water as one of the reactants. Thus, if a compound is represented by the formula AB in which A and B are atoms or groups and water is represented by the formula HOH, the hydrolysis reaction may be represented by the

  • hydrolyzable tannin (chemical compound)

    tannin: Hydrolyzable tannins (decomposable in water, with which they react to form other substances), yield various water-soluble products, such as gallic acid and protocatechuic acid and sugars. Gallotannin, or common tannic acid, is the best known of the hydrolyzable tannins. It is produced by extraction with…

  • hydrolyzer process (chemical process)

    soap and detergent: Continuous soapmaking—the hydrolyzer process: The boiling process is very time consuming; settling takes days. To produce soap in quantity, huge kettles must be used. For this reason, continuous soapmaking has largely replaced the old boiling process. Most continuous processes today employ fatty acids in the saponification reaction…

  • hydromagnetics (physics)

    Magnetohydrodynamics (MHD), the description of the behaviour of a plasma (q.v.), or, in general, any electrically conducting fluid in the presence of electric and magnetic fields. A plasma can be defined in terms of its constituents, using equations to describe the behaviour of the electrons, ions,

  • hydromancy (occult practice)

    divination: Interpretive divination: Hydromancy (divination by water) is usually less dramatic, ranging from the reading of reflections in a shallow surface, in the manner of the crystal gazer, to construing the movements of floating objects, as in the reading of tea leaves.

  • Hydromantes (amphibian genus)

    Caudata: Annotated classification: …Desmognathus in North America and Hydromantes in western North America and the central Mediterranean region) and about 105 species. Family Proteidae (olms and mud puppies) The olm is blind, has little pigment, has an elongated body, and is cave-dwelling; mud puppies

  • hydromechanics (physics)

    Fluid mechanics, science concerned with the response of fluids to forces exerted upon them. It is a branch of classical physics with applications of great importance in hydraulic and aeronautical engineering, chemical engineering, meteorology, and zoology. The most familiar fluid is of course

  • hydromedusa (cnidarian)

    cnidarian: Size range and diversity of structure: Hydromedusae are smaller and more delicate than scyphomedusae or cubomedusae; they may be completely absent from the life cycle of some hydrozoan species. Some other species produce medusae, but the medusae never separate themselves from the polyps. Cubozoans have medusae commonly known as box jellyfish,…

  • hydromel (alcoholic beverage)

    mead: …grapevines do not flourish; the hydromel of the Greeks and Romans was probably like the mead drunk by the Celts and Anglo-Saxons, although the Roman mulsum, or mulse, was not mead but wine sweetened with honey. In Celtic and Anglo-Saxon literature, such as the writings of Taliesin and in the…

  • Hydromeles (mollusk genus)

    gastropod: Reproduction and life cycles: One pteropod, Hydromeles, has an internal brood chamber that apparently ruptures, freeing the young into the body cavity of the parent; the escape of the young may cause the parent’s death.

  • hydrometallation (chemistry)

    organometallic compound: Hydrometallation: The addition of a metal hydride to a multiple bond is called hydrometallation, and it leads to the formation of a metal-carbon bond. M―H + H2C=CH2 → MH2C―CH3 This reaction is driven mainly by the high C―H bond strength relative to most E―H bond…

  • hydrometallurgy (science)

    Hydrometallurgy, extraction of metal from ore by preparing an aqueous solution of a salt of the metal and recovering the metal from the solution. The operations usually involved are leaching, or dissolution of the metal or metal compound in water, commonly with additional agents; separation of the

  • hydrometeor (meteorology)

    Hydrometeor, any water or ice particles that have formed in the atmosphere or at the Earth’s surface as a result of condensation or sublimation. Water or ice particles blown from the ground into the atmosphere are also classed as hydrometeors. Some well-known hydrometeors are clouds, fog, rain,

  • hydrometeorology (science)

    Hydrometeorology, branch of meteorology that deals with problems involving the hydrologic cycle, the water budget, and the rainfall statistics of storms. The boundaries of hydrometeorology are not clear-cut, and the problems of the hydrometeorologist overlap with those of the climatologist, the

  • hydrometer (measurement instrument)

    Hydrometer, device for measuring some characteristics of a liquid, such as its density (weight per unit volume) or specific gravity (weight per unit volume compared with water). The device consists essentially of a weighted, sealed, long-necked glass bulb that is immersed in the liquid being

  • Hydrometridae (insect)

    Marsh treader, any insect of the family Hydrometridae (order Heteroptera), so named because of its slow, deliberate manner of moving as it walks along the surface of a pond or crawls among shore vegetation. Marsh treaders, worldwide in distribution, are usually found among the cattails in marshy

  • hydromica (mineral)

    Hydrous mica, any of the illite group of clay minerals, including illite, bramallite (a sodium illite), and glauconite. They are structurally related to the micas; glauconite is also a member of the common-mica group. The hydrous micas predominate in shales and mudstones, but they also occur in

  • hydromorphic plant (botany)

    tree: Tree roots: Hydrophytic trees have various modifications that facilitate their survival and growth in the aqueous environment. Some species produce a high frequency of lenticels on the bark that facilitate gas exchange. Others exhibit greater permeation of oxygen through the bark and into the cambium at lower…

  • Hydromys (rodent genus)

    water rat: Natural history: Water rats of the genus Hydromys live in the mountains and coastal lowlands of Australia, New Guinea, and some nearby islands. The earless water rat (Crossomys moncktoni) inhabits mountains of eastern New Guinea, where it prefers cold, fast-flowing streams bordered by tropical forest or grass. The African water rat is…

  • Hydromys chrysogaster (rodent)

    water rat: Natural history: The golden-bellied water rat (Hydromys chrysogaster) of Australia and New Guinea is the largest, with a body 20 to 39 cm long and a slightly shorter tail (20 to 33 cm). Living by freshwater lakes, estuaries, and rivers and in coastal mangrove swamps, it is tolerant…

  • hydronephrosis (pathology)

    renal system disease: Obstruction to the flow of urine: …leading to the condition called hydronephrosis, in which a greatly swollen sac is surrounded by a mere rind of atrophied renal tissue. A massive hydronephrosis, with negligible renal substance remaining, may suggest removal of the kidney.

  • hydronium ion (chemical ion)

    acid–base reaction: The Brønsted–Lowry definition: The hydronium ion (H3O+), which is the hydrogen ion in aqueous solution, also belongs to this class. The charge of these ionic acids, of course, always must be balanced by ions of opposite charges, but these oppositely charged ions usually are irrelevant to the acid–base properties…

  • hydronymy (language)

    name: Categories of names: …names of bodies of water, hydronymy; and names of mountains, oronymy. Additional terms are not generally used (though one occasionally hears words like chrematonymy—names of things).

  • hydropathy (medicine)

    Hydropathy, therapeutic system that professes to cure all disease with water, either by bathing in it or by drinking it. Although water therapy is currently used to treat certain ailments, its effectiveness is generally accepted to be limited. Most authorities agree that many disease and injury

  • hydrophane (mineral)

    opal: …extremely porous variety, known as hydrophane, can absorb surprising quantities of water; it is almost opaque when dry but nearly transparent when saturated. Light-coloured stones are often dyed to resemble rarer, more deeply coloured varieties.

  • Hydrophasianus chirurgus (bird)

    jacana: …eastern Australian coast; and the pheasant-tailed jacana (Hydrophasianus chirurgus), of India and the Philippines, a handsome black, yellow, and white bird that acquires long tail feathers in breeding season.

  • Hydrophiinae (reptile subfamily)

    sea snake: …two independently evolved groups: the true sea snakes (subfamily Hydrophiinae), which are related to Australian terrestrial elapids, and the sea kraits (subfamily Laticaudinae), which are related to the Asian cobras. Although their venom is the most potent of all snakes, human fatalities are rare because sea snakes are not aggressive,…

  • hydrophilicity (chemistry)

    alcohol: Physical properties of alcohols: …is referred to as a hydrophilic (“water-loving”) group, because it forms hydrogen bonds with water and enhances the solubility of an alcohol in water. Methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol are all miscible with water. Alcohols with higher molecular weights tend to be less water-soluble, because the…

  • Hydrophiloidea (insect)

    Water scavenger beetle, any of the approximately 3,200 species of the predominately aquatic insect superfamily Hydrophiloidea (order Coleoptera). These beetles are found swimming in marshy freshwater ponds throughout the world, especially in warm regions. Water scavenger beetles have smooth, oval,

  • hydrophily (pollination)

    Ceratophyllales: …unusual in that they have underwater pollination. When the male flowers are mature, the individual anthers break off and settle through the water until they reach a groove near the stigma of a female flower, leading to pollination.

  • Hydrophis (snake genus)

    sea snake: >Hydrophis specializes in burrowing eels.

  • Hydrophis cyanocinctus (reptile)

    sea snake: …a 2019 study of the blue-banded sea snake (or annulated sea snake, Hydrophis cyanocinctus) found a highly vascularized area between the snout and the top of the head, which allows oxygen to be transported directly from the water to the snake’s brain. Sea snakes give birth in the ocean to…

  • hydrophobia (pathology)

    Rabies, acute, ordinarily fatal, viral disease of the central nervous system that is usually spread among domestic dogs and wild carnivorous animals by a bite. All warm-blooded animals, including humans, are susceptible to rabies infection. The virus, a rhabdovirus, is often present in the salivary

  • hydrophobia cat (mammal)

    skunk: Spotted skunks (genus Spilogale) live from southwestern Canada to Costa Rica. Except for a white spot between the eyes, their spots are actually a series of interrupted stripes running down the back and sides. These are about the size of a tree squirrel and are…

  • hydrophobic cement (cement)

    cement: Types of portland cement: Hydrophobic cement is obtained by grinding portland cement clinker with a film-forming substance such as oleic acid in order to reduce the rate of deterioration when the cement is stored under unfavourable conditions.

  • hydrophobicity (chemistry)

    alcohol: Physical properties of alcohols: …of the molecule, which is hydrophobic (“water-hating”), is larger with increased molecular weight. Because they are strongly polar, alcohols are better solvents than hydrocarbons for ionic compounds and other polar substances.

  • hydrophone (instrument)

    Hydrophone, device for converting sound waves into electrical signals, similar in operation to a microphone but used primarily for detecting sound waves from an underwater source, such as a submarine. Usually an array of hydrophones is employed to pinpoint the source: the array is connected to an

  • hydrophotometer (instrument)

    undersea exploration: Collection of biological samples: …include the submarine photometer, the hydrophotometer, and the Secchi disk. The submarine photometer records directly to depths of about 150 metres the infrared, visible, and ultraviolet portions of the spectrum. The hydrophotometer has a self-contained light source that allows greater latitude in observation because it can be used at any…

  • Hydrophyllaceae (plant subfamily)
  • Hydrophylloideae (plant subfamily)
  • Hydrophyllum (plant)

    Waterleaf, any of about eight species of herbaceous plants constituting a genus (Hydrophyllum) in the borage family (Boraginaceae) and native to damp woodlands of North America. Light-greenish mottling on the leaves, suggesting watermarks on paper, gives the genus its name. Notable members of the

  • Hydrophyllum canadense (plant)

    waterleaf: The broad-leaved waterleaf (H. canadense), also 60 cm tall, has maplelike leaves. Some species are used in wildflower gardens; they are valued for their attractive leaves and clusters of small white to purplish flowers with stamens that extend beyond the petals.

  • Hydrophyllum macrophyllum (plant)

    waterleaf: The large-leaved waterleaf (H. macrophyllum) is similar to the Virginia waterleaf but is rough and hairy and about 60 cm tall. The broad-leaved waterleaf (H. canadense), also 60 cm tall, has maplelike leaves. Some species are used in wildflower gardens; they are valued for their attractive…

  • Hydrophyllum virginianum (plant)

    waterleaf: 5-foot-) tall Virginia waterleaf (Hydrophyllum virginianum), with five- to seven-lobed leaves; it is also called Shawnee salad and John’s cabbage in reference to the edible tender young shoots. The large-leaved waterleaf (H. macrophyllum) is similar to the Virginia waterleaf but is rough and hairy and about 60…

  • hydrophyte (botany)

    tree: Tree roots: Hydrophytic trees have various modifications that facilitate their survival and growth in the aqueous environment. Some species produce a high frequency of lenticels on the bark that facilitate gas exchange. Others exhibit greater permeation of oxygen through the bark and into the cambium at lower…

  • hydroplane (vehicle)

    Gold Cup: …boats since 1911 have been hydroplanes, usually of unlimited engine displacement. The Gold Cup is one of a series of unlimited hydroplane races sponsored annually by the American Power Boat Association and culminating with the award of a national championship.

  • Hydroplane II (racehorse)

    Citation: Breeding and early years: In 1941 Wright purchased Hydroplane II from Britain and had her shipped to America via the Pacific Ocean to avoid the Atlantic conflicts of World War II. Her first two foals proved rather ordinary, but on April 11, 1945, out of a mating with Bull Lea, she dropped her…

  • hydroponics (horticulture)

    Hydroponics, the cultivation of plants in nutrient-enriched water, with or without the mechanical support of an inert medium such as sand or gravel. Plants have long been grown with their roots immersed in solutions of water and fertilizer for scientific studies of their nutrition. Early commercial

  • Hydropotes inermis (mammal)

    Chinese water deer, (Hydropotes inermis), very small Asian deer of the family Cervidae (order Artiodactyla), native to fertile river bottoms in Korea and the Yangtze River (Chang Jiang) valley in China. It is the only species of deer in which males lack antlers; instead, they are armed with long,

  • hydropower

    Hydroelectric power, electricity produced from generators driven by turbines that convert the potential energy of falling or fast-flowing water into mechanical energy. In the generation of hydroelectric power, water is collected or stored at a higher elevation and led downward through large pipes

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