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second largest of the Eolie Islands (Lipari Islands), in the Tyrrhenian Sea (of the Mediterranean) off northeastern Sicily. It has an area of 10 square miles (26 square km)....

northeasternmost of the Eolie (Lipari) Islands, in the Tyrrhenian Sea (of the Mediterranean), off northeastern Sicily. It has an area of 5 square miles (12 square km). Of volcanic formation, the island is still active, and fluid lava flows continuously from its crater to...

southernmost of the Eolie Islands, in the Tyrrhenian Sea (of the Mediterranean), off northeastern Sicily. It is administered as part of northern Sicily, southern Italy. Vulcano has an area of 8 square miles (21 square km). Although the last major eruptions were in 1888–90, fumaroles of sulfurous vapour testify to cont...

...is calculated from the average F values of its members. High values of F are found in small populations whose members marry one another over many generations. Such groups are called isolates. Thus, the Samaritans, who have remained a small but distinctive group since the 8th century bc, are considerably inbred, and in the United States some religious groups also live...

...assigned to a specific group. A few of these languages are currently thought to be unrelated to any of the established genetic groupings and are listed individually in the table; these solitary languages are called isolates....

...pawn weaknesses are disadvantageous in direct proportion to their exploitability, which tends to increase as pieces are exchanged. A pawn with no friendly pawns on adjoining files is called an isolated pawn; isolated pawns may confer middlegame compensation through control of important squares (if located in the centre) or by giving rooks adjoining open files along which to attack. A pawn......

...the function cannot be expressed as an infinite series in powers of z) although, at points arbitrarily close to the singularity, the function may be analytic, in which case it is called an isolated singularity. In general, because a function behaves in an anomalous manner at singular points, singularities must be treated separately when analyzing the function, or mathematical model, in.....

Johann Heinrich von Thünen, a Prussian landowner, introduced an early theory of agricultural location in Der isolierte Staat (1826) (The Isolated State). The Thünen model suggests that accessibility to the market (town) can create a complete system of agricultural land use. His model envisaged a single market surrounded by farmland, both situated on a plain of complete....

Isolated thunderstorms tend to occur where there are light winds that do not change dramatically with height and where there is abundant moisture at low and middle levels of the atmosphere—that is, from near the surface of the ground up to around 10,000 metres (33,000 feet) in altitude. These storms are sometimes called air-mass or local thunderstorms. They are mostly vertical in......

a language in which each word form consists typically of a single morpheme. Examples are Classical Chinese (to a far greater extent than the modern Chinese languages) and Vietnamese. An isolating language tends also to be an analytic language, so that...

in medicine, separation of an infected individual (human or animal) from the healthy until that individual is no longer able to transmit the disease. In its strictest sense, the practice of isolation differs from that of quarantine, which is the detention of an individual who may have been exposed to a communicable disease u...

in chemistry, separation of a substance into its components and the removal of impurities. There are a large number of important applications in fields such as medicine and manufacturing....

Almost all productions (the so-called happenings of the 1960s and guerrilla theatre are notable exceptions) endeavour to achieve two basic aims. First, every production seeks to impart a special quality to the theatrical area. Use of a theatrical building may in itself provide a heightened sense of locale. Otherwise, special decoration of familiar locales (town, market square) may transform......

Impedance-matching transformers are used to match the impedance of a source and that of its load, for most efficient transfer of energy. Isolation transformers are usually employed for reasons of safety to isolate a piece of equipment from the source of power....

National policy of avoiding political or economic entanglements with other countries. Isolationism has been a recurrent theme in U.S. history. It was given expression in the Farewell Address of Pres. George Washington and in the early 19th-century Monroe Doctrine. The term is most often applied to the political atmosphere in the U.S. in the 1930s. The failure ...

Between World Wars I and II Canada followed an isolationist foreign policy, mainly a consequence of the return to government in 1921 of the Liberal Party, which had come to depend on French Canadian support. French Canadians were overwhelmingly isolationist, and they strengthened the general disposition of Canadians to express their new national feelings by becoming completely autonomous within......

...The embryos of mammals are normally bacteriologically sterile, and germfree young can be obtained by cesarean operation, under germfree conditions, with transfer of the mature embryo into a sterile isolator. These young must be fed by hand to avoid contamination by the mother. Subsequent reproduction of hand-reared germfree mammals allows routine production of germfree colonies. Germfree rats.....

small mountainous group of islets belonging to Italy, in the Mediterranean just off the western coast of Sicily, with a total area of 15 square miles (39 square km). The principal islands are Favignana, the largest (7 square miles [18 square km]), Levanzo, and Marettimo. In the Battle of the Aegates in 241 bc, the Carthaginian fleet was defeated there by the Roman ...

volcanic group in the Tyrrhenian Sea (of the Mediterranean) off the north coast of Sicily, Italy. The group, with a total land area of 34 square miles (88 square km), consists of seven major islands and several islets lying in a general “Y” shape. The base of the “Y” is formed by the westernmost i...

group of islands in the Mediterranean Sea between Malta and Tunisia, south of Sicily; administratively they form the commune of Lampedusa. The group consists of the islands of Lampedusa and Linosa and the Isolotto (islet) Lampione, standing on the eastern edge of the submarine platform o...

the nutritive material of an egg, used as food by a developing, embryonic animal. Eggs with relatively little, uniformly distributed yolk are termed isolecithal. This condition occurs in invertebrates and in all but the lowest mammals. Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than......

an amino acid present in most common proteins, sometimes comprising 2 to 10 percent by weight. First isolated in 1904 from fibrin, a protein involved in blood-clot formation, isoleucine is one of several so-called essential amino acids for chicks, rats, and other higher animals, including man; i.e., they...

Johann Heinrich von Thünen, a Prussian landowner, introduced an early theory of agricultural location in Der isolierte Staat (1826) (The Isolated State). The Thünen model suggests that accessibility to the market (town) can create a complete system of agricultural land use. His model envisaged a single market surrounded by farmland, both situated on a plain of complete....

Hunting by native islanders and early European colonists led to the extermination of hutias on various islands. For example, the Puerto Rican hutia (Isolobodon portoricensis) was probably indigenous to Hispaniola and introduced to Puerto Rico and some of the Virgin Islands, but it is now extinct. Some hutias are not endangered, but others are rare and becoming more so owing to human......

principal characters of a famous medieval love-romance, based on a Celtic legend (itself based on an actual Pictish king). Though the archetypal poem from which all extant forms of the legend are derived has not been preserved, a comparison of the early versions yields an idea of its content....

...blue to purplish, sometimes white, flowers, 12 cm across, among heart-shaped leaves. It is native to tropical America. This vine bears seeds containing the alkaloids d-lysergic and d-isolysergic acids (similar to LSD), and the seeds are used traditionally among Mexico’s Zapotec Indians for ceremonial and curative purposes. Common morning glory (I. purpurea), an annua...

in nuclear physics, any of two or more nuclides (species of atomic nuclei) that consist of the same number of protons and the same number of neutrons but differ in energy and manner of radioactive decay, and that exist for a measurable interval of time. The half-life of...

in nuclear physics, any of two or more nuclides (species of atomic nuclei) that consist of the same number of protons and the same number of neutrons but differ in energy and manner of radioactive decay, and that exist for a measurable interval of time. The half-life of...

...level. Results are in close agreement with the measured decay time, indicating that the width of recoil-free gamma rays in fact is determined entirely by the lifetime of the decaying state. The isomer shift, the change in the energy of a nuclear gamma ray due to the electrostatic interaction between nuclear and electronic charge, provides a measurement of the change in the nuclear-charge......

any one of a class of enzymes that catalyze reactions involving a structural rearrangement of a molecule. Alanine racemase, for example, catalyzes the conversion of L-alanine into its isomeric (mirror-image) form, D-alanine. An isomerase called mutarotase catalyzes the conversion of αあるふぁ-d-glucose into βべーた-d-glucose. ...

There is a wide range of rates of half-lives for the gamma-emission process. Usually dipole transitions (see below Gamma transition), in which the gamma ray carries off one ℏ unit of angular momentum, are fast, less than nanoseconds (one nanosecond equals 10−9 second). The law of conservation of angular momentum requires that the sum of angular momenta of the radiat...

the existence of molecules that have the same numbers of the same kinds of atoms (and hence the same formula) but differ in chemical and physical properties. The roots of the word isomer are Greek—isos plus meros, or “equal parts.” Stated colloquial...

the chemical process by which a compound is transformed into any of its isomeric forms, i.e., forms with the same chemical composition but with different structure or configuration and, hence, generally with different physical and chemical properties. An example is the conversion of butane, a hydrocarbon with four carbon atoms joined in a straight chain, to its branched-...

When a muscle is to lift a constant load (isotonic conditions) after stimulation starts, the force increases, just as in an isometric contraction, and, when the force is equal to the load, the muscle begins to shorten and lifts the load. When both the activity of the muscle and the force in it begin to decline, the load stretches the muscle back to its initial length. The tension in the muscle......

method of graphic representation of three-dimensional objects, used by engineers, technical illustrators, and, occasionally, architects. The technique is intended to combine the illusion of depth, as in a perspective rendering, with the undistorted presentation of the object’s principal dimensions, that is, those parallel to a chosen se...

method of graphic representation of three-dimensional objects, used by engineers, technical illustrators, and, occasionally, architects. The technique is intended to combine the illusion of depth, as in a perspective rendering, with the undistorted presentation of the object’s principal dimensions, that is, those parallel to a chosen se...

one of the crystal systems to which a given crystalline solid can be assigned. Crystals in this system are referred to three mutually perpendicular axes of equal lengths. If the atoms or atom groups in the solid are represented by points and the points are connected, the resulting lattice will consist of a...

...arachnids, including other scorpions. Less-common but regular prey includes pill bugs, snails, and small vertebrates such as lizards, snakes, and rodents. The only known specialist scorpion is the Australian spiral burrow, or spider-hunting, scorpion (Isometroides vescus), which feeds solely on burrowing spiders....

...be bent, without stretching, so that it forms a strake around the cylinder? In particular, this means that distances measured along the surface (intrinsic) are unchanged. Two surfaces are said to be isometric if one can be bent (or transformed) into the other without changing intrinsic distances. (For example, because a sheet of paper can be rolled into a tube without stretching, the sheet and....

...υうぷしろん vertices are distinguished by such names as x1, x2, · · · xυうぷしろん. Two graphs G and H are said to be isomorphic (written G ≃ H) if there exists a one–one correspondence between their vertex sets that preserves adjacency. For example, G1 and......

in modern algebra, a one-to-one correspondence (mapping) between two sets that preserves binary relationships between elements of the sets. For example, the set of natural numbers can be mapped onto the set of even natural numbers by multiplying each natural number by 2. The ...

Many remaining problems in the specification of minerals were resolved by the law of isomorphism, the recognition that chemically similar substances possess similar crystal forms, discovered in 1818 by the German chemist Eilhardt Mitscherlich. Berzelius had provided both the patronage and the foundational concepts for Mitscherlich’s own career. In contemporary mineralogy disputes, Berzelius...

...are thin and nonornamented. They are often brightly coloured, as in the Tellinidae. The shell is laterally compressed and thus more bladelike, but the adductor muscles are still of similar size (the isomyarian form). Such structural features adapt the animal for rapid movement through the sand; long siphons project to the surface above. Deep burrowing has been achieved by a different mechanism....

river formed by the confluence of the Tugaloo and Seneca rivers at Hartwell Dam, Georgia, U.S. It constitutes the boundary between Georgia and South Carolina as it flows southeastward past Augusta and Savannah, Ga., into the Atlantic Ocean after a cour...

drug used in the treatment and prevention of tuberculosis. Isoniazid commonly is used in combination with other drugs, such as rifampin, ethambutol, pyrazinamide, or streptomycin; these drugs are used with isoniazid in order to prevent, or at least delay, the development of isoniazid-resistant strains of tuberculin bacilli. Treatment usually is continued for m...

drug used in the treatment and prevention of tuberculosis. Isoniazid commonly is used in combination with other drugs, such as rifampin, ethambutol, pyrazinamide, or streptomycin; these drugs are used with isoniazid in order to prevent, or at least delay, the development of isoniazid-resistant strains of tuberculin bacilli. Treatment usually is continued for m...

synthetic drug used in the treatment of moderate to severe pain. It is an opioid analgesic, and thus its effects on the body resemble those of opium or morphine, one of opium’s purified constituents. A common trade name for meperidine is Demerol....

any of a class of organic compounds having the molecular structure R−N+ ≡ C, in which R is a combining group derived by removal of a hydrogen atom from an organic compound. The isocyanides are isomers of the nitriles;...

...in the warfare among the three Korean kingdoms on the peninsula. Although the rulers continued to worship Mount Miwa, the religious focus of the court seems to have been concentrated upon the Isonokami Shrine at Tenri, south of Nara. The rulers there seem to have been somewhat more military in nature than their Miwa predecessors, and archaeological findings suggest that the most treasured......

...the basis of representation in public office, and the Solonian Council of Four Hundred was increased to 500 (50 from each tribe, with members selected from demes according to their numbers). Isonomia, the principle of equality of rights for all, was one of the proudest boasts of the reformers, and there is no doubt that Cleisthenes’ work led to a much wider and more active......

(1915–17), 12 battles along the Isonzo River on the eastern sector of the Italian Front in World War I....

(1915–17), 12 battles along the Isonzo River on the eastern sector of the Italian Front in World War I....

...catalyst to convert unbranched alkanes to their branched-chain isomers. In one such application, butane is isomerized to 2-methylpropane for use as a starting material in the preparation of 2,2,4-trimethylpentane (isooctane), which is a component of high-octane gasoline....

...bandicoot (Perameles, or Thylacis, nasuta), a vaguely ratlike brown animal whose rump may be black-barred, is the common form in eastern Australia. The three species of short-nosed bandicoots, Isoodon (incorrectly Thylacis), are found in New Guinea, Australia, and Tasmania. Rabbit-eared bandicoots, or bilbies, are species of Thylacomys......

Paraffins can be arranged either in straight chains (normal paraffins, such as butane; see figure) or branched chains (isoparaffins). Most of the paraffin compounds in naturally occurring crude oils are normal paraffins, while isoparaffins are frequently produced in refinery processes. The normal paraffins are uniquely poor as motor fuels, while isoparaffins have good engine-combustion......

...may be sung with either ofthe adjacent registers. These tones of the same fundamental frequency, sound level, and basic sound category in different vocal registers have recently been defined as isoparametric tones. In the untrained male voice, the transition between the midvoice and the high falsetto sounds abrupt; this so-called register break is similar to the noisy gearshift in a......

Polystyrene pellets can be impregnated with isopentane at room temperature and modest pressure. When the pellets are heated, they can be made to fuse together at the same time that the isopentane evaporates, foaming the polystyrene and cooling the assembly at the same time. Usually the pellets are prefoamed to some extent before being put into a mold to form a cup or some form of rigid......

...a compound derived from acetic acid and coenzyme A (CoA), a complex substance that participates in many reactions that are controlled by enzymes. Previously unknown compounds, mevalonic acid and isopentenyl pyrophosphate (IPPP), occur as important intermediates in the process....

in mathematics, the determination of the shape of the closed plane curve having a given length and enclosing the maximum area. (In the absence of any restriction on shape, the curve is a circle.) The calculus of variations evolved from attempts to solve this problem and the brachistochrone (“least-time”) problem....

in French literature, a medieval collection of fables, often versions of Aesop’s Fables....

...and momentarily extinguished, with short eclipses interrupting longer periods of light. Analogous to the flashing mode are occulting and group-occulting characters. A special class of light is the isophase, which alternates eclipses and flashes of exactly equal duration....

...by the attack of wasps). Tannins are used in making leather, and gallic acid is employed in the production of inks. Three of the most important aromatic dicarboxylic acids are called phthalic, isophthalic, and terephthalic acid, for the ortho, meta, and para isomers, respectively. Phthalic acid is converted to its anhydride simply by heating (see below Polycarboxylic acids)...

...over water in the Southern Hemisphere, this timberline exists only in the Northern Hemisphere. It crosses northern Siberia, Alaska, and Canada, and far-northern Scandinavia. Several climatic isopleths (imaginary lines connecting points of equal values for various climatic variables) have been proposed as quantitative approximations of this timberline. The Köppen–Supan line was......

any member of the order Isopoda (class Crustacea), a group of diverse, widely occurring forms including marine, freshwater, and terrestrial species. Most are free-living, but a number of marine species are parasitic on other animals. They are usually inconspicuous. Most of the 10,000 species, which include the pill bug, the sow bug, and the gribble...

any member of the order Isopoda (class Crustacea), a group of diverse, widely occurring forms including marine, freshwater, and terrestrial species. Most are free-living, but a number of marine species are parasitic on other animals. They are usually inconspicuous. Most of the 10,000 species, which include the pill bug, the sow bug, and the gribble...

...weak acids that readily condense (polymerize) to form anions containing several molecules of the acid anhydride. If these condensed acids contain only one type of acid anhydride, they are called isopoly acids, and their salts are called isopoly salts. The acid anhydrides also can condense with other acids (e.g., phosphoric or silicic acids) to form heteropoly acids, which can form heteropoly......

The amphoteric metals of groups VB (vanadium, niobium, and tantalum) and VIB (chromium, molybdenum, and tungsten) in the +5 and +6 oxidation states, respectively, form weak acids that readily condense (polymerize) to form anions containing several molecules of the acid anhydride. If these condensed acids contain only one type of acid anhydride, they are called isopoly acids, and their salts are......

...to form anions containing several molecules of the acid anhydride. If these condensed acids contain only one type of acid anhydride, they are called isopoly acids, and their salts are called isopoly salts. The acid anhydrides also can condense with other acids (e.g., phosphoric or silicic acids) to form heteropoly acids, which can form heteropoly salts. The condensation reactions, which......

a colourless, volatile liquid hydrocarbon obtained in processing petroleum or coal tar and used as a chemical raw material. The formula is C5H8....

Isoprene rubber (IR) is manufactured by the polymerization of synthetic isoprene, which is obtained from the thermal cracking of the naphtha fraction of petroleum. Polymerization is conducted in solution, using both anionic and Ziegler-Natta catalysts. The product is at most 98 percent cis-1,4 polyisoprene, and its structure is not as regular as natural rubber in other respects. As a......

...be connected in different ways to produce the variety of carbon atom arrangements found in monoterpenes and sesquiterpenes (molecules containing 15 carbon atoms). Wallach’s proposal, called the isoprene rule, has helped chemists understand the structures of the more complex members of the class. The fundamental five-carbon unit typically has four carbon atoms in a linear chain with the.....

Class of organic compounds made up of two or more structural units derived from isoprene....

Another metabolic cycle, the isoprenoid pathway, produces essential oils, carotenoid pigments, certain plant hormones, and rubber. These metabolites (often called secondary metabolites) are unique to plants and serve such functions as attracting pollinating insects, photosynthesis, and growth and development. Plant seedlings use the glyoxylic acid cycle to convert fats (principally from seeds)......

one of the most common members of the alcohol family of organic compounds. Isopropyl alcohol was the first commercial synthetic alcohol. It is easily synthesized from the reaction of propylene with sulfuric acid, followed by hydrolysis....

Benzene is converted to isopropylbenzene (cumene) by treatment with propylene and an acidic catalyst. Oxidation yields a hydroperoxide (cumene hydroperoxide), which undergoes acid-catalyzed rearrangement to phenol and acetone. Although this process seems more complicated than the Dow process, it is advantageous because it produces two valuable industrial products: phenol and acetone....

any of a group of cellulose-eating insects, the social system of which shows remarkable parallels with those of ants and bees, although it has evolved independently. Even though termites are not closely related to ants, they are sometimes referred to as white ants. Phylogenetic studies have shown that the closest relative t...

Citronellal is converted by treatment with acid into the monocyclic monoterpene alcohol isopulegol, from which a mixture of stereoisomeric menthols is produced by catalytic hydrogenation. The process is used commercially to supplement the natural sources of menthol (oil of peppermint), widely used as a flavouring and in medicinal preparations. Citral, upon reduction with sodium amalgam, yields......

in music, the organizing principle of much of 14th-century French polyphony, characterized by the extension of the rhythmic texture (talea) of an initial section to the entire composition, despite the variation of corresponding melodic features (color); the term was coined around 1900 by the German musicologist Friedrich Ludwig...

property that is characteristic of families of related subatomic particles differing principally in the values of their electric charge. The families of similar particles are known as isospin multiplets: two-particle families are called doublets, three-particle families are called triplets, and so on....

genus of parasitic protozoans of the sporozoan subclass Coccidia. Isospora causes the disease known as coccidiosis in humans, dogs, and cats. The species that attack humans, I. hominis and I. belli, inhabit the digestive tract and are endemic in many areas of southern Europe, Asia, Afr...

ideal theoretical balance of all large portions of Earth’s lithosphere as though they were floating on the denser underlying layer, the asthenosphere, a section of the upper mantle composed of weak, plastic rock that is about 110 km (70 miles) below the surface. Isostasy controls the regional elevations of continents and ...

ideal theoretical balance of all large portions of Earth’s lithosphere as though they were floating on the denser underlying layer, the asthenosphere, a section of the upper mantle composed of weak, plastic rock that is about 110 km (70 miles) below the surface. Isostasy controls the regional elevations of continents and ...

...aluminum catalyst. In the case of a generalized ethylenic compound, CH2=CHR, stereoregular polymerization may yield three different arrangements of the polymer: an isotactic polymer, a syndiotactic polymer, and an atactic polymer. These have the following arrangements of their molecular chains:...

genus of trilobites (extinct arthropods) restricted to Europe and North America during the Ordovician Period (about 488 million to 444 million years ago). Isotelus was relatively large for a trilobite and was characterized by its distinctive flat shape. The head and the tail were well developed and ...

line drawn on a map or chart joining points with the same temperature. Isotherms are commonly used in meteorology to show the distribution of temperature at the Earth’s surface or on a chart indicating constant level or constant pressure. They are also used to show the time variation of temperature with height in the atmosphere or with depth in soil or water; the characte...

Because heat engines may go through a complex sequence of steps, a simplified model is often used to illustrate the principles of thermodynamics. In particular, consider a gas that expands and contracts within a cylinder with a movable piston under a prescribed set of conditions. There are two particularly important sets of conditions. One condition, known as an isothermal expansion, involves......

...conditions, however, all one needs to know is how the density changes when the pressure is changed by a small amount, and this is described by the compressibility of the fluid—either the isothermal compressibility, βべーたT, or the adiabatic compressibility, βべーたS, according to circumstance. When an element of fluid is compressed, the work done on...

...Except under very extreme conditions, however, all one needs to know is how the density changes when the pressure is changed by a small amount, and this is described by the compressibility of the fluid—either the isothermal compressibility, βべーたT, or the adiabatic compressibility, βべーたS, according to circumstance. When an element of fluid is......

...its mass for the entire year; a subpolar (or polythermal) glacier contains ice below the freezing temperature, except for surface melting in the summer and a basal layer of temperate ice; and a temperate glacier is at the melting temperature throughout its mass, but surface freezing occurs in winter. A polar or subpolar glacier may be frozen to its bed (cold-based), or it may be at the......

IRM (isothermal remanent magnetization) results from the application of a magnetic field at a constant (isothermal) temperature, often room temperature....

...The latter form corresponds to the variables with which the stress-strain relations were written above. Sometimes ρろー0f is called the strain energy for states of isothermal (constant θしーた) elastic deformation; ρろー0e has the same interpretation for adiabatic (s = constant) elastic deformation, achieved when the time......

...Carbon disulfide, S=C=S, is a common and important organic solvent and raw material containing a thiocarbonyl group; it is used in the manufacture of rayon. Isothiocyanates, R−N=C=S, have cumulated bonding similar to that in carbon disulfide. Allyl isothiocyanate,......

any of two or more species of atoms or nuclei that have the same number of neutrons. Thus, chlorine-37 and potassium-39 are isotones, because the nucleus of this species of chlorine consists of 17 protons and 20 neutrons, whereas the nucleus of this species of potassium contains 19 protons and 20 neutrons....

When a muscle is to lift a constant load (isotonic conditions) after stimulation starts, the force increases, just as in an isometric contraction, and, when the force is equal to the load, the muscle begins to shorten and lifts the load. When both the activity of the muscle and the force in it begin to decline, the load stretches the muscle back to its initial length. The tension in the muscle......

One of two or more species of atoms of a chemical element having nuclei with the same number of protons but different numbers of neutrons....

...release of various radioactive transitions leads to the fundamental question of nuclear binding energies and stabilities. A much-used method of displaying nuclear-stability relationships is an isotope chart, those positions on the same horizontal row corresponding to a given proton number (Z) and those on the same vertical column to a given neutron number (N). Such a map is......

radiochemical method of analysis for measuring the mass and quantity of an element in a substance. The procedure involves adding to a substance a known quantity of a radioisotope of the element to be measured and mixing it with the stable isotope of the element. A sample is then taken from the mixture and analyzed. By measuring the amount of ...

Isotopes are atoms that have the same atomic number (and, hence, generally the same chemistry) but different mass. The difference in mass becomes chemically important in certain instances. For example, when a carbon-hydrogen bond is replaced by a carbon-deuterium bond (deuterium being an isotope of hydrogen with about twice the mass), the vibrational frequencies of that bond are changed. The......

Isotopic geochemistry has several principal roles in geology. One is concerned with the enrichment or impoverishment of certain isotopic species that results from the influence of differences in mass of molecules containing different isotopes. Measurements of the proportions of various isotopic species can be used as a form of geologic thermometer. The ratio of oxygen-16 to oxygen-18 in calcium......

Isotopic geochemistry has several principal roles in geology. One is concerned with the enrichment or impoverishment of certain isotopic species that results from the influence of differences in mass of molecules containing different isotopes. Measurements of the proportions of various isotopic species can be used as a form of geologic thermometer. The ratio of oxygen-16 to oxygen-18 in calcium......