Nature is a British multidisciplinary scientific journal, first published on 4 November 1869. It is one of the most recognizable scientific journals in the world, was ranked the world's most cited scientific journal by the Science Edition of the 2010 Journal Citation Reports and is ascribed an impact factor of 40.137, making it one of the world's top academic journals. It is one of the few remaining academic journals that publishes original research across a wide range of scientific fields. Research scientists are the primary audience for the journal, but summaries and accompanying articles are intended to make many of the most important papers understandable to scientists in other fields and the educated public. Towards the front of each issue are editorials and feature articles on issues of general interest to scientists, including current affairs, science funding, scientific ethics and research breakthroughs. There are sections on books and short science fiction stories; the remainder of the journal consists of research papers, which are dense and technical.
Because of strict limits on the length of papers the printed text is a summary of the work in question with many details relegated to accompanying supplementary material on the journal's website. There are many fields of research in which important new advances and original research are published as either articles or letters in Nature; the papers that have been published in this journal are internationally acclaimed for maintaining high research standards. Fewer than 8% of submitted papers are accepted for publication. In 2007 Nature received the Prince of Asturias Award for Humanity; the enormous progress in science and mathematics during the 19th century was recorded in journals written in German or French, as well as in English. Britain underwent enormous technological and industrial changes and advances in the latter half of the 19th century. In English the most respected scientific journals of this time were the refereed journals of the Royal Society, which had published many of the great works from Isaac Newton, Michael Faraday through to early works from Charles Darwin.
In addition, during this period, the number of popular science periodicals doubled from the 1850s to the 1860s. According to the editors of these popular science magazines, the publications were designed to serve as "organs of science", in essence, a means of connecting the public to the scientific world. Nature, first created in 1869, was not the first magazine of its kind in Britain. One journal to precede Nature was Recreative Science: A Record and Remembrancer of Intellectual Observation, created in 1859, began as a natural history magazine and progressed to include more physical observational science and technical subjects and less natural history; the journal's name changed from its original title to Intellectual Observer: A Review of Natural History, Microscopic Research, Recreative Science and later to the Student and Intellectual Observer of Science and Art. While Recreative Science had attempted to include more physical sciences such as astronomy and archaeology, the Intellectual Observer broadened itself further to include literature and art as well.
Similar to Recreative Science was the scientific journal Popular Science Review, created in 1862, which covered different fields of science by creating subsections titled "Scientific Summary" or "Quarterly Retrospect", with book reviews and commentary on the latest scientific works and publications. Two other journals produced in England prior to the development of Nature were the Quarterly Journal of Science and Scientific Opinion, established in 1864 and 1868, respectively; the journal most related to Nature in its editorship and format was The Reader, created in 1864. These similar journals all failed; the Popular Science Review survived longest, lasting 20 years and ending its publication in 1881. The Quarterly Journal, after undergoing a number of editorial changes, ceased publication in 1885; the Reader terminated in 1867, Scientific Opinion lasted a mere 2 years, until June 1870. Not long after the conclusion of The Reader, a former editor, Norman Lockyer, decided to create a new scientific journal titled Nature, taking its name from a line by William Wordsworth: "To the solid ground of nature trusts the Mind that builds for aye".
First owned and published by Alexander Macmillan, Nature was similar to its predecessors in its attempt to "provide cultivated readers with an accessible forum for reading about advances in scientific knowledge." Janet Browne has proposed that "far more than any other science journal of the period, Nature was conceived and raised to serve polemic purpose." Many of the early editions of Nature consisted of articles written by members of a group that called itself the X Club, a group of scientists known for having liberal and somewhat controversial scientific beliefs relative to the time period. Initiated by Thomas Henry Huxley, the group consisted of such important scientists as Joseph Dalton Hooker, Herbert Spencer, John Tyndall, along with another five scientists and mathematicians, it was in part its scientific liberality that made Nature a longer-lasti
In chemistry in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, either saturated or unsaturated. Most occurring fatty acids have an unbranched chain of an number of carbon atoms, from 4 to 28. Fatty acids are not found in organisms, but instead as three main classes of esters: triglycerides and cholesterol esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells; the concept of fatty acid was introduced by Michel Eugène Chevreul, though he used some variant terms: graisse acide and acide huileux. Fatty acids differ by length categorized as short to long. Short-chain fatty acids are fatty acids with aliphatic tails of five or fewer carbons. Medium-chain fatty acids are fatty acids with aliphatic tails of 6 to 12 carbons, which can form medium-chain triglycerides. Long-chain fatty acids are fatty acids with aliphatic tails of 13 to 21 carbons. Long chain fatty acids are fatty acids with aliphatic tails of 22 or more carbons.
Saturated fatty acids have no C=C double bonds. They have the same formula CH3nCOOH, with variations in "n". An important saturated fatty acid is stearic acid, which when neutralized with lye is the most common form of soap. Unsaturated fatty acids have one or more C=C double bonds; the C=C double bonds can give either cis or trans isomers. Cis A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain; the rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has; when a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. Α-Linolenic acid, with three double bonds, favors a hooked shape.
The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be packed, therefore can affect the melting temperature of the membrane or of the fat. Trans A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain; as a result, they do not cause the chain to bend much, their shape is similar to straight saturated fatty acids. In most occurring unsaturated fatty acids, each double bond has three n carbon atoms after it, for some n, all are cis bonds. Most fatty acids in the trans configuration are not found in nature and are the result of human processing; the differences in geometry between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, in the construction of biological structures. The position of the carbon atoms in a fatty acid can be indicated from the −COOH end, or from the −CH3 end.
If indicated from the −COOH end the C-1, C-2, C-3, …. Notation is used. If the position is counted from the other, −CH3, end the position is indicated by the ω-n notation; the positions of the double bonds in a fatty acid chain can, therefore, be indicated in two ways, using the C-n or the ω-n notation. Thus, in an 18 carbon fatty acid, a double bond between C-12 and C-13 is reported either as Δ12 if counted from the −COOH end, or as ω-6 if counting from the −CH3 end; the "Δ" is the Greek letter delta. Omega is the last letter in the Greek alphabet, is therefore used to indicate the “last” carbon atom in the fatty acid chain. Since the ω-n notation is used exclusively to indicate the positions of the double bonds close to the −CH3 end in essential fatty acids, there is no necessity for an equivalent “Δ”-like notation - the use of the “ω-n” notation always refers to the position of a double bond. Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids.
The difference is relevant to gluconeogenesis. The following table describes the most common systems of naming fatty acids; when circulating in the plasma are not in their ester, fatty acids are known as non-esterified fatty acids or free fatty acids. FFAs are always bound to a transport protein, such as albumin. Fatty acids are produced industrially by the hydrolysis of triglycerides, with the removal of glycerol. Phospholipids represent another source; some fatty acids are produced synthetically by hydrocarboxylation of alkenes. Template:Says whom? In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, the mammary glands during lactation. Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids. Pyruvate is decarboxylated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids occurs; this cannot occur directly.
To obtain cytosol
Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, not consumed in the catalyzed reaction and can continue to act repeatedly. Because of this, only small amounts of catalyst are required to alter the reaction rate in principle. In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst reacts to form a temporary intermediate, which regenerates the original catalyst in a cyclic process. A substance which provides a mechanism with a higher activation energy does not decrease the rate because the reaction can still occur by the non-catalyzed route. An added substance which does reduce the reaction rate is not considered a catalyst but a reaction inhibitor. Catalysts may be classified as either heterogeneous. A homogeneous catalyst is one whose molecules are dispersed in the same phase as the reactant's molecules.
A heterogeneous catalyst is one whose molecules are not in the same phase as the reactant's, which are gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are considered as a third category. In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations; the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have a lower activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature and for the same reactant concentrations. However, the detailed mechanics of catalysis is complex. Catalysts may bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to reactive forms, such as chemisorbed hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions are typical chemical reactions. The catalyst participates in this slowest step, rates are limited by amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or sublimate in a solid–gas system; the production of most industrially important chemicals involves catalysis. Most biochemically significant processes are catalysed.
Research into catalysis is a major field in applied science and involves many areas of chemistry, notably organometallic chemistry and materials science. Catalysis is relevant to many aspects of environmental science, e.g. the catalytic converter in automobiles and the dynamics of the ozone hole. Catalytic reactions are preferred in environmentally friendly green chemistry due to the reduced amount of waste generated, as opposed to stoichiometric reactions in which all reactants are consumed and more side products are formed. Many transition metals and transition metal complexes are used in catalysis as well. Catalysts called. A catalyst works by providing an alternative reaction pathway to the reaction product; the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates oxygen, as shown below. 2 H2O2 → 2 H2O + O2This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow.
In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available. This reaction is affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms. Upon the addition of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly; this effect is seen by the effervescence of oxygen. The manganese dioxide is not consumed in the reaction, thus may be recovered unchanged, re-used indefinitely. Accordingly, manganese dioxide catalyses this reaction. Catalytic activity is denoted by the symbol z and measured in mol/s, a unit, called katal and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the catalyst under certain conditions, in relation to a specific chemical reaction. Catalytic activity of one katal of a catalyst means one mole of that catalyst will catalyse 1 mole of the reactant to product in one second. A catalyst may and will have different catalytic activity for di
Coke is a grey and porous fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air — a destructive distillation process. It is an important industrial product, used in iron ore smelting, but as a fuel in stoves and forges when air pollution is a concern; the unqualified term "coke" refers to the product derived from low-ash and low-sulfur bituminous coal by a process called coking. A similar product called pet coke, is obtained from crude oil in oil refineries. Coke may be formed by geologic processes. Historical sources dating to the 4th century describe the production of coke in ancient China; the Chinese first used coke for heating and cooking no than the ninth century. By the first decades of the eleventh century, Chinese ironworkers in the Yellow River valley began to fuel their furnaces with coke, solving their fuel problem in that tree-sparse region. In 1589, a patent was granted to Thomas Proctor and William Peterson for making iron and steel and melting lead with "earth-coal, sea-coal and peat".
The patent contains a distinct allusion to the preparation of coal by "cooking". In 1590, a patent was granted to the Dean of York to "purify pit-coal and free it from its offensive smell". In 1620, a patent was granted to a company composed of William St. John and other knights, mentioning the use of coke in smelting ores and manufacturing metals. In 1627, a patent was granted to Sir John Hacket and Octavius de Strada for a method of rendering sea-coal and pit-coal as useful as charcoal for burning in houses, without offense by smell or smoke. In 1603, Hugh Plat suggested that coal might be charred in a manner analogous to the way charcoal is produced from wood; this process was not employed until 1642. It was considered an improvement in quality, brought about an "alteration which all England admired"—the coke process allowed for a lighter roast of the malt, leading to the creation of what by the end of the 17th century was called pale ale. In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron.
Coke's superior crushing strength allowed blast furnaces to become larger. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Before this time, iron-making used large quantities of charcoal, produced by burning wood; as the coppicing of forests became unable to meet the demand, the substitution of coke for charcoal became common in Great Britain, coke was manufactured by burning coal in heaps on the ground so that only the outer layer burned, leaving the interior of the pile in a carbonized state. In the late 18th century, brick beehive ovens were developed, which allowed more control over the burning process. In 1768, John Wilkinson built a more practical oven for converting coal into coke. Wilkinson improved the process by building the coal heaps around a low central chimney built of loose bricks and with openings for the combustion gases to enter, resulting in a higher yield of better coke. With greater skill in the firing and quenching of the heaps, yields were increased from about 33% to 65% by the middle of the 19th century.
The Scottish iron industry expanded in the second quarter of the 19th century, through the adoption of the hot-blast process in its coalfields. In 1802, a battery of beehives was set up near Sheffield, to coke the Silkstone seam for use in crucible steel melting. By 1870, there were 14,000 beehive ovens in operation on the West Durham coalfields, capable of producing 4,000,000 long tons of coke; as a measure of the extent of the expansion of coke making, it has been estimated that the requirements of the iron industry were about 1,000,000 long tons a year in the early 1850s, whereas by 1880 the figure had risen to 7,000,000 long tons, of which about 5,000,000 long tons were produced in Durham county, 1,000,000 long tons in the South Wales coalfield, 1,000,000 long tons in Yorkshire and Derbyshire. In the first years of steam railway locomotives, coke was the normal fuel; this resulted from an early piece of environmental legislation. This was not technically possible to achieve until the firebox arch came into use, but burning coke, with its low smoke emissions, was considered to meet the requirement.
This rule was dropped, cheaper coal became the normal fuel, as railways gained acceptance among the public. In the US, the first use of coke in an iron furnace occurred around 1817 at Isaac Meason's Plumsock puddling furnace and rolling mill in Fayette County, Pennsylvania. In the late 19th century, the coalfields of western Pennsylvania provided a rich source of raw material for coking. In 1885, the Rochester and Pittsburgh Coal and Iron Company constructed the world's longest string of coke ovens in Walston, with 475 ovens over a length of 2 km, their output reached 22,000 tons per month. The Minersville Coke Ovens in Huntingdon County, were listed on the National Register of Historic Places in 1991. Between 1870 and 1905, the number of beehive ovens in the US skyrocketed from about 200 to 31,000, which produced nearly 18,000,000 tons of coke in the Pittsburgh area alone. One observer boasted that if loaded into a train, “the year's production would make up a train so long that the engine in front of it would go to
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings. The simplest such chemicals are naphthalene, having two aromatic rings, the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar molecules found in tar deposits, they are produced by the thermal decomposition of organic matter. PAHs are abundant in the universe, have been found to have formed as early as the first couple of billion years after the Big Bang, in association with formation of new stars and exoplanets; some studies suggest. Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life. By definition, polycyclic aromatic hydrocarbons have multiple cycles, precluding benzene from being considered a PAH. Naphthalene is considered the simplest polycyclic aromatic hydrocarbon by the US EPA and US CDC for policy contexts. Other authors consider PAHs to start with the tricyclic species anthracene.
PAHs are not considered to contain heteroatoms or carry substituents. PAHs with five or six-membered rings are most common; those composed only of six-membered rings are called alternant PAHs. The following are examples of PAHs that vary in the number and arrangement of their rings: Principal PAH Compounds PAHs are nonpolar and lipophilic. Larger PAHs are insoluble in water, although some smaller PAHs are soluble and known contaminants in drinking water; the larger members are poorly soluble in organic solvents and in lipids. They are colorless; the aromaticity varies for PAHs. According to Clar's rule, the resonance structure of a PAH that has the largest number of disjoint aromatic pi sextets—i.e. Benzene-like moieties—is the most important for the characterization of the properties of that PAH. Benzene-substructure resonance analysis for Clar's rule For example, in phenanthrene one Clar structure has two sextets—the first and third rings—while the other resonance structure has just one central sextet.
In contrast, in anthracene the resonance structures have one sextet each, which can be at any of the three rings, the aromaticity spreads out more evenly across the whole molecule. This difference in number of sextets is reflected in the differing ultraviolet–visible spectra of these two isomers, as higher Clar pi-sextets are associated with larger HOMO-LUMO gaps. Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, one in the first and fourth rings. Superposition of these structures reveals that the aromaticity in the outer rings is greater compared to the inner rings. Polycyclic aromatic compounds characteristically reduce to the radical anions; the redox potential correlates with the size of the PAH. Polycyclic aromatic hydrocarbons are found in natural sources such as creosote, they can result from the incomplete combustion of organic matter. PAHs can be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal.
PAHs are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources. The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other biofuels such as dung or crop residues contribute more than half of annual global PAH emissions due to biofuel use in India and China; as of 2004, industrial processes and the extraction and use of fossil fuels made up more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States. Wildfires are another notable source. Higher outdoor air and water concentrations of PAHs have been measured in Asia and Latin America than in Europe, the U. S. and Canada. PAHs are found as complex mixtures. Lower-temperature combustion, such as tobacco smoking or wood-burning, tends to generate low molecular weight PAHs, whereas high-temperature industrial processes generate PAHs with higher molecular weights. Most PAHs are insoluble in water, which limits their mobility in the environment, although PAHs sorb to fine-grained organic-rich sediments.
Aqueous solubility of PAHs decreases logarithmically as molecular mass increases. Two-ringed PAHs, to a lesser extent three-ringed PAHs, dissolve in water, making them more available for biological uptake and degradation. Further, two- to four-ringed PAHs volatilize sufficiently to appear in the atmosphere predominantly in gaseous form, although the physical state of four-ring PAHs can depend on temperature. In contrast, compounds with five or more rings have low solubility in water and low volatility. In solid state, these compounds are less accessible for biological uptake or degradation, increasing their persistence in the environment. Spiral galaxy NGC 5529 has been
Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, petroleum, or peat. Production and trade in pine-derived tar was a major contributor in the economies of Northern Europe and Colonial America, its main use was in preserving wooden sailing vessels against rot. The largest user was the Royal Navy of the United Kingdom. Demand for tar declined with the advent of steel ships. Tar-like products can be produced from other forms of organic matter, such as peat. Mineral products resembling tar can be produced from fossil hydrocarbons, such as petroleum. Coal tar is produced from coal as a byproduct of coke production. "Tar" and "pitch" can be used interchangeably. There is a tendency to use "tar" for "pitch" for more solid substances. Both "tar" and "pitch" are applied to viscous forms of asphalt, such as the asphalt found in occurring tar pits. "Rangoon tar" known as "Burmese oil" or "Burmese naphtha", is a form of petroleum.
Oil sands exclusively produced in Alberta, are colloquially referred to as "tar sands" but are in fact composed of bitumen. Note, similar heavy crude grades from Venezuela are not referred to as "tar sands" by Wikipedia or the environmental community. In Northern Europe, the word "tar" refers to a substance, derived from the wood and roots of pine. In earlier times it was used as a water repellent coating for boats and roofs, it is still used as an additive in the flavoring of candy and other foods. Wood tar is microbicidal. Producing tar from wood was known in ancient Greece and has been used in Scandinavia since the Iron Age. For centuries, dating back at least to the 14th century, tar was among Sweden's most important exports. Sweden exported 13,000 barrels of tar in 1615 and 227,000 barrels in the peak year of 1863. Production nearly stopped in the early 20th century, when other chemicals replaced tar, wooden ships were replaced by steel ships. Traditional wooden boats are still sometimes tarred.
The heating of pine wood causes pitch to drip away from the wood and leave behind charcoal. Birch bark is used to make fine tar, known as "Russian oil", suitable for leather protection; the by-products of wood tar are charcoal. When deciduous tree woods are subjected to destructive distillation, the products are methanol and charcoal. Tar kilns are dry distillation ovens used in Scandinavia for producing tar from wood, they were built close from limestone or from more primitive holes in the ground. The bottom is sloped into an outlet hole to allow the tar to pour out; the wood is split into dimensions of a finger, stacked densely, covered tight with dirt and moss. If oxygen can enter, the wood might catch fire, the production would be ruined. On top of this, a fire lit. After a few hours, the tar continues to do so for a few days. Tar was used as tar paper and to seal the hulls of ships and boats. For millennia, wood tar was used to waterproof sails and boats, but today, sails made from inherently waterproof synthetic substances have reduced the demand for tar.
Wood tar is still used to seal traditional wooden boats and the roofs of historical shingle-roofed churches, as well as painting exterior walls of log buildings. Tar is a general disinfectant. Pine tar oil, or wood tar oil, is used for the surface treatment of wooden shingle roofs, boats and tubs and in the medicine and rubber industries. Pine tar has good penetration on the rough wood. An old wood tar oil recipe for the treatment of wood is one-third each genuine wood tar, balsam turpentine, boiled or raw linseed oil or Chinese tung oil. In Finland, wood tar was once considered a panacea reputed to heal "even those cut in twain through their midriff". A Finnish proverb states that "if sauna and tar won't help, the disease is fatal." Wood tar is used in traditional Finnish medicine because of its microbicidal properties. Wood tar is available diluted as tar water, which has numerous uses: As a flavoring for candies and alcohol; as a spice for food, like meat. As a scent for saunas. Tar water is mixed into water, turned into steam in the sauna.
As an anti-dandruff agent in shampoo. As a component of cosmetics. Mixing tar with linseed oil varnish produces tar paint. Tar paint has a translucent brownish hue and can be used to saturate and tone wood and protect it from weather. Tar paint can be toned with various pigments, producing translucent colors and preserving the wood texture. In English and French, "tar" is a substance derived from coal, it was one of the products of gasworks. Tar made from coal or petroleum is considered toxic and carcinogenic because of its high benzene content, though coal tar in low concentrations is used as a topical medicine. Coal and petroleum tar has a pungent odour. Coal tar is listed at number 1999 in the United Nations list of dangerous goods. Bitumen Creosote Pitch Pitch drop experiment Resin Rollins Tars Tarring and feathering Tar Heels Tar pit Tarmac Tar tar ^ "Geotimes – February 2005 – Mummy tar in ancient Egypt". Retrieved January 9, 2006. Details history and uses of "Rangoon Tar"
The calorie is a unit of energy. The Calorie is 1,000 calories; that capital C, distinguishing Calorie from calorie, is a long-established scientific convention but is not always understood more widely. Where the context is about food and exercise, the term appears without the capital C; the Calorie is termed the large calorie or kilocalorie — symbols: Cal, kcal — or food calorie, defined as the heat energy involved in warming one kilogram of water by one degree Celsius. The small calorie was defined as the heat energy to raise the temperature of one gram of water — rather than a kilogram — by the same amount. Although both units relate to the metric system, they have been considered obsolete, or deprecated, in scientific usage, since the adoption of the SI system, but the small calorie is still used in laboratory measurements and calculations, with the values thus established being reported in kilocalories. The calorie was first defined by Nicolas Clément in 1824 as a unit of heat energy, it entered French and English dictionaries between 1841 and 1867.
The word comes from Latin calor, meaning'heat'. The small calorie was introduced by Pierre Antoine Favre and Johann T. Silbermann in 1852. In 1879, Marcellin Berthelot introduced the convention of capitalizing the large Calorie to distinguish the senses; the use of the calorie for nutrition was introduced to the American public by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887. The alternate spelling calory is archaic; the energy needed to increase the temperature of a given mass of water by 1 °C depends on the atmospheric pressure and the starting temperature. Accordingly, several different precise definitions of the calorie have been used; the pressure is taken to be the standard atmospheric pressure. The temperature increase can be expressed as one kelvin, which means the same as an increment of one degree Celsius; the two definitions most common in older literature appear to be the 15 °C calorie and the thermochemical calorie. Until 1948, the latter was defined as 4.1833 international joules.
The calorie was first defined to measure energy in the form of heat in experimental calorimetry. In a nutritional context, the kilojoule is the SI unit of food energy, although the kilocalorie is still in common use; the word calorie is popularly used with the number of kilocalories of nutritional energy measured. To avoid confusion, it is sometimes written Calorie to make the distinction, although this is not understood. To facilitate comparison, specific energy or energy density figures are quoted as "calories per serving" or "kilocalories per 100 g". A nutritional requirement or consumption is expressed in calories per day. One gram of fat in food contains nine calories, while a gram of either a carbohydrate or a protein contains four calories. Alcohol in a food contains seven calories per gram. In other scientific contexts, the term calorie always refers to the small calorie. Though it is not an SI unit, it is still used in chemistry. For example, the energy released in a chemical reaction per mole of reagent is expressed in kilocalories per mole.
This use was due to the ease with which it could be calculated in laboratory reactions in aqueous solution: a volume of reagent dissolved in water forming a solution, with concentration expressed in moles per liter, will induce a temperature change in degrees Celsius in the total volume of water solvent, these quantities can be used to calculate energy per mole. It is occasionally used to specify energy quantities that relate to reaction energy, such as enthalpy of formation and the size of activation barriers. However, its use is being superseded by the SI unit, the joule, multiples thereof such as the kilojoule. In the past a bomb calorimeter was utilised to determine the energy content of food by burning a sample and measuring a temperature change in the surrounding water. Today this method is not used in the USA and has been succeeded by calculating the energy content indirectly from adding up the energy provided by energy-containing nutrients of food; the fibre content is subtracted to account for the fact fibre is not digested by the body