Paint is any pigmented liquid, liquefiable, or mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most used to protect, color, or provide texture to objects. Paint can be made or purchased in many colors—and in many different types, such as watercolor, etc. Paint is stored and applied as a liquid, but most types dry into a solid. In 2003 and 2004, South African archeologists reported finds in Blombos Cave of a 100,000-year-old human-made ochre-based mixture that could have been used like paint. Further excavation in the same cave resulted in the 2011 report of a complete toolkit for grinding pigments and making a primitive paint-like substance. Cave paintings drawn with red or yellow ochre, manganese oxide, charcoal may have been made by early Homo sapiens as long as 40,000 years ago. Ancient colored walls at Dendera, which were exposed for years to the elements, still possess their brilliant color, as vivid as when they were painted about 2,000 years ago.
The Egyptians mixed their colors with a gummy substance, applied them separately from each other without any blending or mixture. They appear to have used six colors: white, blue, red and green, they first covered the area with white traced the design in black, leaving out the lights of the ground color. They used minium for red, of a dark tinge. Pliny mentions some painted ceilings in his day in the town of Ardea, done prior to the foundation of Rome, he expresses great surprise and admiration after the lapse of so many centuries. Paint was made with the yolk of eggs and therefore, the substance would harden and adhere to the surface it was applied to. Pigment was made from plants and different soils. Most paints used either water as a base. A still extant example of 17th-century house oil painting is Ham House in Surrey, where a primer was used along with several undercoats and an elaborate decorative overcoat; the process was done by hand by the painters and exposed them to lead poisoning due to the white-lead powder.
In 1718, Marshall Smith invented Engine for the Grinding of Colours" in England. It is not known how it operated, but it was a device that increased the efficiency of pigment grinding dramatically. Soon, a company called Emerton and Manby was advertising exceptionally low-priced paints, ground with labour-saving technology: One Pound of Colour ground in a Horse-Mill will paint twelve Yards of Work, whereas Colour ground any other Way, will not do half that Quantity. By the proper onset of the Industrial Revolution, paint was being ground in steam-powered mills and an alternative to lead-based pigments was found in a white derivative of zinc oxide. Interior house painting became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was increasingly used as an inexpensive binder. In 1866, Sherwin-Williams in the United States opened as a large paint-maker and invented a paint that could be used from the tin without preparation.
It was not until the stimulus of World War II created a shortage of linseed oil in the supply market that artificial resins, or alkyds, were invented. Cheap and easy to make, they held the color well and lasted for a long time; the vehicle is composed of the binder. In this case, once the paint has dried or cured nearly all of the diluent has evaporated and only the binder is left on the coated surface. Thus, an important quantity in coatings formulation is the "vehicle solids", sometimes called the "resin solids" of the formula; this is the proportion of the wet coating weight, binder, i.e. the polymer backbone of the film that will remain after drying or curing is complete. The binder is the film-forming component of paint, it is the only component, always present among all the various types of formulations. Many binders must be thinned; the type of thinner, if present, varies with the binder. The binder imparts properties such as gloss, durability and toughness. Binders include synthetic or natural resins such as alkyds, vinyl-acrylics, vinyl acetate/ethylene, polyesters, melamine resins, silanes or siloxanes or oils.
Binders can be categorized according to the mechanisms for film formation. Thermoplastic mechanisms include coalescence. Drying refers to simple evaporation of the thinner to leave a coherent film behind. Coalescence refers to a mechanism that involves drying followed by actual interpenetration and fusion of discrete particles. Thermoplastic film-forming mechanisms are sometimes described as "thermoplastic cure" but, a misnomer because no chemical curing reactions are required to knit the film. Thermosetting mechanisms, on the other hand, are true curing mechanism that involve chemical reaction among the polymers that make up the binder. Thermoplastic mechanisms: Some films are formed by simple cooling of the binder. For example, encaustic or wax paints are liquid when warm, harden upon cooling. In many cases, they liquify if reheated. Paints that dry by solvent evaporation and contain the solid binder dissolved in a solvent are known as lacquers. A solid film forms; because no chemical crosslinking is involved, the film can re-dissolve in solvent.
Passive fire protection
Passive fire protection is an integral component of the components of structural fire protection and fire safety in a building. PFP attempts to contain fires or slow the spread, such as by fire-resistant walls and doors. PFP systems must comply with the associated listing and approval use and compliance in order to provide the effectiveness expected by building codes. Fire protection in a building, offshore facility or a ship is a system that includes: Active fire protection can include manual or automatic fire detection and fire suppression. Passive fire protection includes compartmentalization of the overall building through the use of fire-resistance rated walls and floors. Organization into smaller fire compartments, consisting of one or more rooms or floors, prevents or slows the spread of fire from the room of fire origin to other building spaces, limiting building damage and providing more time to the building occupants for emergency evacuation or to reach an area of refuge. Fire prevention includes minimizing ignition sources, as well as educating the occupants and operators of the facility, ship or structure concerning operation and maintenance of fire-related systems for correct function, emergency procedures including notification for fire service response and emergency evacuation.
The aim for fire protection systems is demonstrated in fire testing the ability to maintain the item or the side to be protected at or below either 140 °C or ca. 550 °C, considered the critical temperature for structural steel, above which it is in jeopardy of losing its strength, leading to collapse. This is based, in most countries, on the basic test standards for walls and floors, such as BS 476: Part 22: 1987, BS EN 1364-1: 1999 & BS EN 1364-2: 1999 or ASTM E119. Smaller components, such as fire dampers, fire doors, etc. follow suit in the main intentions of the basic standard for walls and floors. Fire testing involves live fire exposures upwards of 1100 °C, depending on the fire-resistance rating and duration one is after. More items than just fire exposures are required to be tested to ensure the survivability of the system under realistic conditions. To accomplish these aims, many different types of materials are employed in the design and construction of systems. For instance, common endothermic building materials include calcium silicate board and gypsum wallboard.
During fire testing of concrete floor slabs, water can be seen to boil out of a slab. Gypsum wall board loses all its strength during a fire; the use of endothermic materials is proven to be sound engineering practice. The chemically bound water inside these materials sublimes. During this process, the unexposed side cannot exceed the boiling point of water. Once the hydrates are spent, the temperature on the unexposed side of an endothermic fire barrier tends to rise rapidly. Too much water can be a problem, however. Concrete slabs that are too wet, will explode in a fire, why test laboratories insist on measuring water content of concrete and mortar in fire test specimens, before running any fire tests. PFP measures can include intumescents and ablative materials; the point is, that whatever the nature of the materials, they on their own bear no rating. They must be organised into systems, which bear a rating when installed in accordance with certification listings or established catalogues, such as DIN 4102 Part 4 or the Canadian National Building Code.
Passive fire protection measures are intended to contain a fire in the fire compartment of origin, thus limiting the spread of fire and smoke for a limited period of time, as determined the local building code and fire code. Passive fire protection measures, such as firestops, fire walls, fire doors, are tested to determine the fire-resistance rating of the final assembly expressed in terms of hours of fire resistance. A certification listing provides the limitations of the rating. Contrary to active fire protection measures, passive fire protection means do not require electric or electronic activation or a degree of motion. Exceptions to that particular rule of thumb are fire dampers and fire door closers, which must move and shut in order to work, as well as all intumescent products, which swell, thus move, in order to function; as the name suggests, passive fire protection remains inactive in the coating system until a fire occurs. There are two types of PFP: intumescent fire protection and vermiculite fire protection.
In vermiculite fire protection, the structural steel members are covered with vermiculite materials a thick layer. This is a cheaper option as compared to an intumescent one, but is crude and aesthetically unpleasant. Moreover, if the environment is corrosive in nature the vermiculite option is not advisable, as there is the possibility of water seeping into it, there it is difficult to monitor for corrosion. Intumescent fireproofing is a layer of paint, applied along with the coating system on the structural steel members; the thickness of this intumescent coating is dependent on the steel section used. For calculation of DFT a factor called Hp/A, referred to as "section factor" and expressed in m−1, is used. Intumescent coatings are applied as an intermediate coat in a coating system; because of the low thickness of this intumescent coating, nice finish, anti-corrosi
Education is the process of facilitating learning, or the acquisition of knowledge, values and habits. Educational methods include storytelling, teaching and directed research. Education takes place under the guidance of educators and learners may educate themselves. Education can take place in formal or informal settings and any experience that has a formative effect on the way one thinks, feels, or acts may be considered educational; the methodology of teaching is called pedagogy. Formal education is divided formally into such stages as preschool or kindergarten, primary school, secondary school and college, university, or apprenticeship. A right to education has been recognized by the United Nations. In most regions, education is compulsory up to a certain age. Etymologically, the word "education" is derived from the Latin word ēducātiō from ēducō, related to the homonym ēdūcō from ē- and dūcō. Education began in prehistory, as adults trained the young in the knowledge and skills deemed necessary in their society.
In pre-literate societies, this was achieved orally and through imitation. Story-telling passed knowledge and skills from one generation to the next; as cultures began to extend their knowledge beyond skills that could be learned through imitation, formal education developed. Schools existed in Egypt at the time of the Middle Kingdom. Plato founded the Academy in the first institution of higher learning in Europe; the city of Alexandria in Egypt, established in 330 BCE, became the successor to Athens as the intellectual cradle of Ancient Greece. There, the great Library of Alexandria was built in the 3rd century BCE. European civilizations suffered a collapse of literacy and organization following the fall of Rome in CE 476. In China, Confucius, of the State of Lu, was the country's most influential ancient philosopher, whose educational outlook continues to influence the societies of China and neighbours like Korea and Vietnam. Confucius gathered disciples and searched in vain for a ruler who would adopt his ideals for good governance, but his Analects were written down by followers and have continued to influence education in East Asia into the modern era.
The Aztecs had a well-developed theory about education, which has an equivalent word in Nahuatl called tlacahuapahualiztli. It means "the art of raising or educating a person" or "the art of strengthening or bringing up men." This was a broad conceptualization of education, which prescribed that it begins at home, supported by formal schooling, reinforced by community living. Historians cite that formal education was mandatory for everyone regardless of social class and gender. There was the word neixtlamachiliztli, "the act of giving wisdom to the face." These concepts underscore a complex set of educational practices, oriented towards communicating to the next generation the experience and intellectual heritage of the past for the purpose of individual development and his integration into the community. After the Fall of Rome, the Catholic Church became the sole preserver of literate scholarship in Western Europe; the church established cathedral schools in the Early Middle Ages as centres of advanced education.
Some of these establishments evolved into medieval universities and forebears of many of Europe's modern universities. During the High Middle Ages, Chartres Cathedral operated the famous and influential Chartres Cathedral School; the medieval universities of Western Christendom were well-integrated across all of Western Europe, encouraged freedom of inquiry, produced a great variety of fine scholars and natural philosophers, including Thomas Aquinas of the University of Naples, Robert Grosseteste of the University of Oxford, an early expositor of a systematic method of scientific experimentation, Saint Albert the Great, a pioneer of biological field research. Founded in 1088, the University of Bologne is considered the first, the oldest continually operating university. Elsewhere during the Middle Ages, Islamic science and mathematics flourished under the Islamic caliphate, established across the Middle East, extending from the Iberian Peninsula in the west to the Indus in the east and to the Almoravid Dynasty and Mali Empire in the south.
The Renaissance in Europe ushered in a new age of scientific and intellectual inquiry and appreciation of ancient Greek and Roman civilizations. Around 1450, Johannes Gutenberg developed a printing press, which allowed works of literature to spread more quickly; the European Age of Empires saw European ideas of education in philosophy, religion and sciences spread out across the globe. Missionaries and scholars brought back new ideas from other civilizations – as with the Jesuit China missions who played a significant role in the transmission of knowledge and culture between China and Europe, translating works from Europe like Euclid's Elements for Chinese scholars and the thoughts of Confucius for European audiences; the Enlightenment saw the emergence of a more secular educational outlook in Europe. In most countries today, full-time education, whether at school or otherwise, is compulsory for all children up to a certain age. Due to this the proliferation of compulsory education, combined with population growth, UNESCO has calculated that in the next 30 years more people will receive formal education than in all of human history thus far.
Formal education occurs in a structured environment. Formal education takes place in a school environme
Karelian Research Centre of RAS
Karelian Research Centre of RAS — federal public budgetary institution Karelian Research Centre of the Russian Academy of Sciences based in Petrozavodsk. Founded in 1946; as of the beginning of 2010 the Centre employed 751, including 3 Corresponding Academicians, 70 Doctors of Science and 214 Candidates of Science. Main tasks for KarRC RAS: organization and implementation of basic and applied research under governmental and regional programmes, as well as under assignments from RAS divisions and exploration projects. List of major transformations KarRC RAS has gone through: 1930 — Complex Karelian Research Institute was founded 1937 — it was reorganized into Karelian Research Institute of Culture 1946 — Karelian-Finnish Research Facility of the USSR AS with its scientific and general subdivisions was established 1949 — the Facility was renamed as the Karelian-Finnish Branch of the USSR AS 1956 — the Branch was renamed as the Karelian Branch of the USSR AS 1963 — Karelian Branch was closed, the divisions became part of ministries and departments 1967 — Karelian Branch of the USSR AS was reopened as a unity of 6 research institutions 1990 — Karelian Branch was transformed into Karelian Research Centre of the USSR AS 1991 — became Karelian Research Centre of the Russian Academy of Sciences 2007 — renamed to the Russian Academy Institution Karelian Research Centre of the Russian Academy of Sciences 2011 — renamed to Federal Public Budgetary Institution of Science Karelian Research Centre of the Russian Academy of Sciences 2014 — renamed to Federal Public Budgetary Institution Karelian Research Centre of the Russian Academy of Sciences On 24.09.1930 the Council of People’s Commissars of the Autonomous Karelian SSR passed the resolution “On foundation of the Karelian Research Institute – KRI”.
KRI began operating in 1931, E. Gylling was appointed the director. KRI was set up to comprise 6 structural units for: forestry and forest industry natural productive forces agriculture socio-economic history and revolution ethnography and linguisticsThe units were on reinforced and enlarged, Kivach Strict Nature Reserve and Louhi mire research stations were added to KRI structure. In the first year of KRI operation, 19 expeditions and field trips were organized. Owing to systematic sampling and collecting work valuable field materials were detected and preserved, the baseline for scientific research was enriched; the first KRI scientific session took place in April 1932, with over 40 presentations delivered there. One of the biggest problems for the Institute was the shortage of human resources with relevant qualifications and experience. A wide practice was to invite scholars from Moscow. KRI presidium was set up, made up of 93 members, including some most prominent scientists of the USSR — N. Ya.
Marr, I. I. Meshchaninov, A. E. Fersman, N. M. Druzhinin, M. K. Azadovsky, D. V. Bubrikh, A. Ya. Bryusov, V. I. Ravdonikas, others. On 11.01.1937 the resolution was adopted transforming KRI into the Karelian Research Institute of Culture, where only the humanities were retained. Further redundancies and closing of structural units followed. Units of the natural sciences and economic profiles were transferred to corresponding governmental authorities, the rest were either or disposed of. In this period the institute studied the history of Karelia, its culture and folk poetry. In 1937—1938 political repressions affected the institute’s staff more, dismissals continued; the institute’s vice director S. A. Makaryev, leading specialists E. A. Haapalainen, N. V. Khrisanfov, N. N. Vinogradov, director of the library E. P. Oshevenskaya were arrested and executed on false accusations of setting up an espionage and rebel nationalist organization at the institute; when the Karelian-Finnish Republic was founded in 1940 it was announced that KRIC needs to be transformed into the regional branch of the USSR Academy of Sciences, but World War II impeded the realization of this intention.
During the war, the institute’s archives were moved deeper into the country, KRIC itself was evacuated to Syktyvkar, where the institute’s activities were temporarily halted in 1942 and resumed in 1943. In the summer of 1944, after the liberation of Petrozavodsk, KRIC was moved back. In 1945 the idea of reform re-surfaced, the first step was the transformation of KRIC into the Institute of History and Literature made up of three sections: of history, literature & folk art. HLL Institute was comprised in the Karelian-Finnish Research Facility of the USSR AS. On 31.01.1946 the resolution was adopted on the establishment of the Karelian-Finnish Research Facility of the USSR AS. It was made up of the following units: Geology and Water Economy, Soil Science and Botany, Industry & Economics, Laboratory of Forest Chemistry, HLL Institute. A. A. Polkanov was appointed the director, but had to resign in 1947 because of poor health, ceding the position to I. I. Gorsky. In 1948 the Industry and Economics Section was split into Economics Section and Laboratory of Non-metalliferous Minerals, an
Gasoline, gas or petrol is a colorless petroleum-derived flammable liquid, used as a fuel in spark-ignited internal combustion engines. It consists of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, a 42-U. S.-gallon barrel of crude oil yields about 19 U. S. gallons of gasoline after processing in an oil refinery, though this varies based on the crude oil assay. The characteristic of a particular gasoline blend to resist igniting too early is measured by its octane rating. Gasoline is produced in several grades of octane rating. Tetraethyl lead and other lead compounds are no longer used in most areas to increase octane rating. Other chemicals are added to gasoline to improve chemical stability and performance characteristics, control corrosiveness and provide fuel system cleaning. Gasoline may contain oxygen-containing chemicals such as ethanol, MTBE or ETBE to improve combustion. Gasoline used in internal combustion engines can have significant effects on the local environment, is a contributor to global human carbon dioxide emissions.
Gasoline can enter the environment uncombusted, both as liquid and as vapor, from leakage and handling during production and delivery. As an example of efforts to control such leakage, many underground storage tanks are required to have extensive measures in place to detect and prevent such leaks. Gasoline contains other known carcinogens. "Gasoline" is a North American word. The Oxford English Dictionary dates its first recorded use to 1863 when it was spelled "gasolene"; the term "gasoline" was first used in North America in 1864. The word is a derivation from the word "gas" and the chemical suffixes "-ol" and "-ine" or "-ene". However, the term may have been influenced by the trademark "Cazeline" or "Gazeline". On 27 November 1862, the British publisher, coffee merchant and social campaigner John Cassell placed an advertisement in The Times of London: The Patent Cazeline Oil, safe and brilliant … possesses all the requisites which have so long been desired as a means of powerful artificial light.
This is the earliest occurrence of the word to have been found. Cassell discovered that a shopkeeper in Dublin named Samuel Boyd was selling counterfeit cazeline and wrote to him to ask him to stop. Boyd did not reply and changed every ‘C’ into a ‘G’, thus coining the word "gazeline"; the name "petrol" is used in place of "gasoline" in most Commonwealth countries. "Petrol" was first used as the name of a refined petroleum product around 1870 by British wholesaler Carless, Capel & Leonard, who marketed it as a solvent. When the product found a new use as a motor fuel, Frederick Simms, an associate of Gottlieb Daimler, suggested to Carless that they register the trademark "petrol", but by this time the word was in general use inspired by the French pétrole, the registration was not allowed. Carless registered a number of alternative names for the product, but "petrol" nonetheless became the common term for the fuel in the British Commonwealth. British refiners used "motor spirit" as a generic name for the automotive fuel and "aviation spirit" for aviation gasoline.
When Carless was denied a trademark on "petrol" in the 1930s, its competitors switched to the more popular name "petrol". However, "motor spirit" had made its way into laws and regulations, so the term remains in use as a formal name for petrol; the term is used most in Nigeria, where the largest petroleum companies call their product "premium motor spirit". Although "petrol" has made inroads into Nigerian English, "premium motor spirit" remains the formal name, used in scientific publications, government reports, newspapers; the use of the word gasoline instead of petrol outside North America can be confusing. Shortening gasoline to gas, which happens causes confusion with various forms of gaseous products used as automotive fuel like compressed natural gas, liquefied natural gas and liquefied petroleum gas ). In many languages, the name is derived from benzene, such as Benzin in benzina in Italian. Argentina and Paraguay use the colloquial name nafta derived from that of the chemical naphtha.
The first internal combustion engines suitable for use in transportation applications, so-called Otto engines, were developed in Germany during the last quarter of the 19th century. The fuel for these early engines was a volatile hydrocarbon obtained from coal gas. With a boiling point near 85 °C, it was well-suited for early carburetors; the development of a "spray nozzle" carburetor enabled the use of less volatile fuels. Further improvements in engine efficiency were attempted at higher compression ratios, but early attempts were blocked by the premature explosion of fuel, known as knocking. In 1891, the Shukhov cracking process became the world's first commercial method to break down heavier hydrocarbons in crude oil to increase the percentage of lighter products compared to simple distillation; the evolution of gasoline followed the evolution of oil as the dominant source of energy in the industrializing world. Prior to World War One, Britain was the world's greatest industrial power and depended on its navy to protect the shipping of raw materials from its colonies.
Germany was industrializing and, like Britain, lacked many natural resources which had to be shipped to the home country. By the 1890s, Germany
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air, entrained or otherwise mixed into the mass. It is an unwanted by-product of fires, but may be used for pest control, communication and offensive capabilities in the military, cooking, or smoking, it is used in rituals where incense, sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, preservative for various foodstuffs. Smoke is a component of internal combustion engine exhaust gas diesel exhaust. Smoke inhalation is the primary cause of death in victims of indoor fires; the smoke kills by a combination of thermal damage and pulmonary irritation caused by carbon monoxide, hydrogen cyanide and other combustion products. Smoke is an aerosol of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light; this effect has been likened to three-dimensional textured privacy glass — a smoke cloud does not obstruct an image, but scrambles it.
The composition of smoke depends on the nature of the conditions of combustion. Fires with high availability of oxygen burn at a high temperature and with small amount of smoke produced. High temperature leads to production of nitrogen oxides. Sulfur content yields sulfur dioxide. Carbon and hydrogen are completely oxidized to carbon dioxide and water. Fires burning with lack of oxygen produce a wider palette of compounds, many of them toxic. Partial oxidation of carbon produces carbon monoxide, nitrogen-containing materials can yield hydrogen cyanide and nitrogen oxides. Hydrogen gas can be produced instead of water. Content of halogens such as chlorine may lead to production of e.g. hydrogen chloride, phosgene and chloromethane, bromomethane and other halocarbons. Hydrogen fluoride can be formed from fluorocarbons, whether fluoropolymers subjected to fire or halocarbon fire suppression agents. Phosphorus and antimony oxides and their reaction products can be formed from some fire retardant additives, increasing smoke toxicity and corrosivity.
Pyrolysis of polychlorinated biphenyls, e.g. from burning older transformer oil, to lower degree of other chlorine-containing materials, can produce 2,3,7,8-tetrachlorodibenzodioxin, a potent carcinogen, other polychlorinated dibenzodioxins. Pyrolysis of fluoropolymers, e.g. teflon, in presence of oxygen yields carbonyl fluoride. Pyrolysis of burning material incomplete combustion or smoldering without adequate oxygen supply results in production of a large amount of hydrocarbons, both aliphatic and aromatic, terpenes. Heterocyclic compounds may be present. Heavier hydrocarbons may condense as tar. Presence of such smoke, and/or brown oily deposits during a fire indicates a possible hazardous situation, as the atmosphere may be saturated with combustible pyrolysis products with concentration above the upper flammability limit, sudden inrush of air can cause flashover or backdraft. Presence of sulfur can lead to formation of e.g. hydrogen sulfide, carbonyl sulfide, sulfur dioxide, carbon disulfide, thiols.
Partial oxidation of the released hydrocarbons yields in a wide palette of other compounds: aldehydes, alcohols, carboxylic acids. The visible particulate matter in such smokes is most composed of carbon. Other particulates may be composed of solid particles of ash; the presence of metals in the fuel yields particles of metal oxides. Particles of inorganic salts may be formed, e.g. ammonium sulfate, ammonium nitrate, or sodium chloride. Inorganic salts present on the surface of the soot particles may make them hydrophilic. Many organic compounds the aromatic hydrocarbons, may be adsorbed on the surface of the solid particles. Metal oxides can be present when metal-containing fuels are burned, e.g. solid rocket fuels containing aluminium. Depleted uranium projectiles after impacting the target ignite, producing particles of uranium oxides. Magnetic particles, spherules of magnetite-like ferrous ferric oxide, are present in coal smoke. Magnetic remanence, recorded in the iron oxide particles, indicates the strength of Earth's magnetic field when they were cooled beyond their Curie temperature.
Fly ash is composed of silica and calcium oxide. Cenospheres are present in smoke from liquid hydrocarbon fu
Gas is one of the four fundamental states of matter. A pure gas may be made up of individual atoms, elemental molecules made from one type of atom, or compound molecules made from a variety of atoms. A gas mixture would contain a variety of pure gases much like the air. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles; this separation makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric and gravitational fields are considered negligible, as indicated by the constant velocity vectors in the image; the gaseous state of matter is found between the liquid and plasma states, the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention. High-density atomic gases super cooled to low temperatures are classified by their statistical behavior as either a Bose gas or a Fermi gas.
For a comprehensive listing of these exotic states of matter see list of states of matter. The only chemical elements that are stable diatomic homonuclear molecules at STP are hydrogen, nitrogen and two halogens: fluorine and chlorine; when grouped together with the monatomic noble gases – helium, argon, krypton and radon – these gases are called "elemental gases". The word gas was first used by the early 17th-century Flemish chemist Jan Baptist van Helmont, he identified the first known gas other than air. Van Helmont's word appears to have been a phonetic transcription of the Ancient Greek word χάος Chaos – the g in Dutch being pronounced like ch in "loch" – in which case Van Helmont was following the established alchemical usage first attested in the works of Paracelsus. According to Paracelsus's terminology, chaos meant something like "ultra-rarefied water". An alternative story is that Van Helmont's word is corrupted from gahst, signifying a ghost or spirit; this was because certain gases suggested a supernatural origin, such as from their ability to cause death, extinguish flames, to occur in "mines, bottom of wells and other lonely places".
In contrast, French-American historian Jacques Barzun speculated that Van Helmont had borrowed the word from the German Gäscht, meaning the froth resulting from fermentation. Because most gases are difficult to observe directly, they are described through the use of four physical properties or macroscopic characteristics: pressure, number of particles and temperature; these four characteristics were observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies led to a mathematical relationship among these properties expressed by the ideal gas law. Gas particles are separated from one another, have weaker intermolecular bonds than liquids or solids; these intermolecular forces result from electrostatic interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another. Gaseous compounds with polar covalent bonds contain permanent charge imbalances and so experience strong intermolecular forces, although the molecule while the compound's net charge remains neutral.
Transient, randomly induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these intermolecular forces varies within a substance which determines many of the physical properties unique to each gas. A comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion; the drifting smoke particles in the image provides some insight into low-pressure gas behavior. Compared to the other states of matter, gases have low viscosity. Pressure and temperature influence the particles within a certain volume; this variation in particle separation and speed is referred to as compressibility. This particle separation and size influences optical properties of gases as can be found in the following list of refractive indices. Gas particles spread apart or diffuse in order to homogeneously distribute themselves throughout any container; when observing a gas, it is typical to specify a frame of length scale.
A larger length scale corresponds to a global point of view of the gas. This region must be sufficient in size to contain a large sampling of gas particles; the resulting statistical analysis of this sample size produces the "average" behavior of all the gas particles within the region. In contrast, a smaller length scale corresponds to a particle point of view. Macroscopically, the gas characteristics measured are either in terms of the gas particles themselves or their surroundings. For example, Robert Boyle studied pneumatic chemistry for a small portion of his career. One of his experiments related the macroscopic properties of volume of a gas, his experiment used a J-tube manometer which looks like a test tube in the shape of the letter J. Boyle trapped an inert gas in the closed end of the test tube with a column of mercury, thereby ma