Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure. Bronze is an alloy containing copper, but instead of zinc it has tin. Both bronze and brass may include small proportions of a range of other elements including arsenic, phosphorus, aluminium and silicon; the distinction is historical. Modern practice in museums and archaeology avoids both terms for historical objects in favour of the all-embracing "copper alloy". Brass is used for decoration for its bright gold-like appearance, it is used in zippers. Brass is used in situations in which it is important that sparks not be struck, such as in fittings and tools used near flammable or explosive materials. Brass has higher malleability than zinc; the low melting point of brass and its flow characteristics make it a easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses.
The density of brass is 8.4 to 8.73 grams per cubic centimetre. Today 90% of all brass alloys are recycled; because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is transported to the foundry where it is melted and recast into billets. Billets are extruded into the desired form and size; the general softness of brass means that it can be machined without the use of cutting fluid, though there are exceptions to this. Aluminium makes brass more corrosion-resistant. Aluminium causes a beneficial hard layer of aluminium oxide to be formed on the surface, thin and self-healing. Tin has a similar effect and finds its use in seawater applications. Combinations of iron, aluminium and manganese make brass wear and tear resistant. To enhance the machinability of brass, lead is added in concentrations of around 2%. Since lead has a lower melting point than the other constituents of the brass, it tends to migrate towards the grain boundaries in the form of globules as it cools from casting.
The pattern the globules form on the surface of the brass increases the available lead surface area which in turn affects the degree of leaching. In addition, cutting operations can smear the lead globules over the surface; these effects can lead to significant lead leaching from brasses of comparatively low lead content. In October 1999 the California State Attorney General sued 13 key manufacturers and distributors over lead content. In laboratory tests, state researchers found the average brass key, new or old, exceeded the California Proposition 65 limits by an average factor of 19, assuming handling twice a day. In April 2001 manufacturers agreed to reduce lead content to 1.5%, or face a requirement to warn consumers about lead content. Keys plated with other metals are not affected by the settlement, may continue to use brass alloys with higher percentage of lead content. In California, lead-free materials must be used for "each component that comes into contact with the wetted surface of pipes and pipe fittings, plumbing fittings and fixtures."
On January 1, 2010, the maximum amount of lead in "lead-free brass" in California was reduced from 4% to 0.25% lead. The so-called dezincification resistant brasses, sometimes referred to as CR brasses, are used where there is a large corrosion risk and where normal brasses do not meet the standards. Applications with high water temperatures, chlorides present, or deviating water qualities play a role. DZR-brass is excellent in water boiler systems; this brass alloy must be produced with great care, with special attention placed on a balanced composition and proper production temperatures and parameters to avoid long-term failures. The high malleability and workability good resistance to corrosion, traditionally attributed acoustic properties of brass, have made it the usual metal of choice for construction of musical instruments whose acoustic resonators consist of long narrow tubing folded or coiled for compactness. Collectively known as brass instruments, these include the trombone, trumpet, baritone horn, tenor horn, French horn, many other "horns", many in variously-sized families, such as the saxhorns.
Other wind instruments may be constructed of brass or other metals, indeed most modern student-model flutes and piccolos are made of some variety of brass a cupronickel alloy similar to nickel silver/German silver. Clarinets low clarinets such as the contrabass and subcontrabass, are sometimes made of metal because of limited supplies of the dense, fine-grained tropical hardwoods traditionally preferred for smaller woodwinds. For the same reason, some low clarinets and contrabassoons feature a hybrid construction, with long, straight sections of wood, curved joints, and/or bell of metal; the use of metal avoids the risks of exposing wooden instruments to changes in temperature or humid
Korea is a region in East Asia. Since 1948, it has been divided between two distinct sovereign states: South Korea. Korea consists of the Korean Peninsula, Jeju Island, several minor islands near the peninsula. Korea is bordered by China to the northwest, Russia to the northeast, neighbours Japan to the east by the Korea Strait and the Sea of Japan. During the first half of the 1st millennium, Korea was divided between the three competing states of Baekje and Silla, together known as the "Three Kingdoms of Korea". In the second half of the 1st millennium and Goguryeo were conquered by Silla, leading to the "Unified Silla" period. Meanwhile, Balhae formed in the north following the collapse of Goguryeo. Unified Silla collapsed into three separate states due to civil war, ushering in the Later Three Kingdoms. Toward the end of the 1st millennium Goryeo, a revival of Goguryeo, defeated the two other states and unified the Korean Peninsula as one single state. Around the same time, Balhae collapsed and its last crown prince fled south to Goryeo.
Goryeo, whose name developed into the modern exonym "Korea", was a cultured state that created the world's first metal movable type in 1234. However, multiple invasions by the Mongol Empire during the 13th century weakened the nation, which agreed to become a vassal state after decades of fighting. Following military resistance under King Gongmin which ended Mongol political influence in Goryeo, severe political strife followed, Goryeo fell to a coup led by General Yi Seong-gye, who established Joseon in 1392; the first 200 years of Joseon were marked by relative peace. During this period, the Korean alphabet was created by Sejong the Great in the 15th century and there was increasing influence of Confucianism. During the part of the dynasty, Korea's isolationist policy earned it the Western nickname of the "Hermit Kingdom". By the late 19th century, the country became the object of imperial design by the Empire of Japan. After the First Sino-Japanese War, despite the Korean Empire's effort to modernize, it was annexed by Japan in 1910 and ruled by Imperial Japan until the end of World War II in August 1945.
In 1945, the Soviet Union and the United States agreed on the surrender of Japanese forces in Korea in the aftermath of World War II, leaving Korea partitioned along the 38th parallel. The North was under Soviet occupation and the South under U. S. occupation. These circumstances soon became the basis for the division of Korea by the two superpowers, exacerbated by their inability to agree on the terms of Korean independence; the Communist-inspired government in the North received backing from the Soviet Union in opposition to the pro-Western government in the South, leading to Korea's division into two political entities: North Korea, South Korea. Tensions between the two resulted in the outbreak of the Korean War in 1950. With involvement by foreign troops, the war ended in a stalemate in 1953, but without a formalized peace treaty; this status contributes to the high tensions. Both governments of the two Koreas claim to be the sole legitimate government of the region. "Korea" is the modern spelling of "Corea", a name attested in English as early as 1614.
Korea was transliterated as Cauli in The Travels of Marco Polo, of the Chinese 高麗. This was the Hanja for the Korean kingdom of Goryeo, which ruled most of the Korean peninsula during Marco Polo's time. Korea's introduction to the West resulted from trade and contact with merchants from Arabic lands, with some records dating back as far as the 9th century. Goryeo's name was a continuation of Goguryeo the northernmost of the Three Kingdoms of Korea, known as Goryeo beginning in the 5th century; the original name was a combination of the adjective go with the name of a local Yemaek tribe, whose original name is thought to have been either *Guru or *Gauri. With expanding British and American trade following the opening of Korea in the late 19th century, the spelling "Korea" appeared and grew in popularity; the name Korea is now used in English contexts by both North and South Korea. In South Korea, Korea as a whole is referred to as Hanguk; the name references Samhan, referring to the Three Kingdoms of Korea, not the ancient confederacies in the southern Korean Peninsula.
Although written in Hanja as 韓, 幹, or 刊, this Han has no relation to the Chinese place names or peoples who used those characters but was a phonetic transcription of a native Korean word that seems to have had the meaning "big" or "great" in reference to leaders. It has been tentatively linked with the title khan used by the nomads of Central Asia. In North Korea, China and Japan, Korea as a whole is referred to as. "Great Joseon" was the name of the kingdom ruled by the Joseon dynasty from 1393 until their declaration of the short-lived Great Korean Empire in 1897. King Taejo had named them for the earlier Kojoseon, who ruled northern Korea from its legendary prehistory until their conquest in 108 BC by China's Han Empire; this go is the Hanja 古 and
Paris is the capital and most populous city of France, with an area of 105 square kilometres and an official estimated population of 2,140,526 residents as of 1 January 2019. Since the 17th century, Paris has been one of Europe's major centres of finance, commerce, fashion and the arts; the City of Paris is the centre and seat of government of the Île-de-France, or Paris Region, which has an estimated official 2019 population of 12,213,364, or about 18 percent of the population of France. The Paris Region had a GDP of €681 billion in 2016, accounting for 31 percent of the GDP of France, was the 5th largest region by GDP in the world. According to the Economist Intelligence Unit Worldwide Cost of Living Survey in 2018, Paris was the second most expensive city in the world, after Singapore, ahead of Zurich, Hong Kong and Geneva. Another source ranked Paris as most expensive, on a par with Singapore and Hong-Kong, in 2018; the city is a major rail and air-transport hub served by two international airports: Paris-Charles de Gaulle and Paris-Orly.
Opened in 1900, the city's subway system, the Paris Métro, serves 5.23 million passengers daily, is the second busiest metro system in Europe after Moscow Metro. Gare du Nord is the 24th busiest railway station in the world, the first located outside Japan, with 262 million passengers in 2015. Paris is known for its museums and architectural landmarks: the Louvre was the most visited art museum in the world in 2018, with 10.2 million visitors. The Musée d'Orsay and Musée de l'Orangerie are noted for their collections of French Impressionist art, the Pompidou Centre Musée National d'Art Moderne has the largest collection of modern and contemporary art in Europe; the historical district along the Seine in the city centre is classified as a UNESCO Heritage Site. Popular landmarks in the centre of the city include the Cathedral of Notre Dame de Paris and the Gothic royal chapel of Sainte-Chapelle, both on the Île de la Cité. Paris received 23 million visitors in 2017, measured by hotel stays, with the largest numbers of foreign visitors coming from the United States, the UK, Germany and China.
It was ranked as the third most visited travel destination in the world in 2017, after Bangkok and London. The football club Paris Saint-Germain and the rugby union club Stade Français are based in Paris; the 80,000-seat Stade de France, built for the 1998 FIFA World Cup, is located just north of Paris in the neighbouring commune of Saint-Denis. Paris hosts the annual French Open Grand Slam tennis tournament on the red clay of Roland Garros. Paris will host the 2024 Summer Olympics; the 1938 and 1998 FIFA World Cups, the 2007 Rugby World Cup, the 1960, 1984, 2016 UEFA European Championships were held in the city and, every July, the Tour de France bicycle race finishes there. The name "Paris" is derived from the Celtic Parisii tribe; the city's name is not related to the Paris of Greek mythology. Paris is referred to as the City of Light, both because of its leading role during the Age of Enlightenment and more because Paris was one of the first large European cities to use gas street lighting on a grand scale on its boulevards and monuments.
Gas lights were installed on the Place du Carousel, Rue de Rivoli and Place Vendome in 1829. By 1857, the Grand boulevards were lit. By the 1860s, the boulevards and streets of Paris were illuminated by 56,000 gas lamps. Since the late 19th century, Paris has been known as Panam in French slang. Inhabitants are known in French as Parisiens, they are pejoratively called Parigots. The Parisii, a sub-tribe of the Celtic Senones, inhabited the Paris area from around the middle of the 3rd century BC. One of the area's major north–south trade routes crossed the Seine on the île de la Cité; the Parisii minted their own coins for that purpose. The Romans began their settlement on Paris' Left Bank; the Roman town was called Lutetia. It became a prosperous city with a forum, temples, an amphitheatre. By the end of the Western Roman Empire, the town was known as Parisius, a Latin name that would become Paris in French. Christianity was introduced in the middle of the 3rd century AD by Saint Denis, the first Bishop of Paris: according to legend, when he refused to renounce his faith before the Roman occupiers, he was beheaded on the hill which became known as Mons Martyrum "Montmartre", from where he walked headless to the north of the city.
Clovis the Frank, the first king of the Merovingian dynasty, made the city his capital from 508. As the Frankish domination of Gaul began, there was a gradual immigration by the Franks to Paris and the Parisian Francien dialects were born. Fortification of the Île-de-la-Citie failed to avert sacking by Vikings in 845, but Paris' strategic importance—with its bridges prevent
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
A latch or catch is a type of mechanical fastener that joins two objects or surfaces while allowing for their regular separation. A latch engages another piece of hardware on the other mounting surface. Depending upon the type and design of the latch, this engaged bit of hardware may be known as a keeper or strike. A latch is not the same as the locking mechanism of a door or window, although they are found together in the same product. Latches range in complexity from flexible one-piece flat springs of metal or plastic, such as are used to keep blow molded plastic power tool cases closed, to multi-point cammed latches used to keep large doors closed. A single-throw bolt; the bolt can be engaged in its strike plate. The locking mechanism prevents the bolt from being retracted by force. Latchbolt or Latch bolt An common latch type part of a lockset, it is a spring-loaded bolt with an angled edge; when the door is pushed closed, the angled edge of the latchbolt engages with the lip of the strike plate.
Once the door is closed, the bolt automatically extends into the strike plate, holding the door closed. The latchbolt is disengaged when the user turns the door handle, which via the lockset's mechanism, manually retracts the latchbolt, allowing the door to open. Deadlocking latchbolt is an elaboration on the latchbolt which includes a guardbolt to prevent “shimming” or “jimmying” of the latch bolt; when the door is closed, the latchbolt and guardbolt are retracted together, the door closes with the latchbolt entering the strike plate. The strike plate, holds the guardbolt in its depressed position: a mechanism within the lockset holds the latchbolt in the projected position; this arrangement prevents the latchbolt from being depressed through the use of a credit card or some other tool, which would lead to unauthorized entry. Draw Latch is a two part latch where one side has an arm that can clasp to the other half, as it closes the clasp pulls the two parts together. Used on tool boxes, chests and windows.
Doesn't need to be closed to secure both halves. Spring bolt lock: A locking mechanism used with a latchbolt A slam latch uses a spring and is activated by the shutting or slamming of a door. Like all latches, a slam latch; the slam latch derives its name from its ability to slam doors and drawers shut without damaging the latch. A slam latch is rugged and ideal for industrial and construction applications. A cam lock is a type of latch consisting of a cam; the base is where the key or tool is used to rotate the cam, what does the latching. Cams can offset. Found on garage cabinets, file cabinets, tool chests, other locations where privacy and security is needed. A Norfolk latch is a type of latch incorporating a simple thumb-actuated lever and used to hold wooden gates and doors closed. In a Norfolk latch, the handle is fitted to a backplate independently of the thumb piece. Introduced around 1800–1820, Norfolk latches, originating in the English county of the same name, differ from the older Suffolk latch, which lacked a back plate to which the thumbpiece is attached.
A Suffolk latch is a type of latch incorporating a simple thumb-actuated lever and used to hold wooden gates and doors closed. The Suffolk latch originated in the English county of Suffolk in the 16th century and stayed in common use until the 19th century, they have come back into favour on garden gates and sheds. They were common from the 17th century to around 1825, their lack of a back plate made them different from the and neighbouring Norfolk latch. Both the Suffolk latch and Norfolk latch are thought to have been named by architectural draughtsman William Twopenny. Many of these plates found their way into other parts of the world. A crossbar, sometimes called a bolt, is a primitive fastener consisting of a post barring a door. Crossbars were common, simple fasteners consisting of a plank or beam mounted to one side of a door by a set of cleats; the board could be slid past the frame to block the door. Alternatively, the bar can be a separate piece, placed into open cleats or hooks, extending across the frame on both sides.
The effect of this device is the opposite of the crash bar in that its operation is to permit the door to be opened inward rather than outward. On a set of double doors, the same principle needn't extend past the frame; the bar extends into another set of cleats on the other door such as to interfere with the door opening. A cabin hook is a hooked bar; the bar is attached permanently to a ring or staple, fixed with screws or nails to woodwork or a wall at the same level as the eye screw. The eye screw is screwed into the adjacent wall or onto the door itself. Used to hold a cupboard, door or gate open or shut. A cabin hook is used in many situations to hold a door open, like on ships to prevent doors from swinging and banging against other woodwork as the ship moves due to wave action; this usage spread to other domains, where a door was required to be held open or a self-closing device is used to close the door. Many buildings are built with fire-resistant doors to separate different parts of buildings and to allow people to be protected from fire and smoke.
When using a cabin hook in such a situation, one should keep in mind that a fire-resistant door is an expensive and h
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India and the 1st century BC book On Agriculture by Marcus Terentius Varro. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Antonie van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis and anthrax. Microorganisms include all unicellular organisms and so are diverse. Of the three domains of life identified by Carl Woese, all of the Archaea and Bacteria are microorganisms; these were grouped together in the two domain system as Prokaryotes, the other being the eukaryotes. The third domain Eukaryota includes all multicellular organisms and many unicellular protists and protozoans.
Some protists are related to some to green plants. Many of the multicellular organisms are microscopic, namely micro-animals, some fungi and some algae, but these are not discussed here, they live in every habitat from the poles to the equator, geysers and the deep sea. Some are adapted to extremes such as hot or cold conditions, others to high pressure and a few such as Deinococcus radiodurans to high radiation environments. Microorganisms make up the microbiota found in and on all multicellular organisms. A December 2017 report stated that 3.45-billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel and other bioactive compounds, they are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora.
They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. The possible existence of microorganisms was discussed for many centuries before their discovery in the 17th century. By the fifth century BC, the Jains of present-day India postulated the existence of tiny organisms called nigodas; these nigodas are said to be born in clusters. According to the Jain leader Mahavira, the humans destroy these nigodas on a massive scale, when they eat, breathe and move. Many modern Jains assert that Mahavira's teachings presage the existence of microorganisms as discovered by modern science; the earliest known idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a 1st-century BC book titled On Agriculture in which he called the unseen creatures animalcules, warns against locating a homestead near a swamp: … and because there are bred certain minute creatures that cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases.
In The Canon of Medicine, Avicenna suggested that tuberculosis and other diseases might be contagious. Akshamsaddin mentioned the microbe in his work Maddat ul-Hayat about two centuries prior to Antonie Van Leeuwenhoek's discovery through experimentation: It is incorrect to assume that diseases appear one by one in humans. Disease infects by spreading from one person to another; this infection occurs through seeds that are so small they are alive. In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or without contact over long distances. Antonie Van Leeuwenhoek is considered to be the father of microbiology, he was the first in 1673 to discover, describe and conduct scientific experiments with microoorganisms, using simple single-lensed microscopes of his own design. Robert Hooke, a contemporary of Leeuwenhoek used microscopy to observe microbial life in the form of the fruiting bodies of moulds.
In his 1665 book Micrographia, he made drawings of studies, he coined the term cell. Louis Pasteur exposed boiled broths to the air, in vessels that contained a filter to prevent particles from passing through to the growth medium, in vessels without a filter, but with air allowed in via a curved tube so dust particles would settle and not come in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment. Nothing grew in the broths in the course of Pasteur's experiment; this meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur supported the germ theory of disease. In 1876, Robert Koch established, he found that the blood of cattle which were infected with anthrax always had large numbers of Bacillus anthracis. Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, this caused the healthy animal to become sick.
He found that he could grow the bacteria in a nutrient broth inject it into a heal
Porcelain is a ceramic material made by heating materials including kaolin, in a kiln to temperatures between 1,200 and 1,400 °C. The toughness and translucence of porcelain, relative to other types of pottery, arises from vitrification and the formation of the mineral mullite within the body at these high temperatures. Though definitions vary, porcelain can be divided into three main categories: hard-paste, soft-paste and bone china; the category that an object belongs to depends on the composition of the paste used to make the body of the porcelain object and the firing conditions. Porcelain evolved in China and was achieved at some point about 2,000 to 1,200 years ago slowly spread to other East Asian countries, Europe and the rest of the world, its manufacturing process is more demanding than that for earthenware and stoneware, the two other main types of pottery, it has been regarded as the most prestigious type of pottery for its delicacy and its white colour. It combines well with both glazes and paint, can be modelled well, allowing a huge range of decorative treatments in tablewares and figurines.
It has many uses in technology and industry. The European name, porcelain in English, come from the old Italian porcellana because of its resemblance to the surface of the shell. Porcelain is referred to as china or fine china in some English-speaking countries, as it was first seen in imports from China. Properties associated with porcelain include low elasticity. Porcelain has been described as being "completely vitrified, impermeable, white or artificially coloured and resonant". However, the term "porcelain" lacks a universal definition and has "been applied in an unsystematic fashion to substances of diverse kinds which have only certain surface-qualities in common". Traditionally, East Asia only classifies pottery into low-fired wares and high-fired wares, without the European concept of stoneware, high-fired but not white or translucent. Terms such as "proto-porcelain", "porcellaneous" or "near-porcelain" may be used in cases where the ceramic body approaches whiteness and translucency.
Kaolin is the primary material from which porcelain is made though clay minerals might account for only a small proportion of the whole. The word paste is an old term for both the fired materials. A more common terminology for the unfired material is "body"; the composition of porcelain is variable, but the clay mineral kaolinite is a raw material. Other raw materials can include feldspar, ball clay, bone ash, quartz and alabaster; the clays used are described as being long or short, depending on their plasticity. Long clays have high plasticity. In soil mechanics, plasticity is determined by measuring the increase in content of water required to change a clay from a solid state bordering on the plastic, to a plastic state bordering on the liquid, though the term is used less formally to describe the ease with which a clay may be worked. Clays used for porcelain are of lower plasticity and are shorter than many other pottery clays, they wet quickly, meaning that small changes in the content of water can produce large changes in workability.
Thus, the range of water content within which these clays can be worked is narrow and must be controlled. The following section provides background information on the methods used to form, finish and fire ceramic wares. Unlike their lower-fired counterparts, porcelain wares do not need glazing to render them impermeable to liquids and for the most part are glazed for decorative purposes and to make them resistant to dirt and staining. Many types of glaze, such as the iron-containing glaze used on the celadon wares of Longquan, were designed for their striking effects on porcelain. Biscuit porcelain is unglazed. Porcelain wares may be decorated under the glaze using pigments that include cobalt and copper or over the glaze using coloured enamels. Like many earlier wares, modern porcelains are biscuit-fired at around 1,000 °C, coated with glaze and sent for a second glaze-firing at a temperature of about 1,300 °C or greater. Another early method is "once-fired", where the glaze is applied to the unfired body and the two fired together in a single operation.
In this process, "green" ceramic wares are heated to high temperatures in a kiln to permanently set their shapes. Porcelain is fired at a higher temperature than earthenware so that the body can vitrify and become non-porous. Porcelain originated in China, it took a long time to reach the modern material; until recent times all East Asian porcelain was of the hard-paste type. There is no precise date to separate the production of proto-porcelain from that of porcelain. Although proto-porcelain wares exist dating from the Shang dynasty, by the time of the Eastern Han dynasty period, glazed ceramic wares had developed into porcelain, which Chinese defined as high-fired ware. By the late Sui dynasty and early Tang dynasty the additional Western requirements of whiteness and translucency had b