1.
Photograph
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A photograph or photo is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic medium such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scenes visible wavelengths of light into a reproduction of what the eye would see. The process and practice of creating photographs is called photography, the word photograph was coined in 1839 by Sir John Herschel and is based on the Greek φῶς, meaning light, and γραφή, meaning drawing, writing, together meaning drawing with light. The first permanent photograph, a copy of an engraving, was made in 1822 using the bitumen-based heliography process developed by Nicéphore Niépce. In 1829 Niépce entered into a partnership with Louis Daguerre and the two collaborated to work out a similar but more sensitive and otherwise improved process, after Niépces death in 1833, Daguerre concentrated on silver halide-based alternatives. He named this first practical process for making photographs with a camera the daguerreotype and its existence was announced to the world on 7 January 1839 but working details were not made public until 19 August. Other inventors soon made improvements which reduced the exposure time from a few minutes to a few seconds, making portrait photography truly practical. The daguerreotype had shortcomings, notably the fragility of the image surface. Each was a unique opaque positive that could only be duplicated by copying it with a camera, inventors set about working out improved processes that would be more practical. By the end of the 1850s the daguerreotype had been replaced by the expensive and more easily viewed ambrotype and tintype. The mid-1930s saw the introduction of Kodachrome and Agfacolor Neu, the first easy-to-use color films of the modern multi-layer chromogenic type, the needs of the motion picture industry generated a number of special processes and systems, perhaps the best-known being the now-obsolete three-strip Technicolor process. Non-digital photographs are produced with a chemical process. In the two-step process the film captures a negative image. To produce an image, the negative is most commonly transferred onto photographic paper. Printing the negative onto transparent film stock is used to motion picture films. Alternatively, the film is processed to invert the negative image, such positive images are usually mounted in frames, called slides. Before recent advances in photography, transparencies were widely used by professionals because of their sharpness. Most photographs published in magazines were taken on color transparency film, originally, all photographs were monochromatic or hand-painted in color
2.
Camera obscura
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The surroundings of the projected image have to be relatively dark for the image to be clear, so many historical camera obscura experiments were performed in dark rooms. The term camera obscura also refers to constructions or devices that use of the principle within a box. Camerae obscurae with a lens in the opening have been used since the second half of the 16th century, before the term camera obscura was first used in 1604, many other expressions were used including cubiculum obscurum, cubiculum tenebricosum, conclave obscurum and locus obscurus. Rays of light travel in straight lines and change when they are reflected and partly absorbed by an object, retaining information about the color, lit objects reflect rays of light in all directions. The human eye itself works much like a camera obscura with an opening, a biconvex lens, a camera obscura device consists of a box, tent or room with a small hole in one side. Light from a scene passes through the hole and strikes a surface inside, where the scene is reproduced, inverted and reversed. The image can be projected onto paper, and can then be traced to produce an accurate representation. In order to produce a reasonably clear projected image, the aperture has to be about 1/100th the distance to the screen, many camerae obscurae use a lens rather than a pinhole because it allows a larger aperture, giving a usable brightness while maintaining focus. As the pinhole is made smaller, the image gets sharper, with too small a pinhole, however, the sharpness worsens, due to diffraction. Using mirrors, as in an 18th-century overhead version, it is possible to project a right-side-up image, another more portable type is a box with an angled mirror projecting onto tracing paper placed on the glass top, the image being upright as viewed from the back. There are theories that occurrences of camera obscura effects inspired paleolithic cave paintings and it is also suggested that camera obscura projections could have played a role in Neolithic structures. Perforated gnomons projecting an image of the sun were described in the Chinese Zhoubi Suanjing writings. The location of the circle can be measured to tell the time of day. In Arab and European cultures its invention was later attributed to Egyptian astronomer. Some ancient sightings of gods and spirits, especially in worship, are thought to possibly have been conjured up by means of camera obscura projections. In these writings it is explained how the image in a collecting-point or treasure house is inverted by an intersecting point that collected the light. Light coming from the foot of a person would partly be hidden below. Rays from the head would partly be hidden above and partly form the part of the image
3.
Pewter
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Pewter is a malleable metal alloy, traditionally 85–99% tin, with the remainder consisting of copper, antimony, bismuth and sometimes, less commonly today, lead. Copper and antimony act as hardeners while lead is common in the grades of pewter. It has a low melting point, around 170–230 °C, depending on the mixture of metals. The word pewter is probably a variation of the word spelter, Pewter was first used around the beginning of the Bronze Age in the Near East. The earliest piece of pewter found is from an Egyptian tomb from 1450 BC, the constituents of pewter were first controlled in the 12th century by town guilds in France. By the 15th century, the Worshipful Company of Pewterers controlled pewter constituents in England and this company originally had two grades of pewter, but in the 16th century a third grade was added. The first type, known as metal, was used for tableware. It consisted of tin with as much copper as it could absorb, the second type, known as trifling metal or trifle, was used for holloware and is made up of fine metal with approximately 4% lead. The last type of pewter, known as lay or ley metal, was used for items that were not in contact with food or drink and it consisted of tin with 15% lead. These three alloys were used, with variation, until the 20th century. Older pewters with higher lead content are heavier, tarnish faster, pewters containing lead are no longer used in items that will come in contact with the human body due to health concerns stemming from the lead content. Modern pewters are available that are free of lead, although many pewters containing lead are still being produced for other purposes. A typical European casting alloy contains 94% tin, 1% copper, a European pewter sheet would contain 92% tin, 2% copper, and 6% antimony. Asian pewter, produced mostly in Malaysia, Singapore, and Thailand, contains a percentage of tin, usually 97. 5% tin, 1% copper. This makes the alloy slightly softer, Pewter items are often found in churches. Pewter was the chief tableware until the making of porcelain, mass production of pottery, porcelain and glass products has seen pewter universally replaced in day-to-day life. Pewter artifacts continue to be produced, mainly as decorative or specialty items, Pewter was also used around East Asia. Although some items still exist, Ancient Roman pewter is rare, in the early 19th century, changes in fashion caused a decline in the use of pewter flatware
4.
Asphalt
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Asphalt, also known as bitumen is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in deposits or may be a refined product. Until the 20th century, the term asphaltum was also used, the word is derived from the Ancient Greek ἄσφαλτος ásphaltos. The primary use of asphalt/bitumen is in construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including production of roofing felt, the terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt is the carefully refined residue from the process of selected crude oils. Outside the United States, the product is often called bitumen, geologists often prefer the term bitumen. Common usage often refers to forms of asphalt/bitumen as tar. Naturally occurring asphalt/bitumen is sometimes specified by the crude bitumen. Its viscosity is similar to that of cold molasses while the material obtained from the distillation of crude oil boiling at 525 °C is sometimes referred to as refined bitumen. The Canadian province of Alberta has most of the reserves of natural bitumen, covering 142,000 square kilometres. Additionally, most natural bitumens contain organosulfur compounds, resulting in a sulfur content of up to 4%. Nickel and vanadium are found in the <10 ppm level, as is typical of some petroleum, the substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase, and it is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structure is extremely large. Asphalt/bitumen can sometimes be confused with tar, which is a visually similar black. During the early and mid-20th century when town gas was produced, coal tar was a readily available byproduct, the addition of tar to macadam roads led to the word tarmac, which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, other examples of this confusion include the La Brea Tar Pits and the Canadian oil sands, both of which actually contain natural bitumen rather than tar. Pitch is another term used at times to refer to asphalt/bitumen
5.
Royal Society
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Founded in November 1660, it was granted a royal charter by King Charles II as The Royal Society. The society is governed by its Council, which is chaired by the Societys President, according to a set of statutes and standing orders. The members of Council and the President are elected from and by its Fellows, the members of the society. As of 2016, there are about 1,600 fellows, allowed to use the postnominal title FRS, there are also royal fellows, honorary fellows and foreign members, the last of which are allowed to use the postnominal title ForMemRS. The Royal Society President is Venkatraman Ramakrishnan, who took up the post on 30 November 2015, since 1967, the society has been based at 6–9 Carlton House Terrace, a Grade I listed building in central London which was previously used by the Embassy of Germany, London. The Royal Society started from groups of physicians and natural philosophers, meeting at variety of locations and they were influenced by the new science, as promoted by Francis Bacon in his New Atlantis, from approximately 1645 onwards. A group known as The Philosophical Society of Oxford was run under a set of rules still retained by the Bodleian Library, after the English Restoration, there were regular meetings at Gresham College. It is widely held that these groups were the inspiration for the foundation of the Royal Society, I will not say, that Mr Oldenburg did rather inspire the French to follow the English, or, at least, did help them, and hinder us. But tis well known who were the men that began and promoted that design. This initial royal favour has continued and, since then, every monarch has been the patron of the society, the societys early meetings included experiments performed first by Hooke and then by Denis Papin, who was appointed in 1684. These experiments varied in their area, and were both important in some cases and trivial in others. The Society returned to Gresham in 1673, there had been an attempt in 1667 to establish a permanent college for the society. Michael Hunter argues that this was influenced by Solomons House in Bacons New Atlantis and, to a lesser extent, by J. V. The first proposal was given by John Evelyn to Robert Boyle in a letter dated 3 September 1659, he suggested a scheme, with apartments for members. The societys ideas were simpler and only included residences for a handful of staff and these plans were progressing by November 1667, but never came to anything, given the lack of contributions from members and the unrealised—perhaps unrealistic—aspirations of the society. During the 18th century, the gusto that had characterised the early years of the society faded, with a number of scientific greats compared to other periods. The pointed lightning conductor had been invented by Benjamin Franklin in 1749, during the same time period, it became customary to appoint society fellows to serve on government committees where science was concerned, something that still continues. The 18th century featured remedies to many of the early problems
6.
Louis Daguerre
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Louis-Jacques-Mandé Daguerre was a French artist and photographer, recognized for his invention of the daguerreotype process of photography. He became known as one of the fathers of photography, though he is most famous for his contributions to photography, he was also an accomplished painter and a developer of the diorama theatre. Louis Daguerre was born in Cormeilles-en-Parisis, Val-dOise, France and he was apprenticed in architecture, theatre design, and panoramic painting to Pierre Prévost, the first French panorama painter. Exceedingly adept at his skill of theatrical illusion, he became a designer for the theatre, and later came to invent the diorama. In 1829, Daguerre partnered with Nicéphore Niépce, an inventor who had produced the worlds first heliograph in 1822, Niépce died suddenly in 1833, but Daguerre continued experimenting, and evolved the process which would subsequently be known as the daguerreotype. After efforts to interest private investors proved fruitless, Daguerre went public with his invention in 1839, under assurances of strict confidentiality, Daguerre explained and demonstrated the process only to the Academys perpetual secretary François Arago, who proved to be an invaluable advocate. Members of the Academy and other individuals were allowed to examine specimens at Daguerres studio. The images were enthusiastically praised as nearly miraculous, and news of the daguerreotype quickly spread, in 1839, he was elected to the National Academy of Design as an Honorary Academician. Daguerre died on 10 July 1851 in Bry-sur-Marne,12 km from Paris, a monument marks his grave there. Daguerres name is one of the 72 names inscribed on the Eiffel tower, in the mid-1820s, prior to his association with Daguerre, Niépce used a coating of bitumen of Judea to make the first permanent camera photographs. The bitumen was hardened where it was exposed to light and the portion was then removed with a solvent. A camera exposure lasting for hours or days was required, Niépce and Daguerre later refined this process, but unacceptably long exposures were still needed. After the death of Niépce in 1833, Daguerre concentrated his attention on the properties of silver salts. The plate was exposed in the camera. Upon seeing the image, the contents of which are unknown, Daguerre said, the latent image on a daguerreotype plate was developed by subjecting it to the vapor given off by mercury heated to 75 °C. The resulting visible image was then fixed by removing the silver iodide with concentrated and heated salt water. Later, a solution of the more effective hypo was used instead, the resultant plate produced an exact reproduction of the scene. The image was laterally reversed—as images in mirrors are—unless a mirror or inverting prism was used during exposure to flip the image, daguerreotypes were usually portraits, the rarer landscape views and other unusual subjects are now much sought-after by collectors and sell for much higher prices than ordinary portraits
7.
Henry Fox Talbot
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His work in the 1840s on photomechanical reproduction led to the creation of the photoglyphic engraving process, the precursor to photogravure. He was the holder of a patent which affected the early development of commercial photography in Britain. He was also a photographer who contributed to the development of photography as an artistic medium. He published The Pencil of Nature, which was illustrated with original salted paper prints from his calotype negatives, and made important early photographs of Oxford, Paris, Reading. Talbot was the child of William Davenport Talbot, of Lacock Abbey, near Chippenham, Wiltshire. Talbot was educated at Rottingdean, Harrow School and at Trinity College, Cambridge, where he was awarded the Porson Prize in Classics in 1820, from 1822 to 1872, he communicated papers to the Royal Society, many of them on mathematical subjects. At an early period, he began optical researches, which bore fruit in connection with photography. At a meeting of the Royal Institution on 25 January 1839, within a fortnight, he communicated the general nature of his process to the Royal Society, followed by more complete details a few weeks later. Daguerre did not publicly reveal any details until mid-August, although by the spring it had become clear that his process. In the case of images, that could require an exposure of an hour or two if something more than a silhouette of objects against a bright sky was wanted. This reduced the exposure time in the camera to only a minute or two for subjects in bright sunlight. The simpler salted paper process was used when making prints from calotype negatives. Talbot announced his calotype process in 1841, and in August he licensed Henry Collen, the most celebrated practitioners of the process were Hill & Adamson. Another notable calotypist was Levett Landon Boscawen Ibbetson, in 1842, Talbot received the Rumford Medal of the Royal Society for his photographic discoveries. In 1852, Talbot discovered that gelatine treated with potassium dichromate and this later provided the basis for the important carbon printing process and related technologies. Dichromated gelatine is still used for some laser holography, Talbots later photographic work was concentrated on photomechanical reproduction methods. Talbot created the engraving process, later perfected by others as the photogravure process. Daguerres work on his process had commenced at about the time as Talbots earliest work on his salted paper process
8.
Photo manipulation
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Photo manipulation involves transforming or altering a photograph using various methods and techniques to achieve desired results. For example, Ansel Adams employed some of the common manipulations using darkroom exposure techniques. There are a number of applications available for digital image manipulation. Photo manipulation dates back to some of the earliest photographs captured on glass, the practice began not long after the creation of the first photograph by Joseph Nicéphore Niépce who developed heliography and made the first photographic print from a photoengraved printing plate. Negatives can be manipulated while still in the camera using double-exposure techniques, in the early 19th century, photography and the technology that made it possible was rather crude and cumbersome. While the equipment and technology progressed over time, it wasnt until the late 20th Century that photography evolved into the digital realm. At the onset, digital photography was considered by some to be a new approach. Close observation of the photograph raises questions and brings to light certain details in the photograph that simply do not add up, Photo manipulation has been used to deceive or persuade viewers or improve storytelling and self-expression. Often even subtle and discreet changes can have a impact on how we interpret or judge a photograph. As early as the American Civil War, photographs were published as engravings based on more than one negative, Joseph Stalin made use of photo retouching for propaganda purposes. On May 5,1920 his predecessor Vladimir Lenin held a speech for Soviet troops that Leon Trotsky attended, Stalin had Trotsky retouched out of a photograph showing Trotsky in attendance. In a well known case of damnatio memoriae image manipulation, NKVD leader Nikolai Yezhov, in the 1930s, artist John Heartfield used a type of photo manipulation known as the photomontage to critique Nazi propaganda. Some ethical theories have been applied to image manipulation, during a panel on the topic of ethics in image manipulation Aude Oliva theorized that categorical shifts are necessary in order for an edited image to be viewed as a manipulation. In Image Act Theory, Carson Reynolds extended speech act theory by applying it to photo editing, in How to Do Things with Pictures, William Mitchell details the long history of photo manipulation and discusses it critically. A notable incident of controversial photo manipulation occurred over a photograph that was altered to fit the vertical orientation of a 1982 National Geographic magazine cover, the altered image made two Egyptian pyramids appear closer together than they actually were in the original photograph. The incident triggered a debate about the appropriateness of falsifying an image and we regarded that afterwards as a mistake, and we wouldn’t repeat that mistake today. There are other incidents of questionable photo manipulation in journalism, one such incident arose in early 2005 after Martha Stewart was released from prison. Newsweek used a photograph of Stewarts face on the body of a much slimmer woman for their cover, staley also explained that Newsweek disclosed on page 3 that the cover image of Martha Stewart was a composite
9.
University of Texas at Austin
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Founded in 1881 as The University of Texas, its campus is in Austin, Texas—approximately 1 mile from the Texas State Capitol. The institution has the nations seventh-largest single-campus enrollment, with over 50,000 undergraduate and graduate students and over 24,000 faculty, UT Austin was inducted into the American Association of Universities in 1929, becoming only the third university in the American South to be elected. It is a center for academic research, with research expenditures exceeding $550 million for the 2014–2015 school year. J. Pickle Research Campus and the McDonald Observatory, among university faculty are recipients of the Nobel Prize, Pulitzer Prize, the Wolf Prize, the Emmy Award, the Turing Award, and the National Medal of Science, as well as many other awards. UT Austin student athletes compete as the Texas Longhorns and are members of the Big 12 Conference and its Longhorn Network is the only sports network featuring the college sports of a single university. The first mention of a university in Texas can be traced to the 1827 constitution for the Mexican state of Coahuila y Tejas. Although Title 6, Article 217 of the Constitution promised to establish education in the arts and sciences. On April 18,1838, An Act to Establish the University of Texas was referred to a committee of the Texas Congress. On January 26,1839, the Texas Congress agreed to set aside fifty leagues of land towards the establishment of a publicly funded university, in addition,40 acres in the new capital of Austin were reserved and designated College Hill. In 1845, Texas was annexed into the United States, interestingly, the states Constitution of 1845 failed to mention higher education. On February 11,1858, the Seventh Texas Legislature approved O. B,102, an act to establish the University of Texas, which set aside $100,000 in United States bonds toward construction of the states first publicly funded university. The legislature also designated land reserved for the encouragement of railroad construction toward the universitys endowment, Texas secession from the Union and the American Civil War delayed repayment of the borrowed monies. At the end of the Civil War in 1865, The University of Texas endowment was just over $16,000 in warrants, the more valuable lands reverted to the fund to support general education in the state. The legislature additionally appropriated $256,272.57 to repay the funds taken from the university in 1860 to pay for frontier defense, the 1883 grant of land increased the land in the Permanent University Fund to almost 2.2 million acres. Under the Act of 1858, the university was entitled to just over 1,000 acres of land for every mile of railroad built in the state. On March 30,1881, the legislature set forth the structure and organization. By popular election on September 6,1881, Austin was chosen as the site, galveston, having come in second in the election was designated the location of the medical department. On November 17,1882, on the original College Hill, smite the earth, smite the rocks with the rod of knowledge and fountains of unstinted wealth will gush forth
10.
Austin, Texas
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Austin is the capital of the U. S. state of Texas and the seat of Travis County. It is the 11th-most populous city in the U. S. and it is the fastest growing large city in the United States and the second most populous capital city after Phoenix, Arizona. As of the U. S. Census Bureaus July 1,2015 estimate and it is the cultural and economic center of the Austin–Round Rock metropolitan area, which had an estimated population of 2,056,405 as of July 1,2016. In the 1830s, pioneers began to settle the area in central Austin along the Colorado River, in 1839, the site was officially chosen to replace Houston as the new capital of the Republic of Texas and was incorporated under the name Waterloo. Shortly thereafter, the name was changed to Austin in honor of Stephen F. Austin, the Father of Texas and the republics first secretary of state. The city subsequently grew throughout the 19th century and became a center for government and education with the construction of the Texas State Capitol and the University of Texas at Austin. After a lull in growth from the Great Depression, Austin resumed its development into a city and, by the 1980s, it emerged as a center for technology. A number of Fortune 500 companies have headquarters or regional offices in Austin, including Amazon. com, cisco, eBay, Google, IBM, Intel, Oracle Corporation, Texas Instruments, 3M, and Whole Foods Market. Dells worldwide headquarters is located in nearby Round Rock, a suburb of Austin, residents of Austin are known as Austinites. They include a mix of government employees, college students, musicians, high-tech workers, blue-collar workers. The city also adopted Silicon Hills as a nickname in the 1990s due to an influx of technology. In the late 1800s, Austin was known as the City of the Violet Crown because of the glow of light across the hills just after sunset. Even today, many Austin businesses use the term Violet Crown in their name, Austin is known as a clean-air city for its stringent no-smoking ordinances that apply to all public places and buildings, including restaurants and bars. The FBI ranked Austin as the second-safest major city in the U. S. for the year 2012, U. S. News & World Report named Austin the best place to live in the U. S. in 2017. Austin, Travis County and Williamson County have been the site of habitation since at least 9200 BC. When settlers arrived from Europe, the Tonkawa tribe inhabited the area, the Comanches and Lipan Apaches were also known to travel through the area. Spanish colonists, including the Espinosa-Olivares-Aguirre expedition, traveled through the area for centuries, in 1730, three missions from East Texas were combined and reestablished as one mission on the south side of the Colorado River, in what is now Zilker Park, in Austin. The mission was in area for only about seven months
11.
X-ray fluorescence
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X-ray fluorescence is the emission of characteristic secondary X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. When materials are exposed to short-wavelength X-rays or to gamma rays, ionization consists of the ejection of one or more electrons from the atom, and may occur if the atom is exposed to radiation with an energy greater than its ionization energy. X-rays and gamma rays can be enough to expel tightly held electrons from the inner orbitals of the atom. The removal of an electron in this way makes the structure of the atom unstable. In falling, energy is released in the form of a photon, thus, the material emits radiation, which has energy characteristic of the atoms present. The term fluorescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy, each element has electronic orbitals of characteristic energy. Following removal of an electron by an energetic photon provided by a primary radiation source. There are a number of ways in which this can happen. The main transitions are given names, an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, and so on. Each of these transitions yields a fluorescent photon with an energy equal to the difference in energy of the initial and final orbital. Once sorted, the intensity of each characteristic radiation is directly related to the amount of element in the material. This is the basis of a technique in analytical chemistry. Figure 2 shows the form of the sharp fluorescent spectral lines obtained in the wavelength-dispersive method. In order to excite the atoms, a source of radiation is required, conventional X-ray generators are most commonly used, because their output can readily be tuned for the application, and because higher power can be deployed relative to other techniques. However, gamma ray sources can be used without the need for a power supply. When the energy source is a synchrotron or the X-rays are focused by an optic like a polycapillary, as a result, atomic information on the sub-micrometre scale can be obtained. X-ray generators in the range 20–60 kV are used, which allow excitation of a range of atoms. The continuous spectrum consists of bremsstrahlung radiation, radiation produced when high-energy electrons passing through the tube are progressively decelerated by the material of the tube anode, a typical tube output spectrum is shown in figure 3
12.
Tin
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Tin is a chemical element with symbol Sn and atomic number 50. It is a metal in group 14 of the periodic table. It is obtained chiefly from the mineral cassiterite, which contains tin dioxide, Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, metallic tin is not easily oxidized in air. The first alloy used on a scale was bronze, made of tin and copper. After 600 BC, pure metallic tin was produced, pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony, and lead, was used for flatware from the Bronze Age until the 20th century. In modern times, tin is used in alloys, most notably tin/lead soft solders. Another large application for tin is corrosion-resistant tin plating of steel, inorganic tin compounds are rather non-toxic. Because of its low toxicity, tin-plated metal was used for packaging as tin cans. However, overexposure to tin may cause problems with metabolizing essential trace elements such as copper and zinc, Tin is a soft, malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a sound known as the tin cry can be heard from the twinning of the crystals. Tin melts at the low temperature of about 232 °C, the lowest in group 14, the melting point is further lowered to 177.3 °C for 11 nm particles. β-tin, which is stable at and above room temperature, is malleable, in contrast, α-tin, which is stable below 13.2 °C, is brittle. α-tin has a cubic crystal structure, similar to diamond. α-tin has no properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications and these two allotropes, α-tin and β-tin, are more commonly known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C, in cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as tin pest. Commercial grades of tin resist transformation because of the effect of the small amounts of bismuth, antimony, lead
