Copper is a chemical element with symbol Cu and atomic number 29. It is a soft and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, constantan used in strain gauges and thermocouples for temperature measurement. Copper is one of the few metals; this led to early human use in several regions, from c. 8000 BC. Thousands of years it was the first metal to be smelted from sulfide ores, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3500 BC. In the Roman era, copper was principally mined on Cyprus, the origin of the name of the metal, from aes сyprium corrupted to сuprum, from which the words derived and copper, first used around 1530.
The encountered compounds are copper salts, which impart blue or green colors to such minerals as azurite and turquoise, have been used and as pigments. Copper used in buildings for roofing, oxidizes to form a green verdigris. Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complexed hemoglobin in fish and other vertebrates. In humans, copper is found in the liver and bone; the adult body contains between 2.1 mg of copper per kilogram of body weight. Copper and gold are in group 11 of the periodic table; the filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds.
Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are weak. This observation explains the low high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms; the softness of copper explains its high electrical conductivity and high thermal conductivity, second highest among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates from scattering of electrons on thermal vibrations of the lattice, which are weak in a soft metal; the maximum permissible current density of copper in open air is 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively. Copper is one of a few metallic elements with a natural color other than silver.
Pure copper acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells corresponds to orange light; as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. Copper does not react with water, but it does react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion. A green layer of verdigris can be seen on old copper structures, such as the roofing of many older buildings and the Statue of Liberty. Copper tarnishes when exposed to some sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising 69% of occurring copper. The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.
Seven metastable isotopes have been characterized. Isotopes with a mass number above 64 decay by β−, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways.62Cu and 64Cu have significant applications. 62Cu is used in 62Cu-PTSM as a radioactive tracer for positron emission tomography. Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million. In nature, copper occurs in a variety of minerals, including native copper, copper sulfides such as chalcopyrite, digenite and chalcocite, copper sulfosalts such as tetrahedite-tennantite, enargite, copper carbonates such as azurite and malachite, as copper or copper oxides such as cuprite and tenorite, respectively; the largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal
Booker T. Washington
Booker Taliaferro Washington was an American educator, author and advisor to presidents of the United States. Between 1890 and 1915, Washington was the dominant leader in the African-American community. Washington was from the last generation of black American leaders born into slavery and became the leading voice of the former slaves and their descendants, they were newly oppressed in the South by disenfranchisement and the Jim Crow discriminatory laws enacted in the post-Reconstruction Southern states in the late 19th and early 20th centuries. Washington was a key proponent of African-American businesses and one of the founders of the National Negro Business League, his base was the Tuskegee Institute, a black college in Tuskegee, Alabama. As lynchings in the South reached a peak in 1895, Washington gave a speech, known as the "Atlanta compromise", which brought him national fame, he called for black progress through education and entrepreneurship, rather than trying to challenge directly the Jim Crow segregation and the disenfranchisement of black voters in the South.
Washington mobilized a nationwide coalition of middle-class blacks, church leaders, white philanthropists and politicians, with a long-term goal of building the community's economic strength and pride by a focus on self-help and schooling. But, secretly, he supported court challenges to segregation and restrictions on voter registration. Black militants in the North, led by W. E. B. Du Bois, at first supported the Atlanta compromise, but disagreed and opted to set up the National Association for the Advancement of Colored People to work for political change, they tried with limited success to challenge Washington's political machine for leadership in the black community, but built wider networks among white allies in the North. Decades after Washington's death in 1915, the civil rights movement of the 1950s took a more active and militant approach, based on new grassroots organizations based in the South, such as Congress of Racial Equality, the Student Nonviolent Coordinating Committee and Southern Christian Leadership Conference.
Washington mastered the nuances of the political arena in the late 19th century, which enabled him to manipulate the media, raise money, develop strategy, push, reward friends, distribute funds, while punishing those who opposed his plans for uplifting blacks. His long-term goal was to end the disenfranchisement of the vast majority of African Americans, who still lived in the South. In 1856, Washington was born into slavery in Virginia as the son of an African-American slave. After emancipation, she moved the family to West Virginia to join her husband Washington Ferguson; as a young man, Washington worked his way through Hampton Normal and Agricultural Institute and attended college at Wayland Seminary. In 1881, Washington was named as the first leader of the new Tuskegee Institute in Alabama, founded for the higher education of blacks. Washington attained national prominence for his Atlanta Address of 1895, which attracted the attention of politicians and the public, he became a popular spokesperson for African-American citizens.
He built a nationwide network of supporters in many black communities, with black ministers and businessmen composing his core supporters. Washington played a dominant role in black politics, winning wide support in the black community of the South and among more liberal whites, he gained access to top national leaders in politics and education. Washington's efforts included cooperating with white people and enlisting the support of wealthy philanthropists. Beginning in 1912, he built a relationship with philanthropist Julius Rosenwald, who served on the board of trustees for the rest of his life and made substantial donations to Tuskegee. In addition, they collaborated on a pilot program for Tuskegee architects to design six model schools that could be built for African-American students in rural areas of the South. Given their success in 1913 and 1914, through the Rosenwald Foundation, established in 1917, Rosenwald expanded the program to encourage school construction through giving matching funds to communities who committed to operate the schools.
Thousands of new, small rural schools to improve education for blacks throughout the South were built, most after Washington's death in 1915. Washington had asserted that the surest way for blacks to gain equal social rights was to demonstrate "industry, thrift and property." Northern critics called Washington's widespread organization the "Tuskegee Machine". After 1909, Washington was criticized by the leaders of the new NAACP W. E. B. Du Bois, who demanded a stronger tone of protest in order to advance the civil rights agenda. Washington replied that confrontation would lead to disaster for the outnumbered blacks in society, that cooperation with supportive whites was the only way to overcome pervasive racism in the long run. At the same time, he secretly funded litigation for civil rights cases, such as challenges to southern constitutions and laws that had disenfranchised blacks across the South since the turn of the century. African Americans were still affiliated with the Republican Party, Washington was on close terms with national Republican Party leaders.
He was asked for political advice by presidents Theodore Roosevelt and William Howard Taft. In addition to his contributions in education, Washington wrote 14 books. During a difficult period of transition, he did much to improve the working rel
Booker T. Washington Memorial half dollar
The Booker T. Washington Memorial half dollar was designed by Isaac Scott Hathaway and minted in silver between 1946 and 1951; the obverse depicts Booker T. Washington; the reverse shows the cabin in which Washington was born, now the Booker T. Washington National Monument, the Hall of Fame for Great Americans, in which Washington is honored; the description on the reverse reads "From slave cabin to Hall of Fame." Early United States commemorative coins
San Francisco Mint
The San Francisco Mint is a branch of the United States Mint and was opened in 1854 to serve the gold mines of the California Gold Rush. It outgrew its first building and moved into a new one in 1874; this building, the Old United States Mint known affectionately as The Granite Lady, is one of the few that survived the great 1906 San Francisco earthquake. It served until 1937. Within the first year of its operation, the San Francisco mint turned $4 million in gold bullion into coins; the second building, completed in 1874, was designed by Alfred B. Mullett in a conservative Greek Revival style with a sober Doric order; the building had a central pedimented portico flanked by projecting wings in an E-shape. The building sat on a concrete and granite foundation, designed to thwart tunneling into its vaults, which at the time of the 1906 fire held $300 million a third of the United States' gold reserves. Heroic efforts by Superintendent of the Mint, Frank A. Leach, his men preserved the building and the bullion that backed the nation's currency.
The mint resumed operation soon thereafter, continuing until 1937. In 1961 the Old Mint, as it had become known, was designated a National Historic Landmark, it became a California Historical Landmark in 1974. The given name of "The Granite Lady" is somewhat of a misnomer as most of the building is made from sandstone. While the base/basement of the building is made of granite, the entire external and upper stories are made of sandstone; the Granite Lady was a marketing term given in the 1970s. The Old Mint was open to visitors until 1993. In 2003 the federal government sold the structure to the City of San Francisco for one dollar—an 1879 silver dollar struck at the mint— for use as a historical museum to be called the San Francisco Museum at the Mint. In the fall of 2005, ground was broken for renovations that would turn the central court into a glass-enclosed galleria. In 2006 Congress created the San Francisco Old Mint Commemorative Coin, the first coin to honor a United States mint; the first phase of renovations were completed in 2011.
In 2014, the San Francisco Museum and Historical Society began raising money for the second phase, which would have included permanent exhibitions. In 2015, the City of San Francisco looked for a new tenant to renovate and program the space with Activate San Francisco Events being selected as an interim tenant; as the City's 2016 public re-opening event, continuing the tradition of a similar event from past years, on the first weekend in March, the Old Mint hosted a "San Francisco History Days" event with over sixty participating historic organizations. Until a new tenant is found, the Old Mint will continue to be used for special events, some open to the public. In April 2016, the California Historical Society agreed to undertake the restoration of the building and its preservation as a public space; the new Mint was opened in 1937. Beginning in 1955, circulating coinage from San Francisco was suspended for 13 years. In 1968, it took over most proof coinage production from the Philadelphia Mint, but continued striking a supplemental circulating coinage from 1968 through 1974.
From 1975 to 2012, the San Francisco Mint has been used only for proof coinage, with the exception of the Susan B. Anthony dollar from 1979–81 and a portion of the mintage of cents in the early 1980s; the dollars bear a mintmark of an "S", but the cents are otherwise indistinguishable from those minted at Philadelphia. In 2012, the San Francisco mint started to mint circulation strike quarters in the America the Beautiful quarter series, marked with an "S" mintmark and only issued for collectors. From 1962 to 1988, the San Francisco Mint was an assay office; the San Francisco Mint only admits visitors on rare exception. On May 15, 1987, to commemorate the 50th anniversary of the Mint, a limited number of people were allowed to tour the facility; this tour was advertised in the San Francisco Chronicle newspaper, with a phone number to call to reserve a spot. In 2006, the United States Mint released a gold five dollar commemorative coin which commemorates the 100th year after the old San Francisco mint survived an earthquake.
The mint played a part in the city's recovery after the earthquake, providing shelter for many as it was one of the few buildings left standing. The coin was minted as both a proof coin and an uncirculated coin, is no longer available directly from the United States Mint. On June 15, 2006 President George W. Bush signed Public Law 109-230, legislation authorizing the production of the 2006 San Francisco $5 commemorative gold coin as well as its $1 silver counterpart; the production of the $5 denomination was limited to a maximum mintage of 100,000 coins, but separate mintage figures for each of the proof and uncirculated coins have not yet been released. The $1 silver version was limited to only 500,000 coins, both in proof and uncirculated products, but distinct mintage figures for both products has not been stated; the obverse was sculpted by Joseph Menna. Features Coin Finishes: proof, uncirculated Maximum Mintage: 100,000 - The final mintages were 16,938 uncirculated, 47,275 proof. United States Mint Facility: San Francisco Public Law: 109-230 In 2006, t
Silver is a chemical element with symbol Ag and atomic number 47. A soft, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, reflectivity of any metal; the metal is found in the Earth's crust in the pure, free elemental form, as an alloy with gold and other metals, in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold and zinc refining. Silver has long been valued as a precious metal. Silver metal is used in many bullion coins, sometimes alongside gold: while it is more abundant than gold, it is much less abundant as a native metal, its purity is measured on a per-mille basis. As one of the seven metals of antiquity, silver has had an enduring role in most human cultures. Other than in currency and as an investment medium, silver is used in solar panels, water filtration, ornaments, high-value tableware and utensils, in electrical contacts and conductors, in specialized mirrors, window coatings, in catalysis of chemical reactions, as a colorant in stained glass and in specialised confectionery.
Its compounds are used in X-ray film. Dilute solutions of silver nitrate and other silver compounds are used as disinfectants and microbiocides, added to bandages and wound-dressings and other medical instruments. Silver is similar in its physical and chemical properties to its two vertical neighbours in group 11 of the periodic table and gold, its 47 electrons are arranged in the configuration 4d105s1 to copper and gold. This distinctive electron configuration, with a single electron in the highest occupied s subshell over a filled d subshell, accounts for many of the singular properties of metallic silver. Silver is an soft and malleable transition metal, though it is less malleable than gold. Silver crystallizes in a face-centered cubic lattice with bulk coordination number 12, where only the single 5s electron is delocalized to copper and gold. Unlike metals with incomplete d-shells, metallic bonds in silver are lacking a covalent character and are weak; this observation explains the low high ductility of single crystals of silver.
Silver has a brilliant white metallic luster that can take a high polish, and, so characteristic that the name of the metal itself has become a colour name. Unlike copper and gold, the energy required to excite an electron from the filled d band to the s-p conduction band in silver is large enough that it no longer corresponds to absorption in the visible region of the spectrum, but rather in the ultraviolet. Protected silver has greater optical reflectivity than aluminium at all wavelengths longer than ~450 nm. At wavelengths shorter than 450 nm, silver's reflectivity is inferior to that of aluminium and drops to zero near 310 nm. High electrical and thermal conductivity is common to the elements in group 11, because their single s electron is free and does not interact with the filled d subshell, as such interactions lower electron mobility; the electrical conductivity of silver is the greatest of all metals, greater than copper, but it is not used for this property because of the higher cost.
An exception is in radio-frequency engineering at VHF and higher frequencies where silver plating improves electrical conductivity because those currents tend to flow on the surface of conductors rather than through the interior. During World War II in the US, 13540 tons of silver were used in electromagnets for enriching uranium because of the wartime shortage of copper. Pure silver has the highest thermal conductivity of any metal, although the conductivity of carbon and superfluid helium-4 are higher. Silver has the lowest contact resistance of any metal. Silver forms alloys with copper and gold, as well as zinc. Zinc-silver alloys with low zinc concentration may be considered as face-centred cubic solid solutions of zinc in silver, as the structure of the silver is unchanged while the electron concentration rises as more zinc is added. Increasing the electron concentration further leads to body-centred cubic, complex cubic, hexagonal close-packed phases. Occurring silver is composed of two stable isotopes, 107Ag and 109Ag, with 107Ag being more abundant.
This equal abundance is rare in the periodic table. The atomic weight is 107.8682 u. Both isotopes of silver are produced in stars via the s-process, as well as in supernovas via the r-process. Twenty-eight radioisotopes have been characterized, the most stable being 105Ag with a half-life of 41.29 days, 111Ag with a half-life of 7.45 days, 112Ag with a half-life of 3.13 hours. Silver has numerous nuclear isomers, the most stable being 108mAg, 110mAg and 106mAg. All of the remaining radioactive isotopes have half-lives of less than an hour, the majority of these have half-lives of less than three minutes. Isotopes of silver range in relative atomic mass from 92.950 u
The Denver Mint is a branch of the United States Mint that struck its first coins on February 1, 1906. The mint is still operating and producing coins for circulation, as well as mint sets and commemorative coins. Coins produced at the Denver Mint bear a D mint mark; the Denver Mint is the single largest producer of coins in the world.. The predecessors of the Denver Mint were the men of Clark and Company. During the Pikes Peak Gold Rush, they coined gold dust brought from the gold fields by the miners. In 1858, Austin M. Clark, Milton E. Clark and Emanuel Henry Gruber founded a brokerage firm in Leavenworth and established an office in Denver at the beginning of the Colorado Gold Rush. Desiring to save on shipping and insurance costs associated with shipping gold back east, the firm opened a private mint. On 25 July 1860, the mint opened in a two-story brick building on the corner of Market and 16th Streets, minting $10 gold pieces at the rate of "fifteen or twenty coins a minute". "On the face is a representation of the peak, its base surrounded by a forest of timber and'Pikes Peak Gold' encircling the summit.
Under its base is the word'Denver', beneath it'Ten D.'. On the reverse is the American Eagle encircled by the name of the firm'Clark, Gruber & Co.', beneath the date,'1860'."A $20 gold coin was added, "the weight will be greater, but the value the same as the United States coin of like denomination". A $5 and a $2.5 gold coin were added, with production reaching $18,000 per week. On the front was the "head of the Goddess of Liberty surrounded by thirteen stars, with "Clark & Company" in the tiara. "Pikes's Peak Gold, Denver" was on the other side, with "5D." or "2 1/2 D."In the three years of operation, they minted $594,305 worth of Pike's Peak Gold in the form of gold coins. Additionally, they purchased 77,000 troy ounces of raw gold, shipped "large amounts of dust" to the Philadelphia Mint; the building and minting equipment was formally bought by the US Treasury in April 1863. Clark, Gruber & Co. remained a bank until bought by the First National Bank of Denver in 1865. Established by an Act of Congress on April 21, 1862, the United States Mint at Denver opened for business in late 1863 as a United States Assay Office.
Operations began in the facilities of Clark and Company, located at 16th and Market Streets and acquired by the government for $25,000, which it was able to print off at the location. Unlike Clark and Company, the Denver plant performed no coinage of gold as first intended. One reason given by the Director of the Mint for the lack of coinage at Denver was, "…the hostility of the Indian tribes along the routes, doubtless instigated by rebel emissaries and bad white men." Gold and nuggets brought there by miners from the surrounding area were accepted by the Assay Office for melting and stamping of cast gold bars. The bars were returned to the depositors as imparted bars stamped with the weight and fineness of the gold. Most of the gold came from the rich beds of placer gold found in the streams and first discovered in 1858, the same year Denver was founded; when the supply of gold was exhausted from the streams, the emphasis turned to lode mining, uncovering veins of ore with a high percentage of gold and silver.
By 1859, the yearly value of the gold and silver deposited at the Assay Office was over $5.6 million. During its early years as an Assay Office, the Denver plant was the city's most substantial structure; the United States Treasury did not expand its smelting and refining operations at the same rate as the discovery and production of gold. In 1872 a group of businessmen led by Judge Hiram Bond, Joseph Miner and Denver Mayor Joseph E. Bates set up a firm Denver Smelting and Refining Works which built an independent complementary plant which processed ore into ingots which were assayed and stamped by the Denver Mint. There was new hope for branch mint status when Congress provided for the establishment of a mint at Denver for gold and silver coin production; the site for the new mint at West Colfax and Delaware streets was purchased on April 22, 1896, for $60,000. Construction began in 1897. Appropriations to complete and equip the plant were insufficient, the transfer of assay operations to the new building were delayed until September 1, 1904.
Coinage operations began on February 1, 1906, advancing the status of the Denver facility to Branch Mint. In addition, before the new machinery to be used at the Mint was installed for use, it was first sent to the St. Louis Exposition of 1904 for display. Silver coins were minted in Denver for the first time in 1906. During the first year, 167 million coins were produced, including $20 gold coins, $10 gold coins, $5 gold coins, assorted denominations of silver coins; the Denver Mint is mentioned in The Andy Griffith Show episode "A Black Day for Mayberry". The Denver Mint is featured in the 1993 Sylvester Stallone film Cliffhanger, as the production point of the money stolen in the film, the departure point for the plane; the Mint is mentioned in both the title and lyrics of the Jimmy Eat World song "Lucky Denver Mint". The Denver Mint appears anachronistically in the 1870s in the 1967 The Wild Wild West episode "The Night of the Circus of Death". To above, The Mint is anachronistically set in the 1870s in the 1960 Shotgun Slade episode "The Missing Train".
The 1960 episode "Cold Hard Cash" of The Rifleman, set a few ye
Iowa Centennial half dollar
The Iowa Centennial half dollar was designed by Adam Pietz and minted in 1946. The obverse depicts the Iowa Old Capitol Building in Iowa City, the reverse shows the state seal. Since 1936, no new commemorative coins had been approved, as the many abuses and scandals involved with past commemorative coin issues had caused both Congress and then-president Franklin D. Roosevelt to oppose any bills for new commemoratives after a Congressional hearing held on April 15, 1937. However, with Harry S. Truman in office, the state of Iowa was able to get the bill for the Iowa Centennial half dollar passed on August 7th, 1946; the bill authorized a minimum of 100,000 coins to be minted. Former mint engraver Adam Pietz was selected by Mint director Nellie Tayloe Ross to design and sculpt the coin; the coins were sold by the Iowa Centennial Committee $2.50 for Iowans, $3 for those outside of the state. The discounted price for Iowans came as a result of the committee wanting all Iowans to buy a coin if they wanted one.
A majority of the coins minted were sold, with 500 pieces was set side for distribution in 1996, 500 more for 2046. In 1996, the coins that were set aside for release that year were offered for $500 each in special holders. Early United States commemorative coins Half dollar Media related to Iowa Centennial half dollar at Wikimedia Commons