title: "Hoover Dam" content: river's basin covered several states, and the river eventually entered Mexico. Though the Fall-Davis report called for a dam "at or near Boulder Canyon", the Reclamation Service (which was renamed the Bureau of Reclamation the following year) found that canyon unsuitable. One potential site at Boulder Canyon was bisected by a geologic fault; two others were so narrow there was no space for a construction camp at the bottom of the canyon or for a spillway. The Service investigated Black Canyon and found it ideal; a railway could be laid from the railhead in Las Vegas to the top of


title: "Hoover Dam" content: the dam site. Despite the site change, the dam project was referred to as the "Boulder Canyon Project". With little guidance on water allocation from the Supreme Court, proponents of the dam feared endless litigation. A Colorado attorney proposed that the seven states which fell within the river's basin (California, Nevada, Arizona, Utah, New Mexico, Colorado and Wyoming) form an interstate compact, with the approval of Congress. Such compacts were authorized by Article I of the United States Constitution but had never been concluded among more than two states. In 1922, representatives of seven states met with then-Secretary of Commerce


title: "Hoover Dam" content: Herbert Hoover. Initial talks produced no result, but when the Supreme Court handed down the "Wyoming v. Colorado" decision undermining the claims of the upstream states, they became anxious to reach an agreement. The resulting Colorado River Compact was signed on November 24, 1922. Legislation to authorize the dam was introduced repeatedly by two California Republicans, Representative Phil Swing and Senator Hiram Johnson, but representatives from other parts of the country considered the project as hugely expensive and one that would mostly benefit California. The 1927 Mississippi flood made Midwestern and Southern congressmen and senators more sympathetic toward the dam


title: "Hoover Dam" content: project. On March 12, 1928, the failure of the St. Francis Dam, constructed by the city of Los Angeles, caused a disastrous flood that killed up to 600 people. As that dam was a curved-gravity type, similar in design to the arch-gravity as was proposed for the Black Canyon dam, opponents claimed that the Black Canyon dam's safety could not be guaranteed. Congress authorized a board of engineers to review plans for the proposed dam. The Colorado River Board found the project feasible, but warned that should the dam fail, every downstream Colorado River community would be destroyed, and that


title: "Hoover Dam" content: the river might change course and empty into the Salton Sea. The Board cautioned: "To avoid such possibilities, the proposed dam should be constructed on conservative if not ultra-conservative lines." On December 21, 1928, President Coolidge signed the bill authorizing the dam. The Boulder Canyon Project Act appropriated $165 million for the Hoover Dam along with the downstream Imperial Dam and All-American Canal, a replacement for Beatty's canal entirely on the U.S. side of the border. It also permitted the compact to go into effect when at least six of the seven states approved it. This occurred on March 6,


title: "Hoover Dam" content: 1929, with Utah's ratification; Arizona did not approve it until 1944. Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch-gravity dam, the design of which was overseen by the Bureau's chief design engineer John L. Savage. The monolithic dam would be thick at the bottom and thin near the top, and would present a convex face towards the water above the dam. The curving arch of the dam would transmit the water's force into the abutments, in this case the


title: "Hoover Dam" content: rock walls of the canyon. The wedge-shaped dam would be thick at the bottom, narrowing to at the top, leaving room for a highway connecting Nevada and Arizona. On January 10, 1931, the Bureau made the bid documents available to interested parties, at five dollars a copy. The government was to provide the materials; but the contractor was to prepare the site and build the dam. The dam was described in minute detail, covering 100 pages of text and 76 drawings. A $2 million bid bond was to accompany each bid; the winner would have to post a $5 million


title: "Hoover Dam" content: performance bond. The contractor had seven years to build the dam, or penalties would ensue. The Wattis Brothers, heads of the Utah Construction Company, were interested in bidding on the project, but lacked the money for the performance bond. They lacked sufficient resources even in combination with their longtime partners, Morrison-Knudsen, which employed the nation's leading dam builder, Frank Crowe. They formed a joint venture to bid for the project with Pacific Bridge Company of Portland, Oregon; Henry J. Kaiser & W. A. Bechtel Company of San Francisco; MacDonald & Kahn Ltd. of Los Angeles; and the J.F. Shea Company


title: "Hoover Dam" content: of Portland, Oregon. The joint venture was called Six Companies, Inc. as Bechtel and Kaiser were considered one company for purposes of Six in the name. The name was descriptive and was an inside joke among the San Franciscans in the bid, where "Six Companies" was also a Chinese benevolent association in the city. There were three valid bids, and Six Companies' bid of $48,890,955 was the lowest, within $24,000 of the confidential government estimate of what the dam would cost to build, and five million dollars less than the next-lowest bid. The city of Las Vegas had lobbied hard


title: "Hoover Dam" content: to be the headquarters for the dam construction, closing its many speakeasies when the decision maker, Secretary of the Interior Ray Wilbur, came to town. Instead, Wilbur announced in early 1930 that a model city was to be built in the desert near the dam site. This town became known as Boulder City, Nevada. Construction of a rail line joining Las Vegas and the dam site began in September 1930. Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed


title: "Hoover Dam" content: descend on it. A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on the project, together with their families. Another camp, on the flats along the Colorado River, was officially called Williamsville, but was known to its inhabitants as "Ragtown". When construction began, Six Companies hired large numbers of workers, with more than 3,000 on the payroll by 1932 and with employment peaking at 5,251 in July 1934. "Mongolian" (Chinese) labor was prevented by the


title: "Hoover Dam" content: construction contract, while the number of blacks employed by Six Companies never exceeded thirty, mostly lowest-pay-scale laborers in a segregated crew, who were issued separate water buckets. As part of the contract, Six Companies, Inc. was to build Boulder City to house the workers. The original timetable called for Boulder City to be built before the dam project began, but President Hoover ordered work on the dam to begin in March 1931 rather than in October. The company built bunkhouses, attached to the canyon wall, to house 480 single men at what became known as River Camp. Workers with families


title: "Hoover Dam" content: were left to provide their own accommodations until Boulder City could be completed, and many lived in Ragtown. The site of Hoover Dam endures extremely hot weather, and the summer of 1931 was especially torrid, with the daytime high averaging . Sixteen workers and other riverbank residents died of heat prostration between June 25 and July 26, 1931. The Industrial Workers of the World (IWW or "Wobblies"), though much-reduced from their heyday as militant labor organizers in the early years of the century, hoped to unionize the Six Companies workers by capitalizing on their discontent. They sent eleven organizers, several


title: "Hoover Dam" content: of whom were arrested by Las Vegas police. On August 7, 1931, the company cut wages for all tunnel workers. Although the workers sent away the organizers, not wanting to be associated with the "Wobblies", they formed a committee to represent them with the company. The committee drew up a list of demands that evening and presented them to Crowe the following morning. He was noncommittal. The workers hoped that Crowe, the general superintendent of the job, would be sympathetic; instead he gave a scathing interview to a newspaper, describing the workers as "malcontents". On the morning of the 9th,


title: "Hoover Dam" content: Crowe met with the committee and told them that management refused their demands, was stopping all work, and was laying off the entire work force, except for a few office workers and carpenters. The workers were given until 5 p.m. to vacate the premises. Concerned that a violent confrontation was imminent, most workers took their paychecks and left for Las Vegas to await developments. Two days later, the remainder were talked into leaving by law enforcement. On August 13, the company began hiring workers again, and two days later, the strike was called off. While the workers received none of


title: "Hoover Dam" content: their demands, the company guaranteed there would be no further reductions in wages. Living conditions began to improve as the first residents moved into Boulder City in late 1931. A second labor action took place in July 1935, as construction on the dam wound down. When a Six Companies manager altered working times to force workers to take lunch on their own time, workers responded with a strike. Emboldened by Crowe's reversal of the lunch decree, workers raised their demands to include a $1-per-day raise. The company agreed to ask the Federal government to supplement the pay, but no money


title: "Hoover Dam" content: was forthcoming from Washington. The strike ended. Before the dam could be built, the Colorado River needed to be diverted away from the construction site. To accomplish this, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were in diameter. Their combined length was nearly 16,000 ft, or more than . The contract required these tunnels to be completed by October 1, 1933, with a $3,000-per-day fine to be assessed for any delay. To meet the deadline, Six Companies had to complete work by early 1933, since


title: "Hoover Dam" content: only in late fall and winter was the water level in the river low enough to safely divert. Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly afterward, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining the tunnels with concrete. First the base, or invert, was poured. Gantry cranes, running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the


title: "Hoover Dam" content: overheads were filled in. The concrete lining is thick, reducing the finished tunnel diameter to . The river was diverted into the two Arizona tunnels on November 13, 1932; the Nevada tunnels were kept in reserve for high water. This was done by exploding a temporary cofferdam protecting the Arizona tunnels while at the same time dumping rubble into the river until its natural course was blocked. Following the completion of the dam, the entrances to the two outer diversion tunnels were sealed at the opening and halfway through the tunnels with large concrete plugs. The downstream halves of the


title: "Hoover Dam" content: tunnels following the inner plugs are now the main bodies of the spillway tunnels. The inner diversion tunnels were plugged at approximately one-third of their length, beyond which they now carry steel pipes connecting the intake towers to the power plant and outlet works. The inner tunnels' outlets are equipped with gates that can be closed to drain the tunnels for maintenance. To protect the construction site from the Colorado River and to facilitate the river's diversion, two cofferdams were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted. The


title: "Hoover Dam" content: cofferdams were designed to protect against the possibility of the river's flooding a site at which two thousand men might be at work, and their specifications were covered in the bid documents in nearly as much detail as the dam itself. The upper cofferdam was high, and thick at its base, thicker than the dam itself. It contained of material. When the cofferdams were in place and the construction site was drained of water, excavation for the dam foundation began. For the dam to rest on solid rock, it was necessary to remove accumulated erosion soils and other loose materials


title: "Hoover Dam" content: in the riverbed until sound bedrock was reached. Work on the foundation excavations was completed in June 1933. During this excavation, approximately of material was removed. Since the dam was an arch-gravity type, the side-walls of the canyon would bear the force of the impounded lake. Therefore, the side-walls were excavated too, to reach virgin rock, as weathered rock might provide pathways for water seepage. Shovels for the excavation came from the Marion Power Shovel Company. The men who removed this rock were called "high scalers". While suspended from the top of the canyon with ropes, the high-scalers climbed down


title: "Hoover Dam" content: the canyon walls and removed the loose rock with jackhammers and dynamite. Falling objects were the most common cause of death on the dam site; the high scalers' work thus helped ensure worker safety. One high scaler was able to save a life in a more direct manner: when a government inspector lost his grip on a safety line and began tumbling down a slope towards almost certain death, a high scaler was able to intercept him and pull him into the air. The construction site had, even then, become a magnet for tourists; the high scalers were prime attractions


title: "Hoover Dam" content: and showed off for the watchers. The high scalers received considerable media attention, with one worker dubbed the "Human Pendulum" for swinging co-workers (and, at other times, cases of dynamite) across the canyon. To protect themselves against falling objects, some high scalers took cloth hats and dipped them in tar, allowing them to harden. When workers wearing such headgear were struck hard enough to inflict broken jaws, they sustained no skull damage, Six Companies ordered thousands of what initially were called "hard boiled hats" (later "hard hats") and strongly encouraged their use. The cleared, underlying rock foundation of the dam


title: "Hoover Dam" content: site was reinforced with grout, called a grout curtain. Holes were driven into the walls and base of the canyon, as deep as into the rock, and any cavities encountered were to be filled with grout. This was done to stabilize the rock, to prevent water from seeping past the dam through the canyon rock, and to limit "uplift"—upward pressure from water seeping under the dam. The workers were under severe time constraints due to the beginning of the concrete pour, and when they encountered hot springs or cavities too large to readily fill, they moved on without resolving the


title: "Hoover Dam" content: problem. A total of 58 of the 393 holes were incompletely filled. After the dam was completed and the lake began to fill, large numbers of significant leaks into the dam caused the Bureau of Reclamation to look into the situation. It found that the work had been incompletely done, and was based on less than a full understanding of the canyon's geology. New holes were drilled from inspection galleries inside the dam into the surrounding bedrock. It took nine years (1938–47) under relative secrecy to complete the supplemental grout curtain. The first concrete was poured into the dam on


title: "Hoover Dam" content: June 6, 1933, 18 months ahead of schedule. Since concrete heats and contracts as it cures, the potential for uneven cooling and contraction of the concrete posed a serious problem. Bureau of Reclamation engineers calculated that if the dam were to be built in a single continuous pour, the concrete would take 125 years to cool, and the resulting stresses would cause the dam to crack and crumble. Instead, the ground where the dam would rise was marked with rectangles, and concrete blocks in columns were poured, some as large as and high. Each five-foot form contained a series of


title: "Hoover Dam" content: steel pipes; cool riverwater would be poured through the pipes, followed by ice-cold water from a refrigeration plant. When an individual block had cured and had stopped contracting, the pipes were filled with grout. Grout was also used to fill the hairline spaces between columns, which were grooved to increase the strength of the joins. The concrete was delivered in huge steel buckets and almost 7 feet in diameter; Crowe was awarded two patents for their design. These buckets, which weighed when full, were filled at two massive concrete plants on the Nevada side, and were delivered to the site


title: "Hoover Dam" content: in special railcars. The buckets were then suspended from aerial cableways which were used to deliver the bucket to a specific column. As the required grade of aggregate in the concrete differed depending on placement in the dam (from pea-sized gravel to 9-inch or 23 cm stones), it was vital that the bucket be maneuvered to the proper column. When the bottom of the bucket opened up, disgorging of concrete, a team of men worked it throughout the form. Although there are myths that men were caught in the pour and are entombed in the dam to this day, each


title: "Hoover Dam" content: bucket deepened the concrete in a form by only an inch, and Six Companies engineers would not have permitted a flaw caused by the presence of a human body. A total of of concrete was used in the dam before concrete pouring ceased on May 29, 1935. In addition, were used in the power plant and other works. More than of cooling pipes were placed within the concrete. Overall, there is enough concrete in the dam to pave a two-lane highway from San Francisco to New York. Concrete cores were removed from the dam for testing in 1995; they showed


title: "Hoover Dam" content: that "Hoover Dam's concrete has continued to slowly gain strength" and the dam is composed of a "durable concrete having a compressive strength exceeding the range typically found in normal mass concrete". Hoover Dam concrete is not subject to alkali–silica reaction (ASR), as the Hoover Dam builders happened to use nonreactive aggregate, unlike that at downstream Parker Dam, where ASR has caused measurable deterioration. With most work finished on the dam itself (the powerhouse remained uncompleted), a formal dedication ceremony was arranged for September 30, 1935, to coincide with a western tour being made by President Franklin D. Roosevelt. The


title: "Hoover Dam" content: morning of the dedication, it was moved forward three hours from 2 p.m. Pacific time to 11 a.m.; this was done because Secretary of the Interior Harold L. Ickes had reserved a radio slot for the President for 2 p.m. but officials did not realize until the day of the ceremony that the slot was for 2 p.m. Eastern Time. Despite the change in the ceremony time, and temperatures of , 10,000 people were present for the President's speech, in which he avoided mentioning the name of former President Hoover, who was not invited to the ceremony. To mark the


title: "Hoover Dam" content: occasion, a three-cent stamp was issued by the United States Post Office Department—bearing the name "Boulder Dam", the official name of the dam between 1933 and 1947. After the ceremony, Roosevelt made the first visit by any American president to Las Vegas. Most work had been completed by the dedication, and Six Companies negotiated with the government through late 1935 and early 1936 to settle all claims and arrange for the formal transfer of the dam to the Federal Government. The parties came to an agreement and on March 1, 1936, Secretary Ickes formally accepted the dam on behalf of


title: "Hoover Dam" content: the government. Six Companies was not required to complete work on one item, a concrete plug for one of the bypass tunnels, as the tunnel had to be used to take in irrigation water until the powerhouse went into operation. There were 112 deaths reported as associated with the construction of the dam. The first was J. G. Tierney, a surveyor who drowned on December 20, 1922, while looking for an ideal spot for the dam. The last death on the project's official fatality list occurred on December 20, 1935, when an "electrician's helper", Patrick Tierney, the son of J.


title: "Hoover Dam" content: G. Tierney, fell from an intake tower. Included in the fatality list are three workers, one in 1932 and two in 1933, who committed suicide onsite. Ninety-six of the deaths occurred during construction at the site. Of the 112 fatalities, 91 were Six Companies employees, three were BOR employees, and one was a visitor to the site, with the remainder employees of various contractors not part of Six Companies. Not included in the official number of fatalities were deaths that were recorded as pneumonia. Workers alleged that this diagnosis was a cover for death from carbon monoxide poisoning (brought on


title: "Hoover Dam" content: by the use of gasoline-fueled vehicles in the diversion tunnels), and a classification used by Six Companies to avoid paying compensation claims. The site's diversion tunnels frequently reached , enveloped in thick plumes of vehicle exhaust gases. A total of 42 workers were recorded as having died from pneumonia and were not included in the above total; none were listed as having died from carbon monoxide poisoning. No deaths of non-workers from pneumonia were recorded in Boulder City during the construction period. The initial plans for the facade of the dam, the power plant, the outlet tunnels and ornaments clashed


title: "Hoover Dam" content: with the modern look of an arch dam. The Bureau of Reclamation, more concerned with the dam's functionality, adorned it with a Gothic-inspired balustrade and eagle statues. This initial design was criticized by many as being too plain and unremarkable for a project of such immense scale, so Los Angeles-based architect Gordon B. Kaufmann, then the supervising architect to the Bureau of Reclamation, was brought in to redesign the exteriors. Kaufmann greatly streamlined the design and applied an elegant Art Deco style to the entire project. He designed sculptured turrets rising seamlessly from the dam face and clock faces on


title: "Hoover Dam" content: the intake towers set for the time in Nevada and Arizona — both states are in different time zones, but since Arizona does not observe Daylight Saving Time, the clocks display the same time for more than half the year. At Kaufmann's request, Denver artist Allen Tupper True was hired to handle the design and decoration of the walls and floors of the new dam. True's design scheme incorporated motifs of the Navajo and Pueblo tribes of the region. Although some initially were opposed to these designs, True was given the go-ahead and was officially appointed consulting artist. With the


title: "Hoover Dam" content: assistance of the National Laboratory of Anthropology, True researched authentic decorative motifs from Indian sand paintings, textiles, baskets and ceramics. The images and colors are based on Native American visions of rain, lightning, water, clouds, and local animals — lizards, serpents, birds — and on the Southwestern landscape of stepped mesas. In these works, which are integrated into the walkways and interior halls of the dam, True also reflected on the machinery of the operation, making the symbolic patterns appear both ancient and modern. With the agreement of Kaufmann and the engineers, True also devised for the pipes and machinery


title: "Hoover Dam" content: an innovative color-coding which was implemented throughout all BOR projects. True's consulting artist job lasted through 1942; it was extended so he could complete design work for the Parker, Shasta and Grand Coulee dams and power plants. True's work on the Hoover Dam was humorously referred to in a poem published in "The New Yorker", part of which read, "lose the spark, and justify the dream; but also worthy of remark will be the color scheme". Complementing Kaufmann and True's work, the Norwegian-born, naturalized American sculptor Oskar J.W. Hansen designed many of the sculptures on and around the dam. His


title: "Hoover Dam" content: works include the monument of dedication plaza, a plaque to memorialize the workers killed and the bas-reliefs on the elevator towers. In his words, Hansen wanted his work to express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment", because "[t]he building of Hoover Dam belongs to the sagas of the daring." Hansen's dedication plaza, on the Nevada abutment, contains a sculpture of two winged figures flanking a flagpole. Surrounding the base of the monument is a terrazzo floor embedded with a "star map". The map depicts


title: "Hoover Dam" content: the Northern Hemisphere sky at the moment of President Roosevelt's dedication of the dam. This is intended to help future astronomers, if necessary, calculate the exact date of dedication. The bronze figures, dubbed "Winged Figures of the Republic", were each formed in a continuous pour. To put such large bronzes into place without marring the highly polished bronze surface, they were placed on ice and guided into position as the ice melted. Hansen's bas-relief on the Nevada elevator tower depicts the benefits of the dam: flood control, navigation, irrigation, water storage, and power. The bas-relief on the Arizona elevator depicts,


title: "Hoover Dam" content: in his words, "the visages of those Indian tribes who have inhabited mountains and plains from ages distant." Excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. The excavation of this U-shaped structure located at the downstream toe of the dam was completed in late 1933 with the first concrete placed in November 1933. Filling of Lake Mead began February 1, 1935, even before the last of the concrete was poured that May. The powerhouse was one of the projects uncompleted at the time of the formal dedication on September 30, 1935;


title: "Hoover Dam" content: a crew of 500 men remained to finish it and other structures. To make the powerhouse roof bombproof, it was constructed of layers of concrete, rock, and steel with a total thickness of about , topped with layers of sand and tar. In the latter half of 1936, water levels in Lake Mead were high enough to permit power generation, and the first three Allis Chalmers built Francis turbine-generators, all on the Nevada side, began operating. In March 1937, one more Nevada generator went online and the first Arizona generator by August. By September 1939, four more generators were operating,


title: "Hoover Dam" content: and the dam's power plant became the largest hydroelectricity facility in the world. The final generator was not placed in service until 1961, bringing the maximum generating capacity to 1,345 megawatts at the time. Original plans called for 16 large generators, eight on each side of the river, but two smaller generators were installed instead of one large one on the Arizona side for a total of 17. The smaller generators were used to serve smaller communities at a time when the output of each generator was dedicated to a single municipality, before the dam's total power output was placed


title: "Hoover Dam" content: on the grid and made arbitrarily distributable. Before water from Lake Mead reaches the turbines, it enters the intake towers and then four gradually narrowing penstocks which funnel the water down towards the powerhouse. The intakes provide a maximum hydraulic head (water pressure) of as the water reaches a speed of about . The entire flow of the Colorado River passes through the turbines. The spillways and outlet works (jet-flow gates) are rarely used. The jet-flow gates, located in concrete structures above the river and also at the outlets of the inner diversion tunnels at river level, may be used


title: "Hoover Dam" content: to divert water around the dam in emergency or flood conditions, but have never done so, and in practice are used only to drain water from the penstocks for maintenance. Following an uprating project from 1986 to 1993, the total gross power rating for the plant, including two 2.4 megawatt Pelton turbine-generators that power Hoover Dam's own operations is a maximum capacity of 2080 megawatts. The annual generation of Hoover Dam varies. The maximum net generation was 10.348 TWh in 1984, and the minimum since 1940 was 2.648 TWh in 1956. The average power generated was 4.2 TWh/year for 1947–2008.


title: "Hoover Dam" content: In 2015, the dam generated 3.6 TWh. The amount of electricity generated by Hoover Dam has been decreasing along with the falling water level in Lake Mead due to the prolonged drought in the 2010s and high demand for the Colorado River's water. Lake Mead fell to a new record low elevation of on July 1, 2016 before beginning to rebound slowly. Under its original design, the dam will no longer be able to generate power once the water level falls below , which could occur as early as 2017. To lower the minimum power pool elevation from , five


title: "Hoover Dam" content: wide-head turbines, designed to work efficiently with less flow, were installed. Due to the low water levels, by 2014 it was providing power only during periods of peak demand. Control of water was the primary concern in the building of the dam. Power generation has allowed the dam project to be self-sustaining: proceeds from the sale of power repaid the 50-year construction loan, and those revenues also finance the multimillion-dollar yearly maintenance budget. Power is generated in step with and only with the release of water in response to downstream water demands. Lake Mead and downstream releases from the dam


title: "Hoover Dam" content: also provide water for both municipal and irrigation uses. Water released from the Hoover Dam eventually reaches several canals. The Colorado River Aqueduct and Central Arizona Project branch off Lake Havasu while the All-American Canal is supplied by the Imperial Dam. In total, water from the Lake Mead serves 18 million people in Arizona, Nevada and California and supplies the irrigation of over of land. In 2018, the Los Angeles Department of Water and Power (LADWP) proposed a $3 billion pumped hydro storage project - a "battery" of sorts - that would use wind and solar power to recirculate water


title: "Hoover Dam" content: back up to Lake Mead from a pumping station 20 miles downriver. Electricity from the dam's powerhouse was originally sold pursuant to a fifty-year contract, authorized by Congress in 1934, which ran from 1937 to 1987. In 1984, Congress passed a new statute which set power allocations to southern California, Arizona, and Nevada from the dam from 1987 to 2017. The powerhouse was run under the original authorization by the Los Angeles Department of Water and Power and Southern California Edison; in 1987, the Bureau of Reclamation assumed control. In 2011, Congress enacted legislation extending the current contracts until 2067,


title: "Hoover Dam" content: after setting aside 5% of Hoover Dam's power for sale to Native American tribes, electric cooperatives, and other entities. The new arrangement began on October 1, 2017. The Bureau of Reclamation reports that the energy generated under the contracts ending in 2017 was allocated as follows: The dam is protected against over-topping by two spillways. The spillway entrances are located behind each dam abutment, running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weir with each spillway containing four and steel-drum gates. Each gate weighs and can be operated manually or automatically. Gates are


title: "Hoover Dam" content: raised and lowered depending on water levels in the reservoir and flood conditions. The gates could not entirely prevent water from entering the spillways but could maintain an extra of lake level. Water flowing over the spillways falls dramatically into , spillway tunnels before connecting to the outer diversion tunnels, and reentering the main river channel below the dam. This complex spillway entrance arrangement combined with the approximate elevation drop from the top of the reservoir to the river below was a difficult engineering problem and posed numerous design challenges. Each spillway's capacity of was empirically verified in post-construction tests


title: "Hoover Dam" content: in 1941. The large spillway tunnels have only been used twice, for testing in 1941 and because of flooding in 1983. Both times, when inspecting the tunnels after the spillways were used, engineers found major damage to the concrete linings and underlying rock. The 1941 damage was attributed to a slight misalignment of the tunnel invert (or base), which caused cavitation, a phenomenon in fast-flowing liquids in which vapor bubbles collapse with explosive force. In response to this finding, the tunnels were patched with special heavy-duty concrete and the surface of the concrete was polished mirror-smooth. The spillways were modified


title: "Hoover Dam" content: in 1947 by adding flip buckets, which both slow the water and decrease the spillway's effective capacity, in an attempt to eliminate conditions thought to have contributed to the 1941 damage. The 1983 damage, also due to cavitation, led to the installation of aerators in the spillways. Tests at Grand Coulee Dam showed that the technique worked, in principle. There are two lanes for automobile traffic across the top of the dam, which formerly served as the Colorado River crossing for U.S. Route 93. In the wake of the September 11, 2001 terrorist attacks, authorities expressed security concerns and the


title: "Hoover Dam" content: Hoover Dam Bypass project was expedited. Pending the completion of the bypass, restricted traffic was permitted over Hoover Dam. Some types of vehicles were inspected prior to crossing the dam while semi-trailer trucks, buses carrying luggage, and enclosed-box trucks over long were not allowed on the dam at all, and were diverted to U.S. Route 95 or Nevada State Routes 163/68. The four-lane Hoover Dam Bypass opened on October 19, 2010. It includes a composite steel and concrete arch bridge, the Mike O'Callaghan–Pat Tillman Memorial Bridge, downstream from the dam. With the opening of the bypass, through traffic is no


title: "Hoover Dam" content: longer allowed across Hoover Dam; dam visitors are allowed to use the existing roadway to approach from the Nevada side and cross to parking lots and other facilities on the Arizona side. Hoover Dam opened for tours in 1937 after its completion, but following Japan's attack on Pearl Harbor on December 7, 1941, it was closed to the public when the United States entered World War II, during which only authorized traffic, in convoys, was permitted. After the war, it reopened September 2, 1945, and by 1953, annual attendance had risen to 448,081. The dam closed on November 25, 1963,


title: "Hoover Dam" content: and March 31, 1969, days of mourning in remembrance of Presidents Kennedy and Eisenhower. In 1995, a new visitors' center was built, and the following year, visits exceeded one million for the first time. The dam closed again to the public on September 11, 2001; modified tours were resumed in December and a new "Discovery Tour" was added the following year. Today, nearly a million people per year take the tours of the dam offered by the Bureau of Reclamation. Increased security concerns by the government have led to most of the interior structure being inaccessible to tourists. As a


title: "Hoover Dam" content: result, few of True's decorations can now be seen by visitors. The changes in water flow and use caused by Hoover Dam's construction and operation have had a large impact on the Colorado River Delta. The construction of the dam has been implicated in causing the decline of this estuarine ecosystem. For six years after the construction of the dam, while Lake Mead filled, virtually no water reached the mouth of the river. The delta's estuary, which once had a freshwater-saltwater mixing zone stretching south of the river's mouth, was turned into an inverse estuary where the level of salinity


title: "Hoover Dam" content: was higher close to the river's mouth. The Colorado River had experienced natural flooding before the construction of the Hoover Dam. The dam eliminated the natural flooding, threatening many species adapted to the flooding, including both plants and animals. The construction of the dam devastated the populations of native fish in the river downstream from the dam. Four species of fish native to the Colorado River, the Bonytail chub, Colorado pikeminnow, Humpback chub, and Razorback sucker, are listed as endangered. During the years of lobbying leading up to the passage of legislation authorizing the dam in 1928, the press generally


title: "Hoover Dam" content: referred to the dam as "Boulder Dam" or as "Boulder Canyon Dam", even though the proposed site had shifted to Black Canyon. The Boulder Canyon Project Act of 1928 (BCPA) never mentioned a proposed name or title for the dam. The BCPA merely allows the government to "construct, operate, and maintain a dam and incidental works in the main stream of the Colorado River at Black Canyon or Boulder Canyon". When Secretary Wilbur spoke at the ceremony starting the building of the railway between Las Vegas and the dam site on September 17, 1930, he named the dam "Hoover Dam",


title: "Hoover Dam" content: citing a tradition of naming dams after Presidents, though none had been so honored during their terms of office. Wilbur justified his choice on the ground that Hoover was "the great engineer whose vision and persistence ... has done so much to make <nowiki>[the dam]</nowiki> possible". One writer complained in response that "the Great Engineer had quickly drained, ditched, and dammed the country." After Hoover's election defeat in 1932 and the accession of the Roosevelt administration, Secretary Ickes ordered on May 13, 1933, that the dam be referred to as "Boulder Dam". Ickes stated that Wilbur had been imprudent in


title: "Hoover Dam" content: naming the dam after a sitting president, that Congress had never ratified his choice, and that it had long been referred to as Boulder Dam. Unknown to the general public, Attorney General Homer Cummings informed Ickes that Congress had indeed used the name "Hoover Dam" in five different bills appropriating money for construction of the dam. The official status this conferred to the name "Hoover Dam" had been noted on the floor of the House of Representatives by Congressman Edward T. Taylor of Colorado on December 12, 1930, but was likewise ignored by Ickes. When Ickes spoke at the dedication


title: "Hoover Dam" content: ceremony on September 30, 1935, he was determined, as he recorded in his diary, "to try to nail down for good and all the name Boulder Dam." At one point in the speech, he spoke the words "Boulder Dam" five times within thirty seconds. Further, he suggested that if the dam were to be named after any one person, it should be for California Senator Hiram Johnson, a lead sponsor of the authorizing legislation. Roosevelt also referred to the dam as Boulder Dam, and the Republican-leaning "Los Angeles Times", which at the time of Ickes' name change had run an


title: "Hoover Dam" content: editorial cartoon showing Ickes ineffectively chipping away at an enormous sign "HOOVER DAM," reran it showing Roosevelt reinforcing Ickes, but having no greater success. In the following years, the name "Boulder Dam" failed to fully take hold, with many Americans using both names interchangeably and mapmakers divided as to which name should be printed. Memories of the Great Depression faded, and Hoover to some extent rehabilitated himself through good works during and after World War II. In 1947, a bill passed both Houses of Congress unanimously restoring the name "Hoover Dam." Ickes, who was by then a private citizen, opposed


title: "Hoover Dam" content: the change, stating, "I didn't know Hoover was that small a man to take credit for something he had nothing to do with." Hoover Dam was recognized as a National Civil Engineering Landmark in 1984. It was listed on the National Register of Historic Places in 1981, and was designated a National Historic Landmark in 1985, cited for its engineering innovations. Other sources Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the


title: "Horror fiction" content: de France wrote one of the twelve lais as a werewolf story entitled "Bisclavret". The Countess Yolande commissioned a werewolf story entitled "Guillaume de Palerme". Anonymous writers penned two werewolf stories, "Biclarel" and "Melion". Much of horror fiction derived itself from the cruelest faces in world history, particularly those who lived in the fifteenth-century. "Dracula" can be traced to the Prince of Wallachia Vlad III whose alleged war crimes were published in German pamphlets in the late Fifteenth Century. The 1499 pamphlet published by Markus Ayrer is most notable for its woodcut imagery. The alleged crimes of the Giles de


title: "History of Russia" content: policy had made Russia into a major European power. Alexander I continued this policy, wresting Finland from the weakened kingdom of Sweden in 1809 and Bessarabia from the Ottomans in 1812. After Russian armies liberated allied Georgia from Persian occupation in 1802, they clashed with Persia over control and consolidation over Georgia, as well as the Iranian territories that comprise modern-day Azerbaijan and Dagestan. They also became involved in the Caucasian War against the Caucasian Imamate. In 1813, the war with Persia concluded with a Russian victory, forcing Qajar Iran to cede swaths of its territories in the Caucasus to


title: "Henry VIII of England" content: not least because he needed to retain Henry's support, his own power, and the possibility of actually achieving the plan he set out. Cromwell made the various income streams put in place by Henry VII more formal and assigned largely autonomous bodies for their administration. The role of the King's Council was transferred to a reformed Privy Council, much smaller and more efficient than its predecessor. A difference emerged between the financial health of the king, and that of the country, although Cromwell's fall undermined much of his bureaucracy, which required his hand to keep order among the many new


title: "Hoosier Hysteria" content: college ranks. And in Division II St. Joseph's, University of Indianapolis and University of Southern Indiana have added their own successes to the legend of Indiana basketball. Wabash College won the Men's Division III NCAA Championship in 1982 and their 1905 24-0 team was considered World Champions; DePauw University and Manchester College were Div III National Finalists. It is safe to say that the terms "Final Four" and "March Madness" have grown out of the tradition of Hoosier Hysteria. The Ball State Cardinals have won several conference championships and earned a number of NCAA Tournament berths over the years, including:


title: Italy content: 251,192 Jehovah's Witnesses, 30,000 Waldensians, 25,000 Seventh-day Adventists, 26,925 Latter-day Saints, 15,000 Baptists (plus some 5,000 Free Baptists), 7,000 Lutherans, 4,000 Methodists (affiliated with the Waldensian Church). One of the longest-established minority religious faiths in Italy is Judaism, Jews having been present in Ancient Rome since before the birth of Christ. Italy has for centuries welcomed Jews expelled from other countries, notably Spain. However, as a result of the Holocaust, about 20% of Italian Jews lost their lives. This, together with the emigration that preceded and followed World War II, has left only around 28,400 Jews in Italy. Soaring immigration


title: Italy content: in the last two decades has been accompanied by an increase in non-Christian faiths.There are more than 800,000 followers of faiths originating in the Indian subcontinent with some 70,000 Sikhs with 22 gurdwaras across the country, The Italian state, as a measure to protect religious freedom, devolves shares of income tax to recognised religious communities, under a regime known as Eight per thousand. Donations are allowed to Christian, Jewish, Buddhist and Hindu communities; however, Islam remains excluded, since no Muslim communities have yet signed a concordat with the Italian state. Taxpayers who do not wish to fund a religion contribute


title: "Isaac Newton" content: of the Sun or any other body that could be considered at rest, but rather "the common centre of gravity of the Earth, the Sun and all the Planets is to be esteem'd the Centre of the World", and this centre of gravity "either is at rest or moves uniformly forward in a right line" (Newton adopted the "at rest" alternative in view of common consent that the centre, wherever it was, was at rest). Newton's postulate of an invisible force able to act over vast distances led to him being criticised for introducing "occult agencies" into science. Later, in


title: "Isaac Newton" content: Testament, remained unpublished until 1785. Scholars long debated whether Newton disputed the doctrine of the Trinity. His first biographer, Sir David Brewster, who compiled his manuscripts, interpreted Newton as questioning the veracity of some passages used to support the Trinity, but never denying the doctrine of the Trinity as such. In the twentieth century, encrypted manuscripts written by Newton and bought by John Maynard Keynes (among others) were deciphered and it became known that Newton did indeed reject Trinitarianism. Later works—"The Chronology of Ancient Kingdoms Amended" (1728) and "Observations Upon the Prophecies of Daniel and the Apocalypse of St. John"


title: "Italian language" content: nation was unified in 1861. Italian is a Romance language, and is therefore a descendant of Vulgar Latin (the spoken form of non-classical Latin). Standard Italian is based on Tuscan, especially its Florentine dialect, and is therefore an Italo-Dalmatian language, to which Sicilian and the extinct Dalmatian also belong, among a few others. Unlike most other Romance languages, Italian retains Latin's contrast between short and long consonants. As in most Romance languages, stress is distinctive. In particular, among the Romance languages, Italian is the closest to Latin in terms of vocabulary. Lexical similarity is 89% with French, 87% with Catalan,


title: Iron content: Iron Iron is a chemical element with symbol Fe (from ) and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space. Like the other


title: Iron content: group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +7, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, exposing fresh surfaces for corrosion. Iron metal has been used since ancient times, although copper alloys, which


title: Iron content: have lower melting temperatures, were used even earlier in human history. Pure iron is relatively soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon, from the smelting process. A certain proportion of carbon (between 0.002% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron


title: Iron content: alloys formed with other metals (alloy steels) are by far the most common industrial metals because they have a great range of desirable properties and iron-bearing rock is abundant. Iron chemical compounds have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen transport proteins


title: Iron content: in vertebrates. Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. In adult human males are some 3.8 grams of iron, and 2.3 grams in females, for whom iron is distributed in hemoglobin and throughout the body. Iron is a critical element in the metabolism of hundreds of proteins and enzymes involved in diverse body functions, such as oxygen transport, DNA synthesis, and cell growth. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the


title: Iron content: Brinell test, Rockwell test and the Vickers hardness test. The data on iron is so consistent that it is often used to calibrate measurements or to compare tests. However, the mechanical properties of iron are significantly affected by the sample's purity: pure, single crystals of iron are actually softer than aluminium, and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell. An increase in the carbon content will cause a significant increase in the hardness and tensile strength of iron. Maximum hardness of 65 R is achieved with a 0.6% carbon content, although the alloy has low


title: Iron content: tensile strength. Because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the physical properties of iron at high pressures and temperatures have also been studied extensively. The form of iron that is stable under standard conditions can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form, as described in the next section. Iron represents an example of allotropy in a metal. At least four allotropic forms of iron are known as α, γ, δ, and ε;


title: Iron content: at very high pressures and temperatures, some controversial experimental evidence exists for a stable β phase. As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic (bcc) crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. Finally, at 770 °C (the Curie point, T) iron's magnetic ordering changes from paramagnetic to ferromagnetic. As it passes through the Curie temperature, iron


title: Iron content: does not change its structure, but "magnetic domains" appear, where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain have the same axis orientation; however, the electrons of neighboring domains have other orientations with the result of mutual cancellation and no magnetic field. In magnetized iron, the electronic spins of the domains are aligned and the magnetic effects are reinforced. Although each domain contains billions of atoms, they are very small, about 10 micrometres across. This happens because the two unpaired electrons on each iron atom


title: Iron content: are in the d and d orbitals, which do not point directly at the nearest neighbors in the body-centered cubic lattice and therefore do not participate in metallic bonding; thus, they can interact magnetically with each other so that their spins align. At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron; the higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. The β-phase, if it exists, would appear at pressures of at least 50 GPa and temperatures


title: Iron content: of at least 1500 K and have an orthorhombic or a double hcp structure. These high-pressure phases of iron are important as endmember models for the solid parts of planetary cores. The inner core of the Earth is generally presumed to be an iron-nickel alloy with ε (or β) structure. Somewhat confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure has not changed. The melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater


title: Iron content: pressures, studies put the γ-ε-liquid triple point at pressures that differ by tens of gigapascals and 1000 K in the melting point. Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells. The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and


title: Iron content: more into the inert core by the nucleus; however, they are higher than the values for the previous element manganese because that element has a half-filled 3d subshell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium. Naturally occurring iron consists of four stable isotopes: 5.845% of Fe, 91.754% of Fe, 2.119% of Fe and 0.282% of Fe. Of these stable isotopes, only Fe has a nuclear spin (−). The nuclide Fe theoretically can undergo double electron capture to Cr, but the process has never been observed and only a lower limit


title: Iron content: on the half-life of 3.1×10 years has been established. Fe is an extinct radionuclide of long half-life (2.6 million years). It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide Ni. Much of the past work on isotopic composition of iron has focused on the nucleosynthesis of Fe through studies of meteorites and ore formation. In the last decade, advances in mass spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work is driven by the Earth and


title: Iron content: planetary science communities, although applications to biological and industrial systems are emerging. In phases of the meteorites "Semarkona" and "Chervony Kut," a correlation between the concentration of Ni, the granddaughter of Fe, and the abundance of the stable iron isotopes provided evidence for the existence of Fe at the time of formation of the Solar System. Possibly the energy released by the decay of Fe, along with that released by Al, contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of Ni present in extraterrestrial material may bring further insight into the


title: Iron content: origin and early history of the Solar System. The most abundant iron isotope Fe is of particular interest to nuclear scientists because it represents the most common endpoint of nucleosynthesis. Since Ni (14 alpha particles) is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (see silicon burning process), it is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle, resulting in Zn, requires a great deal more energy. This Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays


title: Iron content: by two successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to radioactive Co, and then to stable Fe. As such, iron is the most abundant element in the core of red giants, and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as Earth. It is also very common in the universe, relative to other stable metals of approximately the same atomic weight. Iron is the sixth most abundant element in the Universe, and the most common refractory element. Although a further tiny energy gain could


title: Iron content: be extracted by synthesizing Ni, which has a marginally higher binding energy than Fe, conditions in stars are unsuitable for this process. Element production in supernovas and distribution on Earth greatly favor iron over nickel, and in any case, Fe still has a lower mass per nucleon than Ni due to its higher fraction of lighter protons. Hence, elements heavier than iron require a supernova for their formation, involving rapid neutron capture by starting Fe nuclei. In the far future of the universe, assuming that proton decay does not occur, cold fusion occurring via quantum tunnelling would cause the light


title: Iron content: nuclei in ordinary matter to fuse into Fe nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron. Metallic or native iron is rarely found on the surface of the Earth because it tends to oxidize, but its oxides are pervasive and represent the primary ores. While it makes up about 5% of the Earth's crust, both the Earth's inner and outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the


title: Iron content: most abundant element on Earth, but only the fourth most abundant element in the Earth's crust, after oxygen, silicon, and aluminium. Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite (FeO), magnetite (FeO), and siderite (FeCO). Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite. Ferropericlase (Mg,Fe)O, a solid solution of periclase (MgO) and wüstite (FeO), makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO; it also


title: Iron content: is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction γ-(Mg,Fe)[SiO] ↔ (Mg,Fe)[SiO] + (Mg,Fe)O transforms γ-olivine into a mixture of perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite. Silicate perovskite may form up to 93% of the lower mantle, and the magnesium iron form, (Mg,Fe)SiO, is considered to be the most abundant mineral in the Earth, making up 38% of its volume. Large deposits of iron are found in banded iron formations. These geological


title: Iron content: formations are a type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor shale and chert. The banded iron formations were laid down in the time between and . The mentioned iron compounds have been used as pigments (compare ochre) since historical time and contribute as well to the color of various geological formations, e.g. the Buntsandstein (British Bunter, colored sandstein). In the case of the Eisensandstein (a jurassic 'iron sandstone', e.g. from Donzdorf) in Germany and Bath stone in the UK, iron pigments contribute to the yellowish color of large amounts of historical


title: Iron content: buildings and sculptures. The proverbial red color of the surface of Mars is derived from an iron oxide-rich regolith. Significant amounts of iron occur in the iron sulfide mineral pyrite (FeS), but it is difficult to extract iron from it and it is therefore not used. In fact, iron is so common that production generally focuses only on ores with very high quantities of it. During weathering, iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as


title: Iron content: iron(III) oxide. About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Although rare, iron meteorites are the main form of natural metallic iron on the Earth's surface. According to the International Resource Panel's Metal Stocks in Society report, the global stock of iron in use in society is 2200 kg per capita. More-developed countries differ in this respect from less-developed countries (7000–14000 vs 2000 kg per capita). Iron shows the characteristic chemical properties of the transition metals, namely the ability to form variable oxidation states differing by steps of one and


title: Iron content: a very large coordination and organometallic chemistry: indeed, it was the discovery of an iron compound, ferrocene, that revolutionalized the latter field in the 1950s. Iron is sometimes considered as a prototype for the entire block of transition metals, due to its abundance and the immense role it has played in the technological progress of humanity. Its 26 electrons are arranged in the configuration [Ar]3d4s, of which the 3d and 4s electrons are relatively close in energy, and thus it can lose a variable number of electrons and there is no clear point where further ionization becomes unprofitable. Iron forms


title: Iron content: compounds mainly in the +2 and +3 oxidation states. Traditionally, iron(II) compounds are called ferrous, and iron(III) compounds ferric. Iron also occurs in higher oxidation states, e.g. the purple potassium ferrate (KFeO), which contains iron in its +6 oxidation state. Although iron(VIII) oxide (FeO) has been claimed, the report could not be reproduced and such a species (at least with iron in its +8 oxidation state) has been found to be improbable computationally. However, one form of anionic [FeO] with iron in its +7 oxidation state, along with an iron(V)-peroxo isomer, has been detected by infrared spectroscopy at 4 K


title: Iron content: after cocondensation of laser-ablated Fe atoms with a mixture of O/Ar. Iron(IV) is a common intermediate in many biochemical oxidation reactions. Numerous organoiron compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy. Many mixed valence compounds contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe(Fe[CN])). The latter is used as the traditional "blue" in blueprints. Iron is the first of the transition metals that cannot reach its group oxidation state of +8, although its heavier congeners ruthenium


title: Iron content: and osmium can, with ruthenium having more difficulty than osmium. Ruthenium exhibits an aqueous cationic chemistry in its low oxidation states similar to that of iron, but osmium does not, favoring high oxidation states in which it forms anionic complexes. In the second half of the 3d transition series, vertical similarities down the groups compete with the horizontal similarities of iron with its neighbors cobalt and nickel in the periodic table, which are also ferromagnetic at room temperature and share similar chemistry. As such, iron, cobalt, and nickel are sometimes grouped together as the iron triad. The iron compounds produced


title: Iron content: on the largest scale in industry are iron(II) sulfate (FeSO·7HO) and iron(III) chloride (FeCl). The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt ((NH)Fe(SO)·6HO). Iron(II) compounds tend to be oxidized to iron(III) compounds in the air. Unlike many other metals, iron does not form amalgams with mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron. Iron is by far the most reactive element in its group; it is pyrophoric when finely divided and dissolves easily in dilute acids, giving


title: Iron content: Fe. However, it does not react with concentrated nitric acid and other oxidizing acids due to the formation of an impervious oxide layer, which can nevertheless react with hydrochloric acid. Iron reacts with oxygen in the air to form various oxide and hydroxide compounds; the most common are iron(II,III) oxide (FeO), and iron(III) oxide (FeO). Iron(II) oxide also exists, though it is unstable at room temperature. Despite their names, they are actually all non-stoichiometric compounds whose compositions may vary. These oxides are the principal ores for the production of iron (see bloomery and blast furnace). They are also used in


title: Iron content: the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS), also known as fool's gold owing to its golden luster. It is not an iron(IV) compound, but is actually an iron(II) polysulfide containing Fe and ions in a distorted sodium chloride structure. The binary ferrous and ferric halides are well-known, with the exception of ferric iodide. The ferrous halides typically arise from treating iron metal with the corresponding hydrohalic acid to give the corresponding hydrated salts. Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric


title: Iron content: chloride being the most common. Ferric iodide is an exception, being thermodynamically unstable due to the oxidizing power of Fe and the high reducing power of I: Nevertheless, milligram amounts of ferric iodide, a black solid, may still be prepared through the reaction of iron pentacarbonyl with iodine and carbon monoxide in the presence of hexane and light at the temperature of −20 °C, making sure that the system is well sealed off from air and water. The standard reduction potentials in acidic aqueous solution for some common iron ions are given below: The red-purple tetrahedral ferrate(VI) anion is such


title: Iron content: a strong oxidizing agent that it oxidizes nitrogen and ammonia at room temperature, and even water itself in acidic or neutral solutions: The Fe ion has a large simple cationic chemistry, although the pale-violet hexaquo ion [Fe(HO)] is very readily hydrolyzed when pH increases above 0 as follows: As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous iron(III) oxide precipitates out of solution. Although Fe has an d configuration, its absorption spectrum is not like that of Mn with its weak, spin-forbidden d–d bands, because Fe has higher positive charge


title: Iron content: and is more polarizing, lowering the energy of its ligand-to-metal charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region. On the other hand, the pale green iron(II) hexaquo ion [Fe(HO)] does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises


title: Iron content: quickly in air to form iron(III) oxide that accounts for the brown deposits present in a sizeable number of streams. Many coordination compounds of iron are known. A typical six-coordinate anion is hexachloroferrate(III), [FeCl], found in the mixed salt tetrakis(methylammonium) hexachloroferrate(III) chloride. Complexes with multiple bidentate ligands have geometric isomers. For example, the "trans"-chlorohydridobis(bis-1,2-(diphenylphosphino)ethane)iron(II) complex is used as a starting material for compounds with the Fe(dppe) moiety. The ferrioxalate ion with three oxalate ligands (shown at right) displays helical chirality with its two non-superposable geometries labelled "Λ" (lambda) for the left-handed screw axis and "Δ" (delta) for the right-handed screw


title: Iron content: axis, in line with IUPAC conventions. Potassium ferrioxalate is used in chemical actinometry and along with its sodium salt undergoes photoreduction applied in old-style photographic processes. The dihydrate of iron(II) oxalate has a polymeric structure with co-planar oxalate ions bridging between iron centres with the water of crystallisation located forming the caps of each octahedron, as illustrated below. Prussian blue, Fe[Fe(CN)], is the most famous of the cyanide complexes of iron. Its formation can be used as a simple wet chemistry test to distinguish between aqueous solutions of Fe and Fe as they react (respectively) with potassium ferricyanide and potassium


title: Iron content: ferrocyanide to form Prussian blue. Iron(III) complexes are quite similar to those of chromium(III) with the exception of iron(III)'s preference for "O"-donor instead of "N"-donor ligands. The latter tend to be rather more unstable than iron(II) complexes and often dissociate in water. Many Fe–O complexes show intense colors and are used as tests for phenols or enols. For example, in the ferric chloride test, used to determine the presence of phenols, iron(III) chloride reacts with a phenol to form a deep violet complex: Among the halide and pseudohalide complexes, fluoro complexes of iron(III) are the most stable, with the colorless


title: Iron content: [FeF(HO)] being the most stable in aqueous solution. Chloro complexes are less stable and favor tetrahedral coordination as in [FeCl]; [FeBr] and [FeI] are reduced easily to iron(II). Thiocyanate is a common test for the presence of iron(III) as it forms the blood-red [Fe(SCN)(HO)]. Like manganese(II), most iron(III) complexes are high-spin, the exceptions being those with ligands that are high in the spectrochemical series such as cyanide. An example of a low-spin iron(III) complex is [Fe(CN)]. The cyanide ligands may easily be detached in [Fe(CN)], and hence this complex is poisonous, unlike the iron(II) complex [Fe(CN)] found in Prussian blue,


title: Iron content: which does not release hydrogen cyanide except when dilute acids are added. Iron shows a great variety of electronic spin states, including every possible spin quantum number value for a d-block element from 0 (diamagnetic) to (5 unpaired electrons). This value is always half the number of unpaired electrons. Complexes with zero to two unpaired electrons are considered low-spin and those with four or five are considered high-spin. Iron(II) complexes are less stable than iron(III) complexes but the preference for "O"-donor ligands is less marked, so that for example [Fe(NH)] is known while [Fe(NH)] is not. They have a tendency


title: Iron content: to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used. Cyanide complexes are technically organometallic but more important are carbonyl complexes and sandwich and half-sandwich compounds. The premier iron(0) compound is iron pentacarbonyl, Fe(CO), which is used to produce carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives the trinuclear cluster, triiron dodecacarbonyl. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state. Ferrocene was an


title: Iron content: extremely important compound in the early history of the branch of organometallic chemistry, and to this day iron is still one of the most important metals in this field. It was first synthesised in 1951 during an attempt to prepare the fulvalene (CH) by oxidative dimerization of cyclopentadiene; the resultant product was found to have molecular formula CHFe and reported to exhibit "remarkable stability". The discovery sparked substantial interest in the field of organometallic chemistry, in part because the structure proposed by Pauson and Kealy (shown at right) was inconsistent with then-existing bonding models and did not explain its unexpected


title: Iron content: stability. Consequently, the initial challenge was to definitively determine the structure of ferrocene in the hope that its bonding and properties would then be understood. The shockingly novel sandwich structure, [Fe(η-CH)], was deduced and reported independently by three groups in 1952: Robert Burns Woodward and Geoffrey Wilkinson investigated the reactivity in order to determine the structure and demonstrated that ferrocene undergoes similar reactions to a typical aromatic molecule (such as benzene), Ernst Otto Fischer deduced the sandwich structure and also began synthesising other metallocenes including cobaltocene; Eiland and Pepinsky provided X-ray crystallographic confirmation of the sandwich structure. Applying valence bond


title: Iron content: theory to ferrocene by considering an Fe centre and two cyclopentadienide anions (CH), which are known to be aromatic according to Hückel's rule and hence highly stable, allowed correct prediction of the geometry of the molecule. Once molecular orbital theory was successfully applied and the Dewar-Chatt-Duncanson model proposed, the reasons for ferrocene's remarkable stability became clear. Ferrocene was not the first organometallic compound known – Zeise's salt, K[PtCl(CH)]·HO was reported in 1831 and Mond's discovery of Ni(CO) occurred in 1888, but it was ferrocene's discovery that began organometallic chemistry as a separate area of chemistry. It was so important that


title: Iron content: Wilkinson and Fischer shared the 1973 Nobel Prize for Chemistry "for their pioneering work, performed independently, on the chemistry of the organometallic, so called sandwich compounds". Ferrocene itself can be used as the backbone of a ligand, e.g. 1,1'-bis(diphenylphosphino)ferrocene (dppf). Ferrocene can itself be oxidized to the ferrocenium cation (Fc); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry. Metallocenes like ferrocene can be prepared by reaction of freshly-cracked cyclopentadiene with iron(II) chloride and base. It is an aromatic substance and undergoes substitution reactions rather than addition reactions on the cyclopentadienyl ligands. For example, Friedel-Crafts acylation of ferrocene


title: Iron content: with acetic anhydride yields acetylferrocene just as acylation of benzene yields acetophenone under similar conditions. Iron-centered organometallic species are used as catalysts. The Knölker complex, for example, is a transfer hydrogenation catalyst for ketones. As iron has been in use for such a long time, it has many different names in different languages. The source of its chemical symbol "Fe" is the Latin word "ferrum", and its descendants are the names of the element in the Romance languages (for example, French "fer", Spanish "hierro", and Italian and Portuguese "ferro"). The word "ferrum" itself possibly comes from the Semitic languages, via


title: Iron content: Etruscan, from a root that also gave rise to Old English "bræs" "brass". The English word "iron" derives ultimately from Proto-Germanic "*isarnan", which is also the source of the German name "Eisen". It was most likely borrowed from Celtic "*isarnon", which ultimately comes from Proto-Indo-European "*is-(e)ro-" "powerful, holy" and finally "*eis" "strong", referencing iron's strength as a metal. Kluge relates "*isarnon" to Illyric and Latin "ira", 'wrath'). The Balto-Slavic names for iron (for example, Russian "железо" ["zhelezo"], Polish "żelazo", Lithuanian "geležis") are the only ones to come directly from the Proto-Indo-European "*gelg-" "iron". In many of these languages, the word


title: Iron content: for "iron" may also be used to denote other objects made of iron or steel, or figuratively because of the hardness and strength of the metal. The Chinese "tiě" (traditional 鐵; simplified 铁) derives from Proto-Sino-Tibetan "*hliek", and was borrowed into Japanese as 鉄 "tetsu", which also has the native reading "kurogane" "black metal" (similar to how iron is referenced in the English word blacksmith). Iron is one of the elements undoubtedly known to the ancient world. It has been worked, or wrought, for millennia. However, iron objects of great age are much rarer than objects made of gold or


title: Iron content: silver due to the ease with which iron corrodes. Beads made from meteoric iron in 3500 BC or earlier were found in Gerzah, Egypt by G. A. Wainwright. The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities. Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools. For example, a dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite


title: Iron content: discovered in the area, deposited by an ancient meteor shower. Items that were likely made of iron by Egyptians date from 3000 to 2500 BC. Meteoritic iron is comparably soft and ductile and easily forged by cold working but may get brittle when heated because of the nickel content. The first iron production started in the Middle Bronze Age but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700 BC. The Hittites established an empire in north-central Anatolia around 1600


title: Iron content: BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society. The Hittites began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC. The subsequent period is called the Iron Age. Artifacts of smelted iron are found in India dating from 1800 to 1200 BC, and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus). Alleged references (compare history of metallurgy in South Asia) to iron


title: Iron content: in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term "ayas" (metal) probably refers to copper and bronze, while iron or "śyāma ayas", literally "black metal", first is mentioned in the post-rigvedic Atharvaveda. Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC. Iron working was introduced to Greece in the late 11th century BC, from which it spread quickly throughout Europe. The spread of ironworking in Central and Western Europe is associated


title: Iron content: with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era. The annual iron output of the Roman Empire is estimated at t, while the similarly populous and contemporary Han China produced around t. In China, iron only appears circa 700–500 BC. Iron smelting may have been introduced into China through Central Asia. The earliest evidence of the use of a blast furnace in China dates to the 1st century AD, and cupola furnaces were used as early as the Warring States period (403–221 BC). Usage of the blast and cupola furnace remained widespread during


title: Iron content: the Song and Tang Dynasties. During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others, including Joseph Hall. Cast iron was first produced in China during 5th century BC, but was hardly in Europe until the medieval period. The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture.


title: Iron content: During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel. Medieval blast furnaces were about tall and made of fireproof brick; forced air was usually provided by hand-operated bellows. Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times. In 1709, Abraham Darby I established a


title: Iron content: coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century. Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first


title: Iron content: iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines. Railways have been central to the formation of modernity and ideas of progress and various languages (e.g. French, Spanish, Italian and German) refer to railways as "iron road". Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making


title: Iron content: good steel by 1000 BC. Then improved versions, Wootz steel by India and Damascus steel were developed around 300 BC and AD 500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron,


title: Iron content: to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities. In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one. Iron plays a certain role in mythology and has found various usage as a metaphor and in folklore. The Greek poet Hesiod's "Works and Days" (lines 109–201) lists different ages of


title: Iron content: man named after metals like gold, silver, bronze and iron to account for successive ages of humanity. The Iron Age was closely related with Rome, and in Ovid's "Metamorphoses" An example of the importance of iron's symbolic role may be found in the German Campaign of 1813. Frederick William III commissioned then the first Iron Cross as military decoration. Berlin iron jewellery reached its peak production between 1813 and 1815, when the Prussian royal family urged citizens to donate gold and silver jewellery for military funding. The inscription "Gold gab ich für Eisen" (I gave gold for iron) was used


title: Iron content: as well in later war efforts. The production of iron or steel is a process consisting of two main stages. In the first stage pig iron is produced in a blast furnace. Alternatively, it may be directly reduced. In the second stage, pig iron is converted to wrought iron, steel, or cast iron. For a few limited purposes when it is needed, pure iron is produced in the laboratory in small quantities by reducing the pure oxide or hydroxide with hydrogen, or forming iron pentacarbonyl and heating it to 250 °C so that it decomposes to form pure iron powder.


title: Iron content: Another method is electrolysis of ferrous chloride onto an iron cathode. Industrial iron production starts with iron ores, principally hematite, which has a nominal formula FeO, and magnetite, with the formula FeO. These ores are reduced to the metal in a carbothermic reaction, i.e. by treatment with carbon. The conversion is typically conducted in a blast furnace at temperatures of about 2000 °C. Carbon is provided in the form of coke. The process also contains a flux such as limestone, which is used to remove silicaceous minerals in the ore, which would otherwise clog the furnace. The coke and limestone


title: Iron content: are fed into the top of the furnace, while a massive blast of air heated to 900 °C, about 4 tons per ton of iron, is forced into the furnace at the bottom. In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide: The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process: Some iron in the high-temperature lower region of the furnace reacts directly with the coke: The flux present to melt impurities in the ore is principally limestone (calcium carbonate)


title: Iron content: and dolomite (calcium-magnesium carbonate). Other specialized fluxes are used depending on the details of the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (also known as quicklime): Then calcium oxide combines with silicon dioxide to form a liquid slag. The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on top of the denser molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron, once cooled, is called pig iron, while the


title: Iron content: slag can be used as a material in road construction or to improve mineral-poor soils for agriculture. Owing to environmental concerns, alternative methods of processing iron have been developed. "Direct iron reduction" reduces iron ore to a ferrous lump called "sponge" iron or "direct" iron that is suitable for steelmaking. Two main reactions comprise the direct reduction process: Natural gas is partially oxidized (with heat and a catalyst): These gases are then treated with iron ore in a furnace, producing solid sponge iron: Silica is removed by adding a limestone flux as described above. Iron is a byproduct of burning


title: Iron content: a mixture of aluminum powder and rust powder. Pig iron is not pure iron, but has 4–5% carbon dissolved in it with small amounts of other impurities like sulfur, magnesium, phosphorus and manganese. As the carbon is the major impurity, the iron (pig iron) becomes brittle and hard. Removing the other impurities results in cast iron, which is used to cast articles in foundries such as stoves, pipes, radiators, lamp-posts and rails. Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including


title: Iron content: finery forges, puddling furnaces, Bessemer converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels. Annealing involves the heating of a piece of steel to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable. Iron is the most widely used of all the metals, accounting for over 90% of worldwide metal production. Its low cost and high strength make it


title: Iron content: indispensable in engineering applications such as the construction of machinery and machine tools, automobiles, the hulls of large ships, and structural components for buildings. Since pure iron is quite soft, it is most commonly combined with alloying elements to make steel. α-Iron is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C). Austenite (γ-iron) is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used


title: Iron content: for making cutlery, and hospital and food-service equipment. Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel. The reduction of contaminants in pig iron that negatively affect material properties, such as sulfur and phosphorus, yields cast iron containing 2–4% carbon, 1–6% silicon, and small amounts of manganese. Pig iron has a melting point in the range of 1420–1470 K,


title: Iron content: which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly and depend on the form the carbon takes in the alloy. "White" cast irons contain their carbon in the form of cementite, or iron carbide (FeC). This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken iron-carbide, a very pale, silvery, shiny material, hence


title: Iron content: the appellation. Cooling a mixture of iron with 0.8% carbon slowly below 723 °C to room temperature results in separate, alternating layers of cementite and α-iron, which is soft and malleable and is called pearlite for its appearance. Rapid cooling, on the other hand, does not allow time for this separation and creates hard and brittle martensite. The steel can then be tempered by reheating to a temperature in between, changing the proportions of pearlite and martensite. The end product below 0.8% carbon content is a pearlite-αFe mixture, and that above 0.8% carbon content is a pearlite-cementite mixture. In gray


title: Iron content: iron the carbon exists as separate, fine flakes of graphite, and also renders the material brittle due to the sharp edged flakes of graphite that produce stress concentration sites within the material. A newer variant of gray iron, referred to as ductile iron, is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, reducing the stress concentrations and vastly increasing the toughness and strength of the material. Wrought iron contains less than 0.25% carbon but large amounts of slag that give it a fibrous characteristic. It is a tough, malleable product, but


title: Iron content: not as fusible as pig iron. If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped within the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing. Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less, with small amounts of manganese, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as


title: Iron content: chromium, vanadium, molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is stainless steel. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost. Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation as a function


title: Iron content: of energy is shown in the graph. The main disadvantage of iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way, a cost amounting to over 1% of the world's economy. Painting, galvanization, passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection. The mechanism of the rusting of iron is as follows: The electrolyte is usually iron(II) sulfate in urban areas (formed when atmospheric sulfur dioxide attacks iron), and salt particles in the atmosphere in


title: Iron content: seaside areas. Although the dominant use of iron is in metallurgy, iron compounds are also pervasive in industry. Iron catalysts are traditionally used in the Haber-Bosch process for the production of ammonia and the Fischer-Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricants. Powdered iron in an acidic solvent was used in the Bechamp reduction the reduction of nitrobenzene to aniline. Iron(III) chloride finds use in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etchant for copper in the


title: Iron content: manufacture of printed circuit boards. It can also be dissolved in alcohol to form tincture of iron, which is used as a medicine to stop bleeding in canaries. Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesis. Iron is


title: Iron content: required for life. The iron–sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Iron-containing proteins participate in transport, storage and used of oxygen. Iron proteins are involved in electron transfer. Examples of iron-containing proteins in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase. The average adult human contains about 0.005% body weight of iron, or about four grams, of which three quarters is in hemoglobin – a level that remains constant despite only about one milligram of iron being absorbed each day, because the human body recycles its hemoglobin for the iron content.


title: Iron content: Iron acquisition poses a problem for aerobic organisms because ferric iron is poorly soluble near neutral pH. Thus, these organisms have developed means to absorb iron as complexes, sometimes taking up ferrous iron before oxidising it back to ferric iron. In particular, bacteria have evolved very high-affinity sequestering agents called siderophores. After uptake in human cells, iron storage is precisely regulated. A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the blood to cells. Transferrin contains Fe in the middle of a distorted octahedron, bonded to one


title: Iron content: nitrogen, three oxygens and a chelating carbonate anion that traps the Fe ion: it has such a high stability constant that it is very effective at taking up Fe ions even from the most stable complexes. At the bone marrow, transferrin is reduced from Fe and Fe and stored as ferritin to be incorporated into hemoglobin. The most commonly known and studied bioinorganic iron compounds (biological iron molecules) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450. These compounds participate in transporting gases, building enzymes, and transferring electrons. Metalloproteins are a group of proteins with metal ion cofactors.


title: Iron content: Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP. Hemoglobin is an oxygen carrier that occurs in red blood cells and contributes their color, transporting oxygen in the arteries from the lungs to the muscles where it is transferred to myoglobin, which stores it until it is needed for the metabolic oxidation of glucose, generating energy. Here the hemoglobin binds to carbon dioxide, produced when glucose is oxidized, which is transported through the veins by hemoglobin (predominantly as bicarbonate anions) back to the lungs where it is