Espionage or spying is the act of obtaining secret or confidential information without the permission of the holder of the information. Spies help agencies uncover secret information. Any individual or spy ring, in the service of a government, company or independent operation, can commit espionage; the practice is clandestine, as it is by definition unwelcome and in many cases illegal and punishable by law. Espionage is a method of intelligence gathering which includes information gathering from public sources. Espionage is part of an institutional effort by a government or commercial concern. However, the term tends to be associated with state spying on potential or actual enemies for military purposes. Spying involving corporations is known as industrial espionage. One of the most effective ways to gather data and information about the enemy is by infiltrating the enemy's ranks; this is the job of the spy. Spies can return information concerning the strength of enemy forces, they can find dissidents within the enemy's forces and influence them to defect.
In times of crisis, spies sabotage the enemy in various ways. Counterintelligence is the practice of thwarting enemy intelligence-gathering. All nations have strict laws concerning espionage and the penalty for being caught is severe. However, the benefits gained through espionage are so great that most governments and many large corporations make use of it. Information collection techniques used in the conduct of clandestine human intelligence include operational techniques, asset recruiting, tradecraft. Today, espionage agencies target terrorists as well as state actors. Since 2008, the United States has charged at least 57 defendants for attempting to spy for China. Intelligence services value certain intelligence collection techniques over others; the former Soviet Union, for example, preferred human sources over research in open sources, while the United States has tended to emphasize technological methods such as SIGINT and IMINT. In the Soviet Union, both political and military intelligence officers were judged by the number of agents they recruited.
Espionage agents are trained experts in a targeted field so they can differentiate mundane information from targets of value to their own organizational development. Correct identification of the target at its execution is the sole purpose of the espionage operation. Broad areas of espionage targeting expertise include: Natural resources: strategic production identification and assessment. Agents are found among bureaucrats who administer these resources in their own countries Popular sentiment towards domestic and foreign policies. Agents recruited from field journalistic crews, exchange postgraduate students and sociology researchers Strategic economic strengths. Agents recruited from science and technology academia, commercial enterprises, more from among military technologists Military capability intelligence. Agents are trained by military espionage education facilities, posted to an area of operation with covert identities to minimize prosecution Counterintelligence operations targeting opponents' intelligence services themselves, such as breaching confidentiality of communications, recruiting defectors or moles Although the news media may speak of "spy satellites" and the like, espionage is not a synonym for all intelligence-gathering disciplines.
It is a specific form of human source intelligence. Codebreaking, aircraft or satellite photography, research in open publications are all intelligence gathering disciplines, but none of them is considered espionage. Many HUMINT activities, such as prisoner interrogation, reports from military reconnaissance patrols and from diplomats, etc. are not considered espionage. Espionage is the disclosure of sensitive information to people who are not cleared for that information or access to that sensitive information. Unlike other forms of intelligence collection disciplines, espionage involves accessing the place where the desired information is stored or accessing the people who know the information and will divulge it through some kind of subterfuge. There are exceptions to physical meetings, such as the Oslo Report, or the insistence of Robert Hanssen in never meeting the people who bought his information; the US defines espionage towards itself as "The act of obtaining, transmitting, communicating, or receiving information about the national defense with an intent, or reason to believe, that the information may be used to the injury of the United States or to the advantage of any foreign nation".
Black's Law Dictionary defines espionage as: "... gathering, transmitting, or losing... information related to the national defense". Espionage is a violation of United States law, 18 U. S. C. §§ 792–798 and Article 106a of the Uniform Code of Military Justice". The United States, like most nations, conducts espionage against other nations, under the control of the National Clandestine Service. Britain's espionage activities are controlled by the Secret Intelligence Service. A spy is a person employed to seek out top secret information from a source. Within the United States Intelligence Community, "asset" is a more common usage. A case officer or Special Agent, who may have diplomatic status and directs the human collector. Cutouts are couriers who do not know the case officer but transfer messages. A
Ottawa is the capital city of Canada. It stands on the south bank of the Ottawa River in the eastern portion of southern Ontario. Ottawa borders Gatineau, Quebec; as of 2016, Ottawa had a city population of 964,743 and a metropolitan population of 1,323,783 making it the fourth-largest city and the fifth-largest CMA in Canada. Founded in 1826 as Bytown, incorporated as Ottawa in 1855, the city has evolved into the political centre of Canada, its original boundaries were expanded through numerous annexations and were replaced by a new city incorporation and amalgamation in 2001 which increased its land area. The city name "Ottawa" was chosen in reference to the Ottawa River, the name of, derived from the Algonquin Odawa, meaning "to trade". Ottawa has the most educated population among Canadian cities and is home to a number of post-secondary and cultural institutions, including the National Arts Centre, the National Gallery, numerous national museums. Ottawa has the highest standard of living in low unemployment.
With the draining of the Champlain Sea around ten thousand years ago, the Ottawa Valley became habitable. Local populations used the area for wild edible harvesting, fishing, trade and camps for over 6500 years; the Ottawa river valley has archaeological sites with arrow heads and stone tools. Three major rivers meet within Ottawa, making it an important trade and travel area for thousands of years; the Algonquins called the Ottawa River Kichi Sibi or Kichissippi meaning "Great River" or "Grand River". Étienne Brûlé regarded as the first European to travel up the Ottawa River, passed by Ottawa in 1610 on his way to the Great Lakes. Three years Samuel de Champlain wrote about the waterfalls in the area and about his encounters with the Algonquins, using the Ottawa River for centuries. Many missionaries would follow the early traders; the first maps of the area used the word Ottawa, derived from the Algonquin word adawe, to name the river. Philemon Wright, a New Englander, created the first settlement in the area on 7 March 1800 on the north side of the river, across from the present day city of Ottawa in Hull.
He, with five other families and twenty-five labourers, set about to create an agricultural community called Wrightsville. Wright pioneered the Ottawa Valley timber trade by transporting timber by river from the Ottawa Valley to Quebec City. Bytown, Ottawa's original name, was founded as a community in 1826 when hundreds of land speculators were attracted to the south side of the river when news spread that British authorities were constructing the northerly end of the Rideau Canal military project at that location; the following year, the town was named after British military engineer Colonel John By, responsible for the entire Rideau Waterway construction project. The canal's military purpose was to provide a secure route between Montreal and Kingston on Lake Ontario, bypassing a vulnerable stretch of the St. Lawrence River bordering the state of New York that had left re-supply ships bound for southwestern Ontario exposed to enemy fire during the War of 1812. Colonel By set up military barracks on the site of today's Parliament Hill.
He laid out the streets of the town and created two distinct neighbourhoods named "Upper Town" west of the canal and "Lower Town" east of the canal. Similar to its Upper Canada and Lower Canada namesakes "Upper Town" was predominantly English speaking and Protestant whereas "Lower Town" was predominantly French and Catholic. Bytown's population grew to 1,000 as the Rideau Canal was being completed in 1832. Bytown encountered some impassioned and violent times in her early pioneer period that included Irish labour unrest that attributed to the Shiners' War from 1835 to 1845 and political dissension evident from the 1849 Stony Monday Riot. In 1855 Bytown was incorporated as a city. William Pittman Lett was installed as the first city clerk guiding it through 36 years of development. On New Year's Eve 1857, Queen Victoria, as a symbolic and political gesture, was presented with the responsibility of selecting a location for the permanent capital of the Province of Canada. In reality, Prime Minister John A. Macdonald had assigned this selection process to the Executive Branch of the Government, as previous attempts to arrive at a consensus had ended in deadlock.
The "Queen's choice" turned out to be the small frontier town of Ottawa for two main reasons: Firstly, Ottawa's isolated location in a back country surrounded by dense forest far from the Canada–US border and situated on a cliff face would make it more defensible from attack. Secondly, Ottawa was midway between Toronto and Kingston and Montreal and Quebec City. Additionally, despite Ottawa's regional isolation it had seasonal water transportation access to Montreal over the Ottawa River and to Kingston via the Rideau Waterway. By 1854 it had a modern all season Bytown and Prescott Railway that carried passengers and supplies the 82-kilometres to Prescott on the Saint Lawrence River and beyond. Ottawa's small size, it was thought, would make it less prone to rampaging politically motivated mobs, as had happened in the previous Canadian capitals; the government owned the land that would become Parliament Hill which they thought would be an ideal location for the Parliament Buildings. Ottawa was th
The United Nations is an intergovernmental organization, tasked to maintain international peace and security, develop friendly relations among nations, achieve international co-operation and be a centre for harmonizing the actions of nations. The headquarters of the UN is in Manhattan, New York City, is subject to extraterritoriality. Further main offices are situated in Geneva, Nairobi and The Hague; the organization is financed by voluntary contributions from its member states. Its objectives include maintaining international peace and security, protecting human rights, delivering humanitarian aid, promoting sustainable development and upholding international law; the UN is the largest, most familiar, most internationally represented and most powerful intergovernmental organization in the world. In 24 October 1945, at the end of World War II, the organization was established with the aim of preventing future wars. At its founding, the UN had 51 member states; the UN is the successor of the ineffective League of Nations.
On 25 April 1945, 50 governments met in San Francisco for a conference and started drafting the UN Charter, adopted on 25 June 1945 in the San Francisco Opera House, signed on 26 June 1945 in the Herbst Theatre auditorium in the Veterans War Memorial Building. This charter took effect on 24 October 1945; the UN's mission to preserve world peace was complicated in its early decades during the Cold War between the United States and Soviet Union and their respective allies. Its missions have consisted of unarmed military observers and armed troops with monitoring and confidence-building roles; the organization's membership grew following widespread decolonization which started in the 1960s. Since 80 former colonies had gained independence, including 11 trust territories, which were monitored by the Trusteeship Council. By the 1970s its budget for economic and social development programmes far outstripped its spending on peacekeeping. After the end of the Cold War, the UN shifted and expanded its field operations, undertaking a wide variety of complex tasks.
The UN has six principal organs: the General Assembly. The UN System agencies include the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, UNICEF; the UN's most prominent officer is the Secretary-General, an office held by Portuguese politician and diplomat António Guterres since 1 January 2017. Non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work; the organization, its officers and its agencies have won many Nobel Peace Prizes. Other evaluations of the UN's effectiveness have been mixed; some commentators believe the organization to be an important force for peace and human development, while others have called the organization ineffective, biased, or corrupt. In the century prior to the UN's creation, several international treaty organizations such as the International Committee of the Red Cross was formed to ensure protection and assistance for victims of armed conflict and strife.
In 1914, a political assassination in Sarajevo set off a chain of events that led to the outbreak of World War I. As more and more young men were sent down into the trenches, influential voices in the United States and Britain began calling for the establishment of a permanent international body to maintain peace in the postwar world. President Woodrow Wilson became a vocal advocate of this concept, in 1918 he included a sketch of the international body in his 14-point proposal to end the war. In November 1918, the Central Powers agreed to an armistice to halt the killing in World War I. Two months the Allies met with Germany and Austria-Hungary at Versailles to hammer out formal peace terms. President Wilson wanted peace, but the United Kingdom and France disagreed, forcing harsh war reparations on their former enemies; the League of Nations was approved, in the summer of 1919 Wilson presented the Treaty of Versailles and the Covenant of the League of Nations to the US Senate for ratification.
On January 10, 1920, the League of Nations formally comes into being when the Covenant of the League of Nations, ratified by 42 nations in 1919, takes effect. However, at some point the League became ineffective when it failed to act against the Japanese invasion of Manchuria as in February 1933, 40 nations voted for Japan to withdraw from Manchuria but Japan voted against it and walked out of the League instead of withdrawing from Manchuria, it failed against the Second Italo-Ethiopian War despite trying to talk to Benito Mussolini as he used the time to send an army to Africa, so the League had a plan for Mussolini to just take a part of Ethiopia, but he ignored the League and invaded Ethiopia, the League tried putting sanctions on Italy, but Italy had conquered Ethiopia and the League had failed. After Italy conquered Ethiopia and other nations left the league, but all of them realised that they began to re-arm as fast as possible. During 1938, Britain and France tried negotiating directly with Hitler but this failed in 1939 when Hitler invaded Czechoslovakia.
When war broke out in 1939, the League closed down and its headquarters in Geneva remained empty throughout the war. The earliest concrete plan for a new world organization began under the aegis of the U. S. State Department in 1939; the text of the "Declaration by United Nations" was drafted at the White House on December 29, 1941, by President Franklin D. Roosevelt, Prime Minister Winston Churchill, Roosevelt aide Harry Hopkins
New York City
The City of New York called either New York City or New York, is the most populous city in the United States. With an estimated 2017 population of 8,622,698 distributed over a land area of about 302.6 square miles, New York is the most densely populated major city in the United States. Located at the southern tip of the state of New York, the city is the center of the New York metropolitan area, the largest metropolitan area in the world by urban landmass and one of the world's most populous megacities, with an estimated 20,320,876 people in its 2017 Metropolitan Statistical Area and 23,876,155 residents in its Combined Statistical Area. A global power city, New York City has been described as the cultural and media capital of the world, exerts a significant impact upon commerce, research, education, tourism, art and sports; the city's fast pace has inspired the term New York minute. Home to the headquarters of the United Nations, New York is an important center for international diplomacy.
Situated on one of the world's largest natural harbors, New York City consists of five boroughs, each of, a separate county of the State of New York. The five boroughs – Brooklyn, Manhattan, The Bronx, Staten Island – were consolidated into a single city in 1898; the city and its metropolitan area constitute the premier gateway for legal immigration to the United States. As many as 800 languages are spoken in New York, making it the most linguistically diverse city in the world. New York City is home to more than 3.2 million residents born outside the United States, the largest foreign-born population of any city in the world. In 2017, the New York metropolitan area produced a gross metropolitan product of US$1.73 trillion. If greater New York City were a sovereign state, it would have the 12th highest GDP in the world. New York is home to the highest number of billionaires of any city in the world. New York City traces its origins to a trading post founded by colonists from the Dutch Republic in 1624 on Lower Manhattan.
The city and its surroundings came under English control in 1664 and were renamed New York after King Charles II of England granted the lands to his brother, the Duke of York. New York served as the capital of the United States from 1785 until 1790, it has been the country's largest city since 1790. The Statue of Liberty greeted millions of immigrants as they came to the U. S. by ship in the late 19th and early 20th centuries and is an international symbol of the U. S. and its ideals of liberty and peace. In the 21st century, New York has emerged as a global node of creativity and entrepreneurship, social tolerance, environmental sustainability, as a symbol of freedom and cultural diversity. Many districts and landmarks in New York City are well known, with the city having three of the world's ten most visited tourist attractions in 2013 and receiving a record 62.8 million tourists in 2017. Several sources have ranked New York the most photographed city in the world. Times Square, iconic as the world's "heart" and its "Crossroads", is the brightly illuminated hub of the Broadway Theater District, one of the world's busiest pedestrian intersections, a major center of the world's entertainment industry.
The names of many of the city's landmarks and parks are known around the world. Manhattan's real estate market is among the most expensive in the world. New York is home to the largest ethnic Chinese population outside of Asia, with multiple signature Chinatowns developing across the city. Providing continuous 24/7 service, the New York City Subway is the largest single-operator rapid transit system worldwide, with 472 rail stations. Over 120 colleges and universities are located in New York City, including Columbia University, New York University, Rockefeller University, which have been ranked among the top universities in the world. Anchored by Wall Street in the Financial District of Lower Manhattan, New York has been called both the most economically powerful city and the leading financial center of the world, the city is home to the world's two largest stock exchanges by total market capitalization, the New York Stock Exchange and NASDAQ. In 1664, the city was named in honor of the Duke of York.
James's older brother, King Charles II, had appointed the Duke proprietor of the former territory of New Netherland, including the city of New Amsterdam, which England had seized from the Dutch. During the Wisconsinan glaciation, 75,000 to 11,000 years ago, the New York City region was situated at the edge of a large ice sheet over 1,000 feet in depth; the erosive forward movement of the ice contributed to the separation of what is now Long Island and Staten Island. That action left bedrock at a shallow depth, providing a solid foundation for most of Manhattan's skyscrapers. In the precolonial era, the area of present-day New York City was inhabited by Algonquian Native Americans, including the Lenape, whose homeland, known as Lenapehoking, included Staten Island; the first documented visit into New York Harbor by a European was in 1524 by Giovanni da Verrazzano, a Florentine explorer in the service of the French crown. He named it Nouvelle Angoulême. A Spanish expedition led by captain Estêvão Gomes, a Portuguese sailing for Emperor Charles V, arrived in New York Harbor in January 1525 and charted the mouth of the Hudson River, which he named Río de San Antonio.
The Padrón Rea
Shortwave radio is radio transmission using shortwave radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band, extends from 1.7–30 MHz. Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the ionosphere. Therefore, short waves directed at an angle into the sky can be reflected back to Earth at great distances, beyond the horizon; this is called skywave or "skip" propagation. Thus shortwave radio can be used for long distance communication, in contrast to radio waves of higher frequency which travel in straight lines and are limited by the visual horizon, about 64 km. Shortwave radio is used for broadcasting of voice and music to shortwave listeners over large areas, it is used for military over-the-horizon radar, diplomatic communication, two-way international communication by amateur radio enthusiasts for hobby and emergency purposes, as well as for long distance aviation and marine communications.
The widest popular definition of the shortwave frequency interval is the ITU Region 1 definition, is the span 1.6–30 MHz, just above the medium wave band, which ends at 1.6 MHz. There are other definitions of the shortwave frequency interval: 1.71 to 30 MHz in ITU Region 2 1.8 to 30 MHz 2.3 to 30 MHz 2.3 to 26.1 MHz In Germany and Austria the ITU Region 1 shortwave radio frequency interval can be subdivided in: de:Grenzwelle: 1.605–3.8 MHz In Germany these shortwave radio frequency intervals have been seen used: the above other definitions The name "shortwave" originated during the early days of radio in the early 20th century, when the radio spectrum was considered divided into long wave, medium wave and short wave bands based on the wavelength of the radio waves. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used for radio communications; the broadcast medium wave band now extends above the 200 m/1,500 kHz limit, the amateur radio 1.8 MHz – 2.0 MHz band is the lowest-frequency band considered to be'shortwave'.
Early long distance radio telegraphy used long waves, below 300 kilohertz. The drawbacks to this system included a limited spectrum available for long distance communication, the expensive transmitters and gigantic antennas that were required, it was difficult to beam the radio wave directionally with long wave, resulting in a major loss of power over long distances. Prior to the 1920s, the shortwave frequencies above 1.5 MHz were regarded as useless for long distance communication and were designated in many countries for amateur use. Guglielmo Marconi, pioneer of radio, commissioned his assistant Charles Samuel Franklin to carry out a large scale study into the transmission characteristics of short wavelength waves and to determine their suitability for long distance transmissions. Franklin rigged up a large antenna at Poldhu Wireless Station, running on 25 kW of power. In June and July 1923, wireless transmissions were completed during nights on 97 meters from Poldhu to Marconi's yacht Elettra in the Cape Verde Islands.
In September 1924, Marconi transmitted daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut. Franklin went on to refine the directional transmission, by inventing the curtain array aerial system. In July 1924, Marconi entered into contracts with the British General Post Office to install high speed shortwave telegraphy circuits from London to Australia, South Africa and Canada as the main element of the Imperial Wireless Chain; the UK-to-Canada shortwave "Beam Wireless Service" went into commercial operation on 25 October 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927. Shortwave communications began to grow in the 1920s, similar to the internet in the late 20th century. By 1928, more than half of long distance communications had moved from transoceanic cables and longwave wireless services to shortwave and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave stations had cost and efficiency advantages over massive longwave wireless installations, however some commercial longwave communications stations remained in use until the 1960s.
Long distance radio circuits reduced the load on the existing transoceanic telegraph cables and hence the need for new cables, although the cables maintained their advantages of high security and a much more reliable and better quality signal than shortwave. The cable companies began to lose large sums of money in 1927, a serious financial crisis threatened the viability of cable companies that were vital to strategic British interests; the British government convened the Imperial Wireless and Cable Conference in 1928 "to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services". It recommended and received Government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly formed company in 1929, Imperial and International Communications Ltd; the name of the company was changed to Cable and Wireless Ltd. in 1934. Long-distance cables had a
Obverse and reverse
Obverse and its opposite, refer to the two flat faces of coins and some other two-sided objects, including paper money, seals, drawings, old master prints and other works of art, printed fabrics. In this usage, obverse reverse means the back face; the obverse of a coin is called heads, because it depicts the head of a prominent person, the reverse tails. In fields of scholarship outside numismatics, the term front is more used than obverse, while usage of reverse is widespread; the equivalent terms used in codicology, manuscript studies, print studies and publishing are "recto" and "verso". The side of a coin with the larger-scale image will be called the obverse and, if that does not serve to distinguish them, the side, more typical of a wide range of coins from that location will be called the obverse. Following this principle, in the most famous of ancient Greek coins, the tetradrachm of Athens, the obverse is the head of Athena and the reverse is her owl. Similar versions of these two images, both symbols of the state, were used on the Athenian coins for more than two centuries.
In the many republics of ancient Greece, such as Athens or Corinth, one side of their coins would have a symbol of the state their patron goddess or her symbol, which remained constant through all of the coins minted by that state, regarded as the obverse of those coins. The opposite side may have varied from time to time. In ancient Greek monarchical coinage, the situation continued whereby a larger image of a deity, is called the obverse, but a smaller image of a monarch appears on the other side, called the reverse. In a Western monarchy, it has been customary, following the tradition of the Hellenistic monarchs and the Roman emperors, for the currency to bear the head of the monarch on one side, always regarded as the obverse; this change happened in the coinage of Alexander the Great, which continued to be minted long after his death. After his conquest of ancient Egypt, he allowed himself to be depicted on the obverse of coins as a god-king, at least because he thought this would help secure the allegiance of the Egyptians, who had regarded their previous monarchs, the pharaohs, as divine.
The various Hellenistic rulers who were his successors followed his tradition and kept their images on the obverse of coins. A movement back to the earlier tradition of a deity being placed on the obverse occurred in Byzantine coinage, where a head of Christ became the obverse and a head or portrait of the emperor became considered the reverse; the introduction of this style in the gold coins of Justinian II from the year 695 provoked the Islamic Caliph, Abd al-Malik, who had copied Byzantine designs, replacing Christian symbols with Islamic equivalents to develop a distinctive Islamic style, with just lettering on both sides of their coins. This script alone style was used on nearly all Islamic coinage until the modern period; the type of Justinian II was revived after the end of Iconoclasm, with variations remained the norm until the end of the Empire. Without images, therefore, it is not always easy to tell which side will be regarded as the obverse without some knowledge. After 695 Islamic coins avoided all images of persons and contained script alone.
The side expressing the Six Kalimas is defined as the obverse. A convention exists to display the obverse to the left and the reverse to the right in photographs and museum displays, but this is not invariably observed; the form of currency follows its function, to serve as a accepted medium of exchange of value. This function rests on a state as guarantor of the value: either as trustworthy guarantor of the kind and amount of metal in a coin, or as powerful guarantor of the continuing acceptance of token coins. Traditionally, most states have been monarchies where the person of the monarch and the state were equivalent for most purposes. For this reason, the obverse side of a modern piece of currency is the one that evokes that reaction by invoking the strength of the state, that side always depicts a symbol of the state, whether it be the monarch or otherwise. If not provided for on the obverse, the reverse side contains information relating to a coin's role as medium of exchange. Additional space reflects the issuing country's culture or government, or evokes some aspect of the state's territory.
Regarding the euro, some confusion regarding the obverse and reverse of the euro coins exists. As agreed by the informal Economic and Finance Ministers Council of Verona in April 1996, despite the fact that a number of countries have a different design for each coin, the distinctive national side for the circulation coins is the obverse and the common European side is the reverse; this rule does not apply to the collector coins. A number of the designs used for obverse national sides of euro coins were taken from the reverse of the nations' former pre-euro coins. Several countries continue to use portraits of the reigning monarch. In Japan, from 1897 to the end of World War II, the following informal conventions existed: the Chrysanthemum Throne, representing the imperial family, appeared on all coins, this side was regarded as the obverse; the Chrys
An alloy is a combination of metals and of a metal or another element. Alloys are defined by a metallic bonding character. An alloy may be a mixture of metallic phases. Intermetallic compounds are alloys with a defined crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a wide variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, brass, duralumin and amalgams; the alloy constituents are measured by mass percentage for practical applications, in atomic fraction for basic science studies. Alloys are classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy, they can be heterogeneous or intermetallic. An alloy is a mixture of chemical elements, which forms an impure substance that retains the characteristics of a metal.
An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are considered useful. Alloys are made by mixing two or more elements, at least one of, a metal; this is called the primary metal or the base metal, the name of this metal may be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture; the mechanical properties of alloys will be quite different from those of its individual constituents. A metal, very soft, such as aluminium, can be altered by alloying it with another soft metal, such as copper. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness, its ability to be altered by heat treatment, steel is one of the most useful and common alloys in modern use.
By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel. Like oil and water, a molten metal may not always mix with another element. For example, pure iron is completely insoluble with copper; when the constituents are soluble, each will have a saturation point, beyond which no more of the constituent can be added. Iron, for example, can hold a maximum of 6.67% carbon. Although the elements of an alloy must be soluble in the liquid state, they may not always be soluble in the solid state. If the metals remain soluble when solid, the alloy forms a solid solution, becoming a homogeneous structure consisting of identical crystals, called a phase. If as the mixture cools the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases, some with more of one constituent than the other phase has.
However, in other alloys, the insoluble elements may not separate until after crystallization occurs. If cooled quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents; as time passes, the atoms of these supersaturated alloys can separate from the crystal lattice, becoming more stable, form a second phase that serve to reinforce the crystals internally. Some alloys, such as electrum, an alloy consisting of silver and gold, occur naturally. Meteorites are sometimes made of occurring alloys of iron and nickel, but are not native to the Earth. One of the first alloys made by humans was bronze, a mixture of the metals tin and copper. Bronze was an useful alloy to the ancients, because it is much stronger and harder than either of its components. Steel was another common alloy. However, in ancient times, it could only be created as an accidental byproduct from the heating of iron ore in fires during the manufacture of iron. Other ancient alloys include pewter and pig iron.
In the modern age, steel can be created in many forms. Carbon steel can be made by varying only the carbon content, producing soft alloys like mild steel or hard alloys like spring steel. Alloy steels can be made by adding other elements, such as chromium, vanadium or nickel, resulting in alloys such as high-speed steel or tool steel. Small amounts of manganese are alloyed with most modern steels because of its ability to remove unwanted impurities, like phosphorus and oxygen, which can have detrimental effects on the alloy. However, most alloys were not created until the 1900s, such as various aluminium, titanium and magnesium alloys; some modern superalloys, such as incoloy and hastelloy, may consist of a multitude of different elements. As a noun, the term alloy is used to describe a mixture of atoms in which the primary constituent is a metal; when used as a verb, the term refers to the act of mixing a metal with other elements. The primary metal is called the matrix, or the solvent; the secondary constituents are called s