Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion; this type of damage produces oxide or salt of the original metal, results in a distinctive orange colouration. Corrosion can occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength and permeability to liquids and gases. Many structural alloys corrode from exposure to moisture in air, but the process can be affected by exposure to certain substances.
Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces; as a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less predictable. Galvanic corrosion occurs when two different metals have physical or electrical contact with each other and are immersed in a common electrolyte, or when the same metal is exposed to electrolyte with different concentrations. In a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate; when immersed separately, each metal corrodes at its own rate. What type of metal to use is determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the marine industry and anywhere water contacts pipes or metal structures.
Factors such as relative size of anode, types of metal, operating conditions affect galvanic corrosion. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials. Galvanic corrosion is prevented by the use of sacrificial anodes. In any given environment, one metal will be either more noble or more active than others, based on how its ions are bound to the surface. Two metals in electrical contact share the same electrons, so that the "tug-of-war" at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the noble metal will take electrons from the active one; the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is useful in predicting and understanding corrosion, it is possible to chemically remove the products of corrosion. For example, phosphoric acid in the form of naval jelly is applied to ferrous tools or surfaces to remove rust.
Corrosion removal should not be confused with electropolishing, which removes some layers of the underlying metal to make a smooth surface. For example, phosphoric acid may be used to electropolish copper but it does this by removing copper, not the products of copper corrosion; some metals are more intrinsically resistant to corrosion than others. There are various ways of protecting metals from corrosion including painting, hot dip galvanizing, combinations of these; the materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, why these elements can be found in metallic form on Earth and have long been valued. More common "base" metals can only be protected by more temporary means; some metals have slow reaction kinetics though their corrosion is thermodynamically favorable. These include such metals as zinc and cadmium. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate.
An extreme example is graphite, which releases large amounts of energy upon oxidation, but has such slow kinetics that it is immune to electrochemical corrosion under normal conditions. Passivation refers to the spontaneous formation of an ultrathin film of corrosion products, known as a passive film, on the metal's surface that act as a barrier to further oxidation; the chemical composition and microstructure of a passive film are different from the underlying metal. Typical passive film thickness on aluminium, stainless steels, alloys is within 10 nanometers; the passive film is different from oxide layers that are formed upon heating and are in the micrometer thickness range – the passive film recovers if removed or damaged whereas the oxide layer does not. Passivation in natural environments such as air and soil at moderate pH is seen in such materials as aluminium, stainless steel and silicon. Passivation is determined by metallurgical and environmental factors; the effect of pH is summarized using Pourbaix diagrams.
Some conditions that inhibit passivation include high pH for aluminium and zinc, low pH or the p
Shekel or Sheqel is any of several ancient units of weight or of currency used throughout the United kingdom of Israel, Kingdom of Israel, Kingdom of Judah, Babylonian province of Yehud, Hasmonean dynasty, Herodian kingdom, Herodian Tetrarchy, Roman province of Judea and in the modern State of Israel. The modern currency unit used in the State of Israel today is known as the Israeli new shekel, which replaced the Old Israeli shekel in 1985; the Hebrew word shekel is based on the Semitic verbal root for "weighing", cognate to the Akkadian šiqlu or siqlu, a unit of weight equivalent to the Sumerian gin2. Use of the word was first attested in c. 2150 BC during the Akkadian Empire under the reign of Naram-Sin, in c. 1700 BC in the Code of Hammurabi. The Š-Q-L root is found in the Hebrew words for "to weigh", "weight" and "consideration", is related to the T-Q-L root in Aramaic and the Θ-Q-L root in Arabic, such as the words thiqal or Mithqal; the famous writing on the wall in the Biblical Book of Daniel includes a cryptic use of the word in Aramaic: "Mene, teqel, u-farsin".
The word shekel came into the English language via the Hebrew Bible, where it is first used in the Book of Genesis. The earliest shekels were a unit of weight, used as other units such as grams and troy ounces for trading before the advent of coins; the shekel was common among western Semitic peoples. Moabites and Phoenicians used the shekel, although proper coinage developed late. Carthaginian coinage was based on the shekel and may have preceded its home town of Tyre in issuing proper coins. Coins were used and may have been invented by the early Anatolian traders who stamped their marks to avoid weighing each time used. Herodotus states that the first coinage was issued by Croesus, King of Lydia, spreading to the golden Daric, issued by the Persian Empire and the silver Athenian obol and drachma. Early coins were money stamped with an official seal to certify their weight. Silver ingots, some with markings were issued. Authorities decided who designed coins; as with many ancient units, the shekel had a variety of values depending on era and region.
When used to pay laborers, recorded wages in the ancient world range widely. The Code of Hammurabi sets the value of unskilled labor at ten shekels per year of work. Records within the Persian Empire give ranges from a minimum of two shekels per month for unskilled labor, to as high as seven to ten shekels per month in some records. A survival wage for an urban household during the Persian period would require at least 22 shekels of income per year. Exodus 30:24 notes that the measures of the ingredients for the holy anointing oil were to be calculated using the Shekel of the Sanctuary, suggesting that there were other common measures of shekel in use, or at least that the Temple authorities defined a standard for the shekel to be used for Temple purposes. According to Jewish law, whenever a census of the Jewish people was to be conducted, every person, counted was required to pay the half-Shekel for his atonement; the Aramaic tekel, similar to the Hebrew shekel, used in the writing on the wall during the feast of Belshazzar according to the Book of Daniel and defined as weighed, shares a common root with the word shekel and may additionally attest to its original usage as a weight.
During the Second Temple period, it was customary among Jews to annually offer the half-Shekel into the Temple treasury, for the upkeep and maintenance of the Temple precincts, as used in purchasing public animal-offerings. This practice not only applied to Jews living in the Land of Israel, but to Jews living outside the Land of Israel. Archaeological excavations conducted at Horvat'Ethry in Israel from 1999 to 2001 by Boaz Zissu and Amir Ganor of the Israeli Antiquities Authority have yielded important finds, the most-prized of which being a half-Shekel coin minted in the 2nd century CE, upon which are embossed the words "Half-Shekel" in paleo-Hebrew, which same coin possesses a silver content of 6.87 grams. According to the Jewish historian Josephus, the annual monetary tribute of the half-Shekel to the Temple at Jerusalem was equivalent to two Athenian drachmæ, each Athenian or Attic drachma weighing a little over 4.3 grams. The Jerusalem shekel was issued from AD 66 to 70 amid the First Jewish Revolt as a means of emphasizing the independence of Judaea from Roman rule.
The Bar Kochba shekel was issued from AD 132 to 135 amid the Bar Kokhba Revolt for similar reasons. The Carthaginian or Punic shekel was around 7.2 grams in silver and 7.5 grams in gold. They were first developed on Sicily during the mid-4th century BC, they were associated with the payment of Carthage's mercenary armies and were debased over the course of each of the Punic Wars, although the Carthaginian Empire's expansion into Spain under the Barcids before the Second and recovery under Hannibal before the Third permitted improving the amount and quality of the currency. Throughout, it was more common for Carthage's holdings in North Africa to employ bronze or no coinage except when paying mercenary armies and for most of the specie to circulate in Spain and Sicily; the Tyrian shekel began t
Susa was an ancient city of the Proto-Elamite, First Persian Empire, Seleucid and Sasanian empires of Iran, one of the most important cities of the Ancient Near East. It is located in the lower Zagros Mountains about 250 km east of the Tigris River, between the Karkheh and Dez Rivers; the site now "consists of three gigantic mounds, occupying an area of about one square kilometer, known as the Apadana mound, the Acropolis mound, the Ville Royale mound."The modern Iranian town of Shush is located at the site of ancient Susa. Shush is the administrative capital of Shush County in Iran's Khuzestan province, it had a population of 64,960 in 2005. Shush is identified as Shushan, mentioned in the Book of other Biblical books. In Elamite, the name of the city was written Ŝuŝun, etc.. The origin of the word Susa is from the local city deity Inshushinak. Susa was one of the most important cities of the Ancient Near East. In historic literature, Susa appears in the earliest Sumerian records: for example, it is described as one of the places obedient to Inanna, patron deity of Uruk, in Enmerkar and the Lord of Aratta.
Susa is mentioned in the Ketuvim of the Hebrew Bible by the name Shushan in Esther, but once each in Nehemiah and Daniel. According to these texts, Nehemiah lived in Susa during the Babylonian captivity of the 6th century BCE, while Esther became queen there, married to King Ahasueurus, saved the Jews from genocide. A tomb presumed to be that of Daniel is located in the area, known as Shush-Daniel. However, a large portion of the current structure is a much construction dated to the late nineteenth century, ca. 1871. Susa is further mentioned in the Book of Jubilees as one of the places within the inheritance of Shem and his eldest son Elam; the site was examined in 1836 by Henry Rawlinson and by A. H. Layard. In 1851, some modest excavation was done by William Loftus. In 1885 and 1886 Marcel-Auguste Dieulafoy and Jane Dieulafoy began the first French excavations. Jacques de Morgan conducted major excavations from 1897 until 1911; these efforts continued under Roland De Mecquenem until 1914, at the beginning of World War I.
French work at Susa resumed after the war, led by De Mecquenem, continuing until World War II in 1940. To supplement the original publications of De Mecquenem the archives of his excavation have now been put online thanks to a grant from the Shelby White Levy Program. Roman Ghirshman took over direction of the French efforts after the end of the war. Together with his wife Tania Ghirshman, he continued there until 1967; the Ghirshmans concentrated on excavating a single part of the site, the hectare sized Ville Royale, taking it all the way down to bare earth. The pottery found at the various levels enabled a stratigraphy to be developed for Susa. During the 1970s, excavations resumed under Jean Perrot. In urban history, Susa is one of the oldest-known settlements of the region. Based on C14 dating, the foundation of a settlement there occurred as early as 4395 BCE. At this stage it was very large for the time, about 15 hectares; the founding of Susa corresponded with the abandonment of nearby villages.
Potts suggests that the settlement may have been founded to try to reestablish the destroyed settlement at Chogha Mish. Chogha Mish was a large settlement, it featured a similar massive platform, built at Susa. Another important settlement in the area is Chogha Bonut, discovered in 1976. Shortly after Susa was first settled over 6000 years ago, its inhabitants erected a monumental platform that rose over the flat surrounding landscape; the exceptional nature of the site is still recognizable today in the artistry of the ceramic vessels that were placed as offerings in a thousand or more graves near the base of the temple platform. Susa's earliest settlement is known as Susa I period. Two settlements named by archeologists Acropolis and Apadana, would merge to form Susa proper; the Apadana was enclosed by 6m thick walls of rammed earth. Nearly two thousand pots of Susa I style were recovered from the cemetery, most of them now in the Louvre; the vessels found are eloquent testimony to the artistic and technical achievements of their makers, they hold clues about the organization of the society that commissioned them.
Painted ceramic vessels from Susa in the earliest first style are a late, regional version of the Mesopotamian Ubaid ceramic tradition that spread across the Near East during the fifth millennium BC. Susa I style was much a product of the past and of influences from contemporary ceramic industries in the mountains of western Iran; the recurrence in close association of vessels of three types—a drinking goblet or beaker, a serving dish, a small jar—implies the consumption of three types of food thought to be as necessary for life in the afterworld as it is in this one. Ceramics of these shapes, which were painted, constitute a large proportion of the vessels from the cemetery. Others are coarse cooking-type jars and bowls with simple bands painted on them and were the grave goods of the sites of humbler citizens as well as adolescents and children; the pottery is made by hand. Although a slow wheel may have bee
Money is any item or verifiable record, accepted as payment for goods and services and repayment of debts, such as taxes, in a particular country or socio-economic context. The main functions of money are distinguished as: a medium of exchange, a unit of account, a store of value and sometimes, a standard of deferred payment. Any item or verifiable record that fulfils these functions can be considered as money. Money is an emergent market phenomenon establishing a commodity money, but nearly all contemporary money systems are based on fiat money. Fiat money, like any note of debt, is without use value as a physical commodity, it derives its value by being declared by a government to be legal tender. Counterfeit money can cause good money to lose its value; the money supply of a country consists of currency and, depending on the particular definition used, one or more types of bank money. Bank money, which consists only of records, forms by far the largest part of broad money in developed countries.
The word "money" is believed to originate from a temple of Juno, on Capitoline, one of Rome's seven hills. In the ancient world Juno was associated with money; the temple of Juno Moneta at Rome was the place. The name "Juno" may derive from the Etruscan goddess Uni and "Moneta" either from the Latin word "monere" or the Greek word "moneres". In the Western world, a prevalent term for coin-money has been specie, stemming from Latin in specie, meaning'in kind'; the use of barter-like methods may date back to at least 100,000 years ago, though there is no evidence of a society or economy that relied on barter. Instead, non-monetary societies operated along the principles of gift economy and debt; when barter did in fact occur, it was between either complete strangers or potential enemies. Many cultures around the world developed the use of commodity money; the Mesopotamian shekel was a unit of weight, relied on the mass of something like 160 grains of barley. The first usage of the term came from Mesopotamia circa 3000 BC.
Societies in the Americas, Asia and Australia used shell money – the shells of the cowry. According to Herodotus, the Lydians were the first people to introduce the use of gold and silver coins, it is thought by modern scholars that these first stamped coins were minted around 650–600 BC. The system of commodity money evolved into a system of representative money; this occurred because gold and silver merchants or banks would issue receipts to their depositors – redeemable for the commodity money deposited. These receipts became accepted as a means of payment and were used as money. Paper money or banknotes were first used in China during the Song dynasty; these banknotes, known as "jiaozi", evolved from promissory notes, used since the 7th century. However, they did not displace commodity money, were used alongside coins. In the 13th century, paper money became known in Europe through the accounts of travelers, such as Marco Polo and William of Rubruck. Marco Polo's account of paper money during the Yuan dynasty is the subject of a chapter of his book, The Travels of Marco Polo, titled "How the Great Kaan Causeth the Bark of Trees, Made Into Something Like Paper, to Pass for Money All Over his Country."
Banknotes were first issued in Europe by Stockholms Banco in 1661, were again used alongside coins. The gold standard, a monetary system where the medium of exchange are paper notes that are convertible into pre-set, fixed quantities of gold, replaced the use of gold coins as currency in the 17th–19th centuries in Europe; these gold standard notes were made legal tender, redemption into gold coins was discouraged. By the beginning of the 20th century all countries had adopted the gold standard, backing their legal tender notes with fixed amounts of gold. After World War II and the Bretton Woods Conference, most countries adopted fiat currencies that were fixed to the U. S. dollar. The U. S. dollar was in turn fixed to gold. In 1971 the U. S. government suspended the convertibility of the U. S. dollar to gold. After this many countries de-pegged their currencies from the U. S. dollar, most of the world's currencies became unbacked by anything except the governments' fiat of legal tender and the ability to convert the money into goods via payment.
According to proponents of modern money theory, fiat money is backed by taxes. By imposing taxes, states create demand for the currency. In Money and the Mechanism of Exchange, William Stanley Jevons famously analyzed money in terms of four functions: a medium of exchange, a common measure of value, a standard of value, a store of value. By 1919, Jevons's four functions of money were summarized in the couplet: Money's a matter of functions four, A Medium, a Measure, a Standard, a Store; this couplet would become popular in macroeconomics textbooks. Most modern textbooks now list only three functions, that of medium of exchange, unit of account, store of value, not considering a standard of deferred payment as a distinguished function, but rather subsuming it in the others. There have been many historical disputes regarding the combination of money's functions, some arguing that they need more separation and that a s
Hyperinflation in the Weimar Republic
Hyperinflation affected the German Papiermark, the currency of the Weimar Republic, between 1921 and 1923. It caused considerable internal political instability in the country, the occupation of the Ruhr by France and Belgium as well as misery for the general populace. To pay for the large costs of the ongoing First World War, Germany suspended the gold standard when the war broke out. Unlike the French Third Republic, which imposed its first income tax to pay for the war, German Emperor Wilhelm II and the German parliament decided unanimously to fund the war by borrowing, a decision criticized by financial experts such as Hjalmar Schacht as a dangerous risk for currency devaluation; the government believed that it would be able to pay off the debt by winning the war, when it would be able to annex resource-rich industrial territory in the west and east. It would be able to impose massive reparations on the defeated Allies; the exchange rate of the mark against the US dollar thus devalued from 4.2 to 7.9 marks per dollar, a preliminary to the extreme postwar inflation.
The strategy failed. The new Weimar Republic was saddled with a massive war debt; that was worsened by the fact. The Treaty of Versailles, with its demand for reparations, further accelerated the decline in the value of the mark, so that 48 paper marks were required to buy a US dollar by late 1919. German currency was stable at about 90 marks per dollar during the first half of 1921; because the WWI Western Front had been in France and Belgium, Germany came out of the war with most of its industrial infrastructure intact. It was in a better position to become the dominant economic force on the European continent. In April 1921, the Reparations Commission announced the "London payment plan", under which Germany would pay reparations in gold or foreign currency in annual installments of 2 billion gold marks, plus 26% of the value of Germany's exports; the first payment was made when it came due in June 1921. It marked the beginning of an rapid devaluation of the mark, which fell in value to 330 marks per dollar.
The total reparations demanded were 132 billion gold marks, but Germany had to pay only 50 billion marks. Since reparations were required to be repaid in hard currency, not the depreciating paper mark, one strategy that Germany used was the mass printing of bank notes to buy foreign currency, used to pay reparations exacerbating the inflation of the paper mark. Late in 1922, Germany failed to pay France an installment of reparations on time, France responded in January 1923 by sending troops to occupy the Ruhr, Germany's main industrial region; the German government ordered a policy of passive resistance in the Ruhr. Workers were told to do nothing. What this meant in practice was a general strike, but all the workers on strike had to be given financial support. The government paid its way by printing more banknotes. Germany was soon awash with paper money; the result was a hyperinflation. A loaf of bread that in Berlin cost around 160 Marks at the end of 1922 cost 200,000,000,000 Marks less than a year From August 1921, Germany began to buy foreign currency with marks at any price, but that only increased the speed of breakdown in the value of the mark.
As the mark sank in international markets and more marks were required to buy the foreign currency, demanded by the Reparations Commission. In the first half of 1922, the mark stabilized at about 320 marks per dollar. International reparations conferences were being held. One, in June 1922, was organized by Jr.. The meetings produced no workable solution, inflation erupted into hyperinflation, the mark falling to 7,400 marks per US dollar by December 1922; the cost-of-living index was 41 in June 1922 and 685 in a 15-fold increase. By fall 1922, Germany found itself unable to make reparations payments; the mark was by now worthless, making it impossible for Germany to buy foreign exchange or gold using paper marks. Instead, reparations were to be paid in goods such as coal. In January 1923, French and Belgian troops occupied the industrial region of Germany in the Ruhr valley to ensure reparations payments. Inflation was exacerbated when workers in the Ruhr went on a general strike and the German government printed more money to continue paying for their passive resistance.
By November 1923, the US dollar was worth 4,210,500,000,000 German marks. The hyperinflation crisis led prominent economists and politicians to seek a means to stabilize German currency. In August 1923, an economist, Karl Helfferich, proposed a plan to issue a new currency, the "Roggenmark", to be backed by mortgage bonds indexed to the market price of rye grain; the plan was rejected because of the fluctuating price of rye in paper marks. Agriculture Minister Hans Luther proposed a plan that substituted gold for rye and led to the issuance of the Rentenmark, backed by bonds indexed to the market price of gold; the gold bonds were indexed at the rate of 2790 gold marks per kilogram of gold, the same as the pre-war gold marks. Rentenmarks were not redeemable in gold but only indexed to the gold bonds; the plan was adopted in monetary reform decrees, on October 13–15, 1923. A new bank, the Rentenbank, was controlled by new German Finance Minister Hans Luther. After November 12, 1923, when Hjalmar Schacht became currency commissioner, Germany's central bank was not allowed to discoun