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Most sectors of GA for which data are available have experienced growth in aircraft numbers and hours flown over the last two decades . The lighter end of the GA spectrum : microlights , amateur built , and airships and balloons , have in particular shown strong growth , although the last of these activities was severely curtailed during the foot @-@ and @-@ mouth outbreak in 2001 , when access to farmland was denied . After strong growth in the late 1980s , traditional flying has shown a slight decline recently , reflecting a move amongst recreational flyers towards microlight aircraft , and increased numbers of foreign @-@ registered aircraft . Recreational helicopter usage has grown primarily due to the introduction of smaller and cheaper aircraft . Glider activity has remained relatively static , although there has been a gradual increase in the number of self @-@ launching motor gliders .
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Business aviation has shown strong growth , although the numbers of aircraft on the UK register have declined . This reflects a shift away from turboprop aircraft towards foreign @-@ registered business jets based in the UK , which are estimated to be growing in numbers . However , twin piston @-@ engined aircraft numbers have declined significantly , reflecting pressures on the light air @-@ taxi segment from increasingly flexible and cheaper scheduled services , and a more sophisticated corporate charter business . The amount of flight training conducted by UK schools has declined , largely at the hands of competition from foreign schools , which benefit from lower costs and better weather .
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Since 1990 the total number of hours flown annually by the GA sector has remained in the range 1 @.@ 25 – 1 @.@ 35 million , the dominant sector being traditional GA flying , which accounts for 0 @.@ 6 million per year . An overall increase in aircraft numbers combined with nil growth in hours flown has brought the annual average utilisation per aircraft down from 157 hours in 1984 to 103 hours in 2002 . The decline in asset utilisation has led to speculation that the economic health of the GA industry is weakening , though the lack of data on profitability makes this difficult to confirm .
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The objective of regulation is to " promote high standards of safety in all aspects of aviation " , and this is the main area of interaction between the CAA and the GA sector . Efforts focus on assuring appropriate standards of airworthiness , pilot qualification , the rules for the movement of aircraft , and equipment to be carried . The CAA was established as the primary regulatory body for all aviation in the UK in 1972 . In 1991 it started working within the Joint Aviation Authorities ( JAA ) framework to implement agreed common standards , known as the Joint Aviation Requirements ( JAR ) , throughout the European Union ( EU ) . In 2003 this was taken a step further when the European Aviation Safety Agency ( EASA ) was established as the central EU regulator , taking over responsibility for legislating airworthiness and environmental regulation from the national authorities . The CAA acts as an agency of EASA on these issues , retaining its original regulatory powers in areas not yet transferred to EASA . Proposed developments seek to establish EASA as the single authority throughout the EU , taking over from individual member states the power to regulate all aviation other than that specifically excluded from the scope of EASA .
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= = = Devolved and self @-@ regulation = = =
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Within this framework certain sectors of GA are governed on a devolved basis . In all cases the CAA / EASA retains responsibility for safety regulation , but representative bodies , particularly of sectors that are not included in the scope of EASA , are granted greater oversight of their activities . The majority of microlight aircraft are regulated by the British Microlight Aircraft Association ( BMAA ) , although a significant number are regulated by the Light Aircraft Association ( LAA ) , formerly known as the Popular Flying Association . The LAA is the primary regulator for amateur built aircraft , as well as vintage and classic aircraft . Parachuting is governed by the British Parachute Association , although the aircraft used in this activity are generally CAA @-@ regulated . Balloon and airship flying is overseen by the British Balloon and Airship Club . The UK @-@ specific National Private Pilot Licence ( NPPL ) is administered by the National Pilots Licensing Group Ltd . , supported by the LAA , the Aircraft Owners and Pilots Association UK , the British Gliding Association , and the British Microlight Aircraft Association . Separate from these devolved groups , gliding in the UK is self @-@ regulated . The British Gliding Association was until recently responsible for glider airworthiness , now formally regulated as a result of EASA legislation , and still retains control of pilot certification . Hang gliding and paragliding activities ( i.e. foot @-@ launched gliders ) are governed by the British Hang Gliding and <unk> Association .
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Under CAA and EASA rules , all aircraft are required to meet certain standards of airworthiness to fly safely and legally . Aircraft that meet these standards are issued with a Certificate of Airworthiness . However , British @-@ registered aircraft which are excluded from the scope of EASA , and which cannot satisfy the requirements for the issue of a Certificate of Airworthiness , may be issued with a Permit to Fly . This allows them to fly in UK airspace subject to certain limitations , for example being restricted to day @-@ time flights under visual flight rules only . A number of organisations ( e.g. the British Microlight Aircraft Association and the Light Aircraft Association ) have obtained a standing over @-@ flight permission for Permit to Fly aircraft within their area of interest with some European countries , notably France . Permits are typically issued to vintage and historic aircraft , amateur built aircraft , and microlights .
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The pilot qualification most relevant to GA is the Private Pilot Licence ( PPL ) , which permits the holder to fly for recreational purposes without remuneration . In addition to the European @-@ wide Joint Aviation Regulations Flight Crew Licensing ( JAR @-@ <unk> ) standard , the CAA also issues UK @-@ specific national licences . In the absence of European standards for <unk> , balloon , and airship pilots , the CAA licenses these according to the original UK PPL standard . As a response to the perception that JAR pilot licensing standards are excessively bureaucratic and expensive for the purposes of recreational pilots , the National Private Pilot Licence ( NPPL ) was introduced in 2002 . The NPPL is easier to obtain than the JAR @-@ <unk> licence , has less stringent medical requirements , is more restrictive in the privileges it grants , and is valid only for flights in British @-@ registered aircraft flying in UK and French airspace . Although there are plans to bring glider pilot licensing within the regulatory framework of EASA , the gliding sector is currently self @-@ regulating in this respect . The British Gliding Association is responsible for defining the standards of initial training , and certifying , via a badge system , pilots who meet those standards . Pilots working in sectors of GA that are commercial operations , such as aerial work and business aviation , are required to hold a professional pilot licence which , at a minimum , is the Commercial Pilot Licence .
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Between 1995 and 2004 there were 2 @,@ 630 accidents involving GA aircraft , of which 139 were fatal , resulting in the loss of 317 lives . The majority of accidents involved small fixed @-@ wing aircraft engaged in private flights , and analysis attributes the most common causes of these to : flight handling skills ; poor judgement or airmanship ; lack of training or experience ; and omission of , or inappropriate , action .
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There were 27 fatal accidents involving GA aircraft in 2007 , resulting in the loss of 48 lives . These compare with 16 accidents claiming a total of 19 lives the previous year , and although the 2007 statistics are higher than average , they are not exceptional .
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The growth in Commercial Air Transport ( CAT ) has eroded the operational freedom of GA , both in the air and on the ground at larger airports . Difficulty with access to larger airports is compounded by a decline in the number of aerodromes generally , and existing sites are often threatened with closure and re @-@ development for more profitable uses . The UK planning system is designed to focus on local issues , and consideration of the national impact of GA operations is not within its remit . This makes aerodrome development difficult , often subjecting those that successfully negotiate the process to restrictions in use .
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Airspace is shared by CAT , military and GA users . It is divided into controlled airspace , in which aircraft must always be under the control of an air traffic controller , and uncontrolled airspace , in which aircraft can operate autonomously . Although GA flights can under certain conditions enter controlled airspace , they operate mainly outside of it .
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Controlled airspace is essential for the provision of a known air traffic environment necessary for the safe operation of CAT . A CAA review found that " mixing [ commercial ] operations with other users is considered undesirable , even untenable " by commercial operators . However this position has resulted in extensive Class A controlled airspace with complex boundaries , including some running down to the ground , prohibiting VFR access to airspace , resulting in high numbers of GA flights operating close to the borders of controlled airspace who could not get formal receipt of an air traffic service . Coupled with pilot navigation errors , hundreds of airspace infringements have been recorded every year .
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Increases in the number of CAT operations , and in the number of airports they operate from , has resulted in a corresponding increase in Class A controlled airspace . Between 1997 and 2006 this area grew in size from 13 per cent of all airspace to 22 per cent nationally , and from 24 per cent to 43 per cent in airspace above England and Wales , leading to a perception within the GA community of being squeezed out . There are particular problems for GA around large airports , where Class A controlled airspace extends to ground level . The concentration of commercial operations and high demand for GA in the South East of England have also resulted in extensive areas of Class A controlled airspace there , which serve to channel uncontrolled GA operations through high @-@ collision @-@ risk hot spots .
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Regional airports , such as Edinburgh Airport , have experienced strong growth in CAT operations in recent years . These operations are commercially and operationally incompatible with GA , and although there is no evidence of deliberate discrimination , the effect has been to discourage or exclude it . GA aircraft are being subject to significant increases in charges , including the imposition of handling fees in some cases . Some airports restrict or deny GA parking , and others limit or refuse certain GA activity . As a result , light GA aircraft are now rarely or never seen at large , busy international airports such as Heathrow , Stansted , Gatwick and Manchester .
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In addition to this de facto loss of facilities , the number of aerodromes in the UK has been in decline over the last 50 years , as a result of increasing urbanisation and the closure of airfields built during WWII . Alternative and more profitable uses for land can also lead to existing aerodromes being threatened with closure , for example North Weald , or actually being closed , as happened to Ipswich <unk> and Bristol Filton Airport . Referring to the importance of a " functioning national network of GA airfields " , especially where GA performs an air transport role , the CAA states that " there could be cause for concern if a significant further loss of airfields were to continue , especially if crucial nodes on the transport network were to be lost . "
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The planning system is critical to the viability and operation of GA aerodromes . With many cities lacking scheduled air transport services between them , and with GA access to commercial airports becoming increasingly difficult and expensive , a viable network of aerodromes supporting GA air transport operations is regarded as an important national issue . However , there is no unified national planning policy specific to GA aerodromes , and planning decisions relating to these are based on local issues that are not required to consider the national impact . Because aircraft are excluded from noise control legislation , the only recourse for people affected by aircraft noise is through the planning process , and this issue is the principal factor on which the majority of planning decisions relating to GA land use are made . GA is a specialist subject often unfamiliar to Local Planning Authorities , and most planning decisions relating to GA either refuse permission , or grant it with restrictive conditions . Little Gransden is just one example of a GA airfield required to comply with planning restrictions on the number of movements permitted , thereby inhibiting further development . Such restrictions , if poorly conceived , can make GA operations unviable or even unsafe .
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Public opinion towards aviation generally is worsening , based on increasing environmental concerns relating to emissions and noise , and private flying has been criticised by respondents to a government consultation on aircraft noise as a frivolous or selfish activity . In terms of environmental complaints and enquiries made to the CAA that relate specifically to GA , noise is " by far " the most common subject . Half of the 2 @,@ 000 noise complaints made annually to the CAA concern GA operations , most of which relate to aerobatics , helicopters using private sites , air balloon incidents , parachute dropping , and alleged low flying .
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Planning guidance on aircraft noise advises that " in some circumstances the public perceive general aircraft noise levels as more disturbing than similar levels around major airports . " This is a result of the tonal characteristics of light aircraft engines and the activities they are engaged in , including : repetitive circuit flying at low @-@ altitude near an aerodrome , during which aircraft are audible for long periods ; slow climbing aircraft engaged in parachute drop or glider tug activities concentrated around the drop zone or aerodrome , also audible for long periods ; erratic and repetitive engine noise from aircraft engaged in aerobatics ; and piston @-@ engines on full power in areas of low background noise , leading to the perception that such noise is more intrusive . In an attempt to alleviate these problems , the majority of aerodromes implement noise abatement procedures designed to route aircraft away from noise sensitive areas , and more than 50 are required by the government to provide consultative facilities in which local concerns can be raised with aerodrome operators .
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SMS Zrínyi ( " His Majesty 's ship Zrínyi " ) was a Radetzky @-@ class pre @-@ dreadnought battleship ( Schlachtschiff ) of the Austro @-@ Hungarian Navy ( K.u.K. Kriegsmarine ) , named for the Zrinski , a noble Croatian family . Zrínyi and her sisters , Erzherzog Franz Ferdinand and Radetzky , were the last pre @-@ dreadnoughts built by the Austro @-@ Hungarian Navy .
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During World War I , Zrínyi saw action in the Adriatic Sea . She served with the Second Division of the Austro @-@ Hungarian Navy 's battleships and shelled Senigallia as part of the bombardment of the key seaport of Ancona , Italy , during May 1915 . However , Allied control of the Strait of Otranto meant that the Austro @-@ Hungarian Navy was , for all intents and purposes , effectively bottled up in the Adriatic . Nonetheless , the presence of the Zrínyi and other battleships tied down a substantial force of Allied ships .
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With the war going against the Austrians by the end of 1918 , Zrínyi was prepared to be transferred to the new State of Slovenes , Croats and Serbs . On 10 November 1918 — just one day before the end of the war , navy officers sailed the battleship out of Pola ( Pula ) and eventually surrendered to a squadron of American submarine chasers . Following the handover to the United States Navy , she was briefly designated USS Zrínyi . In the Treaty of Saint @-@ Germain @-@ en @-@ Laye , the transfer was not recognized ; instead , Zrínyi was given to Italy and broken up for scrap .
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Zrínyi was built at the Stabilimento Tecnico Triestino dockyard in Trieste , the same place where her sister ships were built earlier . She was laid down on 15 November 1908 and launched from the slipway on 12 April 1910 . The teak used on Zrínyi 's deck was the only material Austria @-@ Hungary had to purchase abroad to build the ship . The ship was completed by 15 July 1911 , and on 22 November 1911 she was commissioned into the fleet . She was the last ship of the class to be completed and had a crew of 880 to 890 officers and men .
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Zrínyi was 138 @.@ 8 m ( 455 ft 4 in ) long , and had a beam of 24 @.@ 6 m ( 80 ft 8 in ) and a draft of 8 @.@ 1 m ( 26 ft 9 in ) . She displaced 14 @,@ 508 long tons ( 14 @,@ 741 t ) normally , and up to 15 @,@ 845 long tons ( 16 @,@ 099 t ) with a full combat load . She was powered by two @-@ shaft four @-@ cylinder vertical triple expansion engines rated at 19 @,@ 800 indicated horsepower . The ship had a top speed of 20 @.@ 5 knots ( 38 @.@ 0 km / h ; 23 @.@ 6 mph ) . Zrínyi was the first warship in the Austro @-@ Hungarian Navy to use fuel oil to supplement her 12 Yarrow @-@ type coal @-@ fired boilers . She had a maximum range of 4 @,@ 000 nautical miles ( 7 @,@ 400 km ; 4 @,@ 600 mi ) at a cruising speed of 10 knots ( 19 km / h ; 12 mph ) .
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The ship 's primary armament consisted of four 30 @.@ 5 cm ( 12 in ) 45 @-@ caliber guns in two twin gun turrets . This was augmented by a heavy secondary battery of eight 24 cm ( 9 @.@ 4 in ) guns in four wing turrets . The tertiary battery consisted of twenty 10 cm L / 50 guns in casemated single mounts , four 47 mm ( 1 @.@ 85 in ) L / 44 and one 47 mm L / 33 quick @-@ firing guns . Furthermore , the ship 's boats were equipped with two 66 mm ( 2 @.@ 6 in ) landing guns for operations shore . Three 45 cm ( 17 @.@ 7 in ) torpedo tubes were also carried , one on each broadside and one in the stern .
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The ship was assigned to the Austro @-@ Hungarian Fleet 's 1st Battle Squadron after her 1911 commissioning . In 1912 , Zrínyi and her two sister ships conducted two training cruises into the eastern Mediterranean Sea . On the second cruise into the Aegean Sea , conducted from November to December , Zrínyi and her sister ships were accompanied by the cruiser SMS Admiral Spaun and a pair of destroyers . After returning to Pola , the entire fleet mobilized for possible hostilities , as tensions flared in the Balkans .
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In 1913 , Zrínyi participated in an international naval demonstration in the Ionian Sea to protest the Balkan Wars . Ships from other navies included in the demonstration were the British pre @-@ dreadnought HMS King Edward VII , the Italian pre @-@ dreadnought Ammiraglio di Saint Bon , the French armored cruiser Edgar Quinet , and the German light cruiser SMS Breslau . The most important action of the combined flotilla , which was under the command of British Admiral Cecil Burney , was to blockade the Montenegrin coast . The goal of the blockade was to prevent Serbian reinforcements from supporting the siege at Scutari , where Montenegro had besieged a combined force of Albanians and Ottomans . Pressured by the international blockade , Serbia withdrew its army from Scutari , which was subsequently occupied by a joint Allied ground force .
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During that year , the first of four new dreadnoughts , SMS Viribus Unitis , that made up the Tegetthoff class — the only dreadnoughts built for the Austro @-@ Hungarian Navy — came into active service . With the commissioning of these dreadnoughts , Zrínyi and her sisters were moved from the 1st Division to the 2nd Division of the 1st Battle Squadron .
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At that time of the assassination of Archduke Franz Ferdinand of Austria on 28 June 1914 , the battleships in the Austro @-@ Hungarian Navy consisted of the Radetzky class , the Tegetthoff class ( which still had one ship , SMS Szent István , under construction ) , the Erzherzog Karl class and finally , the older Habsburg class . Along with the remainder of the Austro @-@ Hungarian Navy , Zrínyi was mobilized in late July 1914 to support the flight of SMS Goeben and SMS Breslau . The two German ships broke out of Messina , which was surrounded by the British navy and reached Turkey . The flotilla had advanced as far south as Brindisi in southeastern Italy when news of the successful breakout reached Vienna . The Austro @-@ Hungarian ships were then recalled before seeing action .
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On 23 May 1915 , between two and four hours after news of the Italian declaration of war reached the main Austro @-@ Hungarian naval base at Pola , Zrínyi and the rest of the fleet departed to bombard the Italian and Montenegrin coast . Their focus was on the important naval base at Ancona , and later the coast of Montenegro . The bombardment of Montenegro was part of the larger Austro @-@ Hungarian campaign against the Kingdoms of Montenegro and Serbia , who were members of the Entente , during the first half of 1915 . The attack on Ancona was an immense success , and the ships were unopposed during the operation . The bombardment of the province and the surrounding area resulted in the destruction of an Italian steamer in the port of Ancona itself , and an Italian destroyer , Turbine , was severely damaged further south . On the shore , the infrastructure of the port of Ancona , as well as the surrounding towns , were severely damaged . The railroad yard in Ancona , as well as the port facilities in the town , were damaged or destroyed . The local shore batteries were also suppressed . During the bombardment , Zrínyi also helped to destroy a train , a railway station , and a bridge at Senigallia . Additional targets that were damaged or destroyed included wharves , warehouses , oil tanks , radio stations , and the local barracks . Sixty @-@ three Italians , both civilians and military personnel , were killed in the bombardment . By the time Italian ships from Taranto and Brindisi arrived on the scene , the Austro @-@ Hungarians were safely back in Pola .
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The objective of the bombardment of Ancona was to delay the Italian Army from deploying its forces along the border with Austria @-@ Hungary by destroying critical transportation systems . The surprise attack on Ancona succeeded in delaying the Italian deployment to the Alps for two weeks . This delay gave Austria @-@ Hungary valuable time to strengthen its Italian border and re @-@ deploy some of its troops from the Eastern and Balkan fronts .
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Aside from the attack on Ancona , the Austro @-@ Hungarian battleships were largely confined to Pola for the duration of the war . Their operations were limited by Admiral Anton Haus , the commander of the Austro @-@ Hungarian Navy , who believed that he would need to husband his ships to counter any Italian attempt to seize the Dalmatian coast . Since coal was diverted to the newer Tegetthoff @-@ class battleships , the remainder of the war saw Zrínyi and the rest of the Austro @-@ Hungarian Navy acting as a fleet in being . This resulted in the Allied blockade of the Otranto Strait . With his fleet blockaded in the Adriatic Sea , and with a shortage of coal , Haus followed a strategy based on mines and submarines designed to reduce the numerical superiority of the Allied navies .
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= = = Post @-@ war fate = = =
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After the Austro @-@ Hungarian Empire collapsed in 1918 , the Austrians wanted to turn the fleet over to the newly created State of Slovenes , Croats and Serbs ( later to become a part of the Kingdom of Yugoslavia ) in order to prevent the Italians from claiming the ships as spoils of war . However , the victorious Allies refused to acknowledge the conversations between the Austrians and the south Slavs and , in due course , reallocated the ships . The ship had been boarded by a scratch Yugoslav crew on 10 November 1918 , one day before the Armistice , and had left Pola with her sister ship , Radetzky . They were soon spotted by heavy Italian ships , so the two battleships hoisted American flags and sailed south along the Adriatic coast to Castelli Bay near Spalato ( also known as Split ) . They appealed for American naval forces to meet them and accept their surrender , which a squadron of United States Navy ( USN ) submarine chasers in the area did . She had apparently been turned over to the fledgling south Slav state , as it was a Croat naval officer , Korvettenkapitän Marijan <unk> , who presented the ship as a prize of war to representatives of the United States Navy on the afternoon of 22 November 1919 at Spalato ( Split ) in Dalmatia . Simultaneously she was commissioned as USS Zrínyi and Lieutenant E.E. <unk> , USN , assumed command . The initial American complement consisted of four officers and 174 enlisted men — the latter entirely composed of United States Navy Reserve Force personnel . The ship remained at anchor at Spalato for nearly a year while the negotiations that would determine her ultimate fate dragged on . Only once did she apparently turn her engines over , and that occurred during a severe gale that struck Spalato on 9 February 1920 .
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On the morning of 7 November 1920 , Zrínyi was decommissioned . USS Chattanooga took her in tow and , assisted by Brooks and Hovey , towed the battleship to Italy . Under the terms of the treaties of Versailles and St. Germain , Zrínyi was ultimately turned over to the Italian government at Venice . She was broken up for scrap later that year and into 1921 .
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Geopyxis carbonaria is a species of fungus in the genus Geopyxis , family Pyronemataceae . First described to science in 1805 , and given its current name in 1889 , the species is commonly known as the charcoal loving elf @-@ cup , dwarf acorn cup , stalked bonfire cup , or pixie cup . The small , goblet @-@ shaped fruitbodies of the fungus are reddish @-@ brown with a whitish fringe and measure up to 2 cm ( 0 @.@ 8 in ) across . They have a short , tapered stalk . Fruitbodies are commonly found on soil where brush has recently been burned , sometimes in great numbers . The fungus is distributed throughout many temperate regions of the Northern Hemisphere . It is found in Europe , Turkey , and North America . Although it is primarily a saprotrophic species , feeding on the decomposing organic matter remaining after a fire , it also forms biotrophic associations with the roots of Norway spruce .
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The fungus was first described scientifically in 1805 by Johannes Baptista von Albertini and Lewis David de Schweinitz as Peziza carbonaria . Mordecai Cubitt Cooke illustrated the fruitbodies , spores , and asci in his 1879 work <unk> , seu Icones fungorum . Figures of fungi from all parts of the world . In 1889 , Pier Andrea Saccardo transferred the fungus to the genus Geopyxis , giving the species its current name . <unk> carbonaria , published by Heinrich Rehm in 1884 , is a synonym of G. carbonaria . Louis @-@ Joseph <unk> proposed the variety Geopyxis carbonaria var. sessilis in 1937 , referring to forms producing fruitbodies without a stalk , but the taxon is not considered to have independent taxonomic significance . In 1860 Miles Berkeley and Moses Ashley Curtis described the species Peziza <unk> from collections made in Japan as part of the North Pacific Exploring and Surveying Expedition ( 1853 – 1856 ) . This taxon was synonymized with G. carbonaria by Mien Rifai in 1968 , a taxonomic opinion corroborated by Donald Pfister about a decade later .
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The specific epithet carbonaria derives from the Latin word for " charcoal " . Common names given to the fungus include " charcoal loving elf @-@ cup " , " dwarf acorn cup " , " pixie cup " , and the British Mycological Society approved " stalked bonfire cup " .
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The fruitbodies ( <unk> ) of Geopyxis <unk> are cup shaped , 1 – 2 cm wide , and have fringed whitish margins . The inner spore @-@ bearing surface of the cup , the hymenium , is brick red and smooth , while the exterior surface is a dull yellow , and may be either smooth or have blister @-@ like spots ( pustules ) . The stipe is small ( 1 – 1 @.@ 5 mm long and 1 – 2 mm wide ) , whitish in color , and expands abruptly into the cup . The brownish flesh of the fungus is thin and brittle . It does not have any distinctive taste , but has an unpleasant smell when crushed in water . The edibility of the fungus is not known , but the fruitbodies are insubstantial and unlikely to be harvested for eating .
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In mass , the spores are whitish . The spores are elliptical , smooth , hyaline , devoid of oil droplets ( <unk> ) , and have dimensions of 13 – 18 by 7 – 9 µm . They are thin walled and germinate and grow rapidly in vitro in the absence of external stimuli . The asci are 190 – 225 by 9 – 10 µm . The paraphyses are slightly club @-@ shaped , unbranched , and have irregular orange @-@ brown granules , with tips up to 5 µm wide , and are not forked or lobed . The hypothecium , the layer of cells below the hymenium , is made of densely packed , small irregular cells .
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The closely related <unk> elf cup ( Geopyxis <unk> ) has a pale orange to yellowish fruitbody that is deeply cup shaped before flattening in maturity , and its crushed flesh often has an odor of sulfur . It may be distinguished microscopically by its paraphyses , which lack the orange @-@ brown granules characteristic of G. carbonaria . It also has larger spores , measuring 14 – 22 by 8 – 11 µm . Unlike G. carbonaria , it grows on substrates other than burned wood , including mosses , and needle duff . <unk> <unk> , which grows habitats similar to G. carbonaria , is distinguished microscopically by its spores that contain two oil droplets . Other genera with similar species with which G. carbonaria may be confused in the field include Aleuria , Caloscypha , <unk> , and <unk> .
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Geopyxis carbonaria is widespread on burned soil or charcoal in the spring and throughout the growing season . It is one of the most common pioneer species found on burned ground . The charred litter on the forest floor increases the underlying soil pH as well as the availability of minerals . Fruitbodies are produced from 16 to 139 weeks after a forest fire in areas with coniferous trees . Most fruitbodies are produced in the first year after a burn . The fungus prefers fruiting in microhabitats with thin <unk> duff near standing burned tree trunks . Geopyxis carbonaria fruitbodies are often found in the same post @-@ fire stands as morels , although the former is usually more abundant . Because the pixie cup fruits earlier than morels , it may serve as an indicator of imminent morel fruiting . Other cup fungi often found fruiting in the same area as G. carbonaria include those from the genera Aleuria , Anthracobia , Peziza , and <unk> .
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The fungus is found in Europe ( from where it was originally described ) , and is widespread throughout North America . The North American distribution extends north to Alaska . In 2010 , it was reported for the first time from Turkey .
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Although primarily a saprotrophic fungus involved in the post @-@ fire breakdown of duff and coniferous roots , Geopyxis carbonaria has been shown to be capable of forming ectomycorrhizae with Norway spruce ( Picea abies ) . It had been demonstrated earlier in laboratory experiments that the fungus has a biotrophic interaction with lodgepole pine ( Pinus contorta ) . The hyphae of G. carbonaria were able to infect the cortex of the tree seedling , but did not penetrate the <unk> . These traits suggest that the fungus is a moderate pathogen , with limited ability to cause reductions in seed germination . Additionally , the fungus produces the enzyme polyphenol oxidase , and can break down the complex organic polymer lignin — features characteristic of saprotrophic fungi . The formation of a rudimentary Hartig net , a characteristic of mycorrhizal fungi , indicated that G. carbonaria might be capable of forming mutualistic relationships under the right conditions . <unk> and colleagues suggest that its below @-@ ground association with spruce roots protects it from physical damage in the event of a fire , and the extensive fruitbody production after a fire may reflect " a successful fungal escape from a dying host where the fungus no longer can maintain its biotrophic association " .
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Large fruitings of the fungus are often associated with damage to the host tree , such as that which occurs with burning . A field study conducted in Norway demonstrated that fruit bodies were more likely to be found in areas that were heavily burned , compared to locations with light to moderate burning where the trees remained viable , or in clearcut areas . Fruiting was much denser in spruce forests — with up to 700 – 1000 fruitbodies per square meter — than in pine forests , where fruitbodies were sporadic . Fruitbodies grew by the millions in the year following the Yellowstone fires of 1988 .
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The gold dollar or gold one @-@ dollar piece was a coin struck as a regular issue by the United States Bureau of the Mint from 1849 to 1889 . The coin had three types over its lifetime , all designed by Mint Chief Engraver James B. Longacre . The Type 1 issue had the smallest diameter of any United States coin ever minted .
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A gold dollar had been proposed several times in the 1830s and 1840s , but was not initially adopted . Congress was finally galvanized into action by the increased supply of bullion caused by the California gold rush , and in 1849 authorized a gold dollar . In its early years , silver coins were being hoarded or exported , and the gold dollar found a ready place in commerce . Silver again circulated after Congress in 1853 required that new coins of that metal be made lighter , and the gold dollar became a rarity in commerce even before federal coins vanished from circulation because of the economic disruption caused by the American Civil War .
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Gold did not again circulate in most of the nation until 1879 ; once it did , the gold dollar did not regain its place . In its final years , it was struck in small numbers , causing speculation by hoarders . It was also in demand to be mounted in jewelry . The regular issue gold dollar was last struck in 1889 ; the following year , Congress ended the series .
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In proposing his plan for a mint and a coinage system , Secretary of the Treasury Alexander Hamilton in 1791 proposed that the one @-@ dollar denomination be struck both as a gold coin , and as one of silver , representative of the two metals which he proposed be made legal tender . Congress followed Hamilton 's recommendation only in part , authorizing a silver dollar , but no coin of that denomination in gold .
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In 1831 , the first gold dollar was minted , at the private mint of Christopher Bechtler in North Carolina . Much of the gold then being produced in the United States came from the mountains of North Carolina and Georgia , and the dollars and other small gold coins issued by Bechtler circulated through that region , and were now and then seen further away . Additional one @-@ dollar pieces were struck by August Bechtler , Christopher 's son .
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Soon after the <unk> began to strike their private issues , Secretary of the Treasury Levi Woodbury became an advocate of having the Mint of the United States ( " Mint " , when described as an institution ) strike the one @-@ dollar denomination in gold . He was opposed by the Mint Director , Robert M. Patterson . Woodbury persuaded President Andrew Jackson to have pattern coins struck . In response , Patterson had Mint Second Engraver Christian Gobrecht break off work on the new design for the silver one @-@ dollar coin and work on a pattern for the gold dollar . Gobrecht 's design featured a Liberty cap surrounded by rays on one side , and a palm branch arranged in a circle with the denomination , date , and name of the country on the other .
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Consideration was given to including the gold dollar as an authorized denomination in the revisionary legislation that became the Mint Act of 1837 . The Philadelphia newspaper Public Ledger , in December 1836 , supported a gold dollar , stating that " the dollar is the smallest gold coin that would be convenient , and as it would be eminently so , neither silver nor paper should be allowed to take its place . " Nevertheless , after Mint Director Patterson appeared before a congressional committee , the provision authorizing the gold dollar was deleted from the bill .
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In January 1844 , North Carolina Representative James Iver McKay , the chairman of the Committee on Ways and Means , solicited the views of Director Patterson on the gold dollar . Patterson had more of Gobrecht 's pattern dollar struck to show to committee members , again advising against a coin that if issued would be only about a half inch ( 13 mm ) in diameter . He told Treasury Secretary John C. Spencer that the only gold coins of that size in commerce , the Spanish and Colombian half @-@ escudos , were unpopular and had not been struck for more than twenty years . This seemed to satisfy the committee as nothing more was done for the time , and when a gold dollar was proposed again in 1846 , McKay 's committee recommended against it .
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Even before 1848 , record amounts of gold were flowing to American mints to be struck into coin , but the California Gold Rush vastly increased these quantities . This renewed calls for a gold dollar , as well as for a higher denomination than the eagle ( $ 10 piece ) , then the largest gold coin . In January 1849 , McKay introduced a bill for a gold dollar , which was referred to his committee . There was much discussion in the press about the proposed coin ; one newspaper published a proposal for an annular gold dollar , that is , with a hole in the middle to increase its small diameter . McKay amended his legislation to provide for a double eagle ( $ 20 gold coin ) and wrote to Patterson , who replied stating that the annular gold dollar would not work , and neither would another proposal to have dollar piece consisting of a gold plug in a silver coin . Nevertheless , Gobrecht 's successor as chief engraver , James B. Longacre , prepared patterns , including some with a square hole in the middle .
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McKay got his fellow Democrat , New Hampshire Senator Charles Atherton , to introduce the bill to authorize the gold dollar and the double eagle in the Senate on February 1 , 1849 — Atherton was chairman of the Senate Finance Committee . McKay introduced a version into the House on February 20 ; debate began the same day . The dollar was attacked by congressmen from the Whig Party , then in the minority , on the grounds that it would be too small , would be counterfeited and in bad light might be mistakenly spent as a half dime , the coins being similar in size . McKay did not respond substantively , but stated that if no one wanted these denominations , they would not be called for at the Mint , and would not be coined . Pennsylvania Representative Joseph Ingersoll , a Whig , spoke against the bill , noting that Patterson opposed the new denominations , and that the idea had been repeatedly turned down , whenever considered . Another Whig , Massachusetts 's Charles Hudson , related that Patterson had sent a real and a counterfeit gold dollar to his committee and the majority of members had been unable to tell the difference . McKay made no answer to these claims , but others did , including New York Congressman Henry Nicoll , who assured the House that the counterfeiting allegations were greatly exaggerated . The point was , he indicated , that the double eagle and gold dollar were wanted by the public , and , in the case of the gold dollar could help money circulate in small communities where banknotes were not accepted . Connecticut Representative John A. Rockwell , a Whig , tried to table the bill , but his motion was defeated . The bill passed easily , and met only minimal opposition in the Senate , becoming law on March 3 , 1849 .
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The officers at the Philadelphia Mint , including Chief Coiner Franklin Peale , were mostly the friends and relations of Director Patterson . The outsider in their midst was Chief Engraver James B. Longacre , successor to Gobrecht ( who had died in 1844 ) . A former copper @-@ plate engraver , Longacre had been appointed through the political influence of South Carolina Senator John C. Calhoun .
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When Longacre began work on the two new coins in early 1849 , he had no one to assist him . Longacre wrote the following year that he had been warned by a Mint employee that one of the officers ( undoubtedly Peale ) planned to undermine the chief engraver 's position by having the work of preparing designs and dies done outside Mint premises . Accordingly , when the gold coin bill became law , Longacre apprised Patterson that he was ready to begin work on the gold dollar . The Mint Director agreed , and after viewing a model of the head on the obverse , authorized Longacre to proceed with preparation of dies . According to Longacre ,
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The engraving was unusually minute and required very close and incessant labor for several weeks . I made the original dies and hubs for making the working dies twice over , to secure their perfect adaptation to the coining machinery . I had a wish to execute this work single handed , that I might thus silently reply to those who had questioned my ability for the work . The result , I believe , was satisfactory .
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The Type 1 gold dollar depicts a head of Liberty , facing left , with a coronet or tiara on her head bearing her name . Her hair is gathered in a bun ; she is surrounded by 13 stars representing the original states . The reverse features the date and denomination within a wreath , with the name of the nation near the rim .
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Contemporary reviews of the Type 1 design were generally favorable . The New York Weekly Tribune on May 19 , 1849 described the new dollar as " undoubtedly the neatest , tiniest , lightest , coin in this country ... it is too delicate and beautiful to pay out for potatoes , and sauerkraut , and salt pork . Oberon might have paid Puck with it for bringing the blossom which bewitched Titania . " Willis ' Bank Note List stated that " there is no probability of them ever getting into general circulation ; they are altogether too small . " The North Carolina Standard hoped that they would be struck at the Charlotte Mint and circulated locally to eliminate the problem of small @-@ denomination bank notes from out of state . Coin dealer and numismatic author Q. David Bowers notes that the head of Liberty on the Type 1 dollar is a scaled @-@ down version of that on the double eagle , and " a nicely preserved gold dollar is beautiful to behold " .
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Mint records indicate the first gold dollars were produced on May 7 , 1849 ; Longacre 's diary notes state instead that the first were struck on May 8 . A few coins in proof condition were struck on the first day , along with about 1 @,@ 000 for circulation . There are five major varieties of the 1849 gold dollar from Philadelphia , made as Longacre continued to fine @-@ tune the design . <unk> dies were sent by Longacre 's Engraving Department at the Philadelphia Mint to the branch mints at Charlotte , Dahlonega ( in Georgia ) , and New Orleans ; coins struck at the branches resemble some of the types issued from Philadelphia , depending on when the dies were produced . Of the coins struck at the branch mints in 1849 , only pieces struck at Charlotte ( 1849 @-@ C ) exist in multiple varieties ; most are of what is dubbed the " Closed Wreath " variety . Approximately five of the 1849 @-@ C Open Wreath are known ; one , believed the finest surviving specimen , sold at auction for $ 690 @,@ 000 in 2004 , remaining a record for the gold dollar series as of 2013 . One of the changes made during production was the inclusion of Longacre 's initial " L " on the truncation of Liberty 's neck , the first time a U.S. coin intended for full @-@ scale production had borne the initial of its designer . All issues beginning in 1850 bear the Closed Wreath . Beginning in 1854 , the gold dollar was also struck at the new San Francisco Mint .
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The continued flow of gold from California made silver expensive in terms of gold , and U.S. silver coins began to flow out of the country for melting in 1849 , a flow that accelerated over the next several years as the price of the metal continued to rise . By 1853 , a thousand dollars in silver coin contained $ 1 @,@ 042 worth of bullion . As silver coins vanished , the gold dollar became the only federal coin in circulation between the cent and the quarter eagle ( $ 2 @.@ 50 piece ) . As such , it was struck in large numbers and widely circulated . According to Bowers in his book on the denomination , " the years 1850 to 1853 were the high @-@ water mark of the gold dollar , the glory years of the denomination when the little gold coins took the place of half dollars and silver dollars in everyday transactions . " This time came to an end in 1853 when Congress passed an act reducing the weight of most silver coins , allowing new issues of them to circulate .
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As early as 1851 , New York Congressman William Duer alleged that that Patterson had made the gold dollar too small in diameter on purpose to provoke criticism . Patterson retired that year after 16 years in his position , and under his successor , George N. Eckert , annular gold dollar and half dollar patterns were struck . Public Ledger reported that although gold dollars would not be struck in annular form , gold half dollars would be , to help fill the need for change . With the new Pierce administration , Thomas M. Pettit took office as Mint Director on March 31 , 1853 . In April , Treasury Secretary James Guthrie wrote to Pettit that there were complaints that the gold dollar was too small , often lost or mistaken for a small silver coin , and enquiring about reports the Mint had experimented with annular dollars . Pettit replied , stating that none had been preserved , but enclosed a silver piece of equivalent size . He noted that while there would be technical difficulties in the production of the annular dollar , these could be overcome . In a letter dated May 10 , Pettit proposed an oval @-@ shaped holed piece , or an angular @-@ shaped coin , which would lessen the production problems . Pettit died suddenly on May 31 ; Guthrie did not let the issue fall , but queried Pettit 's replacement , James Ross Snowden , concerning the issue on June 7 . As U.S. coins were required to bear some device emblematic of liberty , the secretary hoped that artists could be found who could find some such design for an annular coin .
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The Act of February 21 , 1853 , that had lightened the silver coins also authorized a gold three @-@ dollar piece , which began to be produced in 1854 . To ensure that the three @-@ dollar piece was not mistaken for other gold coins , it had been made thinner and wider than it would normally be , and Longacre put a distinctive design with an Indian princess on it . Longacre adapted both the technique and the design for the gold dollar , which was made thinner , and thus wider . An adaptation of Longacre 's princess for the larger gold coin was placed on the dollar , and a similar agricultural wreath on the reverse . The idea of making the gold dollar larger in this way had been suggested in Congress as early as 1852 , and had been advocated by Pettit , but Guthrie 's desire for an annular coin stalled the matter . In May 1854 , Snowden sent Guthrie a letter stating that the difficulties with an annular coin , especially in getting the coins to eject properly from the press , were more than trivial .
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Nevertheless , the Type 2 gold dollar ( as it came to be known ) proved unsatisfactory as the mints had difficulty in striking the new coin so that all details were brought out . This was due to the high relief of the design — the three Southern branch mints especially had trouble with the piece . Many of the Type 2 pieces quickly became illegible , and were sent back to Philadelphia for melting and recoinage . On most surviving specimens , the " 85 " in the date is not fully detailed . The Type 2 gold dollar was struck only at Philadelphia in 1854 and 1855 , at the three Southern branch mints in the latter year , and at San Francisco in 1856 , after the design was designated for replacement . To correct the problems , Longacre enlarged the head of Liberty , making it a scaled @-@ down version of the three @-@ dollar piece , and moved the lettering on the obverse closer to the rim . This improved the metal flow and design sharpness so much that early numismatic scholars assumed the reverse was also altered , though in fact no change was made and the Type 2 and Type 3 reverses are identical .
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= = = Design of Type 2 and 3 dollars = = =
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The Type 2 and 3 gold dollars depict Liberty as a Native American princess , with a fanciful feathered headdress not resembling any worn by any Indian tribe . This image is an inexact copy of the design Longacre had made for the three @-@ dollar piece , and is one of a number of versions of Liberty Longacre created based on the Venus <unk> or Crouching Venus , a sculpture then on display in a Philadelphia museum . For the reverse , Longacre adapted the " agricultural wreath " he had created for the reverse of the three @-@ dollar piece , composed of cotton , corn , tobacco , and wheat , blending the produce of North and South . This wreath would appear , later in the 1850s , on the Flying Eagle cent .
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Art historian Cornelius Vermeule deprecated the Indian princess design used by Longacre for the obverses of the Types 2 and 3 gold dollar , and for the three @-@ dollar piece , " the ' princess ' of the gold coins is a banknote engraver 's elegant version of folk art of the 1850s . The plumes or feathers are more like the crest of the Prince of Wales than anything that saw the Western frontiers , save perhaps on a music hall beauty . "
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The gold dollar continued to be produced in the late 1850s , though mintages declined from the figures of two million or more each year between 1850 and 1854 . Only about 51 @,@ 000 gold dollars were produced in 1860 , with over two @-@ thirds of that figure at Philadelphia , just under a third at San Francisco , and 1 @,@ 566 at Dahlonega . Roughly a hundred are known of the last , creating one of the great rarities from Dahlonega in the series .
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The other candidate for the rarest from that mint is the 1861 @-@ D , with an estimated mintage of 1 @,@ 000 and perhaps 45 to 60 known . Two pairs of dies were shipped from Philadelphia to Dahlonega on December 10 , 1860 ; they arrived on January 7 , 1861 , two weeks before Georgia voted to secede from the Union , as the American Civil War began . Under orders from Governor Joseph E. Brown , state militia secured the mint , and at some point , small quantities of dollars and half eagles were produced . Records of how many coins were struck and when have not survived . Since dies crack in time , and all the mints were supplied with them from Philadelphia , coining could not last , and in May 1861 , coins and supplies remaining at Dahlonega were turned over to the treasury of the Confederate States of America , which Georgia had by then joined . Gold coins with a face value of $ 6 were put aside for assay . Normally , they would have been sent to Philadelphia to await the following year 's meeting of the United States Assay Commission , when they would be available for testing . Instead , these were sent to the initial Confederate capital of Montgomery , Alabama , though what was done with them there , and their ultimate fate , are unknown . The rarity of the 1861 @-@ D dollar , and the association with the Confederacy , make it especially prized .
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Dahlonega , like the other two branch mints in the South , closed its doors after the 1861 strikings . It and the Charlotte facility never reopened ; the New Orleans Mint again struck coins from 1879 to 1909 , but did not strike gold dollars again . After 1861 , the only issuance of gold dollars outside Philadelphia was at San Francisco , in 1870 .
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The outbreak of the Civil War shook public confidence in the Union , and citizens began hoarding specie , gold and silver coins . In late December 1861 , banks and then the federal Treasury stopped paying out gold at face value . By mid @-@ 1862 , all federal coins , even the base metal cent , had vanished from commerce in much of the country . The exception was the Far West , where for the most part , only gold and silver were acceptable currencies , and paper money traded at a discount . In the rest of the nation , gold and silver coins could be purchased from banks , exchange agents , and from the Treasury for a premium in the new greenbacks the government began to issue to fill the gap in commerce and finance the war .
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= = Final years , abolition , and collecting = =
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Since gold did not circulate in the United States ( except on the West Coast ) in the postwar period , much of the production of coins of that metal in the United States was double eagles for export . Accordingly , although 1 @,@ 361 @,@ 355 gold dollars were struck in 1862 — the last time production would exceed a million — the mintage fell to 6 @,@ 200 in 1863 and remained low for the rest of the coin 's existence , excepting 1873 and 1874 . The Mint felt it improper to suspend coinage of a coin authorized by Congress , and issued proof coins ( generally a few dozen to the tiny numismatic community ) from specially @-@ polished dies , also producing enough circulation strikes so that the proof coins would not be unduly rare . In 1873 and 1874 , old and worn gold dollars held by the government were melted and recoined , generating large mintages of that denomination . This was done in anticipation of the resumption of specie payments , which did not occur until the end of 1878 . Once specie again circulated at face value , the gold dollar found no place in commerce amid large quantities of silver coinage , either released from hoarding or newly struck by the Mint . The government expected that the resumption of specie payments would cause the dollar and other small gold coins to circulate again , but the public , allowed to redeem paper currency , continued to use it as more convenient than coins .
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In the 1870s and 1880s , public interest grew in the low @-@ mintage gold dollar . Collecting coins was becoming more popular , and a number of numismatists put aside some gold dollars and hoped for increases in value . The Mint most likely channeled its production through some favored Philadelphia dealers , though proof coins could be purchased for $ 1 @.@ 25 at the cashier 's window at the Philadelphia facility . Banks charged a premium for circulation strikes . They were popular in the jewelry trade , mounted into various items . The coins were often exported to China or Japan , where such jewelry was made . The dollars were often damaged in the process ; the Mint refused to sell into this trade and did its best to hinder it . Nevertheless , Mint officials concluded that jewelers were successful at getting the majority of each issue . Proof mintages exceeded 1 @,@ 000 by 1884 , and remained above that mark for the remainder of the series , numbers likely inflated by agents of jewelers , willing to pay the Mint 's premium of $ .25 per coin . Another use for the gold dollar was as a holiday gift ; after its abolition the quarter eagle became a popular present .
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James Pollock , in his final report as Mint Director in 1873 , advocated limiting striking of gold dollars to depositors who specifically requested it . " The gold dollar is not a convenient coin , on account of its small size , and it suffers more proportionately from abrasion than larger coins . " His successors called for its abolition , with James P. Kimball , before he left office in 1889 , writing to Congress that except as jewelry , " little practical use has been found for this coin " . Later that year , the new director , Edward O. Leech , issued a report stating that the gold dollar " is too small for circulation , and ... [ is ] used almost exclusively for the purposes of ornament . The last year in which the gold dollar was struck was 1889 . Congress abolished the gold dollar , along with the three @-@ cent nickel and three @-@ dollar piece , by the Act of September 26 , 1890 .
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A total of 19 @,@ 499 @,@ 337 gold dollars were coined , of which 18 @,@ 223 @,@ 438 were struck at Philadelphia , 1 @,@ 004 @,@ 000 at New Orleans , 109 @,@ 138 at Charlotte , 90 @,@ 232 at San Francisco and 72 @,@ 529 at Dahlonega . According to an advertisement in the February 1899 issue of The Numismatist , gold dollars brought $ 1 @.@ 80 each , still in demand as a birthday present and for jewelry . That journal in 1905 carried news of a customer depositing 100 gold dollars into a bank ; the teller , aware of the value , credited the account with $ 1 @.@ 60 per coin . In 1908 , a dealer offered $ 2 each for any quantity . As coin collecting became a widespread pastime in the early 20th century , gold dollars became a popular specialty , a status they retain . The 2014 edition of R.S. Yeoman 's A Guide Book of United States Coins rates the least expensive gold dollar in very fine condition ( VF @-@ 20 ) at $ 300 , a value given for each of the Type 1 Philadelphia issues from 1849 to 1853 . Those seeking one of each type will find the most expensive to be a specimen of the Type 2 , with the 1854 and 1855 estimated at $ 350 in that condition ; the other two types have dates valued at $ 300 in that grade .
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The gold dollar had a brief resurrection during the period of Early United States commemorative coins . Between 1903 and 1922 nine different issues were produced , with a total mintage of 99 @,@ 799 . These were minted for various public events , did not circulate , and none used Longacre 's design .
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= Johnson – Corey – Chaykovsky reaction =
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The Johnson – Corey – Chaykovsky reaction ( sometimes referred to as the Corey – Chaykovsky reaction or CCR ) is a chemical reaction used in organic chemistry for the synthesis of epoxides , aziridines , and <unk> . It was discovered in 1961 by A. William Johnson and developed significantly by E. J. Corey and Michael Chaykovsky . The reaction involves addition of a sulfur ylide to a ketone , aldehyde , imine , or enone to produce the corresponding 3 @-@ membered ring . The reaction is <unk> favoring trans substitution in the product regardless of the initial stereochemistry . The synthesis of epoxides via this method serves as an important <unk> alternative to the traditional epoxidation reactions of olefins .
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The reaction is most often employed for epoxidation via methylene transfer , and to this end has been used in several notable total syntheses ( See Synthesis of epoxides below ) . Additionally detailed below are the history , mechanism , scope , and enantioselective variants of the reaction . Several reviews have been published .
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The original publication by Johnson concerned the reaction of 9 @-@ <unk> <unk> with substituted benzaldehyde derivatives . The attempted Wittig @-@ like reaction failed and a <unk> oxide was obtained instead , noting that " Reaction between the sulfur <unk> and <unk> did not afford <unk> as had the phosphorus and arsenic <unk> . "
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The subsequent development of ( <unk> ) methanide , ( CH3 ) <unk> and ( <unk> ) methanide , ( CH3 ) <unk> ( known as Corey – Chaykovsky reagents ) by Corey and Chaykovsky as efficient methylene @-@ transfer reagents established the reaction as a part of the organic canon .
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The reaction mechanism for the Johnson – Corey – Chaykovsky reaction consists of nucleophilic addition of the ylide to the carbonyl or imine group . A negative charge is transferred to the heteroatom and because the sulfonium cation is a good leaving group it gets expelled forming the ring . In the related Wittig reaction , the formation of the much stronger phosphorus @-@ oxygen double bond prevents <unk> formation and instead , <unk> takes place through a 4 @-@ membered cyclic intermediate .
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The trans diastereoselectivity observed results from the reversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine with adjacent charges ; density functional theory calculations have shown that the rate @-@ limiting step is rotation of the central bond into the conformer necessary for backside attack on the sulfonium .
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The degree of reversibility in the initial step ( and therefore the diastereoselectivity ) depends on four factors , with greater reversibility corresponding to higher selectivity :
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Stability of the substrate with higher stability leading to greater reversibility by favoring the starting material over the betaine .
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Stability of the ylide with higher stability similarly leading to greater reversibility .
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<unk> hindrance in the betaine with greater hindrance leading to greater reversibility by <unk> formation of the intermediate and slowing the rate @-@ limiting rotation of the central bond .
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<unk> of charges in the betaine by <unk> such as lithium with greater solvation allowing more facile rotation in the betaine intermediate , lowering the amount of reversibility .
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The application of the Johnson – Corey – Chaykovsky reaction in organic synthesis is diverse . The reaction has come to encompass reactions of many types of sulfur ylides with electrophiles well beyond the original publications . It has seen use in a number of high @-@ profile total syntheses , as detailed below , and is generally recognized as a powerful transformative tool in the organic repertoire .
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= = = Types of ylides = = =
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Many types of ylides can be prepared with various functional groups both on the anionic carbon center and on the sulfur . The substitution pattern can influence the ease of preparation for the reagents ( typically from the sulfonium halide , e.g. <unk> iodide ) and overall reaction rate in various ways . The general format for the reagent is shown on the right .
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Use of a sulfoxonium allows more facile preparation of the reagent using weaker bases as compared to sulfonium ylides . ( The difference being that a sulfoxonium contains a doubly bonded oxygen whereas the sulfonium does not . ) The former react slower due to their increased stability . In addition , the <unk> by @-@ products of sulfoxonium reagents are greatly preferred to the significantly more toxic , volatile , and odorous <unk> by @-@ products from sulfonium reagents .
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The vast majority of reagents are <unk> at the ylide carbon ( either R1 or R2 as hydrogen ) . <unk> reagents are much rarer but have been described :
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If the ylide carbon is substituted with an electron @-@ withdrawing group ( EWG ) , the reagent is referred to as a stabilized ylide . These , similarly to sulfoxonium reagents , react much slower and are typically easier to prepare . These are limited in their usefulness as the reaction can become prohibitively sluggish : examples involving amides are widespread , with many fewer involving esters and virtually no examples involving other EWG 's . For these , the related <unk> reaction is typically more appropriate .
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If the ylide carbon is substituted with an aryl or allyl group , the reagent is referred to as a semi @-@ stabilized ylide . These have been developed extensively , second only to the classical methylene reagents ( R1 = R2 = H ) . The substitution pattern on aryl reagents can heavily influence the selectivity of the reaction as per the criteria above .
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If the ylide carbon is substituted with an alkyl group the reagent is referred to as an <unk> ylide . The size of the alkyl groups are the major factors in selectivity with these reagents .
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The R @-@ groups on the sulfur , though typically <unk> , have been used to synthesize reagents that can perform enantioselective variants of the reaction ( See Variations below ) . The size of the groups can also influence diastereoselectivity in <unk> substrates .
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= = = Synthesis of epoxides = = =
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