Acetylene is the chemical compound with the formula C2H2. It is the simplest alkyne; this colorless gas is used as a fuel and a chemical building block. It is unstable in its pure form and thus is handled as a solution. Pure acetylene is odorless, but commercial grades have a marked odor due to impurities; as an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carbon–carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Acetylene was discovered in 1836 by Edmund Davy, who identified it as a "new carburet of hydrogen", it was an accidental discovery while attempting to isolate potassium metal. By heating potassium carbonate with carbon at high temperatures, he produced a residue of what is now known as potassium carbide, which reacted with water to release the new gas, it was rediscovered in 1860 by French chemist Marcellin Berthelot. Berthelot's empirical formula for acetylene, as well as the alternative name "quadricarbure d'hydrogène", were incorrect because chemists at that time used the wrong atomic mass for carbon.
Berthelot was able to prepare this gas by passing vapours of organic compounds through a red-hot tube and collecting the effluent. He found that acetylene was formed by sparking electricity through mixed cyanogen and hydrogen gases. Berthelot obtained acetylene directly by passing hydrogen between the poles of a carbon arc. Commercially available acetylene gas could smell foul due to the impurities divinyl sulfide and phosphine. Since the 1950s, acetylene has been manufactured by the partial combustion of methane, it is a recovered side product in production of ethylene by cracking of hydrocarbons. 400,000 tonnes were produced by this method in 1983. Its presence in ethylene is undesirable because of its explosive character and its ability to poison Ziegler–Natta catalysts, it is selectively hydrogenated into ethylene using Pd–Ag catalysts. Until the 1950s, when oil supplanted coal as the chief source of reduced carbon, acetylene was the main source of organic chemicals in the chemical industry.
It was prepared by the hydrolysis of calcium carbide, a reaction discovered by Friedrich Wöhler in 1862 and still familiar to students: CaC2 + 2H2O → Ca2 + C2H2Calcium carbide production requires high temperatures, ~2000 °C, necessitating the use of an electric arc furnace. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls. In terms of valence bond theory, in each carbon atom the 2s orbital hybridizes with one 2p orbital thus forming an sp hybrid; the other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap to form a strong σ valence bond between the carbons, while on each of the other two ends hydrogen atoms attach by σ bonds; the two unchanged 2p orbitals form a pair of weaker π bonds. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group. At atmospheric pressure, acetylene does not have a melting point; the triple point on the phase diagram corresponds to the melting point at the minimal pressure at which liquid acetylene can exist.
At temperatures below the triple point, solid acetylene can change directly to the vapour by sublimation. The sublimation point at atmospheric pressure is −84.0 °C. At room temperature, the solubility of acetylene in acetone is 27.9 g per kg. For the same amount of dimethylformamide, the solubility is 51 g. At 20.26 bar, the solubility increases to 689.0 and 628.0 g for DMF, respectively. These solvents are used in pressurized gas cylinders. 20% of acetylene is supplied by the industrial gases industry for oxyacetylene gas welding and cutting due to the high temperature of the flame. Combustion of acetylene with oxygen produces a flame of over 3,600 K. Oxyacetylene is the hottest burning common fuel gas. Acetylene is the third-hottest natural chemical flame after dicyanoacetylene's 5,260 K and cyanogen at 4,798 K. Oxy-acetylene welding was a popular welding process in previous decades; the development and advantages of arc-based welding processes have made oxy-fuel welding nearly extinct for many applications.
Acetylene usage for welding has dropped significantly. On the other hand, oxy-acetylene welding equipment is quite versatile – not only because the torch is preferred for some sorts of iron or steel welding, but because it lends itself to brazing, braze-welding, metal heating, the loosening of corroded nuts and bolts, other applications. Bell Canada cable-repair technicians still use portable acetylene-fuelled torch kits as a soldering tool for sealing lead sleeve splices in manholes and in some aerial locations. Oxyacetylene welding may be used in areas where electricity is not accessible; as well, oxy-fuel cutting is still popular, oxy-acetylene cutting is used in many metal fabrication shops. For use in welding and cutting, the working pressures must be controlled by a regulator, since above 15 psi, if subjected to a shockwave, acetylene decomposes explosively into hydrogen and carbon. Calcium carbide was used to generate acetylene used in the lamps for portable or remote applications, it was used for miners and cavers before the widespread
This is a list of 1990 British incumbents. Monarch Head of State – Elizabeth II, Queen of the United Kingdom Prime Minister Head of Government – Margaret Thatcher, Prime Minister of the United Kingdom Head of Government – John Major, Prime Minister of the United Kingdom First Lord of the Treasury Margaret Thatcher, First Lord of the Treasury John Major, First Lord of the Treasury Chancellor of the Exchequer John Major, Chancellor of the Exchequer Norman Lamont, Chancellor of the Exchequer Second Lord of the Treasury John Major, Second Lord of the Treasury Norman Lamont, Second Lord of the Treasury Secretary of State for Foreign and Commonwealth Affairs Douglas Hurd, Secretary of State for Foreign and Commonwealth Affairs Secretary of State for the Home Department David Waddington, Secretary of State for the Home Department Kenneth Baker, Secretary of State for the Home Department Secretary of State for Transport Cecil Parkinson, Secretary of State for Transport Malcolm Rifkind, Secretary of State for Transport Secretary of State for Scotland Malcolm Rifkind, Secretary of State for Scotland Ian Lang, Secretary of State for Scotland Secretary of State for Health Kenneth Clarke, Secretary of State for Health William Waldegrave, Secretary of State for Health Secretary of State for Northern Ireland Peter Brooke, Secretary of State for Northern Ireland Secretary of State for Defence Tom King, Secretary of State for Defence Secretary of State for Trade and Industry Nicholas Ridley, Secretary of State for Trade and Industry Peter Lilley, Secretary of State for Trade and Industry Secretary of State for Education and Science John MacGregor, Secretary of State for Education and Science Kenneth Clarke, Secretary of State for Education and Science Secretary of State for Wales Peter Walker, Secretary of State for Wales David Hunt, Secretary of State for Wales Lord Privy Seal John Ganzoni, 2nd Baron Belstead, Lord Privy Seal David Waddington, Baron Waddington, Lord Privy Seal Leader of the House of Commons Sir Geoffrey Howe, Leader of the House of Commons John MacGregor, Leader of the House of Commons Lord President of the Council Sir Geoffrey Howe, Lord President of the Council John MacGregor, Lord President of the Council Lord Chancellor James Mackay, Baron Mackay of Clashfern, Lord Chancellor Secretary of State for Social Security Tony Newton, Secretary of State for Social Security Chancellor of the Duchy of Lancaster Kenneth Baker, Chancellor of the Duchy of Lancaster Chris Patten, Chancellor of the Duchy of Lancaster Archbishop of Canterbury Robert Runcie, Archbishop of Canterbury Archbishop of York John Habgood, Archbishop of York
The genus Plasmodium is a member of the order Haemosporidia. It is the largest genus within this order and consists of over 250 species, they cause malaria in many different vertebrates. The species in this genus are parasitic with part of their life cycle spent in a vertebrate host and another in an invertebrate host - a mosquito. Vertebrates infected by members of this genus include mammals and reptiles. Host range among the mammalian orders is non uniform. At least 29 species infect non human primates; the listing of host species among the reptiles has been attempted. Ayala in 1978 listed 156 published accounts on 54 valid species and subspecies between 1909 and 1975; the regional breakdown was Africa: 30 reports on 9 species. There are ~550 species recognised in this order organised into 17 genera; the diagnostic criteria of this family are: macrogametes and microgamonts develop independently syzygy is absent microgametocyte produces 8 flagellated microgametes zygote is motile conoid present in ookinete stage only sporozoites naked in oocyst heteroxenous: merogony and gamogony occur in vertebrate host and fertilization and sporogony in definitive host hemozoin pigment produced in some genera Merogony occurs both in erythrocytes and other tissues Merozoites, schizonts or gametocytes can be seen within erythrocytes and may displace the host nucleus Merozoites have a "signet-ring" appearance due to a large vacuole that forces the parasite’s nucleus to one pole Schizonts are round to oval inclusions that contain the staining merozoites Forms gamonts in erythrocytes Gametocytes are'halter-shaped' similar to Haemoproteus but the pigment granules are more confined Hemozoin is present Vectors are either mosquitoes or sandflies.
Vertebrate hosts include mammals and reptiles Mammalian erythrocytes do not possess a nucleus. Although it has been suggested that the nucleus was lost in the erythrocytes better to enable them to traverse capillaries evidence for this is lacking, it appears that this loss along with the mitochondria that the erythrocytes lose may protect the erythrocytes against oxidative stress. The full taxonomic name of a species includes the subgenus but this is omitted in practice; the full name indicates some features of the type of host species. Sixteen subgenera are recognised; the avian species were discovered soon after the description of P. falciparum and a variety of generic names were created. These were subsequently placed into the genus Plasmodium although some workers continued to use the genera Laverinia and Proteosoma for P. falciparum and the avian species respectively. The 5th and 6th Congresses of Malaria held at Istanbul and Lisbon recommended the creation and use of subgenera in this genus.
Laverinia was applied to the species infecting humans and Haemamoeba to those infecting lizards and birds. This proposal was not universally accepted. Bray in 1955 proposed a definition for the subgenus Plasmodium and a second for the subgenus Laverinia in 1958. Garnham described a third subgenus - Vinckeia - in 1964. In 1963 Corradetti and Laird proposed a new classification of the avian malaria parasites, they created four sub-genera - Giovannolaia, Haemamoeba and Novyella - based on the size of the schizonts, the gametocyte forms and the type of exo-erythrocytic schizogony. Additional subgenera have been created since; the recognised subgenera are listed below. Asiamoeba Telford 1988Bennettinia Valkiūnas 1997Carinamoeba Garnham 1966Giovannolaia Corradetti, Garnham & Laird 1963 Haemamoeba Grassi & Feletti 1890Huffia Garnham & Laird 1963Lacertaemoba Telford 1988Laverania Bray 1958Novyella Corradetti, Garnham & Laird 1963Nyssorhynchus Poinar 2005Ophidiella Garnham 1966Papernaia Landau et al 2010Paraplasmodium Telford 1988Plasmodium Bray 1963 emend.
Garnham 1964Sauramoeba Garnham 1966Vinckeia Garnham 1964 The current classification scheme was developed prior to the widespread use of DNA sequence based taxonomy and is based on host and morphological criteria. Plasmodium has since been shown to be paraphytic with the genera Haemoproteus and Hepatocystis. Revision of this genus will be undertaken; this forthcoming reclassification project is not unique to this genus as DNA based taxonomy is revising many traditional groupings of protozoa. The bird infecting taxa can be separated into two groups on the basis of the gametocytes: species with round gametocytes and species with elongated gametocytes; the monophyly of the Bennettinia and Huffia subgenera was subsequently confirmed by molecular studies. The other two genera were found to be paraphytic; the genera were revised and a new subgenus - Papernaia - was created. Laverania Species in this subgenus infect higher primates and have characteristic sickle shaped female gametocytes; the type species is Plasmodium falciparum.
Plasmodium Species infecting higher primates other than those in the subgenus Laverania are placed in the subgenus Plasmodium. The type species is Plasmodium malariae. Vinckeia Parasites infecting other mammals including lower primates are classified in the subgenus Vinckeia; the type species is Plasmodium bubalis. Bennettinia Schizonts contain scant cytoplasm, are often