Carbon tetrachloride known by many other names is an organic compound with the chemical formula CCl4. It is a colourless liquid with a "sweet" smell, it has no flammability at lower temperatures. It was widely used in fire extinguishers, as a precursor to refrigerants and as a cleaning agent, but has since been phased out because of toxicity and safety concerns. Exposure to high concentrations of carbon tetrachloride can affect the central nervous system, degenerate the liver and kidneys. Prolonged exposure can be fatal. Carbon tetrachloride was synthesized by the French chemist Henri Victor Regnault in 1839 by the reaction of chloroform with chlorine, but now it is produced from methane: CH4 + 4 Cl2 → CCl4 + 4 HClThe production utilizes by-products of other chlorination reactions, such as from the syntheses of dichloromethane and chloroform. Higher chlorocarbons are subjected to "chlorinolysis": C2Cl6 + Cl2 → 2 CCl4Prior to the 1950s, carbon tetrachloride was manufactured by the chlorination of carbon disulfide at 105 to 130 °C: CS2 + 3Cl2 → CCl4 + S2Cl2The production of carbon tetrachloride has steeply declined since the 1980s due to environmental concerns and the decreased demand for CFCs, which were derived from carbon tetrachloride.
In 1992, production in the U. S./Europe/Japan was estimated at 720,000 tonnes. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds; because of this symmetrical geometry, CCl4 is non-polar. Methane gas has the same structure, making carbon tetrachloride a halomethane; as a solvent, it is well suited to dissolving other non-polar compounds and oils. It can dissolve iodine, it is somewhat volatile, giving off vapors with a smell characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene smell reminiscent of dry cleaners' shops. Solid tetrachloromethane has two polymorphs: crystalline II below −47.5 °C and crystalline I above −47.5 °C. At −47.3 °C it has monoclinic crystal structure with space group C2/c and lattice constants a = 20.3, b = 11.6, c = 19.9, β = 111°. With a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilled in the environment.
In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction. One specialty use of carbon tetrachloride is in stamp collecting, to reveal watermarks on postage stamps without damaging them. A small amount of the liquid was placed on the back of a stamp, sitting in a black glass or obsidian tray; the letters or design of the watermark could be seen. Carbon tetrachloride was used as a dry cleaning solvent, as a refrigerant, in lava lamps. In case of the latter, carbon tetrachloride is a key ingredient that adds weight to the otherwise buoyant wax, it once was a popular solvent in organic chemistry, because of its adverse health effects, it is used today. It is sometimes useful as a solvent for infrared spectroscopy, because there are no significant absorption bands > 1600 cm−1. Because carbon tetrachloride does not have any hydrogen atoms, it was used in proton NMR spectroscopy. In addition to being toxic, its dissolving power is low, its use has been superseded by deuterated solvents.
Use of carbon tetrachloride in determination of oil has been replaced by various other solvents, such as tetrachloroethylene. Because it has no C-H bonds, carbon tetrachloride does not undergo free-radical reactions, it is a useful solvent for halogenations either by the elemental halogen or by a halogenation reagent such as N-bromosuccinimide. In 1910, the Pyrene Manufacturing Company of Delaware filed a patent to use carbon tetrachloride to extinguish fires; the liquid was vaporized by the heat of combustion and extinguished flames, an early form of gaseous fire suppression. At the time it was believed the gas displaced oxygen in the area near the fire, but research found that the gas inhibits the chemical chain reaction of the combustion process. In 1911, Pyrene patented a portable extinguisher that used the chemical; the extinguisher consisted of a brass bottle with an integrated handpump, used to expel a jet of liquid toward the fire. As the container was unpressurized, it could be refilled after use.
Carbon tetrachloride was suitable for liquid and electrical fires and the extinguishers were carried on aircraft or motor vehicles. In the first half of the 20th century, another common fire extinguisher was a single-use, sealed glass globe known as a "fire grenade," filled with either carbon tetrachloride or salt water; the bulb could be thrown at the base of the flames to quench the fire. The carbon tetrachloride type could be installed in a spring-loaded wall fixture with a solder-based restraint; when the solder melted by high heat, the spring would either break the globe or launch it out of the bracket, allowing the extinguishing agent to be automatically dispersed into the fire. A well-known brand was the "Red Comet,", variously manufactured with other fire-fighting equipment in the Denver, Colorado area by the Red Comet Manufacturing Company from its founding in 1919 until manufacturing operations were closed in the early 1980s. Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the chlorofluorocarbon re
Zeolites are microporous, aluminosilicate minerals used as commercial adsorbents and catalysts. The term zeolite was coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that heating the material, believed to have been stilbite, produced large amounts of steam from water, adsorbed by the material. Based on this, he called the material zeolite, from the Greek ζέω, meaning "to boil" and λίθος, meaning "stone"; the classic reference for the field has been Breck's book Zeolite Molecular Sieves: Structure, And Use. Zeolites occur but are produced industrially on a large scale; as of December 2018, 245 unique zeolite frameworks have been identified, over 40 occurring zeolite frameworks are known. Every new zeolite structure, obtained is examined by the International Zeolite Association Structure Commission and receives a three letter designation. Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others; these positive ions are rather loosely held and can be exchanged for others in a contact solution.
Some of the more common mineral zeolites are analcime, clinoptilolite, natrolite and stilbite. An example of the mineral formula of a zeolite is: Na2Al2Si3O10 the formula for natrolite; these cation exchanged. Natural zeolites form. Zeolites crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Occurring zeolites are pure and are contaminated to varying degrees by other minerals, quartz, or other zeolites. For this reason occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves", consist of Si, Al, O, metals including Ti, Sn, Zn, so on; the term molecular sieve refers to a particular property of these materials, i.e. the ability to selectively sort molecules based on a size exclusion process. This is due to a regular pore structure of molecular dimensions; the maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels.
These are conventionally defined by the ring size of the aperture, for example, the term "8-ring" refers to a closed loop, built from eight tetrahedrally coordinated silicon atoms and 8 oxygen atoms. These rings are not always symmetrical due to a variety of causes, including strain induced by the bonding between units that are needed to produce the overall structure, or coordination of some of the oxygen atoms of the rings to cations within the structure. Therefore, the pores in many zeolites are not cylindrical. Zeolites transform to other minerals under weathering, hydrothermal alteration or metamorphic conditions; some examples: The sequence of silica-rich volcanic rocks progresses from: Clay → quartz → mordenite–heulandite → epistilbite → stilbite → thomsonite–mesolite-scolecite → chabazite → calcite. The sequence of silica-poor volcanic rocks progresses from: Cowlesite → levyne–offretite → analcime → thomsonite–mesolite-scolecite → chabazite → calcite. Industrially important zeolites are produced synthetically.
Typical procedures entail heating aqueous solutions of silica with sodium hydroxide. Equivalent reagents include sodium silicate. Further variations include changes in the cations to include quaternary ammonium cations. Synthetic zeolites hold some key advantages over their natural analogues; the synthetic materials are manufactured in a phase-pure state. It is possible to produce zeolite structures that do not appear in nature. Zeolite A is a well-known example. Since the principal raw materials used to manufacture zeolites are silica and alumina, which are among the most abundant mineral components on earth, the potential to supply zeolites is unlimited. Conventional open-pit mining techniques are used to mine natural zeolites; the overburden is removed to allow access to the ore. The ore may be blasted or stripped for processing by using tractors equipped with ripper blades and front-end loaders. In processing, the ore is crushed and milled; the milled ore may be shipped in bags or bulk. The crushed product may be screened to remove fine material when a granular product is required, some pelletized products are produced from fine material.
As of 2016 the world's annual production of natural zeolite approximates 3 million tonnes. Major producers in 2010 included China, South Korea, Jordan, Turkey Slovakia and the United States; the ready availability of zeolite-rich rock at low cost and the shortage of competing minerals and rocks are the most important factors for its large-scale use. According to the United States Geological Survey, it is that a significant percentage of the material sold as zeolites in some countries is ground or sawn volcanic tuff that contains only a small amount of zeolites; some examples of such usage include dimension stone, lightweight aggregate, pozzolanic cement, soil conditioners. There are over 200 synthetic zeolites that have been synthesized by a process of slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates. Many
Methane clathrate or called methane hydrate, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. Methane clathrates are common constituents of the shallow marine geosphere and they occur in deep sedimentary structures and form outcrops on the ocean floor. Methane hydrates are believed to form by the precipitation or crystallisation of methane migrating from deep along geological faults. Precipitation occurs when the methane comes in contact with water within the sea bed subject to temperature and pressure. In 2008, research on Antarctic Vostok and EPICA Dome C ice cores revealed that methane clathrates were present in deep Antarctic ice cores and record a history of atmospheric methane concentrations, dating to 800,000 years ago.
The ice-core methane clathrate record is a primary source of data for global warming research, along with oxygen and carbon dioxide. Methane hydrates were discovered in Russia in the 1960s, studies for extracting gas from it emerged at the beginning of the 21st century; the nominal methane clathrate hydrate composition is 423, or 1 mole of methane for every 5.75 moles of water, corresponding to 13.4% methane by mass, although the actual composition is dependent on how many methane molecules fit into the various cage structures of the water lattice. The observed density is around 0.9 g/cm3, which means that methane hydrate will float to the surface of the sea or of a lake unless it is bound in place by being formed in or anchored to sediment. One litre of saturated methane clathrate solid would therefore contain about 120 grams of methane, or one cubic metre of methane clathrate releases about 160 cubic metres of gas. Methane forms a structure I hydrate with two dodecahedral and six tetradecahedral water cages per unit cell.
This compares with a hydration number of 20 for methane in aqueous solution. A methane clathrate MAS NMR spectrum recorded at 275 K and 3.1 MPa shows a peak for each cage type and a separate peak for gas phase methane. In 2003, a clay-methane hydrate intercalate was synthesized in which a methane hydrate complex was introduced at the interlayer of a sodium-rich montmorillonite clay; the upper temperature stability of this phase is similar to that of structure. Methane clathrates are restricted to the shallow lithosphere. Furthermore, necessary conditions are found only in either continental sedimentary rocks in polar regions where average surface temperatures are less than 0 °C. In addition, deep fresh water lakes may host gas hydrates as well, e.g. the fresh water Lake Baikal, Siberia. Continental deposits have been located in Siberia and Alaska in sandstone and siltstone beds at less than 800 m depth. Oceanic deposits seem to be widespread in the continental shelf and can occur within the sediments at depth or close to the sediment-water interface.
They may cap larger deposits of gaseous methane. There are two distinct types of oceanic deposit; the most common is dominated by methane contained in a structure I clathrate and found at depth in the sediment. Here, the methane is isotopically light, which indicates that it is derived from the microbial reduction of CO2; the clathrates in these deep deposits are thought to have formed in situ from the microbially produced methane, since the δ13C values of clathrate and surrounding dissolved methane are similar. However, it is thought that fresh water used in the pressurization of oil and gas wells in permafrost and along the continental shelves worldwide combines with natural methane to form clathrate at depth and pressure, since methane hydrates are more stable in fresh water than in salt water. Local variations may be common, since the act of forming hydrate, which extracts pure water from saline formation waters, can lead to local, significant, increases in formation water salinity. Hydrates exclude the salt in the pore fluid from which it forms, thus they exhibit high electric resistivity just like ice, sediments containing hydrates have a higher resistivity compared to sediments without gas hydrates.
These deposits are located within a mid-depth zone around 300–500 m thick in the sediments where they coexist with methane dissolved in the fresh, not salt, pore-waters. Above this zone methane is only present in its dissolved form at concentrations that decrease towards the sediment surface. Below it, methane is gaseous. At Blake Ridge on the Atlantic continental rise, the GHSZ started at 190 m depth and continued to 450 m, where it reached equilibrium with the gaseous phase. Measurements indicated that methane occupied 0-9% by volume in the GHSZ, ~12% in the gaseous zone. In the less common second type found near the sediment surface some samples have a higher proportion of longer-chain hydrocarbons contained in a structure II clathrate. Carbon from this type of clathrate is isotopically heavier and is thought to have migrated upwards from deep sediments, w
Drug delivery refers to approaches, formulations and systems for transporting a pharmaceutical compound in the body as needed to safely achieve its desired therapeutic effect. It may involve scientific site-targeting within the body, or it might involve facilitating systemic pharmacokinetics. Drug delivery is approached via a drug's chemical formulation, but it may involve medical devices or drug-device combination products. Drug delivery is a concept integrated with dosage form and route of administration, the latter sometimes being considered part of the definition. Drug delivery technologies modify drug release profile, absorption and elimination for the benefit of improving product efficacy and safety, as well as patient convenience and compliance. Drug release is from: diffusion, degradation and affinity-based mechanisms; some of the common routes of administration include the enteral, inhalation, transdermal and oral routes.. Many medications such as peptide and protein, antibody and gene based drugs, in general may not be delivered using these routes because they might be susceptible to enzymatic degradation or can not be absorbed into the systemic circulation efficiently due to molecular size and charge issues to be therapeutically effective.
For this reason many protein and peptide drugs have to be delivered by injection or a nanoneedle array. For example, many immunizations are based on the delivery of protein drugs and are done by injection. Current efforts in the area of drug delivery include the development of targeted delivery in which the drug is only active in the target area of the body, sustained release formulations in which the drug is released over a period of time in a controlled manner from a formulation, methods to increase survival of peroral agents which must pass through the stomach's acidic environment. In order to achieve efficient targeted delivery, the designed system must avoid the host's defense mechanisms and circulate to its intended site of action. Types of sustained release formulations include liposomes, drug loaded biodegradable microspheres and drug polymer conjugates. Survival of agents as they pass through the stomach is an issue for agents which cannot be encased in a solid tablet. Thin film drug delivery Magnetic drug delivery Self-microemulsifying drug delivery system Acoustic targeted drug delivery Neural drug delivery systems Drug delivery to the brain Drug carrier Bovine submaxillary mucin coatings Retrometabolic drug design Bioavailability Asymmetric membrane capsule Article in Chemical and Engineering News
New Scientist, first published on 22 November 1956, is a weekly, English-language magazine that covers all aspects of science and technology. New Scientist, based in London, publishes editions in the UK, the United States, Australia. Since 1996 it has been available online. Sold in retail outlets and on subscription, the magazine covers news, features and commentary on science and their implications. New Scientist publishes speculative articles, ranging from the technical to the philosophical; the magazine was founded in 1956 by Tom Margerison, Max Raison and Nicholas Harrison as The New Scientist, with Issue 1 on 22 November, priced one shilling. The British monthly science magazine Science Journal, published 1965–71, was merged with New Scientist to form New Scientist and Science Journal; the cover of New Scientist listed articles in plain text. Page numbering followed academic practice with sequential numbering for each quarterly volume. So, for example, the first page of an issue in March could be 649 instead of 1.
Issues numbered issues separately. From the beginning of 1961 "The" was dropped from the title. From 1965, the front cover was illustrated; until the 1970s, colour was not used except for on the cover. Since its first issue, New Scientist has written about the applications of science, through its coverage of technology. For example, the first issue included an article "Where next from Calder Hall?" on the future of nuclear power in the UK, a topic that it has covered throughout its history. In 1964 there was a regular "Science in British Industry" section with several items. An article in the magazine's 10th anniversary issues provides anecdotes on the founding of the magazine. In 1970, the Reed Group, which went on to become Reed Elsevier, acquired New Scientist when it merged with IPC Magazines. Reed retained the magazine when it sold most of its consumer titles in a management buyout to what is now TI Media. Throughout most of its history, New Scientist has published cartoons as light relief and comment on the news, with contributions from regulars such as Mike Peyton and David Austin.
The Grimbledon Down comic strip, by cartoonist Bill Tidy, appeared from 1970 to 1994. The Ariadne pages in New Scientist commented on the lighter side of science and technology and included contributions from Daedalus; the fictitious inventor devised plausible but impractical and humorous inventions developed by the DREADCO corporation. Daedalus moved to Nature. Issues of New Scientist from Issue 1 to the end of 1989 have been made free to read online. Subsequent issues require a subscription. In the first half of 2013, the international circulation of New Scientist averaged 125,172. While this was a 4.3% reduction on the previous year's figure, it was a much smaller reduction in circulation than many mainstream magazines of similar or greater circulation. For the 2014 UK circulation fell by 3.2% but stronger international sales, increased the circulation to 129,585. See #Website below. In April 2017, New Scientist changed hands when RELX Group known as Reed Elsevier, sold the magazine to Kingston Acquisitions, a group set up by Sir Bernard Gray, Louise Rogers and Matthew O’Sullivan to acquire New Scientist.
Kingston Acquisitions renamed itself New Scientist Ltd. New Scientist contains the following sections: Leader, Technology, Features, CultureLab, The Last Word and Jobs & Careers. A Tom Gauld cartoon appears on the Letters page. A readers' letters section discusses recent articles and discussions take place on the website. Readers contribute observations on examples of pseudoscience to Feedback, offer questions and answers on scientific and technical topics to Last Word. New Scientist has produced a series of books compiled from contributions to Last Word. There are 51 issues a year, with a New Year double issue; the double issue in 2014 was the 3,000th edition of the magazine. The Editor-in-chief is Emily Wilson, Executive Editor is Graham Lawton, Managing Editor is Rowan Hooper and Editor-at-Large is Jeremy Webb. Consultants include Fred Pearce, Marcus Chown, Linda Geddes. Simon Ings and former editor Alun Anderson are contributors.) Percy Cudlipp Nigel Calder Donald Gould Bernard Dixon Michael Kenward David Dickson Alun Anderson Jeremy Webb Roger Highfield Sumit Paul-Choudhury Emily Wilson The New Scientist website carries blogs and news articles.
Users with free-of-charge registration have limited access to new content and can receive emailed New Scientist newsletters. Subscribers to the print edition have full access to all articles and the archive of past content that has so far been digitised. Online readership takes various forms. Overall global views of an online database of over 100,000 articles are 8.0m by 3.6m unique users according to Adobe Reports & Analytics, as of September 2014. On social media there are 1.47m+ Twitter followers, 2.3m+ Facebook likes and 365,000+ Google+ followers as of January 2015. New Scientist has published books derived from its content, many of which are selected questions and answers from the Last Word section of the magazine and website: 1998; the Last Word. ISBN 978-0-19-286199-3 2000; the Last Word 2. ISBN 978-0-19-286204-4 2005. Does Anything Eat Wasps?. ISBN 978-1-86197-973-5 2006. Why Don't Penguins' Feet Freeze?. ISBN 978-1861978769 2007. How to
Integrated Authority File
The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used for documentation in libraries and also by archives and museums; the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero licence; the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, an approach to unambiguous identification of single elements. It comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format; the Integrated Authority File became operational in April 2012 and integrates the content of the following authority files, which have since been discontinued: Name Authority File Corporate Bodies Authority File Subject Headings Authority File Uniform Title File of the Deutsches Musikarchiv At the time of its introduction on 5 April 2012, the GND held 9,493,860 files, including 2,650,000 personalised names.
There are seven main types of GND entities: LIBRIS Virtual International Authority File Information pages about the GND from the German National Library Search via OGND Bereitstellung des ersten GND-Grundbestandes DNB, 19 April 2012 From Authority Control to Linked Authority Data Presentation given by Reinhold Heuvelmann to the ALA MARC Formats Interest Group, June 2012
A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. Chemical substances can be chemical compounds, or alloys. Chemical elements may not be included in the definition, depending on expert viewpoint. Chemical substances are called'pure' to set them apart from mixtures. A common example of a chemical substance is pure water. Other chemical substances encountered in pure form are diamond, table salt and refined sugar. However, in practice, no substance is pure, chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, may change between these phases of matter with changes in temperature or pressure. Chemical substances may be converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, are thus not "substances" in this regard.
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook. According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; the chemical substance index published by CAS includes several alloys of uncertain composition. Non-stoichiometric compounds are a special case that violates the law of constant composition, for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks.
Many minerals, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition"; the latter two consist of multiple chemical substances. For example, charcoal is an complex polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy; the CAS index includes mixtures. Polymers always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.
However, the polymer may be defined by a known precursor or reaction and the molar mass distribution. For example, polyethylene is a mixture of long chains of -CH2- repeating units, is sold in several molar mass distributions, LDPE, MDPE, HDPE and UHMWPE; the concept of a "chemical substance" became established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. He deduced; this is now known as the law of constant composition. With the advancement of methods for chemical synthesis in the realm of organic chemistry. However, there are some controversies regarding this definition because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have the same composition, but differ in configuration of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé.
The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction; this is so, beca