Chloroform, or trichloromethane, is an organic compound with formula CHCl3. It is a colorless, sweet-smelling, dense liquid, produced on a large scale as a precursor to PTFE, it is a precursor to various refrigerants. It is one of a trihalomethane, it is a powerful anesthetic, euphoriant and sedative when inhaled or ingested. The molecule adopts a tetrahedral molecular geometry with C3v symmetry; the total global flux of chloroform through the environment is 660000 tonnes per year, about 90% of emissions are natural in origin. Many kinds of seaweed produce chloroform, fungi are believed to produce chloroform in soil. Abiotic process is believed to contribute to natural chloroform productions in soils although the mechanism is still unclear. Chloroform volatilizes from soil and surface water and undergoes degradation in air to produce phosgene, formyl chloride, carbon monoxide, carbon dioxide, hydrogen chloride, its half-life in air ranges from 55 to 620 days. Biodegradation in water and soil is slow.
Chloroform does not bioaccumulate in aquatic organisms. Chloroform was synthesized independently by several investigators circa 1831: Moldenhawer, a German pharmacist from Frankfurt an der Oder, appears to have produced chloroform in 1830 by mixing chlorinated lime with ethanol. Samuel Guthrie, an American physician from Sackets Harbor, New York appears to have produced chloroform in 1831 by reacting chlorinated lime with ethanol, as well as noting its anaesthetic properties. Justus von Liebig carried out the alkaline cleavage of chloral. Eugène Soubeiran obtained the compound by the action of chlorine bleach on both acetone. In 1834, French chemist Jean-Baptiste Dumas named it. In 1835, Dumas prepared the substance by the alkaline cleavage of trichloroacetic acid. Regnault prepared chloroform by chlorination of chloromethane. In 1842, Robert Mortimer Glover in London discovered the anaesthetic qualities of chloroform on laboratory animals. In 1847, Scottish obstetrician James Y. Simpson was the first to demonstrate the anaesthetic properties of chloroform on humans and helped to popularise the drug for use in medicine.
By the 1850s, chloroform was being produced on a commercial basis by using the Liebig procedure, which retained its importance until the 1960s. Today, chloroform — along with dichloromethane — is prepared and on a massive scale by the chlorination of methane and chloromethane. In industry, chloroform is produced by heating a mixture of chlorine and either chloromethane or methane. At 400–500 °C, a free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds: CH4 + Cl2 → CH3Cl + HCl CH3Cl + Cl2 → CH2Cl2 + HCl CH2Cl2 + Cl2 → CHCl3 + HClChloroform undergoes further chlorination to yield carbon tetrachloride: CHCl3 + Cl2 → CCl4 + HClThe output of this process is a mixture of the four chloromethanes, which can be separated by distillation. Chloroform may be produced on a small scale via the haloform reaction between acetone and sodium hypochlorite: 3 NaClO + 2CO → CHCl3 + 2 NaOH + NaOCOCH3 Deuterated chloroform is an isotopologue of chloroform with a single deuterium atom.
CDCl3 is a common solvent used in NMR spectroscopy. Deuterochloroform is produced by the haloform reaction, the reaction of acetone with sodium hypochlorite or calcium hypochlorite; the haloform process is now obsolete for the production of ordinary chloroform. Deuterochloroform can be prepared by the reaction of sodium deuteroxide with chloral hydrate; the haloform reaction can occur inadvertently in domestic settings. Bleaching with hypochlorite generates halogenated compounds in side reactions. Sodium hypochlorite solution mixed with common household liquids such as acetone, methyl ethyl ketone, ethanol, or isopropyl alcohol can produce some chloroform, in addition to other compounds such as chloroacetone or dichloroacetone. In terms of scale, the most important reaction of chloroform is with hydrogen fluoride to give monochlorodifluoromethane, a precursor in the production of polytetrafluoroethylene: CHCl3 + 2 HF → CHClF2 + 2 HClThe reaction is conducted in the presence of a catalytic amount of mixed antimony halides.
Chlorodifluoromethane is converted into tetrafluoroethylene, the main precursor to Teflon. Before the Montreal Protocol, chlorodifluoromethane was a popular refrigerant; the hydrogen attached to carbon in chloroform participates in hydrogen bonding. Worldwide, chloroform is used in pesticide formulations, as a solvent for fats, rubber, waxes, gutta-percha, resins, as a cleansing agent, grain fumigant, in fire extinguishers, in the rubber industry. CDCl3 is a common solvent used in NMR spectroscopy; as a reagent, chloroform serves as a source of the dichlorocarbene CCl2 group. It reacts with aqueous sodium hydroxide in the presence of a phase transfer catalyst to produce dichlorocarbene, CCl2; this reagent effects ortho-formylation of activated aromatic rings such as phenols, producing aryl aldehydes in a reaction known as the Reimer–Tiemann reaction. Alternatively, the carbene can be trapped by an alkene to form a cyclopropane derivative. In the Kharasch addition, chloroform forms the CHCl2 free radical in addition to alkenes.
The anaesthetic qualities of chloroform were first described in 1842 in a thesis by Robert Mortimer Glover, which won t
Diethyl ether, or ether, is an organic compound in the ether class with the formula 2O, sometimes abbreviated as Et2O. It is a colorless volatile flammable liquid, it is used as a solvent in laboratories and as a starting fluid for some engines. It was used as a general anesthetic, until non-flammable drugs were developed, such as halothane, it has been used as a recreational drug to cause intoxication. Most diethyl ether is produced as a byproduct of the vapor-phase hydration of ethylene to make ethanol; this process uses solid-supported phosphoric acid catalysts and can be adjusted to make more ether if the need arises. Vapor-phase dehydration of ethanol over some alumina catalysts can give diethyl ether yields of up to 95%. Diethyl ether can be prepared both in laboratories and on an industrial scale by the acid ether synthesis. Ethanol is mixed with a strong acid sulfuric acid, H2SO4; the acid dissociates in the aqueous environment producing hydronium ions, H3O+. A hydrogen ion protonates the electronegative oxygen atom of the ethanol, giving the ethanol molecule a positive charge: CH3CH2OH + H3O+ → CH3CH2OH2+ + H2OA nucleophilic oxygen atom of unprotonated ethanol displaces a water molecule from the protonated ethanol molecule, producing water, a hydrogen ion and diethyl ether.
CH3CH2OH2+ + CH3CH2OH → H2O + H+ + CH3CH2OCH2CH3This reaction must be carried out at temperatures lower than 150 °C in order to ensure that an elimination product is not a product of the reaction. At higher temperatures, ethanol will dehydrate to form ethylene; the reaction to make diethyl ether is reversible, so an equilibrium between reactants and products is achieved. Getting a good yield of ether requires that ether be distilled out of the reaction mixture before it reverts to ethanol, taking advantage of Le Chatelier's principle. Another reaction that can be used for the preparation of ethers is the Williamson ether synthesis, in which an alkoxide performs a nucleophilic substitution upon an alkyl halide, it is important as a solvent in the production of cellulose plastics such as cellulose acetate. Diethyl ether has a high cetane number of 85–96 and is used as a starting fluid, in combination with petroleum distillates for gasoline and Diesel engines because of its high volatility and low flash point.
Ether starting fluid is sold and used in countries with cold climates, as it can help with cold starting an engine at sub-zero temperatures. For the same reason it is used as a component of the fuel mixture for carbureted compression ignition model engines. In this way diethyl ether is similar to one of its precursors, ethanol. Diethyl ether is a common laboratory aprotic solvent, it has limited solubility in water and dissolves 1.5 g/100 g water at 25 °C. This, coupled with its high volatility, makes it ideal for use as the non-polar solvent in liquid-liquid extraction; when used with an aqueous solution, the diethyl ether layer is on top as it has a lower density than the water. It is a common solvent for the Grignard reaction in addition to other reactions involving organometallic reagents. Due to its application in the manufacturing of illicit substances, it is listed in the Table II precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances as well as substances such as acetone and sulfuric acid.
William T. G. Morton participated in a public demonstration of ether anesthesia on October 16, 1846 at the Ether Dome in Boston, Massachusetts. However, Crawford Williamson Long, is now known to have demonstrated its use as a general anesthetic in surgery to officials in Georgia, as early as March 30, 1842, Long publicly demonstrated ether's use as a surgical anesthetic on six occasions before the Boston demonstration. British doctors were aware of the anesthetic properties of ether as early as 1840 where it was prescribed in conjunction with opium. Diethyl ether supplanted the use of chloroform as a general anesthetic due to ether's more favorable therapeutic index, that is, a greater difference between an effective dose and a toxic dose. Diethyl ether increases tracheobronchial secretions. Diethyl ether could be mixed with other anesthetic agents such as chloroform to make C. E. mixture, or chloroform and alcohol to make A. C. E. Mixture. In the 21st century, ether is used; the use of flammable ether was displaced by nonflammable fluorinated hydrocarbon anesthetics.
Halothane was the first such anesthetic developed and other used inhaled anesthetics, such as isoflurane and sevoflurane, are halogenated ethers. Diethyl ether was found to have undesirable side effects, such as post-anesthetic nausea and vomiting. Modern anesthetic agents reduce these side effects. Prior to 2005 it was on the World Health Organization's List of Essential Medicines for use as an anesthetic. Ether was once used in pharmaceutical formulations. A mixture of alcohol and ether, one part of diethyl ether and three parts of ethanol, was known as "Spirit of ether", Hoffman's Anodyne or Hoffman's Drops. In the United States this concoction was removed from the Pharmacopeia at some point prior to June 1917, as a study published by William Procter, Jr. in the American Journal of Pharmacy as early as 1852 showed that there were differences in formulation to be found between commercial manufacturers, between international pharmacopoeia, from Hoffman's original recipe. The anesthetic and intoxicating effects of ether have made it a recreational drug.
Diethyl ether in anesthetic dosage is an inhalant which has a long history
Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature and presence of other chemicals of the solution; the extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. Insolubility is the inability to dissolve in a liquid or gaseous solvent. Most the solvent is a liquid, which can be a pure substance or a mixture. One may speak of solid solution, but of solution in a gas. Under certain conditions, the equilibrium solubility can be exceeded to give a so-called supersaturated solution, metastable. Metastability of crystals can lead to apparent differences in the amount of a chemical that dissolves depending on its crystalline form or particle size.
A supersaturated solution crystallises when'seed' crystals are introduced and rapid equilibration occurs. Phenylsalicylate is one such simple observable substance when melted and cooled below its fusion point. Solubility is not to be confused with the ability to'dissolve' a substance, because the solution might occur because of a chemical reaction. For example, zinc'dissolves' in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction; the zinc ions are soluble in the acid. The solubility of a substance is an different property from the rate of solution, how fast it dissolves; the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, inorganic, physical and biochemistry. In all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water, a solvent for most ionic compounds as well as a wide range of organic substances.
This is a crucial factor in much environmental and geochemical work. According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, mole fraction, mole ratio, mass per volume and other units; the extent of solubility ranges from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is applied to poorly or poorly soluble compounds. A number of other descriptive terms are used to qualify the extent of solubility for a given application. For example, U. S. Pharmacopoeia gives the following terms: The thresholds to describe something as insoluble, or similar terms, may depend on the application. For example, one source states that substances are described as "insoluble" when their solubility is less than 0.1 g per 100 mL of solvent. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining.
The solubility equilibrium occurs. The term solubility is used in some fields where the solute is altered by solvolysis. For example, many metals and their oxides are said to be "soluble in hydrochloric acid", although in fact the aqueous acid irreversibly degrades the solid to give soluble products, it is true that most ionic solids are dissolved by polar solvents, but such processes are reversible. In those cases where the solute is not recovered upon evaporation of the solvent, the process is referred to as solvolysis; the thermodynamic concept of solubility does not apply straightforwardly to solvolysis. When a solute dissolves, it may form several species in the solution. For example, an aqueous suspension of ferrous hydroxide, Fe2, will contain the series + as well as other species. Furthermore, the solubility of ferrous hydroxide and the composition of its soluble components depend on pH. In general, solubility in the solvent phase can be given only for a specific solute, thermodynamically stable, the value of the solubility will include all the species in the solution.
Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ though they are both polymorphs of calcium carbonate and have the same chemical formula; the solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance. Solubility may strongly depend on the presence of other species dissolved in the solvent, for example, complex-forming anions in liquids. Solubility will depend on the excess or deficiency of a common ion in the solution, a phenomenon known as the common-ion effect. To a lesser extent, solubility will depend on the ionic strength of solutions; the last two effects can be quantified using the equation for solubility equilibrium. For a solid that dissolves in a redox reaction, solubility is expe
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light propagates through the material. It is defined as n = c v, where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times as fast in vacuum as in water. The refractive index determines how much the path of light is bent, or refracted, when entering a material; this is described by Snell's law of refraction, n1 sinθ1 = n2 sinθ2, where θ1 and θ2 are the angles of incidence and refraction of a ray crossing the interface between two media with refractive indices n1 and n2. The refractive indices determine the amount of light, reflected when reaching the interface, as well as the critical angle for total internal reflection and Brewster's angle; the refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, the wavelength in that medium is λ = λ0/n, where λ0 is the wavelength of that light in vacuum.
This implies that vacuum has a refractive index of 1, that the frequency of the wave is not affected by the refractive index. As a result, the energy of the photon, therefore the perceived color of the refracted light to a human eye which depends on photon energy, is not affected by the refraction or the refractive index of the medium. While the refractive index affects wavelength, it depends on photon frequency and energy so the resulting difference in the bending angle causes white light to split into its constituent colors; this is called dispersion. It can be observed in prisms and rainbows, chromatic aberration in lenses. Light propagation in absorbing materials can be described using a complex-valued refractive index; the imaginary part handles the attenuation, while the real part accounts for refraction. The concept of refractive index applies within the full electromagnetic spectrum, from X-rays to radio waves, it can be applied to wave phenomena such as sound. In this case the speed of sound is used instead of that of light, a reference medium other than vacuum must be chosen.
The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, the phase velocity v of light in the medium, n = c v. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves; the definition above is sometimes referred to as the absolute refractive index or the absolute index of refraction to distinguish it from definitions where the speed of light in other reference media than vacuum is used. Air at a standardized pressure and temperature has been common as a reference medium. Thomas Young was the person who first used, invented, the name "index of refraction", in 1807. At the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers; the ratio had the disadvantage of different appearances. Newton, who called it the "proportion of the sines of incidence and refraction", wrote it as a ratio of two numbers, like "529 to 396".
Hauksbee, who called it the "ratio of refraction", wrote it as a ratio with a fixed numerator, like "10000 to 7451.9". Hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in 1807. In the next years, others started using different symbols: n, m, µ; the symbol n prevailed. For visible light most transparent media have refractive indices between 1 and 2. A few examples are given in the adjacent table; these values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, as is conventionally done. Gases at atmospheric pressure have refractive indices close to 1 because of their low density. All solids and liquids have refractive indices above 1.3, with aerogel as the clear exception. Aerogel is a low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the other end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, but some high-refractive-index polymers can have values as high as 1.76.
For infrared light refractive indices can be higher. Germanium is transparent in the wavelength region from 2 to 14 µm and has a refractive index of about 4. A type of new materials, called topological insulator, was found holding higher refractive index of up to 6 in near to mid infrared frequency range. Moreover, topological insulator material are transparent; these excellent properties make them a type of significant materials for infrared optics. According to the theory of relativity, no information can travel faster than the speed of light in vacuum, but this does not mean that the refractive index cannot be lower than 1; the refractive index measures the phase velocity of light. The phase velocity is the speed at which the crests of the wave move and can be faster than the speed of light in vacuum, thereby give a refractive index below 1; this can occur close to resonance frequencies, for absorbing media, in plasmas, for X-rays. In the X-ray regime the refractive indices are
Palm kernel oil
Palm kernel oil is an edible plant oil derived from the kernel of the oil palm Elaeis guineensis. It should not be confused with the other two edible oils derived from palm fruits: palm oil, extracted from the pulp of the oil palm fruit, coconut oil, extracted from the kernel of the coconut. Palm kernel oil, palm oil, coconut oil are three of the few saturated vegetable fats. Palm kernel oil, semi-solid at room temperature, is more saturated than palm oil and comparable to coconut oil. Oil from the African oil palm Elaeis. European merchants trading with West Africa purchased palm oil for use in Europe, but palm kernel oil remained rare outside West Africa; the USDA has published historical production figures for palm kernel oil for years beginning October 1 and ending September 30: In the 1960s, research and development in oil palm breeding began to expand after Malaysia's Department of Agriculture established an exchange program with West African economies and four private plantations formed the Oil Palm Genetics Laboratory.
The Malaysian government established Kolej Serdang, which became the Universiti Pertanian Malaysia in the 1970s to train agricultural and agroindustrial engineers and agribusiness graduates to conduct research in the field. In 1979 with support from the Malaysian Agricultural Research and Development Institute and UPM, the government set up the Palm Oil Research Institute of Malaysia, a public-and-private-coordinated institution. B. C. Sekhar was appointed chairman. Porim's scientists work in oil palm tree breeding, palm oil nutrition and potential oleochemical use. Porim was renamed Malaysian Palm Oil Board in 2000. Palm kernel oil to coconut oil, is high in saturated fats and is more saturated than palm oil. Palm kernel oil is high in lauric acid, shown to raise blood cholesterol levels, both as LDL-C and HDL-C. However, the raise in total cholesterol concentration is due to more HDL-C than LDL-C. Palm kernel oil does not contain cholesterol or trans fatty acids. Palm kernel oil is used in commercial cooking because it is lower in cost than other oils and remains stable at high cooking temperatures.
The oil can be stored longer than other vegetable oils. The approximate concentration of fatty acids in palm kernel oil is as follows: Splitting of oils and fats by hydrolysis, or under basic conditions saponification, yields fatty acids, with glycerin as a byproduct; the split-off fatty acids are a mixture ranging depending on the type of oil or fat. Resembling coconut oil, palm kernel oil is packed with myristic and lauric fatty acids and therefore suitable for the manufacture of soaps, washing powders and personal care products. Lauric acid is important in soap making: a good soap must contain at least 15 per cent laurate for quick lathering, while soap made for use in sea water is based on 100 per cent laurate. Derivatives of palmitic acid were used in combination with naphtha during World War II to produce napalm. Palm kernel Tropical agriculture Food vs. fuel Palm Oil - Production, Consumption and Imports Statistics by Country Blood on the Palms: Afro-Colombians fight new plantations by David Bacon, July/August 2007 Dollars & Sense
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t