Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2. It is a white coloured crystalline solid at room temperature soluble in water. Calcium chloride is encountered as a hydrated solid with generic formula CaCl2x, where x = 0, 1, 2, 4, 6; these compounds are used for de-icing and dust control. Because the anhydrous salt is hygroscopic, it is used as a desiccant. By depressing the freezing point of water, calcium chloride is used to prevent ice formation and is used to de-ice; this application consumes the greatest amount of calcium chloride. Calcium chloride is harmless to plants and soil; as a de-icing agent, it is much more effective at lower temperatures than sodium chloride. When distributed for this use, it takes the form of small, white spheres a few millimeters in diameter, called prills. Solutions of calcium chloride can prevent freezing at temperature as low as −52 °C, making it ideal for filling agricultural implement tires as a liquid ballast, aiding traction in cold climates.
It is used in domestic and industrial chemical air dehumidifiers. The second largest application of calcium chloride exploits hygroscopic properties and the tackiness of its hydrates. A concentrated solution keeps a liquid layer on the surface of dirt roads, which suppresses formation of dust, it keeps. If these are allowed to blow away, the large aggregate begins to shift around and the road breaks down. Using calcium chloride reduces the need for grading by as much as 50% and the need for fill-in materials as much as 80%; the average intake of calcium chloride as food additives has been estimated to be 160–345 mg/day. Calcium chloride is permitted as a food additive in the European Union for use as a sequestrant and firming agent with the E number E509, it is considered as recognized as safe by the U. S. Food and Drug Administration, its use in organic crop production is prohibited under the US National Organic Program. In marine aquariums, calcium chloride is one way to introduce bioavailable calcium for calcium carbonate-shelled animals such as mollusks and some cnidarians.
Calcium hydroxide or a calcium reactor can be used. As a firming agent, calcium chloride is used in canned vegetables, in firming soybean curds into tofu and in producing a caviar substitute from vegetable or fruit juices, it is used as an electrolyte in sports drinks and other beverages, including bottled water. The salty taste of calcium chloride is used to flavor pickles without increasing the food's sodium content. Calcium chloride's freezing-point depression properties are used to slow the freezing of the caramel in caramel-filled chocolate bars, it is added to sliced apples to maintain texture. In brewing beer, calcium chloride is sometimes used to correct mineral deficiencies in the brewing water, it affects flavor and chemical reactions during the brewing process, can affect yeast function during fermentation. In cheesemaking, calcium chloride is sometimes added to processed milk to restore the natural balance between calcium and protein in casein, it is added before the coagulant. Calcium chloride is used to prevent cork spot and bitter pit on apples by spraying on the tree during the late growing season.
Drying tubes are packed with calcium chloride. Kelp is dried with calcium chloride for use in producing sodium carbonate. Anhydrous calcium chloride has been approved by the FDA as a packaging aid to ensure dryness; the hydrated salt can be dried for re-use but will dissolve in its own water of hydration if heated and form a hard amalgamated solid when cooled. Calcium chloride is used in concrete mixes to accelerate the initial setting, but chloride ions lead to corrosion of steel rebar, so it should not be used in reinforced concrete; the anhydrous form of calcium chloride may be used for this purpose and can provide a measure of the moisture in concrete. Calcium chloride is included as an additive in plastics and in fire extinguishers, in wastewater treatment as a drainage aid, in blast furnaces as an additive to control scaffolding, in fabric softener as a thinner; the exothermic dissolution of calcium chloride is used in self-heating cans and heating pads. In the oil industry, calcium chloride is used to increase the density of solids-free brines.
It is used to provide inhibition of swelling clays in the water phase of invert emulsion drilling fluids. CaCl2 acts as flux material in the Davy process for the industrial production of sodium metal, through the electrolysis of molten NaCl. CaCl2 is used as a flux and electrolyte in the FFC Cambridge process for titanium production, where it ensures the proper exchange of calcium and oxygen ions between the electrodes. Calcium chloride is used in the production of activated charcoal. Calcium chloride is an ingredient used in ceramic slipware, it suspends clay particles so that they float within the solution making it easier to use in a variety of slipcasting techniques. Calcium chloride dihydrate dissolved in ethanol has been used as a sterilant for male animals; the solution is injected into the testes of the animal. Within 1 month, necrosis of testicular tissue results in sterilization. Calcium chloride can act as an irritant by desiccating moist skin. Solid calcium chloride dissolves exothermically, burns can result in the mouth and esophagus if it is ingested.
Ingestion of concentrated solutions or solid products may cause gastrointestinal irritation or ulceration. Consumption of calcium
Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air, its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium; the most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life. The name derives from Latin calx "lime", obtained from heating limestone; some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, in the manufacture of soaps.
On the other hand, the metal in pure form has few applications due to its high reactivity. Calcium is the fifth-most abundant element in the human body; as electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation. Calcium is a ductile silvery metal whose properties are similar to the heavier elements in its group, strontium and radium. A calcium atom has twenty electrons, arranged in the electron configuration 4s2. Like the other elements placed in group 2 of the periodic table, calcium has two valence electrons in the outermost s-orbital, which are easily lost in chemical reactions to form a dipositive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is always divalent in its compounds, which are ionic.
Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX2 is much higher than those of the hypothetical MX. This occurs because of the much greater lattice energy afforded by the more charged Ca2+ cation compared to the hypothetical Ca+ cation. Calcium, strontium and radium are always considered to be alkaline earth metals. Beryllium and magnesium are different from the other members of the group in their physical and chemical behaviour: they behave more like aluminium and zinc and have some of the weaker metallic character of the post-transition metals, why the traditional definition of the term "alkaline earth metal" excludes them; this classification is obsolete in English-language sources, but is still used in other countries such as Japan. As a result, comparisons with strontium and barium are more germane to calcium chemistry than comparisons with magnesium.
Calcium metal melts at 842 °C and boils at 1494 °C. It crystallises in the face-centered cubic arrangement like strontium, its density of 1.55 g/cm3 is the lowest in its group. Calcium can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its low density. While calcium is infeasible as a conductor for most terrestrial applications as it reacts with atmospheric oxygen, its use as such in space has been considered; the chemistry of calcium is that of a typical heavy alkaline earth metal. For example, calcium spontaneously reacts with water more than magnesium and less than strontium to produce calcium hydroxide and hydrogen gas, it reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride. When finely divided, it spontaneously burns in air to produce the nitride. In bulk, calcium is less reactive: it forms a hydration coating in moist air, but below 30% relative humidity it may be stored indefinitely at room temperature.
Besides the simple oxide CaO, the peroxide CaO2 can be made by direct oxidation of calcium metal under a high pressure of oxygen, there is some evidence for a yellow superoxide Ca2. Calcium hydroxide, Ca2, is a strong base, though it is not as strong as the hydroxides of strontium, barium or the alkali metals. All four dihalides of calcium are known. Calcium carbonate and calcium sulfate are abundant minerals. Like strontium and barium, as well as the alkali metals and the divalent lanthanides europium and ytterbium, calcium metal dissolves directly in liquid ammonia to give a dark blue solution. Due to the large size of the Ca2+ ion, high coordination numbers are common, up to 24 in some intermetallic compounds such as CaZn13. Calcium is complexed by oxygen chelates such as EDTA and polyphosphates, which are useful in an
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
In chemistry, an alcohol is any organic compound in which the hydroxyl functional group is bound to a carbon. The term alcohol referred to the primary alcohol ethanol, used as a drug and is the main alcohol present in alcoholic beverages. An important class of alcohols, of which methanol and ethanol are the simplest members, includes all compounds for which the general formula is CnH2n+1OH, it is these simple monoalcohols. The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; when a higher priority group is present in the compound, the prefix hydroxy- is used in its IUPAC name. The suffix -ol in non-IUPAC names typically indicates that the substance is an alcohol. However, many substances that contain hydroxyl functional groups have names which include neither the suffix -ol, nor the prefix hydroxy-. Alcohol distillation originated in India. During 2000 BCE, people of India used. Alcohol distillation was known to Islamic chemists as early as the eighth century.
The Arab chemist, al-Kindi, unambiguously described the distillation of wine in a treatise titled as "The Book of the chemistry of Perfume and Distillations". The Persian physician, alchemist and philosopher Rhazes is credited with the discovery of ethanol; the word "alcohol" is from a powder used as an eyeliner. Al- is the Arabic definite article, equivalent to the in English. Alcohol was used for the fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide Sb2S3, it was considered to be the essence or "spirit" of this mineral. It was used as an antiseptic and cosmetic; the meaning of alcohol was extended to distilled substances in general, narrowed to ethanol, when "spirits" was a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, introduces the word as a term used by "barbarous" authors for "fine powder." Vigo wrote: "the barbarous auctours use alcohol, or alcofoll, for moost fine poudre."The 1657 Lexicon Chymicum, by William Johnson glosses the word as "antimonium sive stibium."
By extension, the word came to refer to any fluid obtained by distillation, including "alcohol of wine," the distilled essence of wine. Libavius in Alchymia refers to "vini alcohol vel vinum alcalisatum". Johnson glosses alcohol vini as "quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat." The word's meaning became restricted to "spirit of wine" in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850. The term ethanol was invented 1892, combining the word ethane with the "-ol" ending of "alcohol". IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important in cases where the relative complexity of the molecule does not make such a systematic name unwieldy. In naming simple alcohols, the name of the alkane chain loses the terminal e and adds the suffix -ol, e.g. as in "ethanol" from the alkane chain name "ethane".
When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the -ol: propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CHCH3. If a higher priority group is present the prefix hydroxy-is used, e.g. as in 1-hydroxy-2-propanone. In cases where the OH functional group is bonded to an sp2 carbon on an aromatic ring the molecule is known as a phenol, is named using the IUPAC rules for naming phenols. In other less formal contexts, an alcohol is called with the name of the corresponding alkyl group followed by the word "alcohol", e.g. methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain; as described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is indicated using the "hydroxy-" prefix. Alcohols are classified into primary and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group.
The primary alcohols have general formulas RCH2OH. The simplest primary alcohol is methanol, for which R=H, the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RR'CHOH, the simplest of, 2-propanol. For the tertiary alcohols the general form is RR'R"COH; the simplest example is tert-butanol, for which each of R, R', R" is CH3. In these shorthands, R, R', R" represent substituents, alkyl or other attached organic groups. In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, 3COH can be named trimethylcarbinol. Alcohols have a long history of myriad uses. For simple mono-alcohols, the focus on this article, the following are most important industrial alcohols: methanol for the production of formaldehyde and as a fuel additive ethanol for alcoholic beverages, fuel additive, solvent 1-propanol, 1-butanol, isobutyl alcohol for use as a solvent a
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.
Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are intermediate between them. Chlorine is a yellow-green gas at room temperature, it is an reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the Pauling scale, behind only oxygen and fluorine. The most common compound of chlorine, sodium chloride, has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, but not recognised as a fundamentally important substance. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, this was confirmed by Sir Humphry Davy in 1810, who named it from Ancient Greek: χλωρός, translit. Khlôros, lit.'pale green' based on its colour.
Because of its great reactivity, all chlorine in the Earth's crust is in the form of ionic chloride compounds, which includes table salt. It is the second-most abundant halogen and twenty-first most abundant chemical element in Earth's crust; these crustal deposits are dwarfed by the huge reserves of chloride in seawater. Elemental chlorine is commercially produced from brine by electrolysis; the high oxidising potential of elemental chlorine led to the development of commercial bleaches and disinfectants, a reagent for many processes in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, many intermediates for the production of plastics and other end products which do not contain the element; as a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary. Elemental chlorine at high concentrations is dangerous and poisonous for all living organisms, was used in World War I as the first gaseous chemical warfare agent.
In the form of chloride ions, chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms, artificially produced chlorinated organics range from inert to toxic. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion. Small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of the immune response against bacteria; the most common compound of chlorine, sodium chloride, has been known since ancient times. Its importance in food was well known in classical antiquity and was sometimes used as payment for services for Roman generals and military tribunes. Elemental chlorine was first isolated around 1200 with the discovery of aqua regia and its ability to dissolve gold, since chlorine gas is one of the products of this reaction: it was however not recognised as a new substance. Around 1630, chlorine was recognized as a gas by the Flemish chemist and physician Jan Baptist van Helmont.
The element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele, he is credited with the discovery. Scheele produced chlorine by reacting MnO2 with HCl: 4 HCl + MnO2 → MnCl2 + 2 H2O + Cl2Scheele observed several of the properties of chlorine: the bleaching effect on litmus, the deadly effect on insects, the yellow-green color, the smell similar to aqua regia, he called it "dephlogisticated muriatic acid air" since it is a gas and it came from hydrochloric acid. He failed to establish chlorine as an element. Common chemical theory at that time held that an acid is a compound that contains oxygen, so a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum. In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum, they did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced.
In 1810, Sir Humphry Davy tried the same experiment again, concluded that the substance was an element, not a compound. He announced his results to the Royal Society on 15 November that year. At that time, he named this new element "chlorine", from the Greek word χλωρος, meaning green-yellow; the name "halogen", meaning "salt producer", was used for chlorine in 1811 by Johann Salomo Christoph Schweigger. This term was used as a generic term to describe all the elements in the chlorine family, after a suggestion by Jöns Jakob Berzelius in 1826. In 1823, Michael Faraday liquefied chlorine for the first time, demonstrated that what was known as "solid chlorine" had a structure of chlorine hydrate. Chlorine gas was first used by French chemist Claude Berthollet to bleach textiles in 1785. Modern bleaches resulted from further work by Berthollet, who first produced sodium hypochlorite in 1789 in his laboratory in the town of Javel, by passing chlorine gas through a solution of sodium carbonate; the resulting liqu
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.