Calcium hydroxide (traditionally called slaked lime) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the chemical formula Ca( OH)₂. It is a colorless crystal or white powder and is produced when quicklime (

calcium oxide Calcium oxide (formula: Ca O), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term '' lime'' connotes calcium-containing ...

) is mixed with

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. Annually, approximately 125 million tons of calcium hydroxide are produced worldwide. Calcium hydroxide has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as

E number E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E526. Limewater, also called milk of lime, is the common name for a

saturated solution In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

of calcium hydroxide.

Solubility

Calcium hydroxide is moderately soluble in water, as seen for many dihydroxides. Its solubility increases from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. Its solubility product ''K''_sp of 5.02 at 25 °C, its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction: : Ca(OH)₂ → Ca²⁺ + 2 OH⁻ The solubility is affected by the

common-ion effect In chemistry, the common-ion effect refers to the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate. This behaviour is a consequence of Le Chatelier's ...

. Its solubility drastically decreases upon addition of hydroxide or calcium sources.

Reactions

When heated to 512 °C, the

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

of water in equilibrium with calcium hydroxide reaches 101kPa (normal atmospheric pressure), which decomposes calcium hydroxide into

and water: : Ca(OH)₂ → CaO + H₂O When carbon dioxide is passed through limewater, the solution takes on a milky appearance due to

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

of insoluble

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

: : Ca(OH)₂ + CO₂ → CaCO₃ + H₂O If excess CO₂ is added: the following reaction takes place: : CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂ The milkiness disappears since calcium bicarbonate is water-soluble. Calcium hydroxide reacts with

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

. This reaction is the basis of

aerated concrete Autoclaved aerated concrete (AAC) also referred to as autoclaved cellular concrete (ACC) or simply autoclaved concrete is a lightweight, Prefabrication, prefabricated concrete building material. Developed in the mid-1920s, it is an alternat ...

. It does not corrode

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

and

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

, owing to passivation of their surface. Calcium hydroxide reacts with

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

to give

calcium hydroxychloride Calcium hydroxychloride or calcium chloride hydroxide is an inorganic compound with the chemical formula . It consists of calcium cations () and chloride () and hydroxide () anions. A white solid, it forms by the reaction of hydrogen chloride wit ...

and then

calcium chloride Calcium chloride is an inorganic compound, a Salt (chemistry), salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with cal ...

. In a process called

sulfation Sulfation (sometimes spelled sulphation in British English) is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected ...

, sulphur dioxide reacts with limewater: : Ca(OH)₂ + SO₂ → CaSO₃ + H₂O Limewater is used in a process known as

lime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and mag ...

to reduce water hardness. It is also used as a neutralizing agent in municipal waste water treatment.

Structure and preparation

Calcium hydroxide adopts a

polymeric A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, bot ...

structure, as do all metal hydroxides. The structure is identical to that of Mg(OH) (''brucite structure''); i.e., the

cadmium iodide Cadmium iodide is an inorganic compound with the formula CdI2. It is a white hygroscopic solid. It also can be obtained as a mono- and tetrahydrate. It has few applications. It is notable for its crystal structure, which is typical for compounds ...

motif. Strong

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

s exist between the layers. Calcium hydroxide is produced commercially by treating (slaking)

quicklime Calcium oxide (formula: Ca O), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term '' lime'' connotes calcium-containin ...

with water: : Alongside the production of quicklime from

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

calcination Calcination is thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), generally f ...

, this is one of the oldest known chemical reactions; evidence of

prehistoric Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

production dates back to at least 7000 BCE.

Uses

Calcium hydroxide is commonly used to prepare

lime mortar Lime mortar or torching is a masonry mortar (masonry), mortar composed of lime (material), lime and an construction aggregate, aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and anci ...

. One significant application of calcium hydroxide is as a flocculant, in water and

sewage treatment Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...

. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide. It is also used in fresh-water treatment for raising the pH of the water so that pipes will not corrode where the base water is acidic, because it is self-regulating and does not raise the pH too much. Another large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide. This conversion is part of the ''causticizing'' step in the

Kraft process The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process involves treatment of wood chip ...

for making pulp. In the causticizing operation, burned lime is added to ''

green liquor Green liquor is the dissolved smelt of sodium carbonate, sodium sulfide and other compounds from the recovery boiler in the kraft process The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood int ...

'', which is a solution primarily of

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

and

sodium sulfate Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 mill ...

produced by dissolving ''smelt'', which is the molten form of these chemicals from the recovery furnace.Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. . In

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit tree, fruit- or nut (fruit), nut-producing trees that are generally grown for commercial production. Orchards are also so ...

crops, calcium hydroxide is used as a fungicide. Applications of 'lime water' prevent the development of cankers caused by the fungal pathogen '' Neonectria galligena''. The trees are sprayed when they are dormant in winter to prevent toxic burns from the highly reactive calcium hydroxide. This use is authorised in the European Union and the United Kingdom under Basic Substance regulations. Calcium hydroxide is used in dentistry, primarily in the specialty of

endodontics Endodontics () is the Specialty (dentistry), dental specialty concerned with the study and treatment of the dental pulp. Overview Endodontics encompasses the study (practice) of the basic and clinical sciences of normal dental pulp, the etiolo ...

due to its antibacterial properties and induction of hard-tissue deposition.

Food industry

Because of its low

toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...

and the mildness of its basic properties, slaked lime is widely used in the

food industry The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditional, ...

, * In USDA certified food production in plants and livestock * To clarify raw juice from

sugarcane Sugarcane or sugar cane is a species of tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fib ...

sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and that is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together with ...

s in the

sugar industry The sugar industry subsumes the production, Sugar refinery, processing and marketing of sugars (mostly sucrose and fructose). Globally, about 80% of sugar is extracted from sugar cane, grown predominantly in the tropics, and 20% from sugar beet, ...

(see

carbonatation Carbonatation is a chemical reaction in which calcium hydroxide reacts with carbon dioxide and forms insoluble calcium carbonate: :Ca(OH)2CO2->CaCO3H_2O The process of forming a carbonate is sometimes referred to as "carbonation", although thi ...

) * To process water for alcoholic beverages and soft drinks * To increase the rate of Maillard reactions (

pretzel A pretzel ( ; from or , ) is a type of baking, baked pastry made from dough that is commonly shaped into a knot. The traditional pretzel shape is a distinctive symmetrical form, with the ends of a long strip of dough intertwined and then twi ...

s) * Pickle cucumbers and other foods * To make Chinese

century egg Century eggs (), also known as alkalized or preserved eggs, are a Chinese dish made by preserving duck, chicken, or quail eggs in a mixture of clay, ash, salt, quicklime, and rice hulls for several weeks to several months, depending on the pr ...

s * In maize preparation: removes the cellulose hull of maize kernels (see

nixtamalization Nixtamalization ( ) is a process for the preparation of maize (corn), or other cereal grain, grain, in which the grain is soaked and cooking, cooked in an alkaline solution, usually limewater (but sometimes aqueous alkali metal carbonates), ...

) * To clear a

brine Brine (or briny water) is a high-concentration solution of salt (typically sodium chloride or calcium chloride) in water. In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawat ...

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

s of calcium and

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

in the manufacture of salt for food and pharmaceutical uses * In fortifying (Ca supplement) fruit drinks, such as orange juice, and

infant formula Infant formula, also called baby formula, simply formula (American English), formula milk, baby milk, or infant milk (British English), is a manufactured food designed and marketed for feeding to babies and infants under 12 months of age, ...

* As a substitute for

baking soda Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt (chemistry), salt compose ...

in making ''

papadam A papadam (also spelled poppadom, among other variants), also known as papad, is a snack that originated in the Indian subcontinent. Dough of black gram bean flour is either deep fried or cooked with dry heat (flipped over an open flame) unt ...

'' * In the removal of carbon dioxide from controlled atmosphere produce storage rooms * In the preparation of mushroom growing substrates

Native American uses

Nixtamalized Corn maize El Salvador recipe

Nahuatl Nahuatl ( ; ), Aztec, or Mexicano is a language or, by some definitions, a group of languages of the Uto-Aztecan language family. Varieties of Nahuatl are spoken by about Nahuas, most of whom live mainly in Central Mexico and have smaller popul ...

, the language of the

Aztecs The Aztecs ( ) were a Mesoamerican civilization that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the ...

, the word for calcium hydroxide is ''nextli''. In a process called ''

'',

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

is cooked with nextli to become , also known as

hominy Hominy is a food item produced from dried maize (corn) kernels that have been treated with an alkali, in a process called nixtamalization ( is the Nahuatl word for "hominy"). "Lye hominy" is a type of hominy made with lye. History The process ...

. Nixtamalization significantly increases the bioavailability of

niacin Nicotinic acid, or niacin, is an organic compound and a vitamer of vitamin B3, an essential human nutrient. It is produced by plants and animals from the amino acid tryptophan. Nicotinic acid is also a prescription medication. Amounts f ...

(vitamin B₃), and is also considered tastier and easier to digest. Nixtamal is often ground into a flour, known as ''

masa ''Masa'' or ''masa de maíz'' (; ) is a dough made from ground nixtamalized maize. It is used for making corn tortillas, '' gorditas'', '' tamales'', '' pupusas'', and many other Latin American dishes. It is dried and powdered into a flour f ...

'', which is used to make tortillas and tamales. Limewater is used in the preparation of maize for

corn tortillas In Mexico and Central America, a corn tortilla or just tortilla (, ) is a type of thin, unleavened flatbread, made from hominy, that is the whole kernels of maize treated with alkali to improve their nutrition in a process called nixtamalizati ...

and other culinary purposes using a process known as

. Nixtamalization makes the niacin nutritionally available and prevents

pellagra Pellagra is a disease caused by a lack of the vitamin niacin (vitamin B3). Symptoms include inflamed skin, diarrhea, dementia, and sores in the mouth. Areas of the skin exposed to friction and radiation are typically affected first. Over tim ...

. Traditionally lime water was used in

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

and

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

to preserve

persimmon The persimmon () is the edible fruit of a number of species of trees in the genus '' Diospyros''. The most widely cultivated of these is the Chinese and Japanese kaki persimmon, ''Diospyros kaki''. In 2022, China produced 77% of the world's p ...

and to remove

astringency An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin '' adstringere'', which means "to bind fast". Astringency, the dry, puckering or numbing mouthfeel caused by th ...

. In chewing coca leaves, calcium hydroxide is usually chewed alongside to keep the

alkaloid Alkaloids are a broad class of natural product, naturally occurring organic compounds that contain at least one nitrogen atom. Some synthetic compounds of similar structure may also be termed alkaloids. Alkaloids are produced by a large varie ...

stimulant Stimulants (also known as central nervous system stimulants, or psychostimulants, or colloquially as uppers) are a class of drugs that increase alertness. They are used for various purposes, such as enhancing attention, motivation, cognition, ...

s chemically available for

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which su ...

by the body. Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt mollusc shells to enhance the effects. It has also been used by some indigenous South American tribes as an ingredient in ''

yopo ''Anadenanthera peregrina'', also known as yopo, jopo, cohoba, parica or calcium tree, is a perennial tree of the genus ''Anadenanthera'' native to the Caribbean and South America. It grows up to tall, and has a thorny bark. Its flowers grow ...

'', a psychedelic snuff prepared from the beans of some ''

Anadenanthera ''Anadenanthera'' is a genus of South American trees in the Legume family, Fabaceae. The genus contains two species, ''Anadenanthera colubrina, A. colubrina'' and ''Anadenanthera peregrina, A. peregrina''. These trees are known to the western wor ...

'' species.

Asian uses

Calcium hydroxide, locally known as ''chuna'', ''choona'' or ''soon'', is typically added to a bundle of

areca nut The areca nut ( or ) or betel nut () is the fruit of the areca palm (''Areca catechu''). The palm is originally native to the Philippines, but was carried widely through the tropics by the Austronesian migrations and trade since at least 15 ...

and

betel Betel (''Piper betle'') is a species of flowering plant in the pepper family Piperaceae, native to Southeast Asia. It is an evergreen, dioecious vine, with glossy heart-shaped leaves and white catkins. Betel plants are cultivated for their lea ...

leaf called "

paan Betel nut chewing, also called betel quid chewing or areca nut chewing, is a practice in which areca nuts (also called "betel nuts") are chewed together with slaked lime and betel leaves for their stimulant and narcotic effects, the prima ...

" to keep the

s chemically available to enter the bloodstream via

sublingual Sublingual (List of abbreviations used in medical prescriptions, abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through Tissue (biology), t ...

absorption. ''Choona'' is a key ingredient in Petha, contributing to its characteristic crunchy and firm texture. It is used in making '' naswar'' (also known as ''nass'' or ''niswar''), a type of dipping tobacco made from fresh tobacco leaves, ''Choona'', and wood ash. It is consumed most in the Pathan diaspora,

Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...

Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

and

Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...

. Villagers also use calcium hydroxide to paint their mud houses in Afghanistan, Pakistan and India.

Hobby uses

In buon

fresco Fresco ( or frescoes) is a technique of mural painting executed upon freshly laid ("wet") lime plaster. Water is used as the vehicle for the dry-powder pigment to merge with the plaster, and with the setting of the plaster, the painting become ...

painting, limewater is used as the colour solvent to apply on fresh plaster. Historically, it is known as the paint

whitewash Whitewash, calcimine, kalsomine, calsomine, asbestis or lime paint is a type of paint made from slaked lime ( calcium hydroxide, Ca(OH)2) or chalk (calcium carbonate, CaCO3), sometimes known as "whiting". Various other additives are sometimes ...

. Limewater is widely used by marine aquarists as a primary supplement of

calcium Calcium is a chemical element; it has 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 it ...

and

alkalinity Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...

for reef aquariums.

Coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s of order

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...

build their

endoskeleton An endoskeleton (From Ancient Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is a structural frame (skeleton) — usually composed of mineralized tissue — on the inside of an animal, overlaid by soft ...

s from

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

(a polymorph of calcium carbonate). When used for this purpose, limewater is usually referred to as ''Kalkwasser''. It is also used in tanning and making

parchment Parchment is a writing material made from specially prepared Tanning (leather), untanned skins of animals—primarily sheep, calves and goats. It has been used as a writing medium in West Asia and Europe for more than two millennia. By AD 400 ...

. The lime is used as a dehairing agent based on its alkaline properties.

Personal care and adornment

Treating one's hair with limewater causes it to stiffen and bleach, with the added benefit of killing any lice or mites living there.

Diodorus Siculus Diodorus Siculus or Diodorus of Sicily (; 1st century BC) was an ancient Greece, ancient Greek historian from Sicily. He is known for writing the monumental Universal history (genre), universal history ''Bibliotheca historica'', in forty ...

described the

Celts The Celts ( , see Names of the Celts#Pronunciation, pronunciation for different usages) or Celtic peoples ( ) were a collection of Indo-European languages, Indo-European peoples. "The Celts, an ancient Indo-European people, reached the apoge ...

as follows: "Their aspect is terrifying... They are very tall in stature, with rippling muscles under clear white skin. Their hair is blond, but not only naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads. They look like wood-demons, their hair thick and shaggy like a horse's mane. Some of them are clean-shaven, but others – especially those of high rank, shave their cheeks but leave a moustache that covers the whole mouth...". Calcium hydroxide is also applied in a leather process called liming.

Interstellar medium

The ion CaOH⁺ has been detected in the atmosphere of

S-type star An S-type star (or just S star) is a cool giant star with approximately equal quantities of carbon and oxygen in its atmosphere. The class was originally defined in 1922 by Paul Merrill for stars with unusual absorption lines and molecular bands ...

Limewater

Limewater is a saturated aqueous solution of calcium hydroxide. Calcium hydroxide is sparsely soluble at room temperature in water (1.5 g/L at 25 °C'Solubility of Inorganic and Metalorganic Compounds – A Compilation of Solubility Data from the Periodical Literature', A. Seidell, W. F. Linke, Van Nostrand (Publisher), 1953 ). "Pure" (i.e. less than or fully saturated) limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. It is basic in nature with a pH of 12.4. Limewater is named after

, not the lime fruit. Limewater may be prepared by mixing calcium hydroxide (Ca(OH)₂) with water and removing excess undissolved solute (e.g. by filtration). When excess calcium hydroxide is added (or when environmental conditions are altered, e.g. when its temperature is raised sufficiently), there results a milky solution due to the homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime.

Health risks

Unprotected exposure to Ca(OH)₂, as with any strong base, can cause skin burns, but it is not acutely toxic.

References

External links

* *
CDC – NIOSH Pocket Guide to Chemical Hazards – Calcium Hydroxide
*
MSDS Data Sheet
{{DEFAULTSORT:Calcium Hydroxide Building materials Calcium compounds Dental materials Hydroxides Inorganic compounds Intoxication E-number additives