Calcium sulfide

Calcium sulfide is the chemical compound with the formula CaS. This white material crystallizes in cubes like rock salt. CaS has been studied as a component in a process that would recycle gypsum, a product of flue-gas desulfurization. Like many salts containing sulfide ions, CaS typically has an odour of H2S, which results from small amount of this gas formed by hydrolysis of the salt.

In terms of its atomic structure, CaS crystallizes in the same motif as sodium chloride indicating that the bonding in this material is highly ionic. The high melting point is also consistent with its description as an ionic solid. In the crystal, each S2− ion is surrounded by an octahedron of six Ca2+ ions, and complementarily, each Ca2+ ion surrounded by six S2− ions.

Calcium sulfide
Calcium sulfide
IUPAC name
Calcium sulfide
Other names
Calcium monosulfide,
Hepar calcies,
Sulfurated lime
3D model (JSmol)
ECHA InfoCard 100.039.869
EC Number 243-873-5
Molar mass 72.143 g/mol
Appearance white crystals
Density 2.59 g/cm3
Melting point 2,525 °C (4,577 °F; 2,798 K)
Solubility insoluble in alcohol
reacts with acid
Halite (cubic), cF8
Fm3m, No. 225
Octahedral (Ca2+); octahedral (S2−)
Main hazards H2S source
Irritant (Xi)
Dangerous for the environment (N)
R-phrases (outdated) R31, R36/37/38, R50
S-phrases (outdated) (S2), S28, S61
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorineSpecial hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Other anions
Calcium oxide
Other cations
Magnesium sulfide
Strontium sulfide
Barium sulfide
Related sulfides
Sodium sulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).


CaS is produced by "carbothermic reduction" of calcium sulfate, which entails the conversion of carbon, usually as charcoal, to carbon dioxide:

CaSO4 + 2 C → CaS + 2 CO2

and can react further:

3 CaSO4 + CaS → 4 CaO + 4 SO2

In the second reaction the sulfate (+6 oxidation state) oxidizes the sulfide (-2 oxidation state) to sulfur dioxide (+4 oxidation state), while it is being reduced to sulfur dioxide itself (+4 oxidation state).

CaS is also a byproduct in the Leblanc process, a once major industrial process for producing sodium carbonate. In that process sodium sulfide reacts with calcium carbonate:[1]

Na2S + CaCO3 → CaS + Na2CO3

Millions of tons of this calcium sulfide byproduct was discarded, causing extensive pollution and controversy.[2]

Milk of lime, Ca(OH)2, reacts with elemental sulfur to give a "lime-sulfur", which has been used as an insecticide. The active ingredient is probably a calcium polysulfide, not CaS.[3]

Reactivity and uses

Calcium sulfide decomposes upon contact with water, including moist air, giving a mixture of Ca(SH)2, Ca(OH)2, and Ca(SH)(OH).

CaS + H2O → Ca(SH)(OH)
Ca(SH)(OH) + H2O → Ca(OH)2 + H2S

It reacts with acids such as hydrochloric acid to release toxic hydrogen sulfide gas.

CaS + 2 HCl → CaCl2 + H2S

Natural occurrence

Oldhamite is the name for mineralogical form of CaS. It is a rare component of some meteorites and has scientific importance in solar nebula research. Burning of coal dumps can also produce the compound.

See also


  1. ^ Christian Thieme (2000). "Sodium Carbonates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_299. ISBN 978-3527306732.
  2. ^ Kiefer, David M. (January 2002). "It was all about alkali". Today's Chemist at Work. 11 (1): 45–6.
  3. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
Barium sulfide

Barium sulfide is the inorganic compound with the formula BaS. BaS is an important precursor to other barium compounds including BaCO3 and the pigment lithopone, ZnS/BaSO4. Like other chalcogenides of the alkaline earth metals, BaS is a short wavelength emitter for electronic displays. It is colorless, although like many sulfides, it is commonly obtained in impure colored forms.

Calcium bromate

Calcium bromate, Ca(BrO3)2, is a calcium salt of bromic acid. It is most commonly encountered as the monohydrate, Ca(BrO3)2•H2O.It can be prepared by reacting calcium hydroxide with sodium bromate or calcium sulfate with barium bromate. Above 180 °C, calcium bromate decomposes to form calcium bromide and oxygen. In theory, electrolysis of calcium bromide solution will also yield calcium bromate.

It is used as a bread dough and flour "improver" or conditioner (E number E924b) in some countries.

Calcium carbide

Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.The pure material is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.Applications of calcium carbide include manufacture of acetylene gas, and for generation of acetylene in carbide lamps; manufacture of chemicals for fertilizer; and in steelmaking.

Calcium oxide

Calcium oxide (CaO), 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 inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is called free lime.Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide, of which quicklime is the base anhydride) are important commodity chemicals.

Divinyl sulfide

Divinyl sulfide is the organosulfur compound with the formula S(CH=CH2)2. It is a colorless liquid with a faint odor. It is found in the oil of some species of Allium.It is notable as the product from hydrogen sulfide and acetylene, a combination that arises when acetylene is generated by hydrolysis of technical grade calcium carbide, which contains impurities of calcium sulfide.Divinylsulfide was first prepared in 1920 by the reaction of sulfur mustard with sodium ethoxide:

(ClCH2CH2)2S + 2 NaOEt → (CH2=CH)2S + 2 EtOH + 2 NaClA variety of monovinyl sulfides are known, often arising from the reactions of thiols and acetylenes.

Döbereiner's triads

In the history of the periodic table, Döbereiner's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Döbereiner's observations of the alkaline earths; namely, that strontium had properties that were intermediate to those of calcium and barium. By 1829, Döbereiner had found other groups of three elements (hence "triads") whose physical properties were similarly related. He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.

Galoter process

The Galoter process (also known as TSK, UTT, or SHC; its newest modifications are called Enefit and Petroter) is a shale oil extraction technology for a production of shale oil, a type of synthetic crude oil. In this process, the oil shale is decomposed into shale oil, oil shale gas, and spent residue. A decomposition is caused by mixing raw oil shale with a hot oil shale ash, generated by combustion of carbonaceous residue (semi-coke) in the spent residue. The process was developed in 1950s and it is used commercially for the shale oil production in Estonia. There are projects for further development of this technology and for expansion of its usage, e.g. in Jordan and USA.


Homeopathy or homœopathy is a system of alternative medicine created in 1796 by Samuel Hahnemann, based on his doctrine of like cures like (similia similibus curentur), a claim that a substance that causes the symptoms of a disease in healthy people would cure similar symptoms in sick people. Homeopathy is a pseudoscience – a belief that is incorrectly presented as scientific. Homeopathic preparations are not effective for treating any condition; large-scale studies have found homeopathy to be no more effective than a placebo, indicating that any positive effects that follow treatment are not due to the treatment itself but instead to factors such as normal recovery from illness, or regression toward the mean.Hahnemann believed the underlying causes of disease were phenomena that he termed miasms, and that homeopathic preparations addressed these. The preparations are manufactured using a process of homeopathic dilution, in which a chosen substance is repeatedly diluted in alcohol or distilled water, each time with the containing vessel being struck against an elastic material, commonly a leather-bound book. Dilution typically continues well past the point where no molecules of the original substance remain. Homeopaths select homeopathics by consulting reference books known as repertories, and by considering the totality of the patient's symptoms, personal traits, physical and psychological state, and life history.Homeopathy is not a plausible system of treatment, as its dogmas about how drugs, illness, the human body, liquids and solutions operate are contradicted by a wide range of discoveries across biology, psychology, physics and chemistry made in the two centuries since its invention. Although some clinical trials produce positive results, multiple systematic reviews have shown that this is because of chance, flawed research methods, and reporting bias. Homeopathic practice has been criticized as unethical because it discourages the use of effective treatments, with the World Health Organization warning against using homeopathy to try to treat severe diseases such as HIV and malaria. The continued practice of homeopathy, despite a lack of evidence of efficacy, has led to it being characterized within the scientific and medical communities as nonsense, quackery, and a sham.There have been four large scale assessments of homeopathy by national or international bodies: the Australian National Health and Medical Research Council; the United Kingdom's House of Commons Science and Technology Committee; the European Academies' Science Advisory Council; and the Swiss Federal Health Office. Each concluded that homeopathy is ineffective, and recommended against the practice receiving any further funding. The National Health Service in England has announced a policy of not funding homeopathic medicine because it is "a misuse of resources". They called on the UK Department of Health to add homeopathic remedies to the blacklist of forbidden prescription items, and the NHS ceased funding homeopathic remedies in November 2017.

Industrial Revolution

The Industrial Revolution was the transition to new manufacturing processes in Europe and the US, in the period from about 1760 to sometime between 1820 and 1840. This transition included going from hand production methods to machines, new chemical manufacturing and iron production processes, the increasing use of steam power and water power, the development of machine tools and the rise of the mechanized factory system. The Industrial Revolution also led to an unprecedented rise in the rate of population growth.

Textiles were the dominant industry of the Industrial Revolution in terms of employment, value of output and capital invested. The textile industry was also the first to use modern production methods.The Industrial Revolution began in Great Britain, and many of the technological innovations were of British origin. By the mid-18th century Britain was the world's leading commercial nation, controlling a global trading empire with colonies in North America and the Caribbean, and with some political influence on the Indian subcontinent, through the activities of the East India Company. The development of trade and the rise of business were major causes of the Industrial Revolution.The Industrial Revolution marks a major turning point in history; almost every aspect of daily life was influenced in some way. In particular, average income and population began to exhibit unprecedented sustained growth. Some economists say that the major impact of the Industrial Revolution was that the standard of living for the general population began to increase consistently for the first time in history, although others have said that it did not begin to meaningfully improve until the late 19th and 20th centuries.GDP per capita was broadly stable before the Industrial Revolution and the emergence of the modern capitalist economy, while the Industrial Revolution began an era of per-capita economic growth in capitalist economies. Economic historians are in agreement that the onset of the Industrial Revolution is the most important event in the history of humanity since the domestication of animals and plants.Although the structural change from agriculture to industry is widely associated with the Industrial Revolution, in the United Kingdom it was already almost complete by 1760.The precise start and end of the Industrial Revolution is still debated among historians, as is the pace of economic and social changes. Eric Hobsbawm held that the Industrial Revolution began in Britain in the 1780s and was not fully felt until the 1830s or 1840s, while T.S. Ashton held that it occurred roughly between 1760 and 1830. Rapid industrialization first began in Britain, starting with mechanized spinning in the 1780s, with high rates of growth in steam power and iron production occurring after 1800. Mechanized textile production spread from Great Britain to continental Europe and the United States in the early 19th century, with important centres of textiles, iron and coal emerging in Belgium and the United States and later textiles in France.An economic recession occurred from the late 1830s to the early 1840s when the adoption of the original innovations of the Industrial Revolution, such as mechanized spinning and weaving, slowed and their markets matured. Innovations developed late in the period, such as the increasing adoption of locomotives, steamboats and steamships, hot blast iron smelting and new technologies, such as the electrical telegraph, widely introduced in the 1840s and 1850s, were not powerful enough to drive high rates of growth. Rapid economic growth began to occur after 1870, springing from a new group of innovations in what has been called the Second Industrial Revolution. These new innovations included new steel making processes, mass-production, assembly lines, electrical grid systems, the large-scale manufacture of machine tools and the use of increasingly advanced machinery in steam-powered factories.

Leblanc process

The Leblanc process was an early industrial process for the production of soda ash (sodium carbonate) used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: production of sodium sulfate from sodium chloride, followed by reaction of the sodium sulfate with coal and calcium carbonate to produce sodium carbonate. The process gradually became obsolete after the development of the Solvay process.

List of homeopathic preparations

The following substances are commonly used in homeopathy today. See Category:Homeopathic remedies for a list of commercial preparations.

List of minerals O (complete)

This list includes those recognised minerals beginning with the letter O. The International Mineralogical Association is the international group that recognises new minerals and new mineral names, however minerals discovered before 1959 did not go through the official naming procedure, although some minerals published previously have been either confirmed or discredited since that date. This list contains a mixture of mineral names that have been approved since 1959 and those mineral names believed to still refer to valid mineral species (these are called "grandfathered" species).

The list is divided into groups:

Introduction • (Main synonyms)

A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P–Q • R • S • T • U–V • W–X • Y–ZThe data was exported from on 29 April 2005; updated up to 'IMA2018'.

The minerals are sorted by name, followed by the structural group ( and ima-cnmnc by, mainly) or chemical class ( and basics), the year of publication (if it's before of an IMA approval procedure), the IMA approval and the Nickel–Strunz code. The first link is to, the second link is to, and the third is to the Handbook of Mineralogy (Mineralogical Society of America).


D – discredited (IMA/CNMNC status).

Q – questionable/ doubtful (IMA/CNMNC, or status).

N – published without approval of the IMA/CNMNC, or just not an IMA approved mineral but with some acceptance in the scientific community nowadays.

I – intermediate member of a solid-solution series.

H – hypothetical mineral (synthetic, anthropogenic, suspended approval procedure, etc.)

ch – incomplete description, hypothetical solid solution end member.

Rd – redefinition of ...

"s.p." – special procedure.

group – a name used to designate a group of species, sometimes only a mineral group name.

no – no link available.

IUPAC – chemical name.

Y: 1NNN – year of publication.

Y: old – known before publications were available.

Magnesium sulfide

Magnesium sulfide is an inorganic compound with the formula MgS. It is a white crystalline material but often is encountered in an impure form that is brown and non-crystalline powder. It is generated industrially in the production of metallic iron.


Phosphorescence is a type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur very slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation.

Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers, paint, and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room.The study of phosphorescent materials led to the discovery of radioactivity in 1896.

Sodium carbonate

Sodium carbonate, Na2CO3, (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, water-soluble salts. All forms have a strongly alkaline taste and give moderately alkaline solutions in water. Historically it was extracted from the ashes of plants growing in sodium-rich soils. Because the ashes of these sodium-rich plants were noticeably different from ashes of wood (once used to produce potash), sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process.

Standard Gibbs free energy of formation

The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).

The table below lists the Standard Gibbs function of formation for several elements and chemical compounds and is taken from Lange's Handbook of Chemistry. Note that all values are in kJ/mol. Far more extensive tables can be found in the CRC Handbook of Chemistry and Physics and the NIST JANAF tables. The NIST Chemistry WebBook (see link below) is an online resource that contains standard enthalpy of formation for various compounds along with the standard absolute entropy for these compounds from which the Standard Gibbs Free Energy of Formation can be calculated.

Standard enthalpy of formation

The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states. The standard pressure value p⦵ = 105 Pa (= 100 kPa = 1 bar) is recommended by IUPAC, although prior to 1982 the value 1.00 atm (101.325 kPa) was used. There is no standard temperature. Its symbol is ΔfH⦵. The superscript Plimsoll on this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 °C or 298.15 K). Standard states are as follows:

For a gas: the hypothetical state it would have assuming it obeyed the ideal gas equation at a pressure of 1 bar

For a solute present in an ideal solution: a concentration of exactly one mole per liter (1 M) at a pressure of 1 bar

For a pure substance or a solvent in a condensed state (a liquid or a solid): the standard state is the pure liquid or solid under a pressure of 1 bar

For an element: the form in which the element is most stable under 1 bar of pressure. One exception is phosphorus, for which the most stable form at 1 bar is black phosphorus, but white phosphorus is chosen as the standard reference state for zero enthalpy of formation.For example, the standard enthalpy of formation of carbon dioxide would be the enthalpy of the following reaction under the above conditions:

C(s, graphite) + O2(g) → CO2(g)All elements are written in their standard states, and one mole of product is formed. This is true for all enthalpies of formation.

The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated in kilojoule per mole (kJ mol−1), but also in kilocalorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the energy per mass or amount guideline).

All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.

The formation reaction is a constant pressure and constant temperature process. Since the pressure of the standard formation reaction is fixed at 1 bar, the standard formation enthalpy or reaction heat is a function of temperature. For tabulation purposes, standard formation enthalpies are all given at a single temperature: 298 K, represented by the symbol ΔfH⦵298 K.

Strontium sulfide

Strontium sulfide is the inorganic compound with the formula SrS. It is a white solid. The compound is an intermediate in the conversion of strontium sulfate, the main strontium ore called celestite, to other more useful compounds.

Calcium compounds
Mineralogy and

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