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Calomel, Terlinguaite-222734.jpg
Amber calomel crystals and bright yellow terlinguaite on gossan matrix, 3 mm. across
Category Halide mineral
(repeating unit)
Strunz classification 3.AA.30
Crystal system Tetragonal
Crystal class Ditetragonal dipyramidal 4/mmm (4/m 2/m 2/m) -
Unit cell a = 4.4795(5) Å, c = 10.9054(9) Å; Z=4
ColorColorless, white, grayish, yellowish white, yellowish grey to ash-grey, brown
Crystal habit Crystals commonly tabular to prismatic, equant pyramidal; common as drusy crusts, earthy, massive.
Twinning Contact and penetration twins on {112},
Cleavage Good on {110}, uneven to imperfect on {011}
Fracture Conchoidal
Tenacity Sectile
Mohs scale hardness1.5
Luster Adamantine
Diaphaneity Transparent to translucent
Specific gravity 7.5
Optical propertiesUniaxial (+)
Refractive index nω = 1.973 nε = 2.656
Ultraviolet fluorescence Brick-red under UV
References [1] [2] [3]

Calomel is a mercury chloride mineral with formula Hg2Cl2 (see mercury(I) chloride). The name derives from Greek kalos (beautiful) and melos (black) because it turns black on reaction with ammonia. This was known to alchemists. [2]

The chloride ion is the anion Cl. It is formed when the element chlorine gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often very soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in and out of cells. Less frequently, the word chloride may also form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion.

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. Minerals are most commonly associated with rocks due to the presence of minerals within rocks. These rocks may consist of one type of mineral, or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.


Calomel occurs as a secondary mineral which forms as an alteration product in mercury deposits. It occurs with native mercury, amalgam, cinnabar, mercurian tetrahedrite, eglestonite, terlinguaite, montroydite, kleinite, moschelite, kadyrelite, kuzminite, chursinite, kelyanite, calcite, limonite and various clay minerals. [1]

Amalgam (chemistry) alloy of mercury with another metal

An amalgam is an alloy of mercury with another metal. It may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore. Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc.

Cinnabar Red mercury sulfide mineral

Cinnabar or cinnabarite, likely deriving from the Ancient Greek: κιννάβαρι (kinnabari), refer to the common bright scarlet to brick-red form of mercury(II) sulfide (HgS) that is the most common source ore for refining elemental mercury, and is the historic source for the brilliant red or scarlet pigment termed vermilion and associated red mercury pigments.

Tetrahedrite sulfosalt series

Tetrahedrite is a copper antimony sulfosalt mineral with formula: (Cu,Fe)
. It is the antimony endmember of the continuous solid solution series with arsenic-bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common. Other elements also substitute in the structure, most notably iron and zinc, along with less common silver, mercury and lead. Bismuth also substitutes for the antimony site and bismuthian tetrahedrite or annivite is a recognized variety. The related, silver dominant, mineral species freibergite, although rare, is notable in that it can contain up to 18% silver.

The type locality is Moschellandsburg, Alsenz-Obermoschel, Rhineland-Palatinate, Germany. [2]

Type locality, also called type area, or type section, is the locality where a particular rock type, stratigraphic unit or mineral species is first identified. If the stratigraphic unit in a locality is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality.

Alsenz-Obermoschel is a Verbandsgemeinde in the Donnersbergkreis, in Rhineland-Palatinate, Germany. It is situated on the river Alsenz, approx. 15 km south of Bad Kreuznach, and 30 km north of Kaiserslautern. The seat of the municipality is in Alsenz.

Rhineland-Palatinate State in Germany

Rhineland-Palatinate is a state of Germany.


Mahogany medicine chest, England, 1801-1900 Mahogany medicine chest, England, 1801-1900 Wellcome L0057102.jpg
Mahogany medicine chest, England, 1801-1900

The first time that the substance that would come to be known as calomel was documented was in Ancient Syria by the Persian medical historian, Rhazes; however, only a few of the compounds he mentioned could be positively identified as calomel as not every alchemist disclosed what compounds went into their drugs. [4] Calomel first entered Western medical literature in 1608, when Oswald Croll wrote about the drug’s preparation in his “Tyroncium Chemicum,” although it was not called calomel until 1655 when the name was created by Sir Turquet de Mayrene. [5] In 1618, Mayrene was the first to publish the preparation and formula for calomel in “Pharmacopoeia of Londinensis.” [4]

Oswald Croll German alchemist

Oswald Croll or Crollius was an alchemist, and professor of medicine at the University of Marburg in Hesse, Germany. A strong proponent of alchemy and using chemistry in medicine, he was heavily involved in writing books and influencing thinkers of his day towards viewing chemistry and alchemy as two separate fields.

By the 19th century, calomel was viewed as a panacea, or miracle drug, and was used to cure almost every disease. Some of these diseases included: syphilis, bronchitis, cholera, ingrown toenails, teething, gout, tuberculosis, influenza, and cancer. Although during the 18th and early 19th century pharmacists used calomel sparingly, by the late 1840s calomel was being prescribed in heroic doses. [6] This was, in part, due to the research of Benjamin Rush who coined the term heroic dose to mean about 20 grains taken four times daily. [7] This stance was supported by Dr. Samuel Cartwright who believed that taking large doses was the “gentlest” on the body. [8] As calomel rose in popularity, more research was done into how it worked.

Panacea Greek goddess of universal health

In Greek mythology, Panacea was a goddess of universal remedy and the daughter of Asclepius and Epione. Panacea and her four sisters each performed a facet of Apollo's art:

Syphilis Sexually transmitted infection

Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum subspecies pallidum. The signs and symptoms of syphilis vary depending in which of the four stages it presents. The primary stage classically presents with a single chancre though there may be multiple sores. In secondary syphilis, a diffuse rash occurs, which frequently involves the palms of the hands and soles of the feet. There may also be sores in the mouth or vagina. In latent syphilis, which can last for years, there are few or no symptoms. In tertiary syphilis, there are gummas, neurological problems, or heart symptoms. Syphilis has been known as "the great imitator" as it may cause symptoms similar to many other diseases.

Bronchitis type of lower respiratory disease

Bronchitis is inflammation of the bronchi in the lungs that causes coughing. Symptoms include coughing up sputum, wheezing, shortness of breath, and chest pain. Bronchitis can be acute or chronic.

J. Annesley was one of the first to write about the different effects of calomel when taken in small or large doses. [8] Through experimentation on dogs, Annesley concluded that calomel acted more like a laxative on the whole body rather than acting specifically on the vascular system or liver as previous physicians believed. [8] In 1853, Samuel Jackson described the harmful effects of calomel on children in his publication for Transactions of Physicians of Philadelphia. [6] He noted that calomel had harmful effects causing gangrene on the skin, loss of teeth, and deterioration of the gums. [6] On May 4, 1863, William A. Hammond, the United States’ Surgeon-General, stated that calomel would no longer be used in the army as it was being abused by soldiers and physicians alike. [6] This caused much debate in the medical field, and eventually led to his removal as Surgeon-General. [9] Calomel continued to be used well into the 1890s and even into the early 20th century. [6] Eventually calomel’s popularity began to wane as more research was done, and scientists discovered that the mercury in the compound was poisoning patients.

Gangrene serious and potentially life-threatening condition

Gangrene is a type of tissue death caused by a lack of blood supply. Symptoms may include a change in skin color to red or black, numbness, swelling, pain, skin breakdown, and coolness. The feet and hands are most commonly affected. Certain types may present with a fever or sepsis.

William A. Hammond American military physician and neurologist

William Alexander Hammond was an American military physician and neurologist. During the American Civil War he was the eleventh Surgeon General of the United States Army (1862–1864) and the founder of the Army Medical Museum.

Calomel was the main of the three componentes of the pill number 9 of the british army during the first World War [10]


Calomel is used as the interface between metallic mercury and a chloride solution in a saturated calomel electrode, which is used in electrochemistry to measure pH and electrical potentials in solutions, In most electrochemical measurements, it is necessary to keep one of the electrodes in an electrochemical cell at a constant potential. This so-called reference electrode allows control of the potential of a working electrode. [11]

Chemical properties

Packets of calomel. Packet of mercurous chloride tablets, Kassel, Germany, 1914- Wellcome L0058828.jpg
Packets of calomel.

Calomel is a powder that is white when pure. When it is exposed to light or contains impurities it takes on a darker tint. [5] Calomel is made up of mercury and chlorine with the chemical formula Hg2Cl2. Depending on how calomel was administered, it affected the body in different ways. Taken orally, calomel damaged mainly the lining of the gastrointestinal tract. Mercury salts (such as calomel) are insoluble in water and therefore do not absorb well through the wall of the small intestine. Some of the calomel in the digestive system will likely be oxidized into a former of mercury that can be absorbed through the intestine, but most of it will not. [12] Oral calomel was actually the safest form of the drug to take, especially in low doses. Most of the calomel ingested will be excreted through urine and stool. [12]

Powdered forms of calomel were much more toxic, as their vapors damaged the brain. Once inhaled, the calomel enters the bloodstream and the mercury binds with the amino acids methionine, cysteine, homocysteine and taurine. [12] This is because of the sulfur group these amino acids contain, which mercury has a high affinity for. It is able to pass through the blood brain barrier and builds up in the brain. Mercury also has the ability to pass through the placenta, causing damage to unborn babies if a pregnant mother is taking calomel. [12]

Calomel was manufactured in two ways - sublimation and precipitation. When calomel first started being manufactured it was done through sublimation. Calomel made through sublimation tends to be a very fine white powder. [5] There was some controversy over the sublimation of calomel. Many argued that the more times calomel was sublimed, the purer it got. Opponents believed that the repeated sublimation made calomel lose some of its therapeutic ability. [4] In 1788 pharmacist Carl Wilhelm Scheele came up with the mechanism to make precipitated calomel. This became rapidly popular in the pharmaceutical industry because it was both a cheaper and safer form of production. [4] Precipitation also tended to form very pure calomel salts. [5]


Calomel was a popular medicine used during the Victorian period and was widely used as a treatment for a variety of ailments during the American Civil War. The medication was available in two forms, blue pills and blue masses. [9] The blue pill was an oral form of calomel containing mercury that was often mixed with a sweet substance, like licorice or sugar in order to be taken by mouth. The blue mass was a solid form of calomel in which a piece could be pinched off and administered by a physician or other medical provider. Neither form of the medication came with a standardization of dosing. There was no way of knowing how much mercurous chloride each dose contained. [9]


Calomel was marketed as a purgative agent to relieve congestion and constipation, however, physicians at the time had no idea what the medication’s mechanism of action was. They learned how calomel worked through trial and error. It was observed that small doses of calomel acted as a stimulant, often leading to bowel movements, while larger doses caused sedation. [6] During the 19th century, calomel was used to treat numerous illnesses and diseases like mumps, typhoid fever, and others--especially those that impact the gastrointestinal tract, such as constipation, dysentery, and vomiting. [7] As the mercury it contained had the effect of softening the gums, it was made the principal constituent of teething powders, until the mid-twentieth century. [13]

Side effects

Medical label. Calomel-bem-10c.jpg
Medical label.

It became popular in the late 18th century to give calomel in extremely high doses, as Benjamin Rush normalized the heroic dose. This caused many patients to experience many painful and sometimes life-threatening side effects. Calomel, in high doses, led to mercury poisoning, which had the potential to cause permanent deformities and even death. Some patients experienced gangrene of the mouth generated by the mercury in the medicine, which caused the tissue on the cheeks and gums inside the mouth to break down and die. Some patients would lose teeth, while others were left with facial deformities. [9] High doses of calomel would often lead to extreme cramping, vomiting, and bloody diarrhea, however, at the time, this was taken as a sign that the calomel was working to purge the system and rid the disease. [7] Calomel was often administered as a treatment for dysentery; the effects of calomel would often worsen the severe diarrhea associated with dysentery and acted as a catalyst in speeding up the effects of dehydration. [9] One victim was Alvin Smith, the eldest brother of Joseph Smith, founder of the Church of Jesus Christ of Latter-day Saints. [14] . It was also used by Charles Darwin to treat the severe gastrointestinal infection that presumably began the inductive phase of his documented Crohn's disease. [15] . Eventually, it was determined that calomel was causing more harm than good, as the side effects were often worse than the illness it was being used to treat; because of this, calomel was removed from medical supply shelves. [7]

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Naproxen chemical compound

Naproxen, sold under the brand name Naprosyn among others, is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, menstrual cramps, inflammatory diseases such as rheumatoid arthritis, and fever. It is taken by mouth. It is available in immediate and delayed release formulations. Onset of effects is within an hour and last for up to twelve hours.

Hydrochlorothiazide chemical compound

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Mercurial diuretic

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Teething is the process by which an infant's first teeth sequentially appear by emerging through the gums, typically arriving in pairs. The mandibular central incisors are the first primary teeth to erupt, usually between 6 and 10 months of age. It can take several years for all 20 teeth to complete the tooth eruption. Though the process of teething is sometimes referred to as "cutting teeth", when teeth emerge through the gums they do not cut through the flesh. Instead, hormones are released within the body that cause some cells in the gums to die and separate, allowing the teeth to come through.

Alendronic acid chemical compound

Alendronic acid, sold under the brand name Fosamax among others, is a bisphosphonate medication used to treat osteoporosis and Paget's disease of bone. It is taken by mouth. Use is often recommended together with vitamin D, calcium supplementation, and lifestyle changes.


Polypharmacy is the concurrent use of multiple medications by a patient. Polypharmacy is most common in the elderly, affecting about 40% of older adults living in their own homes. About 21% of adults with intellectual disability are also exposed to polypharmacy. Polypharmacy is not necessarily ill-advised, but in many instances can lead to negative outcomes or poor treatment effectiveness, often being more harmful than helpful or presenting too much risk for too little benefit. Therefore, health professionals consider it a situation that requires monitoring and review to validate whether all of the medications are still necessary. Concerns about polypharmacy include increased adverse drug reactions, drug interactions, prescribing cascade, and higher costs. Polypharmacy is often associated with a decreased quality of life, including decreased mobility and cognition.

Mercury(I) chloride chemical compound

Mercury(I) chloride is the chemical compound with the formula Hg2Cl2. Also known as the mineral calomel (a rare mineral) or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury(I) compound. It is a component of reference electrodes in electrochemistry.

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Oxybutynin pair of enantiomers

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  3. Calomel on Webmin
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