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]

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]

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

Calomel, Terlinguaite-222734
Amber calomel crystals and bright yellow terlinguaite on gossan matrix, 3 mm. across
CategoryHalide mineral
(repeating unit)
Strunz classification3.AA.30
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal 4/mmm (4/m 2/m 2/m) -
Unit cella = 4.4795(5) Å, c = 10.9054(9) Å; Z=4
ColorColorless, white, grayish, yellowish white, yellowish grey to ash-grey, brown
Crystal habitCrystals commonly tabular to prismatic, equant pyramidal; common as drusy crusts, earthy, massive.
TwinningContact and penetration twins on {112},
CleavageGood on {110}, uneven to imperfect on {011}
Mohs scale hardness1.5
DiaphaneityTransparent to translucent
Specific gravity7.5
Optical propertiesUniaxial (+)
Refractive indexnω = 1.973 nε = 2.656
Ultraviolet fluorescenceBrick-red under UV


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.[4]


Calomel was a widespread and popular medicine for administration to infants as a purgative to treat intestinal worms and "clear out noxious matter" but was used indiscriminately for a great number of ailments. It is tasteless and, mixed with a sweetener, was readily taken. Fumigation tents to supply calomel, heated on a metal plate, as a sublimate within children's lungs were a later method of delivery. As the mercury it contained had the effect of softening the gums, it was made the principle constituent of teething powders, until the mid-twentieth century.[5]

The compound is a laxative and once was a common medicine, especially on the American frontier. It fell out of use at the end of the 19th century due to its toxicity. One victim was Alvin Smith, the eldest brother of Joseph Smith, founder of the Church of Jesus Christ of Latter-day Saints.[6]


  1. ^ a b The Handbook of Mineralogy
  2. ^ a b c Calomel on Mindat
  3. ^ Calomel on Webmin
  4. ^ Kahlert, Heike (2010-09-01), "Reference Electrodes", Electroanalytical Methods, Springer-Verlag Berlin Heidelberg, pp. 291–308, doi:10.1007/978-3-642-02915-8_15, ISBN 978-3-642-02914-1, retrieved 2018-07-10. PDF available.
  5. ^ Swiderski, Richard M. (2009). Calomel in America : mercurial panacea, war, song and ghosts. Boca Raton, FA: BrownWalker Press. pp. 37–9. ISBN 978-1-59942-467-5.
  6. ^ Schmid, Jennifer. "Beautiful Black Poison". Weston A. Price Foundation. Retrieved 2017-10-05.
2,3-Dimercapto-1-propanesulfonic acid

2,3-Dimercapto-1-propanesulfonic acid (abbreviated DMPS) and its sodium salt (known as Unithiol) are chelating agents that form complexes with various heavy metals. They are related to dimercaprol, which is another chelating agent.

The synthesis of DMPS was first reported in 1956 by V. E. Petrunkin. The effects of DMPS on heavy metal poisoning, including with polonium-210, were investigated in the following years. DMPS was found to have some protective effect, prolonging the survival time.A study was undertaken of DMPS use by workers involved in the production of a calomel skin bleaching lotion and in direct contact with mercurous chloride and that already showed elevated urine mercury levels. The sodium salt of DMPS was found to be effective in lowering the body burden of mercury and in decreasing the urinary mercury concentration to normal levels.DMPS administrated to a mercury poisoned

animal model failed to remove the mercury from

tissues and reduce the inorganic mercury

burden in the


A 2008 study reported a case of Stevens–Johnson syndrome (SJS), a potentially serious disease, in a child undergoing chelation therapy with DMPS; the SJS resolved gradually after the chelation therapy was stopped.

Acorus calamus

Acorus calamus (also called sweet flag or calamus, among many common names) is a species of flowering plant, a tall wetland monocot of the family Acoraceae, in the genus Acorus. Although used in traditional medicine over centuries to treat digestive disorders and pain, there is no clinical evidence for its safety or efficacy – and ingested calamus may be toxic – leading to its commercial ban in the United States.

Acousto-optic programmable dispersive filter

An acousto-optic programmable dispersive filter (AOPDF) is a special type of collinear-beam acousto-optic modulator capable of shaping spectral phase and amplitude of ultrashort laser pulses. AOPDF was invented by Pierre Tournois. Typically, quartz crystals are used for the fabrication of the AOPDFs operating in the UV spectral domain, paratellurite crystals are used in the visible and the NIR (up to 4 µm) and calomel in the MIR (3-20 µm). Recently introduced Lithium niobate crystals allow for high-repetition rate operation (> 100 kHz) owing to their high acoustic velocity. The AOPDF is also used for the active control of the carrier-envelope phase of the few-cycle optical pulses and as a part of pulse-measurement schemes. Although sharing a lot in principle of operation with an acousto-optic tunable filter, the AOPDF should not be confused with it, since in the former the tunable parameter is the transfer function and in the latter it is the impulse response

Andrew Plummer

Andrew Plummer FRCP (1697–1756) was a Scottish physician and chemist. He was professor of chemistry at the University of Edinburgh from 1726 to 1755. He developed ideas on the attractive and repulsive forces involved in chemical affinity, which later had influence on his successors William Cullen and Joseph Black. He compounded "Plummer's pills", a mixture of calomel and antimony sulfide with guaiacum; the pills were originally compounded to treat psoriasis but were used for more than a century as an antisyphilitic.

Eli Jones

Eli Jones (1850–1933) was a medical doctor in the 19th–20th centuries who claimed to be able to treat cancer. He is the author of

Cancer - Its Causes, Symptoms and Treatment -Giving the Results of over Forty Years' Experience in the Medical Treatment of this Disease and Definite Medication.

Jones studied conventional medicine and practiced for five years before deciding that the medicine of the day was harmful, because of its dependence upon harsh cathartics like calomel. He then turned to eclectic medicine, which relied upon herbal extracts including those of the Native Americans, went back to school, graduated, and practiced eclectic medicine for another five years. He decided to learn homeopathy, went back to school, and then practiced as a homeopath. He next turned to Physiomedicalism and, after studying, practiced that for another five years. And finally, he studied Dr. Willhelm Heinrich Schüssler's biochemic cell salts, which is similar to homeopathy, but relies upon salts found in the body and practiced that. After his forays into the various medical schools of his time, Jones developed a syncretic practice using all the schools he had learned. He tended to use a low dosage herbal tinctures or homeopathic mother tinctures in high doses. His Definite Medication proposed low dosage herbal extracts and engendered opposition from non-homeopaths.

Jones also published A Journal of Therapeutic Facts for the Busy Doctor, which gave doctors the pro and con experience of various treatments. The 1912 and 1913 issues have been transcribed by David Winston.

Halide minerals

The halide mineral class include those minerals with a dominant halide anion (F−, Cl−, Br− and I−). Complex halide minerals may also have polyatomic anions in addition to or that include halides.

Examples include the following:

Atacamite Cu2Cl(OH)3

Avogadrite (K,Cs)BF

Bararite (ß)(NH4)2SiF6

Bischofite (MgCl2·6H2O)

Brüggenite Ca(IO3)2(H2O)

Calomel HgCl

Carnallite KMgCl3·6H2O

Carnallite KMgCl·6H2O

Cerargyite/Horn Silver AgCl

Chlorargyrite AgCl, bromargyrite AgBr, and iodargyrite AgI

Cryolite Na3AlF6

Cryptohalite (a)(NH4)2SiF6

Dietzeite Ca2(IO3)2CrO4

Eglestonite Hg4OCl2

Embolite AgCl+AgBr

Eriochalcite CuCl2·2H2O

Fluorite CaF2

Halite NaCl

Lautarite Ca(IO3)2

Marshite CuI

Miersite AgI

Nantokite CuCl

Sal Ammoniac NH4Cl

Sylvite KCl

Terlinguaite Hg2OCl

Tolbachite CuCl2

Villaumite NaF

Yttrocerite (Ca,Y,Ce)F2

Yttrofluorite (Ca,Y)F2

Many of these minerals are water-soluble and are often found in arid areas in crusts and other deposits as are various borates, nitrates, iodates, bromates and the like. Some, such as the fluorite group, are not water-soluble. All or most of simple halides of fluorine through iodine of all of the natural alkali metals and alkaline earth metals as well as numerous other metals and cations are found in some quantity at one or more locations. More complex minerals as shown below are also found.

Herbert Brereton Baker

Herbert Brereton Baker (1862–1935) was a British inorganic chemist.He was born in Blackburn, Lancashire, the second son of the Reverend John Baker, vicar of St Johns, Livesey, and Caroline Baker. He was educated locally and at Manchester Grammar School. He secured a scholarship to Balliol College, Oxford, where he was awarded an MA.

He started his career as a schoolmaster at Dulwich College then moved back to Oxford as a Reader in chemistry and was later appointed Professor at Imperial College, London.He conducted pioneering studies on the effects of drying on chemicals and the catalytic effect of moisture in chemical reactions. According to his 1902 FRS application citation he proved that "dry carbon and phosphorus will not inflame when heated in dry oxygen; that dry ammonia and hydrogen chloride when mixed do not unite, and that dry ammonium chloride and calomel respectively vaporise without dissociation... [and that] dry hydrogen and oxygen mixed together are not ignited by exposure to the temperature of melting silver".In June, 1902, he was elected a Fellow of the Royal Society and in 1923 was awarded their Davy Medal for "his researches on the complete drying of gases and liquids". He received the Chemical Society's Longstaff Medal in 1912 and was elected president of the society in 1926.He was made Commander of the Order of the British Empire in 1917.

Heroic medicine

Heroic medicine, also referred to as heroic depletion theory, was a therapeutic method advocating for rigorous treatment of bloodletting, purging, and sweating to shock the body back to health after an illness caused by a humoral imbalance. Rising to the front of orthodox medical practice in the "Age of Heroic Medicine" (1780–1850), it fell out of favor in the mid-19th century as more gentle, palliative treatments became the norm.

Horse Feathers

Horse Feathers is a 1932 Pre-Code comedy film starring the Marx Brothers. It stars the four Marx Brothers (Groucho, Chico, Harpo and Zeppo) and Thelma Todd. It was written by Bert Kalmar, Harry Ruby, S. J. Perelman, and Will B. Johnstone. Kalmar and Ruby also wrote some of the original music for the film. Several of the film's gags were taken from the Marx Brothers' stage comedy from the 1900s, Fun in Hi Skule. The term "horse feathers" was a colloquial American expression for "nonsense" in the 1920s and 1930s but is now archaic.


Kleinite is a rare mineral that has only been found in the United States and Germany that occurs in hydrothermal mercury deposits. It occurs associated with calcite, gypsum and (rarely) barite or calomel. Its color can range from pale yellow/canary yellow to orange, and it is transparent to translucent. As a photosensitive mineral, its coloration darkens when exposed to light.It has been hypothesized that kleinite formed through a "reaction of cinnabar with oxidized meteoric water", with this reaction being the source of kleinite's nitrogen.

List of alchemical substances

Alchemical studies produced a number of substances, which were later classified as particular chemical compounds or mixtures of compounds.

Many of these terms were in common use into the 20th century.

Aqua Fortis – nitric acid, formed by 2 parts saltpetre in 1 part (pure) oil of vitriol (sulfuric acid). (Historically, this process could not have been used, as 98% oil of vitriol was not available.)

Aqua Ragia/Spirit of turpentine/Oil of turpentine/Gum turpentine – turpentine, formed by the distillation of pine tree resin

Aqua Regia (Latin: "royal water") – a mixture of aqua fortis and spirit of salt

Aqua Tofani – arsenic trioxide, As2O3 (extremely poisonous)

Aqua vitae/Spirit of Wine – ethanol, formed by distilling wine

Aurum - gold

Azoth - initially this referred to a supposed universal solvent but later became another name for Mercury

Bismuth (German: Wismuth)

Bitumen - highly viscous liquid or semi-solid form of petroleum


Blue Vitriol/Bluestone – A mineral; copper(II) sulfate pentahydrate.

Brimstone – sulfurFlowers of sulfur – formed by distilling sulfur.Butter (or oil) of antimony – antimony trichloride. Formed by distilling roasted stibnite with corrosive sublimate, or dissolving stibnite in hot concentrated hydrochloric acid and distilling. SbCl3

Cadmia/Tuttia/Tutty – probably zinc carbonate

Calamine – zinc carbonate

Calomel/Horn Quicksilver/horn mercury – mercury(I) chloride, a very poisonous purgative formed by subliming a mixture of mercuric chloride and metallic mercury, triturated in a mortar and heated in an iron pot. The crust formed on the lid was ground to powder and boiled with water to remove the calomel.

Caustic potash/Caustic Wood Alkali – potassium hydroxide, formed by adding lime to potash

Caustic Soda/Caustic Marine Alkali – sodium hydroxide, NaOH, formed by adding lime to natron

Caustic Volatile Alkali – ammonium hydroxide

Chalk – a rock composed of porous biogenic calcium carbonate, CaCO3

Chrome green – chromic oxide and cobalt oxide

Chrome orange – chrome yellow and chrome red

Chrome red – basic lead chromate – PbCrO4+PbO

Chrome yellow/Paris Yellow/Leipzig Yellow – lead chromate, PbCrO4

Cinnabar/Vermilion – refers to several substances, among them: mercury(II) sulfide (HgS), or native vermilion (the common ore of mercury).

Copper Glance – copper(I) sulfide ore.

Corrosive sublimate – mercuric chloride, formed by subliming mercury, calcined green vitriol, common salt, and nitre

Cuprite – copper(I) oxide ore

Dutch White – a pigment, formed from one part of white lead to three of barium sulfate, BaSO4

Flowers of antimony – antimony trioxide, formed by roasting stibnite at high temperature and condensing the white fumes that form. SbO3

Fool's gold – a mineral, iron disulfide or pyrite; can form oil of vitriol on contact with water and air.

Fulminating silver – silver nitride, formed by dissolving silver(I) oxide in ammonia. Very explosive when dry.

Fulminating gold – gold hydrazide, formed by adding ammonia to the auric hydroxide. When dry, can explode on concussion.

Fulminating gold – unstable gold carbonate formed by precipitation by potash from gold dissolved in aqua regia

Galena – lead(II) sulfide. Lead ore.

Glass of antimony – impure antimony tetroxide, SbO4 formed by roasting stibnite. A yellow pigment for glass and porcelain.

Glauber's Salt – sodium sulfate. Na2SO4

Green Vitriol – a mineral; iron(II) sulfate heptahydrate. (or ferrous sulfate)Marcasite – a mineral; iron disulfide. In moist air it turns into green vitriol, FeSO4.

Rouge/Crocus/Colcothar – ferric oxide, formed by burning green vitriol in airGum Arabic – gum from the acacia tree

Gypsum – a mineral; calcium sulfate, CaSO4

Horn Silver/Argentum Cornu – a weathered form of chlorargyrite, an ore of silver chloride

Hydrargyrum - mercury

Luna cornea – silver chloride, formed by heating horn silver till it liquefies and then coolingKalium - potassium

King's yellow – formed by mixing orpiment with white arsenic

Lapis solaris (Bologna stone) – barium sulfide – 1603, Vincenzo Cascariolo

Lead fume – lead oxide, found in flues at lead smelters

Lime/Quicklime (Burnt Lime)/Calx Viva/Unslaked Lime – calcium oxide, formed by calcining limestoneSlaked Lime – calcium hydroxide, Ca(OH)2Liver of sulfur – formed by fusing potash and sulfur

Lunar caustic/lapis infernalis – silver nitrate, formed by dissolving silver in aqua fortis and evaporating

Lye – potash in a water solution, formed by leaching wood ashesPotash/Salt of tartar – potassium carbonate, formed by evaporating lye. K2CO3

Pearlash – formed by baking potash in a kilnMassicot – lead monoxide, PbOLitharge – lead monoxide, formed by fusing and powdering massicot

Minium/Red Lead – trilead tetroxide, Pb3O4; formed by roasting litharge in air

Naples yellow/Cassel yellow – oxychloride of lead, formed by heating litharge with sal ammoniacMercurius praecipitatus – red mercuric oxide

Milk of Sulfur (lac sulphuris) – formed by adding an acid to thion hudor (lime sulfur)

Mosaic gold – stannic sulfide, formed by heating a mixture of tin filings, sulfur, and sal-ammoniac

Natrium - sodium

Natron/Soda Ash/Soda – sodium carbonate, Na2CO3

Nitrum Flammans – ammonium nitrate

Oil of Tartar – concentrated potassium carbonate, K2CO3 solution

Oil of Tartar per Deliquium – potassium carbonate dissolved in the water which its extracts from the air

Oil of Vitriol/Spirit of Vitriol – sulfuric acid, a weak version can be formed by heating green vitriol and blue vitriol. H2SO4

Orpiment – arsenic trisulfide, an ore of arsenic

Pearl white – bismuth nitrate, BiNO3

Philosophers' Wool/nix alba (white snow)/Zinc White – zinc oxide, formed by burning zinc in air, used as a pigment

Plumbago – a mineral, graphite; not discovered in pure form until 1564

Plumbum - lead

Powder of Algaroth – antimonious oxychloride, formed by precipitation when a solution of butter of antimony and spirit of salt is poured into water

Purple of Cassius – formed by precipitating a mixture of gold, stannous and stannic chlorides, with alkali. Used for glass coloring

Quicksilver - Mercury

Realgar – arsenic disulfide, an ore of arsenic

Red Vitriol - cobalt sulfate

Regulus of antimony

Resin of copper – copper(I) chloride (cuprous chloride), formed by heating copper with corrosive sublimate

Sal Ammoniac – ammonium chloride

Sal Petrae (Med. Latin: "stone salt")/Salt of Petra/Saltpetre/Nitrate of potash – potassium nitrate, KNO3, typically mined from covered dungheaps

Salt/Common salt – A mineral; sodium chloride, NaCl, formed by evaporating seawater (impure form)

Salt of Hartshorn/Sal Volatile – ammonium carbonate formed by distilling bones and horns

Spirit of box/Pyroxylic spirit – methanol, CH3OH, distilled wood alcohol

Spirit of Hartshorn – ammonia, formed by the decomposition of sal-ammoniac by unslaked lime

Spirit of Salt/Acidum Salis – the liquid form of hydrochloric acid (also called muriatic acid), formed by mixing common salt with oil of vitriolMarine Acid Air – gaseous form of hydrochloric acidSpiritus fumans – stannic chloride, formed by distilling tin with corrosive sublimateTin salt – hydrated stannous chloride

Butter of tin – hydrated tin(IV) chlorideStibium - antimony

Stibnite – antimony or antimony trisulfide, ore of antimony

Sugar of Lead – lead(II) acetate, formed by dissolving lead oxide in vinegar

Sweet Vitriol – diethyl ether. It could be made by mixing oil of vitriol with spirit of wine and heating it.

Thion Hudor – lime sulfur, formed by boiling flowers of sulfur with slaked lime

Turpeth mineral – hydrolysed form of mercury(II) sulfate

Verdigris – Carbonate of Copper or (more recently) copper(II) acetate. The carbonate is formed by weathering copper. The acetate is formed by vinegar acting on copper. One version was used as a green pigment.

White arsenic – arsenious oxide, formed by subliminating arsenical soot from the roasting ovens

White lead – carbonate of lead, a toxic pigment, produced by corroding stacks of lead plates with dilute vinegar beneath a heap of moistened wood shavings. (replaced by blanc fixe & lithopone)

White vitriol – zinc sulfate, formed by lixiviating roasted zinc blende

Wolfram - tungsten

Venetian White – formed from equal parts of white lead and barium sulfate

Zaffre – impure cobalt arsenate, formed after roasting cobalt ore

Zinc Blende – zinc sulfide

Mercury(I) chloride

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.

Mercury poisoning

Mercury poisoning is a type of metal poisoning due to exposure to mercury. Symptoms depend upon the type, dose, method, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble speaking, trouble hearing, or trouble seeing. High level exposure to methylmercury is known as Minamata disease. Methylmercury exposure in children may result in acrodynia (pink disease) in which the skin becomes pink and peels. Long-term complications may include kidney problems and decreased intelligence. The effects of long-term low-dose exposure to methylmercury are unclear.Forms of mercury exposure include metal, vapor, salt, and organic compound. Most exposure is from eating fish, amalgam based dental fillings, or exposure at work. In fish, those higher up in the food chain generally have higher levels of mercury. Less commonly, poisoning may occur as a method of attempted suicide. Human activities that release mercury into the environment include the burning of coal and mining of gold. Tests of the blood, urine, and hair for mercury are available but do not relate well to the amount in the body.Prevention includes eating a diet low in mercury, removing mercury from medical and other devices, proper disposal of mercury, and not mining further mercury. In those with acute poisoning from inorganic mercury salts, chelation with either dimercaptosuccinic acid (DMSA) or dimercaptopropane sulfonate (DMPS) appears to improve outcomes if given within a few hours of exposure. Chelation for those with long-term exposure is of unclear benefit. In certain communities that survive on fishing, rates of mercury poisoning among children have been as high as 1.7 per 100.


Mersalyl (Mersal) is an organomercury compound (mercurial diuretic). It is only rarely used as a drug, having been superseded by diuretic medications that do not contain mercury and are therefore less toxic. It features a Hg(II) centre. Mersalyl was originally adapted from calomel (HgCl), a diuretic discovered by Paracelsus.


Montroydite is the mineral form of mercury(II) oxide with formula HgO. It is a rare mercury mineral. It was first described for an occurrence in the mercury deposit at Terlingua, Texas and named for Montroyd Sharp who was an owner of the deposit.Montroydite occurs in mercury deposits of hydrothermal origin. Associated minerals include: native mercury, cinnabar, metacinnabar, calomel, eglestonite, terlinguaite, mosesite, kleinite, edgarbaileyite, gypsum, calcite and dolomite.

Potentiometric titration

Potentiometric titration is a technique similar to direct titration of a redox reaction. It is a useful means of characterizing an acid. No indicator is used; instead the potential is measured across the analyte, typically an electrolyte solution. To do this, two electrodes are used, an indicator electrode (the glass electrode and metal ion indicator electrode) and a reference electrode. Reference electrodes generally used are hydrogen electrodes, calomel electrodes, and silver chloride electrodes. The indicator electrode forms an electrochemical half cell with the interested ions in the test solution. The reference electrode forms the other half cell.

The overall electric potential is calculated as Ecell = Eind - Eref + Esol. Esol is the potential drop over the test solution between the two electrodes. Ecell is recorded at intervals as the titrant is added. A graph of potential against volume added can be drawn and the end point of the reaction is halfway between the jump in voltage.

Ecell depends on the concentration of the interested ions with which the indicator electrode is in contact. For example, the electrode reaction may be


As the concentration of Mn+ changes,the Ecell changes correspondingly.

Thus the potentiometric titration involve measurement of Ecell with the addition of titrant.

Types of potentiometric titration:

acid-base titration

(total alkalinity and total acidity), redox titration (HI/HY and cerate),

precipitation titration (halides), and complexometric titration (free EDTA and

Antical #5).

Primm Springs Historic District

The Primm Springs Historic District in Primm Springs, Tennessee is a 8 acres (3.2 ha) historic district which was listed on the National Register of Historic Places in 1985. The listing included 15 contributing buildings, three contributing structures, and two contributing sites.It is the location of a historic mineral springs resort. It runs along the Puppy Branch of Dog Creek, through a hollow, where shale formations release waters with dissolved minerals. There were once five mineral springs; three remained in 1985, "sulphur", "arsenic", and "calomel". The district includes "a good collection of vernacular frame structures including a large hotel, another smaller boarding house, six family summercabins or cottages, a dance hall, two small stores, and two frame residences designed for year round use, as well as a number of outbuildings including springhouses, kitchens, smokehouses, barns, and sheds. Most of the buildings were designed for summer use only."

Saturated calomel electrode

The Saturated calomel electrode (SCE) is a reference electrode based on the reaction between elemental mercury and mercury(I) chloride. It has been widely replaced by the silver chloride electrode, however the calomel electrode has a reputation of being more robust. The aqueous phase in contact with the mercury and the mercury(I) chloride (Hg2Cl2, "calomel") is a saturated solution of potassium chloride in water. The electrode is normally linked via a porous frit to the solution in which the other electrode is immersed. This porous frit is a salt bridge.

In cell notation the electrode is written as:

Silver chloride electrode

A silver chloride electrode is a type of reference electrode, commonly used in electrochemical measurements. For environmental reasons it has widely replaced the saturated calomel electrode. For example, it is usually the internal reference electrode in pH meters and it is often used as reference in reduction potential measurements. As an example of the latter, the silver chloride electrode is the most commonly used reference electrode for testing cathodic protection corrosion control systems in sea water environments.

The electrode functions as a redox electrode and the equilibrium is between the silver metal (Ag) and its salt—silver chloride (AgCl, also called silver(I) chloride).

The corresponding half-reactions can be presented as follows:

or can be written together:

which can be simplified:

This reaction is characterized by fast electrode kinetics, meaning that a sufficiently high current can be passed through the electrode with the 100% efficiency of the redox reaction (dissolution of the metal or cathodic deposition of the silver-ions). The reaction has been proven to obey these equations in solutions of pH values between 0 and 13.5.

The Nernst equation below shows the dependence of the potential of the silver-silver(I) chloride electrode on the activity or effective concentration of chloride-ions:

The standard electrode potential E0 against standard hydrogen electrode (SHE) is 0.230 V ± 10 mV. The potential is however very sensitive to traces of bromide ions which make it more negative. (The more exact standard potential given by an IUPAC review paper is +0.22249 V, with a standard deviation of 0.13 mV at 25 °C.)

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.