Calomel

Calomel is a mercury chloride mineral with formula Hg₂Cl₂ (see mercury(I) chloride). It was used as a medicine from the 16th to early 20th century, despite frequently causing mercury poisoning in patients.

The name derives from Greek kalos (beautiful) and melas (black) because it turns black on reaction with ammonia. This was known to alchemists.

The type locality is Moschellandsburg, Alsenz-Obermoschel, Rhineland-Palatinate, Germany. Calomel first entered Western medical literature in 1608, when Oswald Croll wrote about its preparation in his Tyroncium Chemicum. It was not called calomel until 1655, when the name was created by Théodore de Mayerne, who had published its preparation and formula in "Pharmacopoeia Londinensis" in 1618.—due in part to the research of Benjamin Rush, who coined the term "heroic dose" to mean about taken four times daily. This stance was supported by Samuel Cartwright, who believed that large doses were "gentlest" on the body. As calomel rose in popularity, more research was done into how it worked.

J. Annesley was one of the first to write about the differing effects of calomel when taken in small or large doses. Calomel continued to be used well into the 1890s and even into the early 20th century.

Electrochemistry

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.

Chemical properties

thumb|left|upright|Packets of calomel.

Calomel is a powder that is white when pure, and it has been used as a pigment in painting in 17th century South Americas art and in European medieval manuscripts. When it is exposed to light or contains impurities it takes on a darker tint. 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. Babies given calomel for teething often suffered from acrodynia.

Side effects

thumb|Label from a calomel and [[cinnabar specimen]]

thumb|Disfigurement caused by calomel administered to treat pneumonia (1862). The calomel treatment caused an ulcer to form and spread across the patient's tongue, mouth, cheek, and eye; ultimately killing his upper [[maxilla. ]]

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. Alvin was suffering from a "bilious colic" better known as abdominal pain.

It was also used by Charles Darwin to treat his mysterious chronic gastrointestinal illness, which has recently been attributed to Crohn's disease.

Discontinuation

By the mid-19th century, some physicians had begun to question the usefulness of calomel. In 1863, the Surgeon General of the U.S. Army forbade calomel from inclusion in army medical supplies, a decision that angered many practicing doctors. The use of calomel gradually died out over the course of the late 19th and early 20th centuries, although its use persisted longer in the American South and American West.