Editing Calomel (section)

== Chemical properties ==
[[File:Packet of mercurous chloride tablets, Kassel, Germany, 1914- Wellcome L0058828.jpg|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.<ref>{{Cite journal |last1=Crippa |first1=Mila |last2=Legnaioli |first2=Stefano |last3=Kimbriel |first3=Christine |last4=Ricciardi |first4=Paola |date=2021 |title=New evidence for the intentional use of calomel as a white pigment |url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/jrs.5876 |journal=Journal of Raman Spectroscopy |language=en |volume=52 |issue=1 |pages=15–22 |doi=10.1002/jrs.5876 |bibcode=2021JRSp...52...15C |issn=0377-0486}}</ref> When it is exposed to light or contains impurities it takes on a darker tint.<ref name="Means" /> Calomel is made up of mercury and chlorine with the chemical formula Hg<sub>2</sub>Cl<sub>2</sub>. 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 form of mercury that can be absorbed through the intestine, but most of it will not.<ref name=":1">{{Cite journal|last=Bernhoft|first=Robin|date=December 2011|title=Mercury Toxicity and Treatment: A Review of the Literature|journal=Journal of Environmental and Public Health|volume=2012|pages=460508|pmc=3253456|pmid=22235210|doi=10.1155/2012/460508|doi-access=free}}</ref> 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.<ref name=":1" />

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.<ref name=":1" /> 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.<ref name=":1" />

Calomel was manufactured in two ways - [[Sublimation (phase transition)|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.<ref name="Means" /> 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.<ref name="Urdang" /> In 1788 chemist [[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.<ref name="Urdang" /> Precipitation also tended to form very pure calomel salts.<ref name="Means" />