Calomel was mined for centuries for medicinal and industrial purposes. It is a white, powdery mineral composed of mercury, chlorine, and oxygen. Its most recognizable form is a greyish-white powder.
Calomel has a long history of medicinal use. In the ancient world, it was used to purify water, cure skin afflictions, and treat eating disorders. In the 16th and 17th centuries, it was used as a purgative and a tonic. In the 18th century, it was used to treat syphilis and gout. In the 19th century, it was used to treat diarrhoea and malaria.
More recently, calomel has found uses in the industrial arena. It is used to make batteries and electrical contacts, as a catalyst in chemical reactions, and as a precursor in the manufacture of other compounds.
Calomel can be mined from the earth, or synthesized in a laboratory. The latter method is more expensive, but easier to control, as the purity and uniformity of the resulting powder can be regulated.
When mined, the ore is crushed and heated to a high temperature. This process causes the minerals to become unstable and to react, generating oxide and chlorine. The particles of oxide and chlorine become bonded to the mercury particles, forming calomel.
Calomel is then formed into a hard, black lump called Calomelite. This material can either be sold as it is, or be ground into a greyish white powder.
The use of calomel in the production of pyrotechnic devices has dwindled in recent times, as other, safer compounds are now being used in their manufacture. However, it still has its uses as a catalyst in a variety of industrial processes, as well as a means of purifying water.
Due to its mercury content, calomel can be dangerous to handle. If the powder is exposed to moisture, the mercury can become oxidized, forming a gas which is dangerous to inhale. The best way to use calomel is by heating it in a vertical furnace to a high enough temperature so that all the harmful compounds become volatile and are evaporated away.
