Calomel

Calomel, or mercurous chloride, is an inorganic compound with the formula Hg2Cl2. It consists of the mercurous cation Hg2^2+ and two chloride anions, forming white, crystalline solids. It is sparingly soluble in water and relatively stable under neutral conditions; strong acids or bases can alter its form.

Historically, calomel was used in medicine as a purgative and emetic, commonly administered in tablet form. Its medical use declined in the 20th century due to concerns about mercury toxicity and the availability of safer alternatives. Today it is largely obsolete as a therapeutic agent.

In electrochemistry, calomel is best known for its role in the saturated calomel electrode (SCE), a widely used reference electrode. The SCE contains Hg2Cl2 in contact with a saturated potassium chloride solution and a porous junction, providing a stable reference potential for various electrochemical measurements.

Safety and regulatory status: Calomel contains mercury and is toxic. Ingestion, inhalation of dust, or prolonged exposure can lead to mercury poisoning. It is regulated as a hazardous substance in many jurisdictions and requires careful handling and disposal as hazardous waste.

Summary: Calomel is a historical mercurial compound, once common in medicine and now primarily of interest for its role in electrochemistry and for considerations related to mercury safety and regulation.