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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. [14] When it is exposed to light or contains impurities it takes on a darker tint. [7] Calomel is made up of mercury and chlorine with the chemical formula Hg 2 Cl 2. Depending on ...
The name calomel is thought to come from the Greek καλός "beautiful", and μέλας "black"; or καλός and μέλι "honey" from its sweet taste. [4] The "black" name (somewhat surprising for a white compound) is probably due to its characteristic disproportionation reaction with ammonia, which gives a spectacular black coloration due to the finely dispersed metallic mercury formed.
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.
Inorganic mercury compounds, such as mercury(I)chloride (), were found to have diuretic properties when they were used to treat syphilis. [2] Proposed use of these compounds date back at least to the 16th century, shortly after the beginning of the syphilis epidemic in 1497 following Columbus' return to Europe.
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.
It arises from the reaction of mercury(II) chloride and ammonia (Calomel reaction), where the resulting mercuric amidochloride is highly insoluble. It forms white crystals in the shape of small prisms. It tastes earthy and metallic, but is a deadly poison and should not be ingested. [2]
The most common types of reference electrodes used in analytical chemistry include the standard hydrogen electrode, the saturated calomel electrode, and the Ag/AgCl electrode. [3] The standard hydrogen electrode (SHE) is the primary reference electrode that has a potential of 0 volts at all temperatures and a pressure of 1 atm.
In aqueous solutions, redox potential is a measure of the tendency of the solution to either gain or lose electrons in a reaction. A solution with a higher (more positive) reduction potential than some other molecule will have a tendency to gain electrons from this molecule (i.e. to be reduced by oxidizing this other molecule) and a solution with a lower (more negative) reduction potential ...