Mercury occurs in three forms: Metallic mercury, inorganic salt, and organic salts.

NameChemical FormulaCommon NamesUses
Metallic MercuryHgQuicksilverThermometers, batteries, fluorescent lamps, mining
Methyl MercuryCH₃Hg⁺Toxic environmental contaminant
Dimethyl Mercury(CH₃)₂HgHighly toxic laboratory chemical
Phenylmercuric acetateC₆H₅HgOOCCH₃Fungicide, reduces plant transpiration
ThiomersalC₉H₉HgNaO₂SThimerosalAntiseptic, antifungal agent
Mercuric chlorideHgCl₂Corrosive sublimate, RaskapoorAntiseptic, fungicide, disinfectant
Mercurous chlorideHg₂Cl₂CalomelFungicide, purgative
Mercuric ammonium chlorideHgNH₂ClAntiseptic ointment
Mercuric cyanideHg(CN)₂Hydrargyrum bicyanatumAntiseptic, antisyphilitic
Mercuric iodideHgI₂ProtiodideFormer syphilis treatment
Mercuric oxideHgOSipichandBatteries, pigment
Mercuric sulfateHgSO₄Chemical intermediate
Mercury sulfideHgSCinnabar, vermilionPigment
Mercury thiocyanateHg(SCN)₂Pharaoh’s serpentFireworks

1. Metallic Mercury

It is not poisonous when swallowed as it is not absorbed from the gastrointestinal tract (GIT). However, it is toxic when absorbed in vapor form as inhaled mercury vapors can readily cross biological membranes.

2. Organic Salts of Mercury:

  1. Methyl Mercury: Notably involved in the Minamata Bay disaster in Japan during the 1940s, where industrial release led to the poisoning of fish, which then caused poisoning in humans who consumed the contaminated fish.
  2. Dimethyl Mercury: A highly toxic form of mercury.
  3. Phenylmercuric Acetate: Used as a fungicide and applied to the leaves of plants to reduce transpiration; also used on Christmas trees to slow down the loss of needles.
  4. Thiomersal (also known as Thimerosal): An antiseptic and antifungal agent

3. Inorganic Salts of Mercury:

  1. Mercuric Chloride [HgCl₂, Corrosive sublimate]: White crystalline powder, soluble in water but more so in alcohol. Used to treat syphilis and as a diuretic and astringent. It was also historically used as a preservative and disinfectant.
  2. Mercurous Chloride [Hg₂Cl₂, Calomel]: Also known as sweet mercury, it is a white, tasteless powder used chiefly as a fungicide and abortifacient. Less toxic than HgCl₂ due to its lower solubility in water. It was used as a diuretic and purgative and in teething powders up to the 1950s.
  3. Mercuric Ammonium Chloride [HgNH₂Cl]: An ointment containing 10% HgNH₂Cl is used for eczema and may cause toxicity.
  4. Mercuric Cyanide [Hg(CN)₂]: Odorless, toxic white powder with a bitter metallic taste. Used as an antiseptic and an antisyphilitic. Also known as Hydrargyrum bicyanatum in homeopathy.
  5. Mercuric Iodide – [HgI₂, Protiodide]: Red-orange crystals used in the past as a treatment for syphilis.
  6. Mercuric Nitrite [Hg(NO3)2]: colorless or white soluble crystalline salts are occasionally used as a reagent.
  7. Mercuric Oxide [HgO]: Described as a brick-red powder, used as cathode for mercury batteries.
  8. Mercuric Sulfate [HgSO₄]: Odorless white crystalline powder.
  9. Mercury Sulphide [HgS, Cinnabar, red sulphide of mercury, sindoor, vermilion]: Vermilion, primarily HgS, is a bright red pigment used historically and commonly referred to by various names.
  10. Mercury Thiocyanate [Hg(SCN)₂, Pharaoh’s Serpent]: Known for its use in the “Pharaoh’s serpent” firework. When ignited, it produces a large, complex, serpent-like ash structure.

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