Mercury occurs in three forms: Metallic mercury, inorganic salt, and organic salts.
| Name | Chemical Formula | Common Names | Uses |
|---|---|---|---|
| Metallic Mercury | Hg | Quicksilver | Thermometers, batteries, fluorescent lamps, mining |
| Methyl Mercury | CH₃Hg⁺ | – | Toxic environmental contaminant |
| Dimethyl Mercury | (CH₃)₂Hg | – | Highly toxic laboratory chemical |
| Phenylmercuric acetate | C₆H₅HgOOCCH₃ | – | Fungicide, reduces plant transpiration |
| Thiomersal | C₉H₉HgNaO₂S | Thimerosal | Antiseptic, antifungal agent |
| Mercuric chloride | HgCl₂ | Corrosive sublimate, Raskapoor | Antiseptic, fungicide, disinfectant |
| Mercurous chloride | Hg₂Cl₂ | Calomel | Fungicide, purgative |
| Mercuric ammonium chloride | HgNH₂Cl | – | Antiseptic ointment |
| Mercuric cyanide | Hg(CN)₂ | Hydrargyrum bicyanatum | Antiseptic, antisyphilitic |
| Mercuric iodide | HgI₂ | Protiodide | Former syphilis treatment |
| Mercuric oxide | HgO | Sipichand | Batteries, pigment |
| Mercuric sulfate | HgSO₄ | – | Chemical intermediate |
| Mercury sulfide | HgS | Cinnabar, vermilion | Pigment |
| Mercury thiocyanate | Hg(SCN)₂ | Pharaoh’s serpent | Fireworks |
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:
- 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.
- Dimethyl Mercury: A highly toxic form of mercury.
- 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.
- Thiomersal (also known as Thimerosal): An antiseptic and antifungal agent
3. Inorganic Salts of Mercury:
- 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.
- 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.
- Mercuric Ammonium Chloride [HgNH₂Cl]: An ointment containing 10% HgNH₂Cl is used for eczema and may cause toxicity.
- 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.
- Mercuric Iodide – [HgI₂, Protiodide]: Red-orange crystals used in the past as a treatment for syphilis.
- Mercuric Nitrite [Hg(NO3)2]: colorless or white soluble crystalline salts are occasionally used as a reagent.
- Mercuric Oxide [HgO]: Described as a brick-red powder, used as cathode for mercury batteries.
- Mercuric Sulfate [HgSO₄]: Odorless white crystalline powder.
- 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.
- 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.