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Main article: "Saturated calomel electrode

Mercurous chloride is employed extensively in "electrochemistry, taking advantage of the ease of its oxidation and reduction reactions. The calomel electrode is a "reference electrode, especially in older publications. Over the past 50 years, it has been superseded by the silver/silver chloride (Ag/AgCl) electrode. Although the mercury electrodes have been widely abandoned due to the dangerous nature of "mercury, many chemists believe they are still more accurate and are not dangerous as long as they are handled properly. The differences in experimental potentials vary little from literature values. Other electrodes can vary by 70 to 100 millivolts.["citation needed]


Mercurous chloride decomposes into "mercury(II) chloride and elemental mercury upon exposure to UV light.

Hg2Cl2 → HgCl2 + Hg

The formation of Hg can be used to calculate the number of photons in the light beam, by the technique of "actinometry.

By utilizing a light reaction in the presence of "mercury(II) chloride and "ammonium oxalate, mercury(I) chloride, "ammonium chloride and "carbon dioxide are produced.

2HgCl2 + (NH4)2C2O4 + Light → Hg2Cl2(s) + 2[NH4+][Cl] + 2CO2

This particular reaction was discovered by J.M. Eder (hence the name Eder reaction) in 1880 and reinvestigated by W. E. Rosevaere in 1929.[10]

Related mercury(I) compounds[edit]

"Mercury(I) bromide, Hg2Br2, is a light yellow, whereas "mercury(I) iodide, Hg2I2, is greenish in colour. Both are poorly soluble. "Mercury(I) fluoride is unstable in the absence of a strong acid.

Safety considerations[edit]

Mercury poisoning

Mercurous chloride is "toxic, although due to its low solubility in water it is generally less dangerous than its "mercuric chloride counterpart. It was used in medicine as a "diuretic and "purgative (laxative) in the "United States from the late 1700s through the 1860s. Calomel was also a common ingredient in "teething powders in Britain up until 1954, causing widespread mercury poisoning in the form of "pink disease, which at the time had a mortality rate of 1 in 10.[11] These medicinal uses were later discontinued when the compound's toxicity was discovered.

It has also found uses in cosmetics as soaps and "skin lightening creams, but these preparations are now illegal to manufacture or import in many countries including the US, Canada, Japan and the European Union.[12] A study of workers involved in the production of these preparations showed that the sodium salt of "2,3-dimercapto-1-propanesulfonic acid (DMPS) was effective in lowering the "body burden of mercury and in decreasing the urinary mercury concentration to normal levels.[13]


  1. ^ "Mercury compounds [except (organo) alkyls] (as Hg)". Immediately Dangerous to Life and Health. "National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. "ISBN "0-618-94690-X. 
  3. ^ a b c d e Wikisource-logo.svg Chisholm, Hugh, ed. (1911). "Calomel". "Encyclopædia Britannica (11th ed.). Cambridge University Press. 
  4. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. pp. 696–697. "ISBN "978-0130399137. 
  5. ^ Skoog, Douglas A.; Holler, F. James; Nieman, Timothy A. (1998). Principles of Instrumental Analysis (5th ed.). Saunders College Pub. pp. 253–271. "ISBN "0-03-002078-6. 
  6. ^ Buczacki, S., Pests, Diseases and Disorders of Garden Plants, Collins, 1998, pp 449-50. "ISBN 0-00-220063-5
  7. ^ Koehler, Christopher S. W. (January 2001). "Heavy Metal Medicine". Today's Chemist at Work. "American Chemical Society. 10 (1): 61–65. "ISSN 1062-094X. Retrieved 2009-02-02. 
  8. ^ Johnston, Elizabeth Lichtenstein (1901). Recollections of a Georgia Loyalist...written in 1836. New York: Mansfield & Company.  pp. 82-83.
  9. ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications "ISBN 0-19-855370-6
  10. ^ Roseveare, W. E. (1930). "The X-Ray Photochemical Reaction between Potassium Oxalate and Mercuric Chloride". "J. Am. Chem. Soc. 52 (7): 2612–2619. "doi:10.1021/ja01370a005. 
  11. ^ Sneader, Walter (2005). Drug Discovery: A History. "John Wiley and Sons. pp. 45–46. "ISBN "0-471-89980-1. Retrieved 2009-02-02. 
  12. ^ "Commission Directive 86/199/EEC, OJ L 149, p. 38 of 3.6.1986". 
  13. ^ D. Gonzalez-Ramirez; M. Zuniga-Charles; A. Narro-Juarez; Y. Molina-Recio; K. M. Hurlbut; R. C. Dart; H. V. Aposhian (1 October 1998). "DMPS (2,3-Dimercaptopropane-1-sulfonate, Dimaval) Decreases the Body Burden of Mercury in Humans Exposed to Mercurous Chloride" (free full text). Journal of Pharmacology and Experimental Therapy. 287 (1): 8–12. "PMID 9765315. 

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