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|Molar mass||207.32 g/mol|
|Except where noted otherwise, data are given for|
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references
Lewisite is a chemical compound from a chemical family called arsines. While it is a colorless and odorless liquid when pure it is usually found as an oily, brown liquid with a distinct odor similar to geraniums. It is a chemical weapon, acting as a vesicant (blister agent) and lung irritant, and can be used in combination with mustard gas as mustard-lewisite.
It can easily penetrate ordinary clothing and even rubber; upon skin contact it causes immediate pain and itching with a rash and swelling. Blisters develop after 12 hours, and discomfort lasts for 2 to 3 days. Sufficient absorption can cause systemic poisoning leading to liver necrosis or death.
Inhalation causes a burning pain, sneezing, coughing, vomiting, and possibly pulmonary edema. Ingestion results in severe pain, nausea, vomiting, and tissue damage. Generalised symptoms also include restlessness, weakness, subnormal temperature and low blood pressure.
Lewisite is usually found as a mixture of isomers, 2-chlorovinylarsonous dichloride should predominate but often bis(2-chloroethenyl)arsinous dichloride and tris(2-chlorovinyl) arsine are present. Lewisite can be given any of the preceding names and is also sometimes described as 2-chlorovinyldichloroarsine, (2-chloroethenyl)arsinous dichloride or dichloro- (2-chlorovinyl) arsine. Lewisite hydrolyses in water to form hydrochloric acid, and in contact with alkaline solutions can form poisonous trisodium arsenate.
It is named after the US chemist and soldier Winford Lee Lewis (1878-1943). In 1918 he found the thesis of Julius Arthur Nieuwland at Maloney Hall, a chemical laboratory part of The Catholic University of America, Washington, D.C. in which Nieuwland detailed the synthesis by the combination of allowing arsenic trichloride to react with acetylene in the presence of a hydrochloric acid solution of mercuric chloride.
It was developed into a secret weapon at Nilo Park, Ohio and given the name "the new G-34" to confuse its development with mustard gas. It was not used in the First World War, but experimented with in the 1920s as the "Dew of Death."
After World War I, the US became interested in Lewisite because it was not flammable. It had the military symbol of M1 up into World War II, when it was changed to L. Field trials with Lewisite during the World War II demonstrated that casualty concentrations were not achievable under high humidity due to its rate of hydrolysis and its charactistic odor and lacrymation forced troops to don masks and avoid contaminated areas. The United States produced about 20,000 tons of Lewisite, keeping it on hand primarily as an antifreeze for mustard gas or to penetrate protective clothing in special situations. It was replaced by the mustard gas variant HT (a 60:40 mixture of sulfur mustard and O Mustard), and declared obsolete in the 1950s. It is effectively treated with British anti-Lewisite (dimercaprol). Stockpiles of Lewisite were neutralized with bleach and dumped into the Gulf of Mexico.
Recently, mid 2006, it has been revealed in the world news media that China and Japan are still jointly cleaning up Japan's buried World War II stock of Lewisite in northeastern China. Japan is well behind on its commitment to clean up the site. Residents of China have died over the past twenty years from accidental exposure to the toxin. 
- Domingo Tabangcura, Jr. and G. Patrick Daubert, MD. British anti-Lewisite Development Molecule of the Month, University of Bristol School of Chemistry