Lewisite

Lewisite is a chemical compound. While it is a colourless and odourless liquid when pure it is usually found as a oily, brown liquid with a distinct odour similar to geraniums. It is a chemical weapon, acting as a vesicant and lung irritant, and can be used in combination as mustard-lewisite.

It can easily penetrate ordinary clothing and even rubber, on the skin there is 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 death or liver necrosis.

Inhalation causes a burning pain, sneezing, coughing, vomiting, and possibly lung oedema. Ingestion results in severe pain, nausea, vomiting, and tissue damage. Generalised symptoms also include restlessnesss, 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 preceeding names and is also sometimes described as 2-chlorovinyldichloroarsine, (2-chloroethenyl)arsinous dichloride or dichloro- (2-chlorovinyl) arsine. Its empirical formula is C₂H₂AsCl₃ and can be represented as ClCHCHAsCl₂. Its molecular mass is 207.32, melting point -18°C, boiling point 190°C, at 20°C its vapour pressure is 0.35 mm Hg and its density is 1.89 g/cm³. Lewisite hydrolises in water to form hydrochloric acid, in contact with alkaline solutions ti can form poisonous trisodium arsenate.

It is named after the US chemist and soldier Winford Lee Lewis. He discovered it at the Catholic University of America, Washington DC in 1918 by the synthesis of acetylene and arsenic trichloride, based on the 1904 work of Nieuwland. It was widely experimented with in the 1920s and most of the major combatants in WW II had stores of the chemical.

Lewisite can be decontaminated with British anti-Lewisite (BAL, 2,3-dimercaptopropanol). BAL was discovered just after WW II and effectively rendered Lewisite obsolete.