| The irritating substance diphenylchloroarsine (or diphenylchlorarsine, DA) was first synthesized by Michaelis and LaCoste in 1881. The latter researcher described DA as having “a very powerful irritant action on the mucous membranes of the eyes and nose, causes painful blistering of the skin, and is very dangerous for those working with it, since its vapor causes respiratory embarrassment, faintness, and long-lasting paralysis and anesthesia of the extremities.” These effects, however, required exposure to considerable quantities before manifesting themselves, and because of the entry of mustard (a far superior blister and casualty agent) in World War I, DA proved to be less attractive as a chemical weapon.
Because of their intense effects on the nasal and upper respiratory passages, DA and similar compounds were referred to as “sneeze gas” (sternutators). Like other arsenicals, DA is a white solid, and was originally produced as both a casualty gas and a mask breaker during World War I (first used by Germany in 1917). Military doctrine in World War I involving the use of DA counted on its being able to force soldiers to remove their protective masks, and thus becoming vulnerable to it or other chemical agents. In order to deliver this chemical on the battlefield, DA can be disseminated in powder form (e.g., in a munition), or vapors can be formed by heating it in its solid form. Only very low concentrations of DA are needed to cause severe irritation of the nose and throat, approximately 0.0005 mg per liter of air. The median incapacitating dose (ICD50) of DA is approximately 12mg-min/m3, while the median lethal dose (LD50) is estimated at 15,000mg-min/m3. Due to the availability of other compounds with greater activity and ease of weaponization, however, less importance is attached to DA as a chemical weapon threat nowadays.
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