Ethyldichloroarsine, also known as ED, CY, and ethyl Dick, is an organoarsenic compound with the formula CH<sub>3</sub>CH<sub>2</sub>AsCl<sub>2</sub>. This colourless volatile liquid is a highly toxic vesicant (blister agent) that was used during World War I in chemical warfare. The molecule is pyramidal with the ClâÂÂAsâÂÂCl and CâÂÂAsâÂÂCl angles approaching 90ð (see image). Ethyldichloroarsine has high chronic toxicity, similar to lewisite.