This webpage is maintained by the Centers for Disease Control and Prevention (CDC). The webpage provides information and resources on Lewisite. "Lewisite is a type of chemical warfare agent. This kind of agent is called a vesicant or blistering agent, because it causes blistering of the skin and mucous membranes on contact. [...] Lewisite is an oily, colorless liquid in its pure form and can appear amber to black in its impure form. [...] Lewisite has an odor like geraniums. [...] Lewisite contains arsenic, a poisonous element. [...] Lewisite is also known by its military designation, 'L.'"
Centers for Disease Control and Prevention: http://www.cdc.gov/