Clark II, Jifuenirushianarushin, DC
Diphenylcyanarsine (Clark II) is a colorless crystalline solid that melts at 31.5 degrees C (91 degrees F) and boils/decomposes at 350 degrees C (662 degrees F). In its vapor form it is over eight times heavier than air. It is dispersed in the form of a dust which is not adsorbed by charcoal filters. It is a respiratory irritant which spreads into the lungs causing nausea and vomiting.
Old Chemical Weapons Reference Guide (1998)