What is "diphenylcyanoarsine"

n. A chemical compound that forms colourless, garlic-smelling crystals and causes nausea and headaches, used by the Germans during World War I.

Diphenylcyanoarsine, also called Clark 2 (Chlor-Arsen-Kampfstoff 2, being the successor of Clark 1) by the Germans, was discovered in 1918 by Sturniolo and Bellinzoni and shortly thereafter used like the related Clark 1 gas by the Germans for chemical warfare in the First World War. The substance forms colourless, garlic-smelling crystals and causes nausea, vomiting and headaches. It can subsequently lead to e.g. pulmonary oedema (fluid on the lungs).