Zyklon B

Zyklon B was the trade name of a cyanide-based pesticide invented in Germany in the early 1920s. It consists of hydrogen cyanide, as well as a cautionary eye irritant and one of several adsorbents such as diatomaceous earth. The product is notorious for its use by Nazi Germany during the Holocaust to murder approximately 1.1 million people in gas chambers installed at Auschwitz-Birkenau, Majdanek, and other extermination camps. (Wikipedia)