Cyanide

"All forms of cyanide are poisonous, [including] cyanide salts (such as sodium cyanide and potassium cyanide) either solids or dissolved in liquids, and the gas, hydrogen cyanide (also known as hydrocyanic acid or prussic acid). Hydrogen cyanide gas is commonly called cyanide gas. ... Cyanide salts are used in metallurgy, mainly gold extraction, electroplating and metal cleaning." 

Also see Wikipedia: cyanide.

Facts About Cyanide and Emergency Preparedness & Response, Centers of Disease Control.

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