BS.
Sodium cyanide, NaCN, is water-soluble solid.
It releases Hydrogen Cyanide, NCN, as a gas when exposed to an acid. That is what the gas chamber in California used. Dropped Sodium cyanide into a pail of hydrochloric acid which produced Hydrogen Cyanide, killing the occupants of the chamber.
A hydrogen cyanide concentration of 3500 ppm (about 3200 mg/m3) will kill a human in about 1 minute.
Opps. HCN not NCN.. damn fat fingers.