Rapid quantitative spot test performed on gastric aspirate. A 5 ml sample is mixed with several crystals of ferrous sulfate and 4-5 drops of 2% NaOH (this will precipitate any iron present), boiled, and cooled; then 8-10 drops of 10% HCl are added. Cyanide is present if precipitate intensifies or blue-green color develops. Purplish color indicates presence of salicylate without cyanide, and immediate formation of blue-green indicates presence of both salicylates and cyanide.