cyanide in the alkaline distillate from preliminary treatment is converted to CNCl by reaction with choramine-T at pH < 8 without hydrolyzing to CNO. After the reaction is complete, CNCl forms a red-blue color on addition of a pyridine-barbituric acid reagent. Maximum color absorbance in aqueous solution is between 575 and 582 nm. To obtain colors of comparable intensity, have the same salt content in sample and standards.