determination of cyanide in effluents

The method described for the determination of cyanide in effluents involves distillation of hydrogen cyanide from the solution, using zinc acetate to fix any ferrocyanide or ferricyanide which may be present, followed by absorptiometric determination using the pyridine-benzidine hydrochloride reagent in a modification of ALDRIDGE's method (see W.P.R. Summary, 1944, 17, Abstr. No. 902). Test results are tabulated, showing that, under the conditions described, the method is suitable for the determination of cyanide in concentrations of up to 3 p.p.m. in effluents also containing thiocyanate (in concentrations of up to 25 p.p.m. as cyanide), ferrocyanide and ferricyanide (in concentrations of up to 5 p.p.m. as cyanide), and sodium and calcium chlorides. The method has an accuracy of 0.01 p.p.m. to 0.05 p.p.m., depending on the concentrations of these substances.