Ramesh Chandra and S. L. Sharma
D. A. V. College Jullundur, Panjab, India
Detection of Ferrocyanide, Ferricyanide, and Thiocyanate
Two procedures are available for the detection of ferrocyanide, ferricyanide, and thiocyanate in the presence of each other. Vogell suggests removal of ferrocyanide as thorium ferrocyanide, and subsequently, of ferricyanide as the cadmium salt. Dobbins2 recommends isolation of ferrocyanide and ferricyanide as cadmium salts along with some other anions, and their confirmation with iron(II1) chloride and benzidine respectively. The present authors have worked out a procedure which dispenses with the use of both thorium nitrate and cadmium sulfate, costly reagents in the authors' country. It is based on the fact that ferrocyanide gives a creamish white precipitate of variable composition with calcium chloride in the presence of ammonium chloride, while ferricyanide and thiocyanate remain in solution. Vogel prescribes elimination of ferricyanide before thiocyanate is tested. The present authors, however, find it unnecessary as the black-green color that develops on the addition of
' VOGEL,A. I., "A Textbook of Macro and Semimicro Qualitstive Inorganic Analysis," 4th ed., Longmans, Green and Co. Ltd., London, 1954, p. 427. %DOBBINS, J. T.,"Semimicro Qualitative Analysis," John Wiley &Sons Inc., New York, 1943, p. 375.
iron(II1) chloride to a solution of potassium ferricyanide is not extracted with ether, whereas iron(II1) thiocyanate is extracted with that solvent. In the procedure described, calcium chloride precipitates the same anions, along with the ferrocyanide, as are precipitated by thorium nitrate, viz. fluoride, oxalate, etc. These, however, do not interfere with the subsequent confirmation of ferrocyanide. The semimicro procedure is based on the assumption that 200 mg3of the mixture is taken for the preparation of the ''N&C03 prepared solution." I n a semimicro boiling tube prepare neutral solution from six drops of the "NazCO8 prepared solution" in the usual manner and almost saturate i t with solid NH,CI (about 0.2-0.3 g). Add 8-10 drops of 0.5 N CaCb, heat t o boiling, and let stand 1-2 minutes. Transfer t o a microcone and centrifuge. Use the ppt. far the confirmation of ferrocyanide and the centrifugate for the detection of ferricyanide and thiocyanate after checking for complete elimination of ferrocyanide. Fnrocyanidet Dissolve the residue in a few drops of hot 5 N HCI and add two drops of 0.5 N FPCI~. Blue ppt. or color confirms the presence of fewocyanide. F d c y a n i d e : Add two drops of 0.5 N FeSO. solution to six drops of the centrifugate. Blue ppt. or color shows the presence of fem'cyanide. Thiocyanate: Take six drops of the centrifugate and add 4-6 drops of 0.5 N FeC4, followed by 1 ml of ether. Shake several seconds. Red ethereal layer confirms the presence of thiocyanate. VOGEL,op. Cit., p. 304
Volume 39, Number 8, August 1962
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