Palmer — Potassium Ferricyanide in Alkaline Solution. 141 



Art. XI. — The Apj)lication of Potassium Ferricyanide in 

 Alkaline Solution to the Estimation of Vanadium, and 

 Chromi'icm ; by Howard E. Palmer. 



[Contributions from the Kent Chemical Laboratory of Yale Univ.— ccxiii.] 



In previous pajiers from this laboratory methods for the 

 estimation of cerinm in the presence of the other rare earths,* 

 for the estimation of thallium, f and for the estimation of 

 arsenic, antimony, and tin;}; have been described, based on the 

 oxidizing action of potassium ferricyanide in alkaline solution, 

 and reoxidation by permanganate of the resulting ferrocyanide 

 in acid solution. 



The present paper deals with the application of these reac- 

 tions to the estimation of vanadium and chromium. The 

 reactions involved may be represented by the following 

 equations : 



V,0, + 2K3FeCA + 2KOH=V,0, + 2K,FeC,N, + H,0. 

 Cr^O, + 6K3FeC„N„ + 6KOH= 2CiO, + 6K,FeO,N ^ + 3H,0. 

 5K,FeC,N, + KMnO, + 4H,S0,= 



5K3FeC„N„ + 3K,S0, + MnSO, + 4H,0. 



Estimation of Vanadium. 



A solution of ammonium vanadate was made up by dissolv- 

 ing pure ammonium vanadate in M^ater, and standardized by 

 evaporating definite portions in a platinum crucible and weigh- 

 ing as V^O, after ignition. 



Through definite portions of the standardized solution of 

 ammonium vanadate, made slightly acid with hydrochloric acid, 

 a current of sulphur dioxide was passed until the clear blue 

 color indicated complete reduction of the vanadium to the con- 

 dition of YjO,. The solution was then boiled in a current of car- 

 bon dioxide until the last traces of sulphur dioxide were removed. 

 To the cooled solution a solution of potassium ferricyanide 

 containing at least ten times as much ferricyanide as is theoret- 

 ically necessary for the oxidation, and a solution containing 

 about 6 grams ol' potassium hydroxide were added, having the 

 solutions of ferricyanide and potassium hydroxide sufficiently 

 concentrated so that the total volume of the solution was about 

 100 or 125 cubic centimeters. At least the amounts of ferri- 

 cyanide and potassium hydroxide stated were found to be nec- 

 essary to ensure complete oxidation of the vanadium with the 

 concentration employed, and if the solution was more dilute, 

 more ferricyanide was required. It then became necessary to 

 remove the vanadium before acidification and titration with 



* This Journal, xxvi, 83, f Ibid., xxvii, 379. % Ibid., xxix, 399. 



