80 G. Edgar — Estimation of Iron and Vanadium. 



be boiled repeatedly with hydrochloric acid to reduce the vana- 

 dic acid, the hydrochloric acid removed by means of sulphuric, 

 and the vanadium titrated with permanganate. If then the 

 solution be reduced with hydrogen sulphide, the excess of gas 

 removed by boiling and the solution again titrated with per- 

 manganate, the difference between the two titrations will give 

 the iron present. Glasmann * effects the separation by adding 

 potassium iodide to the sulphuric acid solution, removing the 

 free iodine by means of sulphur dioxide, neutralizing with po- 

 tassium hydroxide, and precipitating the iron by means of a mix- 

 ture of potassium iodide and iodate. The liberated iodine is 

 removed by sodium thiosulphate, the ferric hydroxide filtered 

 off and the vanadium estimated in the filtrate. 



Among other methods of separation may be mentioned that 

 of Classen, f who precipitates the iron electrolytically from a 

 solution of the double oxalates, and Myers, % who deposits the 

 iron using a mercury cathode, the vanadium in both cases 

 remaining in solution. 



In view of the difficulties attendant upon the separation of 

 iron and vanadium, and in view of the increasing importance 

 of such substances as ferrovanadium and vanadate of iron, 

 composed almost entirely of these elements, it has been thought 

 advisable to present a method by which vanadium and iron 

 may be estimated in the presence of each other. 



If a solution containing vanadic acid and iron be reduced by 

 means of sulphur dioxide the reoxidation by potassium perman- 

 ganate proceeds according to the equation 



5Y 2 O 4 +10FeO+4KMnO 4 =5Y 2 O 5 + 5Fe 2 O 3 + 2K 2 O+4MnO(l) 



If this solution, after titration, be passed through a column 

 of amalgamated zinc in the Jones reductor, the receiving flask 

 being charged with a solution of ferric sulphate, the reduction 

 is carried, in the case of vanadic acid, to the condition of V 2 2 § 

 and the reoxidation by permanganate proceeds according to 

 the equation 



5Y 2 O 2 +10FeO + 8KMnO 4 = 5y 2 O 5 +5Fe 2 O 3 +4K 2 O + 8MnO (2) 



The difference in the number of cubic centimeters of per- 

 manganate used in the first and second titrations is evidently 

 used in oxidizing the vanadium from the condition of Y 2 2 to 

 V 2 4 , and multiplied by the factor -00156 (for exactly N/10 solu- 

 tions ) gives the amount of vanadic acid present. This being 

 known, the iron present may be calculated from the amount of 

 permanganate used in either titration. 



*J. russ. Phys. Chem. Ges., xxxvi, 77. 

 fBer. Dtsch. Chem. Ges., xiv, 2771-83. 

 %Z. Amer. Chem/Soc, xxvi, 1124. 

 §Gooch and Edgar, this Journal, xxv, 233. 



