336 Edgar — Estimation of Chromic and Vanadic Acids. 



of the vanadium tetroxide to trioxide as indicated in the 

 equation, 



V 2 4 + 2HI=V 2 3 + 2l + H 2 

 The second titration, therefore, determines the vanadic acid 

 present, and the difference between the first and second fur- 

 nishes the necessary data for the calculation of the chromium. 

 From the small error shown in the results of Table I it is 

 evident that vanadic and chromic acids may be accurately 

 estimated in the presence of one another by the differential 

 reducing action of hydrobromic and hydriodic acids under the 

 conditions used above, the liberated halogen being absorbed in 

 potassium iodide solution and the iodine titrated with sodium 

 thiosulphate. 



