Gooch and Curtis — Halogen Acids upon Vanadic Acid. 41 



Art. IV. — The Action of the Halogen Acids upon Vanadic 

 Acid ; by F. A. Gooch and R. W. Curtis. 



[Contributions from the Kent Chemical Laboratory of Yale University — CXXIII] 



In the study of the interactions between the halogen acids 

 and vanadic acid in solution made chiefly with a view to the 

 analytical applications, it has been shown that if conditions be 

 suitably fixed, vanadic acid may be reduced definitely by hydro- 

 chloric acid and by hydrobromic acid to a condition of oxida- 

 tion corresponding to that of the tetroxide, V 2 4 , and that 

 hydriodic acid may carry the reduction to the stage of the 

 tetroxide or to that of the trioxide, V 2 3 , according to condi- 

 tions. It is the object of this paper to record some results of 

 further study of the conditions of action between vanadic acid 

 and the halogen acids. 



The Reducing Action of Hydrochloric Acid. 



It has been shown in an article from this laboratory* that 

 the reaction of the process, according to which a suitable 

 vanadate is treated with hydrochloric acid, the solution boiled, 

 and the evolved chlorine determined as suggested by Bunsen,f 

 noted by Mohr,^ and utilized by Gibbs,§ is nearly complete in 

 a single operation when the concentration of the hydrochloric 

 acid is sufficient, and that an approximately correct determina- 

 tion of the vanadium may be made by the process when 

 special care is taken to register all the chlorine set free. It 

 appeared, however, that the reaction is reversible, and that in 

 the ordinary process involving a single treatment of the vana- 

 date with strong hydrochloric acid and boiling, the tendency 

 to reverse is not fully overcome. When hydrochloric acid of 

 suitable concentration and the vanadate come to contact, the 

 evolution of chlorine is immediate, some chlorine escapes 

 from the solution, some is retained, and the reaction proceeds 

 to a balance as indicated in the expression 



V,0 6 +2HClzV a 4 +H 3 0+Cl 3 . 



To complete the reduction of the higher oxide it is neces- 

 sary to remove the free chlorine from the system while keep- 

 ing up the requisite strength of the hydrochloric acid. In 

 removing the chlorine by boiling, the concentration of the 

 hydrochloric acid is diminished below the point at which 

 action upon vanadic acid may take place with liberation of 

 chlorine. This is why in pushing the action to completion by 

 the boiling process, it is necessary to increase the concentra- 

 tion of the hydrochloric acid from time to time either by 

 cooling and recharging with gaseous acid or by evaporating off 

 the weak acid and replacing it by strong acid. 



* Gooch and Stookey, this Journal, xiv ? 369 (1902). 



fAnn. Chem. (Liebig), lxxxvi, 265. % Titrirmethode, 5 te AufL, 314. 



SProc. Amer. Acad., xviii, 250. 



