Goocli & Scott — Determination of Vanadic Acid. 427 



Akt. XIV. — The Application of Rapidly Rotating Metal- 

 lic Redactors in the Determination of Vanadic Acid; 

 by F. A. Gooch and Walter Scott. 



(Contributions from the Kent Chemical Laboratory of Yale Univ., — ccci.) 



I. 



The Reduction of Vanadic Acid in Analysis. 



It has been shown by Edgar 1 that vanadic acid in solu- 

 tion with sulphuric acid or hydrochloric acid may be 

 reduced definitely to the condition of the tetroxide by the 

 action of metallic silver, also that the reaction between 

 silver and vanadic acid in presence of sulphuric acid, may 

 be applied in extremely accurate methods for the deter- 

 mination of vanadium, the amount of that element being- 

 indicated either by the loss in weight of the silver, by 

 titration of the dissolved silver sulphate with standard 

 thiocyanate, or by oxidation of the vanadium tetroxide 

 by standard permanganate. It was found that massive 

 silver in the form of fine wire (1-5 grm.) gave complete 

 reduction of 0-1200 grm. V 2 5 , but only after long boiling 

 (1 hr.) of the solution in contact with that metal, and 

 that the form of silver best adapted to the purpose was 

 electrolytic silver deposited from the nitrate solution as a 

 "bush" of finely divided crystals subsequently purified 

 by boiling in dilute sulphuric acid, filtering off in an 

 alundum crucible, and igniting to a low red heat. With 

 silver thus prepared the action is very rapid in a boiling 

 solution of the vanadic and sulphuric acids and a com- 

 plete reduction of an amount of vanadic acid equivalent 

 to 04200 grm. of the pentoxide was obtained by boiling 

 for ten minutes with 2 grm. of the silver. 



The work of which an account is here given originated 

 in an attempt to substitute massive silver for the 

 finely divided silver, the preparation of which is some- 

 what elaborate. Subsequently the experimentation was 

 extended to" the similar use of copper and of zinc as the 

 reducing metal. In all the experiments to be described 

 the vanadic acid acted upon by the reducer was liberated 

 by sulphuric acid from a preparation of ammonium vana- 

 date which yielded on ignition an average content of 

 77-25% of vanadium pentoxide. 



1 Jour. Am. Chem. Soc, 38, 1297, 1916. 



