Gooch & Scott — Determination of Vanadic Acid. 429 



taming sulphuric acid, a reacting surface of about 10 cm. 2 

 of silver insuring the complete reduction of vanadic acid 

 equivalent to about 0-08 grm. of vanadium pentoxide 

 within thirty minutes. Xo advantage was gained when 

 the liquid was stirred by a cylinder of silver or a silver- 

 platinum couple rotating rapidly in the hot solution. 

 We have, however, been able to effect a very considerable 

 improvement in the rapidity of reduction of vanadic acid 

 in presence of sulphuric acid by the use of a rapidly 

 rotating anode of silver in the electrolytic cell containing 

 the dissolved acids. 



Reduction with the Aid of the Silver Anode. — It has 

 been shown by Truchot 2 that when vanadic acid in the 

 presence of very small amounts of sulphuric acid is sub- 

 mitted to the slow action of an electric current of low 

 amperage, between platinum electrodes, vanadium in a 

 condition of oxidation lower than that of the tetroxide 

 may be deposited upon the cathode. The presence of too 

 much sulphuric acid interferes with this deposition. 

 In some experimenting with the rapid reduction of 

 vanadic acid between platinum electrodes in. dilute sul- 

 phuric acid and at high amperage we have found, as is 

 natural (inasmuch as the reduced vanadium compounds 

 remain in solution), that the reduction is irregular and 

 dependent upon the relation of the areas of the anode and 

 the cathode. Our attention was directed, therefore, to the 

 use of an electrolytic cell in which a rapidly rotating 

 cylinder of silver served as the anode. 



In the following experiments, the amounts of ammo- 

 nium vanadate indicated (approximately 0-1 grm.) were 

 dissolved in 75 cm. 3 of hot water, sulphuric acid (10 cm. 3 

 1 :1) was added and the solution was heated to the boiling 

 temperature and then submitted to the action of the elec- 

 tric current passing between a rotating silver anode and 

 a stationary platinum cathode measuring 2 cm. X 5 cm. 

 For the silver anode we made use of a cylindrical silver 

 crucible, 10 cm. long and 2-5 cm. in diameter, dipping in the 

 liquid to a depth of about 4 cm. and exposing to action a 

 surface of about 30 cm. 2 which, after considerable use had 

 resulted in the eating away of the bottom of the crucible 

 so that the anode became an open tube, was practically 

 doubled. The anode was attached to the rotating spindle 



2 Ann. Chem. Anal., 7, 165, 1902. 



