Gooch & Scott — Determination of Vanadic Acid. 433 



solution was treated with silver sulphate (10 cm. 3 of the 

 saturated solution), heated to boiling, filtered from 

 the precipitated silver, diluted to a volume of 150 cm. 2 

 and titrated with standard permanganate. The carefully 

 determined correction in blank, amounting very regularly 

 to 0-2 cm. 3 of the permanganate solution, was applied to 

 the direct results of titration. The record of Table IV 

 shows plainly that excellent results may . be obtained 

 very rapidly in the reduction of vanadic acid with the use 

 of an electrolytic copper anode in the electrolytic cell, and 

 correction with silver sulphate for over-reduction, in the 

 manner described. 



Table IV. 



Redaction of Vanadic Acid by means of Electrolytic Copper in 

 the Electrolytic Cell and Correction by Silver Sulphate. 



v 2 5 



taken as 



ammonium 



vanadate 



grm. 



0-0784 

 00773 



0-0782 

 00776 



v 2 o 5 



found by 



KMn0 4 ' 



(corrected)* 



grm. 



•0782 

 •0775 

 •0784 

 •0778 



Error 

 grm. 



— 0002 



+•0002 

 +•0002 

 +•0002 



Period 



of 



reduction 



min. 



3-5 

 3-5 

 3-5 

 3-5 



Ee volu- 

 tions of 



anode: 

 number 

 per min. 



800 



800 

 800 

 800 



Approxi- 

 mate 

 strength 

 of current 

 amp. 



2 

 2 

 2 



2 



* 0-20 cm. 3 KMnO, solution. 



Reduction of Vanadic Acid by Zinc. — As is well known, 

 the reduction of vanadic acid in sulphuric acid solution is 

 easy and in the Jones reductor action may be readily 

 pushed to the stage of vanadium dioxide, V 2 2 . 5 It is to 

 be expected, therefore, that the reduction by means of the 

 rotating cylinder of zinc will be rapid without the aid of 

 the electric current; nevertheless, in our earlier experi- 

 ments with this device it was found that the dimensions of 

 the rotating cylinder must be considerable in relation to 

 the volume of liquid in order that the stirring of the liquid 

 may be sufficient to bring about the reduction with rapid- 

 ity. For example, at the end of seven minutes the 

 vanadic acid corresponding to 0-1 grm. of the ammonium 

 vanadate in the hot sulphuric acid solution was not com- 

 pletely reduced to the condition of the tetroxide, V 2 4 , by 

 the action of a rod of zinc 0-5 cm. in diameter, making a 



"Roscoe, Ann. Chem. Suppl. vi, 77, 1868; Glasman, Ber. d. chem. Ges., 

 38, 600, 1905; Gooch and Gilbert, this Journal, 15, 389, 1903; Gooch and 

 Edgar, ibid., 25, 233, 1908; ibid., 25, 322, 1908. 



Am. Jour. Sci. 

 15 



•Fourth Series, Vol. XLVI, No. 272.— August, 1918. 



