432 Gooch & Scott — Determination of Vanadic Acid. 



copper the amount of the permanganate solution neces- 

 sary to produce the reading color (in a solution which 

 had undergone treatment precisely as in the usual deter- 

 minations, excepting that the ammonium vanadate was 

 added just before the titration and after the electrolysis, 

 treatment with silver sulphate, boiling, and nitration) 

 was regular and definite. 



Table III. 



Rate of Reduction of Vanadic Acid with the Aid of 

 the Anode of Commercial Copper: 



Preliminary Experiments. 



v 2 o 5 



taken as 



ammonium 



vanadate 



grm. 



v 2 o 5 



found by 



KMn0 4 



(corrected) 



grm. 



Error 

 grm. 



A. 



Period 



of 



reduction 



min. 



Revolutions 



of 



anode 



(approx.) 



per min. 



Strength 



of 



current 



amp. 





At room temperature: 20° 



-23°. 





0-0781 

 0-0784 

 00779 

 0-0784 

 0-0780 

 0-0781 

 00783 

 0-0784 



0-0203 

 0-0292 

 00432 

 00533 

 0-0587 

 0-0680 

 0-0787 

 00953 



—0-0578 

 —00492 

 —00347 

 —00251 

 —00193 

 —00101 

 +0-0004 

 +0-0169 



2 

 3 

 4 

 5 

 6 

 7 

 9 

 11 



800 



800 



800 , 



800 



900 



800 



800 



800 



2 

 2 



2 

 2 

 2 

 2 



2 

 2 





is. 



Started at boiling temperature. 





00779 

 0-0784 

 00779 



00563 

 00809 

 00944 



—00216 

 +0-0025 

 +0-0165 



2 

 3 

 4 



800 

 800 

 800 



2 



2 

 2 



In the experiments recorded in Table IV, therefore, 

 the anode was made of electrolytic copper plated from a 

 solution of iron-free copper sulphate upon a silver tube. 

 The conditions of action were similar to those of the pre- 

 viously described experiments with the silver anode: 

 viz. — volume of solution heated to boiling at the outset, 75 

 cm. 3 ; sulphuric acid (cone), 5 cm. 3 ; diameter of anode 

 2-5 cm. and area exposed to action, 30 cm. 2 ; area of plat- 

 inum cathode, 10 cm. 2 ; revolutions of anode, about 800 

 per minute. At the end of the process of reduction the 



