428 Gooch & Scott — Determination of Vanadic Acid. 



Reduction by Massive Silver. — The first experiments 

 with massive silver were made to test the effect of 

 increasing the superficial area of the silver which is 

 exposed to the action of the vanadic and sulphuric acids. 

 In these experiments pure sheet silver weighing about 5 

 grm. and measuring about 2 centimeters square and a 

 millimeter thick was cut with radial slits, bent to rose 

 form and placed in a trapped Erlenmeyer flask, in a solu- 

 tion made by dissolving the ammonium vanadate in water 

 (50 cm. 3 ) and adding sulphuric acid. The solution was 

 boiled, the volume of the liquid, 75 cm. 3 at the start, being 

 kept above 60 cm. 3 by addition of water as necessary dur- 

 ing the process. At the end of the boiling the silver was 

 removed from the liquid, washed, dried by heating gently 

 and weighed, the loss in weight representing the vana- 

 dium pentoxide reduced according to the expression 

 2Ag V 2 5 . In three of these experiments, the reduced 

 vanadic acid in hot solution was titrated by nearly N/10 

 potassium permanganate standardized against sodium 

 oxalate. A correction (amounting to 0-12 cm. 3 ; 0-00082 

 grm. in terms of V 2 5 ) for the permanganate required to 

 produce a reading color in a similar solution of sul- 

 phuric acid, silver sulphate and unreduced vanadic acid 

 was applied in these determinations. The details of 

 these experiments are given in Table I. 







Table I. 









Reduction of Vanadic Acid by Massive Silver in the 

 Boiling Solution. 





v 2 o 5 



taken as 



mmonium 



vanadate 



grm. 



Loss of 

 silver 

 grm. 



v 2 o 5 



equivalent 



to loss of 



silver 



grm. 



V 2 3 



equivalent 



to KMn0 4 



(corrected) 



grm. 



Error 



by loss of 



silver 



grm. 



By KMn0 4 



process 



grm. 



Time 

 min. 



0-0776 

 0-0807 

 0-0803 

 0-0777 



00902 

 0-0950 

 00941 

 0-0920 



0-0762 

 0-0803 

 00795 

 00777 





—00014 



—0-0004 



—0-0008 



00000 





20 

 25 

 25 

 35 



0-0807 

 00777 

 0-0803 



00950 

 00920 

 00941 



00803 ' 



0-0777 



0-0795 



0-0806 

 0-0778 

 00803 



—00004 



0-0000 



—0-0008 



—00001 



+0-0001 

 00000 



30 

 30 

 30 



These experiments show that massive silver of suffi- 

 cient surface may effect the reduction of vanadic acid 

 within a reasonable time from the boiling solution con- 



