Redactor in the Estimation of Vanadic Acid. 391 



The action of the molecular oxygen of the air is obviously 

 insufficient to bring about the complete oxidation of the lower 

 vanadium oxides in acid solution to the condition of the 

 tetroxide within a reasonable time, and ordinary oxidizers carry 

 the action too far, oxidizing the tetroxide as well as the lower 

 oxides. We have found, however, that silver oxide and silver 

 salts will supply oxygen in a condition of activity sufficient to 

 affect the lower oxides easily while leaving the tetroxide intact. 

 Silver sulphate appears to be the most convenient form in 

 which to use the silver compound. 



In making our experiments with silver sulphate the solu- 

 tion of the vanadic acid was treated in the reductor in the 

 manner described except that the receiving flask was charged 

 at the outset with a saturated solution of silver sulphate 

 — 100 cm3 in each of the first six experiments ; 300 cm3 in the last 

 two. The contents of the flask were boiled and then filtered 

 upon asbestos in a perforated crucible. The solution, now about 

 T00 cm3 in volume, was heated again to the boiling point and 



N 

 titrated with — potassium permanganate. When the reduced 



solution issuing from the reductor meets the silver sulphate a 

 muddy deposition of finely divided silver begins; but upon 

 boiling the mixture the metallic silver gathers into a single 

 spongy mass and leaves the solution so clear that were it not 

 that spongy silver is easily acted upon by the permanganate* 

 the titration might be made without previous filtration. 



Table II. 

 KMn0 4 



V 2 5 

 taken. 



grms. 

 0-0767 

 0-0767 

 0-0767 

 0-0767 

 0-0767 

 0-0767 

 0-1918 

 0-1918 



The results 

 panying table. 



required, 



i N 

 nearly^. 



cm 3 . 

 17* 

 . 17*04 

 17-05 

 16-96 

 16-98 

 17- 

 42-9 

 42-7 



V 2 5 

 found, 

 grms. 

 0-0770 

 0-0771 

 0-0772 

 0-0768 

 0-0769 

 0-0770 

 0-1942 

 0-1933 



Error. 



grms. 

 + 0-0003 

 + 0-0004 

 + 0-0005 

 + 0-0001 

 + 0-0002 

 + 0-0003 

 + 0-0024 

 + 0-0015 

 in the accom- 

 vanadium the 



of these experiments are given 

 For the smaller amounts of 

 determinations are accordant and exact. The wider variations 

 in the last two experiments are probably due to the difficulty 

 of catching the pink end reaction in presence of the reddish 

 yellow color which appears as the vanadic acid is formed in 

 considerable amount. This is a difficulty inherent in the per- 

 manganate process of titration when large amounts of vanadic 

 acid are involved. 



* Giles : Chem. News, xv, 204 (1867). Otto van der Pfordten : Ber. d. d. 

 Chem. Ges., xx, 3375. Friedheim : Ber. d. d. Chem. Ges., xx, 2554. 



