Gooch and Edgar — Reduction of Vanadic Acid. 233 



Art. XXVI. — The Reduction of Vanadic Acid hy Zinc and 

 Magnesium; by F. A. Gooch and Graham Edgak. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clxx.J 



A method recently proposed by B. Glasmann* for the esti- 

 mation of vanadic acid and molybdic acid in association with 

 one another, depends upon the dissimilarity in the action of 

 zinc and magnesium upon the former and the similarity in the 

 action of these metals upon the latter in the presence of hydro- 

 chloric acid. The method consists essentially in treating for 

 an hour to an hour and a half, in a flask closed with a Bunsen 

 valve, each of two aliquot portions of the solution containing 

 a vanadate and a molybdate, the one with zinc and hydrochloric 

 acid under gentle heating and the other with magnesium and 

 hydrochloric acid, opening the flasks to the air, pouring the 

 contents of each flask into a 500 cm3 porcelain dish containing 

 a solution of 10 gms. of manganese sulphate in 300 cm3 of air-free 

 boiling hot water, and titrating with potassium permanganate 

 while stirring actively. The amount of permanganate taken 

 in titrating the contents of the first flask is used presumably 

 in oxidizing the molybdenum from the condition of Mo 2 3 to 

 that of Mo0 3 and the vanadium from the condition of V 2 2 to 

 that of Y„0 5 : the amount of permanganate used in titrating 

 the contents of the second flask shows presumably oxidation 

 corresponding to a change of Mo 2 3 to Mo0 3 and to a change 

 of V 2 2 to V 2 6 . The difference between the amounts of per- 

 manganate used in the two titrations should presumably indi- 

 cate the oxidation of Y 2 2 to V 2 3 and so by calculation give 

 the amount of V 2 5 originally present in the solution. The 

 amount of Y 2 5 having been determined, the amount of Mo0 3 

 originally present is easily calculated from the amount of 

 permanganate used in either titration. 



It is plain that the value of the method depends largely 

 upon the definiteness with which vanadic acid may be reduced 

 to -the condition of V 2 3 by magnesium and left in the con- 

 dition of V 2 2 when the solution is treated with zinc and sub- 

 sequently exposed to the air. 



Concerning the reduction of vanadic acid by magnesium in 

 the presence of hydrochloric acid, Glasmann gives the data 

 and results of three experiments. f Of these two are in fair 

 agreement with the hypothesis ; but, unfortunately, the record 

 of the third experiment is affected by an error of about 10 

 per cent, either typographical or of calculation. It is likewise 



* Ber. Dtsch. chem. Ges. xxxviii, 600. 

 f Titrations Tabelle, II, loc. cit. 



Am. Jour. Sci.— Fourth Series, Vol. XXV, No. 147. — March, 1908. 

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