234 Gooch and Edgar — Reduction of Vanadic Acid. 



interesting to note, though the conditions are different, that 

 in Roscoe's study of the behavior of vanadic acid in the 

 presence of magnesium and sulphuric acid,* to which Glas- 

 mann refers, the variation in the degree of reduction is like- 

 wise considerable, amounting to more than 2 per cent. 



As to the reduction of vanadic acid by zinc, Roscoe's results 

 show a degree of reduction approaching that of V,0„ but 

 with variations of as much as 3 per cent ; and it is well known 

 that the oxidation of solutions thus reduced proceeds rapidly 

 and ultimately results in the condition represented by V,0 4 f 

 Whether reductions may be kept regular and the action of 

 air made so small as not to vitiate the analytical results of 

 Glasmann's method during the short exposure, are matters 

 for experimental determination. According to Glasmann's 

 results in these experiments, the interference w^ould seem to be 

 inappreciable, but here again the calculated results are not in 

 complete accord with the printed data.;}: 



It has seemed desirable, therefore, to consider further the 

 accuracy which may be expected under the conditions of 

 analysis in the reduction of vanadic acid by magnesium and 

 by zinc. 



Reduction by Magnesium. 



Portions of a solution of sodium vanadate, standardized by 

 the very accurate method of Holverscheit,§ were reduced by 

 magnesium in the presence of hydrochloric acid or sulphuric 

 acid. 



In each of the experiments of Table I, A, the reduction 

 was made, in a funnel-trapped flask, by magnesium in the 

 presence of hydrochloric acid added gradually to properly 

 moderate the action. After the magnesium had been used up, 

 the contents of the flask were added to 800 cmS of boiled water 

 containing 1 grm. of manganese sulphate and 2 cm3 of sulphuric 

 acid, and titration was made with nearly JST/IO potassium per- 

 manganate. The conditions of the experiment were essen- 

 tially those of Glasmann's method in respect to reagents and 

 time of action. 



In the experiments of Table I, B, the treatment was modi- 

 fied so that the action might be slower and long continued, 

 with a view to bringing about better contact of the vanadium 

 solution with the magnesium cushioned by evolved hydrogen. 

 The reduction was made in a stoppered flask connected with a 

 hydrogen generator, arranged for the maintenance of an 

 atmosphere of hydrogen during the period of reduction, and 



* Ann. Chem. Suppl. vi, 77 (1868). 



fRoscoe, loc. cit. ; Gooch and Gilbert, this Journal, xv, 390. 



% Titrations Tabelle, I, loc. cit. 



§Inaug. Diss. Berlin, 1890. 



