370 Oooch and Stookey — Reduction of Vanadic Acid 



of chlorine in marked decree. Three stages were noted in the 

 action of hydrochloric acid upon vanadic acid ; the vanadic 

 acid first dissolved to a solution of a deep brown color without 

 perceptible evolution of chlorine ; upon warming, the solution 

 suddenly evolved chlorine and took on a deep green color ; 

 thereafter the evolution of chlorine became weaker, and the 

 solution, giving off a small amount of chlorine on strong boil- 

 ing, assumed a clear blue color. After this, further heating 

 effected no change. It is recommended to raise the tempera- 

 ture gradually in order that the acid may not boil over into the 

 receiver, and to keep this receiver cool so that iodine may not 

 be volatilized by steam from the flask during the prolonged 

 heating. In the experiments with ammonium vanadate, in 

 which the heating was interrupted after the first violent evolu- 

 tion of chlorine, the iodine found in the receiver indicated, 

 according to Rosenheim's figures, about 50 per cent of the 

 vanadium pentoxide present ; in three experiments longer con- 

 tinued the indications advanced about H per cent ; and in three 

 experiments continued presumably to the end — to the appear- 

 ance of this blue color — the amount of pentoxide indicated 

 were 61'77 per cent, 63'71 per cent, 61*89 per cent of the 

 quantities actually taken, and further heating with another 

 receiver until almost all the hydrochloric acid had been volatil- 

 ized, resulted in no further progress in the reaction. Experi- 

 ments with potassium vanadate, and with vanadium pentoxide 

 resulted similarly. Rosenheim draws the inference that a 

 titrimetric method based upon a theory of reduction from Yfi^ 

 to Y5O4 by the action of hydrochloric acid, must lead to false 

 conclusions, and suggests that his results lend probability to 

 the supposition that an oxide of the formula (yfi^^SK ^^ 

 formed, although the actual reductions observed by him are 

 not quantitatively in accord with the formation of such a body 

 — which implies a reduction covering about %Q per cent of the 

 interval between Yfi^ and Yfi^. Rosenheim concludes that 

 the whole method is to be rejected in quantitative estimations. 

 An inspection of Rosenheim's tables, however, shows that the 

 standards of the solutions of thiosulphate and iodine have 

 been interchanged either in the printed record or in the cal- 

 culation of results. In the latter event the actual indications of 

 the process would be about 15 per cent higher than Rosen- 

 heim's figures, but still approximately 20 per cent below the 

 theory of the reduction from Yfi^ to Yfi^. 



In Holverscheit's^ hands the process gave results most irregu- 

 lar and unsatisfactory. Ammonium vanadate was the material 

 taken for the experiments, and the residue obtained by treat- 



* Inaug. Dissert. , Berlin, 1890, 



