Gooch and Curtis— Halogen Acids upon Yanadic Acid. 45 



the liquid and boiling, apparently reached the stage of V a .O„ 

 but, inasmuch as the purity of the synthetic hydrobromic acid 

 was not thoroughly established, we do not regard this particu- 

 lar result as wholly trustworthy. 



The Reducing Action of Hydriodic Acid. 



According to Rosenheim* vanadic acid is not completely 

 reduced to the condition of the tetroxide by the hydriodic 

 acid made nascent when sulphuric acid and potassium iodide 

 interact, analytical results showing an apparent reduction of 

 80 per cent or less. A comparison of the calculated figures 

 with the recorded amounts of the reagents and their standards 

 raises the question as to whether the standards have not been 

 interchanged in the computation^ and in this event Rosen- 

 heim's figures would approximate 100 per cent as nearly as 

 could be expected under the described conditions of manipula- 

 tion. Friedheim and Euler echo Rosenheim's statement.:}; 

 Browning,§ on the other hand, has shown that good analytical 

 results are obtained when solutions of the vanadate, one or two 

 grams of potassium iodide and 10 cm3 Of sulphuric acid of half- 

 strength are boiled to a volume of about 35 cm3 and the residual 

 solution is cooled, neutralized with an alkaline bicarbonate 

 (after the addition of a tartrate to prevent precipitation) and 

 treated for some time with an excess of iodine which is fol- 

 lowed by an excess of arsenious acid, the last being titrated by 

 iodine to the blue end-reaction in presence of starch. 



In Browning's process the estimation of the reduced product 

 in the residue is made the measure of action. In section A of 

 the following table are given the results of experiments in 

 which the treatment was conducted in an atmosphere of carbon 

 dioxide and in which the determinations of the iodine collected 

 in the receiver are set over against the determinations of the 

 reduction in the residue by Browning's process, omitting the 

 addition of a tartrate. 



In section B are given results of experiments differing from 

 those of section A in that in treating the residue the excess of 

 iodine was added before neutralizing with potassium bicar- 

 bonate so that re-oxidation should not be effected in the 

 sensitive alkaline solution by atmospheric oxygen rather than 

 by the iodine which is measurable. 



It will be noted that in every experiment the iodine found 

 in the receiver indicates a trifling reduction beyond the con- 

 dition of the tetroxide V 2 4 , averaging 0-0023 gm. ; and the 

 same in general is true in regard to those determinations of 



* Inaug. Dissert., Berlin, 1888, p. 18. 



f Compare the standard of solutions on p. 15 loc. cit. with the computed 

 results of tables on pp. 15 and 18. 

 JBer. Dtsch. chem. Ges., xxviii, 2070. § This Journal, ii, 185 (1896). 



