33tt Edgar — Estimation of Chromic and Vanadio Acids. 



That vanadic acid is reduced under proper conditions to the 

 state of tetroxide by hydrobromic acid has been shown by 

 Holvescheit,* and that the reduction may be carried to the 

 state of trioxide by hydriodic acid has been shown by Fried- 

 ham and Euler,f by Gooch and Curtis4 and by Steffan.g 

 Chromic acid, however, is reduced to a chromic salt by both 

 hydrobromic|| and hydriodic acid. In 1895, Friedheim and 

 Euler^[, in connection w T ith their work upon the estimation of 

 vanadic and molybdic acids, suggested that vanadic and chromic 

 acids might be estimated in the presence of one another by a 

 process based upon the differential reducing action of hydro- 

 bromic and hydriodic acid : but inasmuch as no experimental 

 data were given and as none have appeared on the subject in 

 the thirteen years now elapsed, the present writer has considered 

 himself justified in investigating the feasibility of such a process. 



The apparatus used will be briefly described. As reduction 

 flask served a 100 cm3 Yoit flask, to the inlet tube of which was 

 sealed a small separatory funnel, serving for admission of acid 

 to the flask and for the entrance of a current of pure hydrogen 

 gas from a Kipp generator. To the outlet tube of the Yoit 

 was sealed a Drexel bottle, provided with a Will and Yarren- 

 trap trap, the two serving as absorption apparatus for the 

 bromine and iodine liberated in the process. 



The experiments were carried out as follows : Portions of 

 standard solutions of sodium vanadate and potassium bichro- 

 mate were measured into the Yoit flask, one to two grams of 

 potassium bromide were added, and the flask connected with 

 the absorption apparatus containing a solution of potassium 

 iodide made alkaline with sodium carbonate or sodium hydrox- 

 ide, and the whole apparatus filled with hydrogen gas. Fif teen 

 to twenty cubic centimeters of concentrated hydrochloric acid 

 were added through the separatory funnel and the solution 

 boiled for ten minutes, the reduction having been found to be 

 always complete in that time. A slow current of hydrogen 

 was maintained to avoid the "sucking back" of the liquid 

 from the Drexel bottle. The apparatus was disconnected, the 

 Yoit flask placed in a beaker, containing cold water, and the 

 alkaline solution in the absorption apparatus cooled by running 

 water. The contents of the trap were washed into the Drexel 

 bottle and the solution therein made slightly acid with hydro- 

 chloric acid. The liberated iodine was titrated with approxi- 

 mately N/10 sodium thiosulphate and the color brought back 

 by a drop or two of N/10 iodine solution, after the addition 

 of starch. The results of this titration are given in the follow- 

 ing table : 



*Inaug. Diss. Berlin, 1890. fBer. Dtsch. Ohem. Ges., xxviii, 2067-2078. 

 % This Journal, ii, 156-162. § Treadwell, Quantitative Analysis, p. 327. 

 IFarsoe, Zeitschr. Anal. Chemie., 1907, 308-310. ^Loc. cit, 





