Gooch and Curtis— Halogen Acids upon Vanadic Acid. 43 



At the end of the operation the decree of reduction was 

 determined by titrating the contents of the flask, after dilu- 

 tion, with potassium permanganate in presence of a manganous 

 salt. The data of the experiments are detailed in the follow- 

 ing table : 



Table I 



V 2 0U per 0-1000 gm. 





NH4VO3 





of vanadate taken. 







taken, 

 gm. 



Time, 

 hrs. 









Exp. 



Calculated. 



Found. 



Difference 



1 



0-1022 



1 

 2 



0-0695 



0-0619 



0-0076 



2 



0-1121 



17 





0-0621 



0-0074 



3 



o-ioio 



18* 





0-0678 



0-0017 



4 



0*0980 



21 





0-0658 



0-0037 



5 



0-1044 



30 





0-0600 



0-0095 



6 



0-1043 



112'i 





0*0691 



0-0004 



The reduction of the vanadic acid to the condition of the 

 tetroxide by the action of hydrochloric acid in the cold is obvi- 

 ously slow, as would be expected, but the results show that it 

 may be made practically complete in this manner. No indica- 

 tion of reduction below the condition of the tetroxide by the 

 agency of hydrochloric acid is apparent. 



The Reducing Action of Hydrobromic Acid. 



In Holverscheit's most excellent method for the estimation 

 of vanadic acid the reduction, effected by the action of hydro- 

 chloric acid and small amounts of potassium bromide, is almost 

 ideally complete to the condition represented by vanadium 

 tetroxide. Under the conditions the concentration of the 

 hydrobromic acid is low, and it was thought to be of interest 

 to investigate the effect of more concentrated hydrobromic 

 acid upon the course of reduction. 



In the first six experiments recorded in the following table, 

 weighed portions of ammonium vanadate were introduced into 

 the reduction flask, the receiver and trap were charged with a 

 solution of potassium iodide (3 gm. : 350 cm3 ), the apparatus was 

 filled with carbon dioxide, hydrobromic acid (15 cm3 ) of sp. gr. 

 1*68 (made by distilling a mixture of potassium bromide and 

 syrupy phosphoric acid) was introduced through the funnel 

 and the mixture was boiled eight or ten minutes. On the 

 addition of the acid the vanadate dissolved and the solution 

 took on a light green color, which on heating changed to red- 

 brown and finally to a clear deep green. After cooling, the 

 degree to which the vanadic acid had been reduced was esti- 

 mated in two ways — by determining by means of standard 

 sodium thiosulphate the iodine set free in the receiver by the 

 bromine evolved, and by oxidizing by standard iodine the 

 reduced product in the flask. The latter process followed the 

 lines recommended by Browning* and consisted essentially in 

 neutralizing the acid in the reduction flask by potassium bicar- 



* Zeitschr. anorg. Chem., xiii, 116. 



