G. Edgar — Vanadic and Mol/ybdic Acids. 333 







Table I 















Time of 



KMnO, 



1 



Volume of 





H 2 S04 



treatment 



N x 1-004 Color of 



solution 



Mo0 3 



sp. gr. 1-84 



with S0 2 



10 



solution 



cm 3 . 



grin. 



cm 3 . 







cm 3 . 





25-0 



0-200 



faintly acid 



10 



min. 



O'lo 



light blue 



35-0 



0-200 



. 5 cm » 



10 



a 



0-05 



faint blue 



50-0 



0-200 



l-0 cm3 



10 



c< 



o-o 



colorless 



75-0 



0-200 



2 .Qcms 



10 



a 



o-o 



u 



50-0 



0-200 



2 -0 cm3 



30 



a 



o-o 



a 



25-0 



0-200 



5'0 cm3 



10 



a 



o-o 



ii 



25-0 



0-400 



5-0™ 3 



10 



a 



o-o 



ic 



50-0 



0-400 



S-QCmi 



10 



a 



o-o 



a 



50-0 



0-400 



io-o cm3 



10 



(C 



00 



a 



50-0 



0-400 



15 . om3 



10 



a 



00 



a 



A series of experiments was than made in which solutions 

 containing vanadic and molybdic acids were diluted to '75 cm3 , 

 acidified with 2 to 3 cm3 of strong sulphuric acid, heated to boiling 

 and subjected to a current of sulphur dioxide for a few minutes 

 until the clear blue color indicated the complete reduction of 

 the vanadic acid to the state of tetroxide. The boiling was 

 continued for some time, a current of carbon dioxide being- 

 passed into the liquid until the last traces of sulphur dioxide 

 had been removed. Titration was then effected by nearly N/10 

 potassium permanganate and the vanadic acid was calculated 

 from the equation, 



5 V 2 4 + 2KMn0 4 + 3H 3 S0 4 = 5 V 2 5 + K 2 S0 4 + MnS0 4 + 3H 2 0. 



The solution, preceded by 100 cm3 hot water, and 125 cm3 of 

 dilute (2J per cent) sulphuric acid, and followed by 100 om3 

 dilute sulphuric acid and 200 cm3 of hot water, was passed slowly 

 through a column of amalgamated zinc in a Jones redactor,* 

 the receiver containing a solution of ferric alum. The hot 

 solution was then titrated with nearly N/10 potassium 

 permanganate, a little phosphoric acid being added to decolorize 

 the ferric salt. 



Since the reduction of vanadic acid is in this case to the 

 condition of dioxide, V~ 2 2 , if the number of centimeters of 

 permanganate used in the titration of the tetroxide be multi- 

 plied by three and the product subtracted from the total 

 number of centimeters of permanganate used in the final titra- 

 tion, the result is the number of centimeters used in oxidizing 

 Mo 2 3 to M0O3, from which the amount of molybdic acid present 

 may be easily calculated. The results, given in Table II, show 

 that molybdic acid and vanadic acid may be accurately estimated 

 in the presence of one another by two processes of reduction 

 and oxidation, the reduction being made first by sulphur 

 dioxide and last by amalgamated zinc. 



* The Chemical Analysis of Iron, Blair, page 225. 



Am. Jour. Sci. — Fourth Series, Vol. XXV, No. 148. — April, 1908. 

 23 



