Edgar — Estimation of Vanadic and Arsenic Acids. 299 



Art. XXII. — The Estimation of Vanadic and Arsenic Acids 

 and of Vanadic and Antimonic Acids, in the Presence of 

 One Another ; by Graham Edgar. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxcvi.] 



Arsenic and Vanadium. 



The almost constant association of arsenic and vanadium in 

 the mineral sources of both elements presents the frequent 

 problem of their separation and estimation and has led to the 

 development of numerous analytical processes to accomplish 

 the desired end. Carnot* precipitates all arsenic acid by boil- 

 ing with a salt of strontium in weakly ammoniacal solution in 

 the presence of ammonium salts. Gribbsf precipitates the 

 arsenic as trisulphide from a solution previously reduced with 

 sulphur dioxide, the vanadium being determined in the filtrate 

 by titration with potassium permanganate. Sehmitz-Du- 

 montj uses hydrogen sulphide under pressure to effect the 

 separation. Frieclheim and Michaelis, § after reducing with 

 sulphur dioxide the solution containing arsenic and vanadic 

 acids, separate the former by repeated distillation with methyl 

 alcohol and hydrochloric acid. Field and Smith [ volatilize 

 the arsenic by heating the dry sulphides of arsenic and vana- 

 dium in a current of hydrochloric acid gas at a temperature 

 between 100° and 250° Centigrade. Friedheim, Decker and 

 Diem^f recommend the volatilization of the arsenic by distilla- 

 tion with potassium iodide and hydrochoric acid, a current of 

 hydrogen being kept up through the apparatus during the 

 process. 



In the present investigation any separation of arsenic and 

 vanadium is avoided by the use of a process of differential 

 reduction to determine these elements in the presence of one 

 another. 



If a solution containing arsenic and vanadic acids is boiled 

 with tartaric or oxalic acids, the vanadic acid is reduced to 

 tetroxide and may be reoxidized in alkaline solution by iodine*"* 

 according to the equation 



V 2 4 + I 2 + H 2 = V 2 5 + 2HI 



If a solution containing arsenic and vanadic acids is reduced 

 with sulphur dioxide under proper conditions, the arsenic acid 



*Compt. Bend., civ, 1803. fChem. Jour., vii, 230. 



{Inaug. Diss., Berlin, 1891. 



§ Berichte tier Deutsch. Chem. Gesellsch., xxviii, 1414. 

 || Journ. Amer. Chem. Soc, xviii, 1051. 

 ""Zeitschr. Anal. Chem., xliv, 648. 



** Browning: Zeitschr. anorg. Chem., vii, 158; Browning and Goodman, 

 this Journal, ii, 355. 



