332 G. Edgar — Van idic and Molybdic Acids. 



Art. XXXVII. — The Determination of Vanadic and Molyb- 

 dic Acids in the Presence of One Another ; by Graham 

 Edgar. 



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



A method has been recently proposed by Glasmann * for the 

 estimation of vanadic and molybdic acids in the presence of 

 one another, based on the different reducing action of zinc and 

 magnesium upon the hydrochloric acid solution of these acids. 

 In a previous paper from this laboratoryf it has been shown 

 that the action of magnesium is irregular and not adapted to 

 an accurate quantitative method. Vanadic acid, however, is 

 reduced to the state of dioxide by a column of amalgamated 

 zinc and may be estimated by titration with potassium perman- 

 ganate, if the receiver be charged with a solution of ferric 

 alum to anticipate the oxidizing action of the aii'4 That 

 molybdic acid is under the same conditions reduced to the state 

 of Mo 2 3 has been shown by Dudley§ and, independently by 

 Randall.| The ease with which vanadic acid is reduced to the 

 state of tetroxide by sulphur dioxide and the difficulty, as has 

 been found, with which this reagent attacks molybdic acid 

 under proper conditions of acidity and concentration, suggest 

 its use in one of two processes of differential action for the 

 determination of these acids. To determine the conditions 

 under which molybdic acid is unaffected by sulphur dioxide, a 

 series of experiments was made in which solutions of molybdic 

 acid of varying concentrations, acidified with varying amounts 

 of sulphuric acid, were heated to boiling and treated with a 

 current of sulphur dioxide for vaiwing lengths of time. The 

 excess of sulphur dioxide was then removed by boiling the 

 solution, a current of carbon dioxide being meanwhile passed 

 into it, and the degree of reduction was determined by titration 

 with nearly N/10 potassium permanganate. The solution of mo- 

 lybdic acid was standardized by the method of Randall^f and 

 by evaporating a portion to dryness and igniting at low red 

 heat. The results of the experiments are given in Table I. 



The results show that if the concentration be not greater 

 than 0*2 grm. of Mo0 3 in 50 cm3 of solution, and the acidity not 

 less than l cmS of sulphuric acid (sp. gr. 1*84) in the same volume, 

 the molybdic acid is not reduced, and that if the acidity be 

 increased to 5 C "' 3 of sulphuric acid, reduction does not occur at 

 even a concentration of 0"4 grm. in 25 cm \ 



*Ber. Dtsch. chem. Gesellseh., xxxviii, 600. 



f Gooch and Edgar, this Journal, xxv, 233. 



X Gooch and Edgar, loc. cit. 



§ Unpublished, but privately communicated by Professor Henry Fay. 



| This Journal, xxiv, Oct. 1907. 



"[[ Loc. cit. 



