D. L. Randall — Behavior of Molybdic Acid. 



Art. XXXII. — The Behavior of Molybdic Acid in the Zinc 

 Reductor ; by D. L. Randall. 



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



There has been a difference of opinion in regard to the 

 degree of reduction obtained when molybdic trioxide, in sul- 

 phuric acid solution, is passed through the column of amalga- 

 mated zinc as applied in the Jones reductor. Jones,* who first 

 determined molybdenum by this method, considered that the 

 reduction goes to the condition represented by the formula 

 Mo 12 19 , the same degree of reduction that Wernkef obtained 

 with zinc and sulphuric acid in a closed flask. Doolittle^: and 

 Eavenson found that, by varying the strength of the acid and the 

 speed at which the molybdenum was passed through, differ- 

 ent degrees of reduction might be obtained. They calculated 

 no formula corresponding to the degree of reduction obtained 

 by them which was lower than that represented by Mo 12 19 . 

 W. A. Noyes and Frohman,§ by taking pains to replace the air in 

 the reductor flask by carbon dioxide, were able to obtain a 

 reduction to the form of Mo 2 3 . Blair jj and Whitfield, how- 

 ever, were unable to press the reduction below the condition 

 represented by the symbol Mo 2i 37 . Miller^f and Frank in 

 repeating the experiments of Blair and Whitfield obtained in 

 general the same results, though by taking extraordinary pre- 

 cautions they were able to get a reduction to a point a little 

 below midway between the conditions represented by the sym- 

 bols Mo a4 0„ and Mo 2 3 . 



The ease with which the reduced molybdenum solution is 

 oxidized by the air has been noted and suggests the possibility 

 of charging the reductor flask with some oxidizer unaffected 

 by air, which shall anticipate the oxidizing effects of the air as 

 the reduced molybdenum compound comes through the reduc- 

 tor and register the oxidation. 



In the first experiments an excess of a standard solution of 

 potassium permanganate was used in the receiver. But it was 

 found, by running blanks, that somewhat more than the theoret- 

 ical amount of permanganate was used up. Table I shows the 

 results of experiments made by charging the reductor flask 

 with 20 cmS of approximately tenth normal standard potassium 

 jDermanganate, passing 300 cm3 of warm dilute (2 - 5 per cent) 

 sulphuric acid through the reductor, adding 20 cm3 of standard 

 ferrous sulphate solution and titrating with permanganate to 

 color. 



* American Institute Mining Engineers, xviii, 705. 



•(•Zeitschr. Anal. Cbem., xiv, 1. % Jour. Amer. Chem. Soc, xvi, 234. 



§ Jour. Amer. Chem. Soc, xvi, 553. || Ibid., xvii, 747. 

 IT Ibid., xxv, 919. 



