Vanadium ferrocyanides

Vanadium Ferrocyanides.—Solutions of vanadates, when treated with potassium ferrocyanide, yield a precipitate of doubtful composition.1 The compound is insoluble in mineral acids of high concentration, and a method involving its precipitation has recently been suggested for the estimation of vanadium in steels.2... 

Other volumetric processes which have been w orked out include the use of potassium ferrocyanide,8 potassium ferricyanide,10 titanous chloride,11 and stannous chloride.12 According to Rosenheim and Yang,13 vanadium pentoxide is best determined in solution by addition of excess of caustic soda and back titration with sulphuric acid at 100° C., using a-naphthophthalein as indicator. 

Vanadium compounds (vanadic acid and vanadium chloride) have been proposed as substitutes for copper sulphide, but without much practical success. Potassium ferrocyanide and ferricyanide are also used to a certain extent. A mixture of these salts with aniline salt and potassium chlorate is printed, and the goods aged. The probable action is that the ferricyanide oxidises the aniline, and is continually regenerated from the ferrocyanide formed by the chloric acid present. Thus these salts play the part of oxygen carriers in a similar manner to the copper and vanadium compounds. In the opinion of technologists, the hlack produced by this process differs somewhat in its properties from that obtained with copper, but this may be ascribed to the presence of prussiaii blue in the former. In place of the aniline hydrochloride and potassium chlorate, a mixture of aniline sulphate and barium chlorate has recently been employed in black-printing. 

Once again a good deal of bromine chemistry is covered in the section on oscillatory reactions. The species BrJ may be involved in olefin brominations at high concentrations of bromine. The kinetics and equilibria of reaction (58) have been studied, and rate constants for (59) and (60) evaluated. The mechanism of oxidtion of ferrocyanide by bromate involves [Fe(CN)sH20] " as an intermediate. The uncatalyzed and the vanadium(V) catalyzed reaction of bromate with methylene blue have been reported. ... 

Salter lists this in his 1869 edition of Field s Chromatography it was evidently a vanadium hexacyanoferrate(II) compound as he states Vanadium Green falls when ferrocyanide of potassium is added to vanadic acid dissolved in a strong acid. It is a beautiful green precipitate, but at present simply a curiosity, owing to the rarity of the metal vanadium. It is otherwise obscure and probably largely unused by artists. However, vanadium, as a transition element, is known to form V " and V compounds the former would reasonably substitute for the Fe ion in iron(III) hexacyanoferrate(II). 

We have investigated copper preparations (Raney s and others), Raney nickel, zinc oxide, iron oxide, vanadium quin-toxide (VjOg), silica gel (SiOj) and some varieties of silicon dioxide applied as carriers, zinc ferrocyanide pure, and with Fe + and Cu + ions, a cobalt-thorium contact for Fischer and Tropsch s s5mthesis, zinc hydroxide with Co + ions, and silica gel with nickel sulphate (II) fixed on it. We have investigated contact fixed on a carrier and without a carrier, with additions of an activator, etc. For example, Co + ions on Zn(0H)2 could be clearly detected potentiometrically and still in the quantity of 3.10 g Co + to a powder electrode. 

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