Reduction with amalgamated zinc the Jones reductor

A suitable form of the Jones reductor, with approximate dimensions, is shown in Fig. 10.17. A perforated porcelain plate, covered with glass wool, supports 

Carry out a blank determination, preferably before passing the iron solution through the reductor, by running the same volumes of acid and water through the apparatus as are used in the actual determination. This should not amount to more than about 0.1 mL of 0.02M permanganate, and should be deducted from the volume of permanganate solution used in the subsequent titration. 

It must be emphasised that if hydrochloric acid has been employed in the original solution of the iron-bearing material, the volume should be reduced to ca 25 mL and then diluted to ca 150mL with 5 per cent sulphuric acid. The determination is carried out as detailed above, but 25 mL of Zimmermann-Reinhardt or preventive solution must be added before titration with standard potassium permanganate solution. For the determination of iron in hydrochloric acid solution, it is more convenient to reduce the solution in a silver reductor 

Applications and limitations of the Jones reductor. Solutions containing 1-10 per cent by volume of sulphuric acid or 3-15 per cent by volume of concentrated hydrochloric acid can be used in the reductor. Sulphuric acid is, however, generally used, as hydrochloric acid may interfere in the subsequent titration, e.g. with potassium permanganate. 

Nitric acid must be absent, for this is reduced to hydroxylamine and other compounds which react with permanganate. If nitric acid is present, evaporate the solution just to dryness, wash the sides of the vessel with about 3 mL of water, carefully add 3-4 mL of concentrated sulphuric acid, and evaporate until fumes of the latter are evolved. Repeat this operation twice to ensure complete removal of the nitric acid, dilute to 100 mL with water, add 5 mL of concentrated sulphuric acid, and proceed with the reduction. 

---

REDUCTION WITH AMALGAMATED ZINC THE JONES REDUCTOR 10.138... 

---