Permanganate indirect determinations with

Equation (19-1) describes the behavior of a solution saturated with solid iodine. This half-reaction occurs, for example, toward the end of a titration of iodide with an oxidant such as permanganate, when the iodide ion concentration becomes relatively low. Near the beginning, and in most indirect determinations, an excess of iodide is present, and the half-reaction is more accurately written... 

With tanning extracts adulterated with cellulosic extracts, the indirect method does not, however, give reliable results, since cellulosic extracts contain non-tannins which are fixed by the hide powder. In such a case the tannin should be determined by the direct method, since these non-tannins have no appreciable action on permanganate the difference between the results of the two methods will give an approximate indication of the extent of the adulteration, if this is at all marked. 

Determination of iron The most important applications of dichromate involve either directly or indirectly the titration of Fe(II). An excess of standard Fe(II) can be added to determine oxidants, or an excess of Fe(III) to determine reductants. These determinations usually can be carried out equally well with Ce(IV). For routine applications, however, the low cost and ease of preparation of standard solutions and the great stability of dichromate offer some advantages. Permanganate is at a disadvantage, expecially if hydrochloric acid solutions are to be used. 

This determination is an indirect one. It is achieved through the formation of a ferrous salt that is titrated with potassium permanganate. Hydroxylamine reduces ferric ions in boiling sulfuric acid according to the reaction... 

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