RESULTS:
Knop' was the first to propose the use of diphenylamine as an indicator
in the titration of ferrous iron by potassium dichromate, whereas Cone and
Cady2 recommended either diphenylamine or diphenylbenzidine as internal
indicators in the titration of zinc by ferrocyanide. Several workers3 have
since shown that these indicators are reliable and useful in oxidationreduction
titrations, but Sarver4 pointed out that end-points are often
passed without any color formation, whereupon the addition of a trace
of ferrous iron will then produce it instantly. Moreover, Watsonb has
recently shown that mercuric chloride has a powerful inhibiting effect on
the color production.
Since diphenylamine and diphenylbenzidine now belong among the
common analytical laboratory indicators it appeared desirable to make an
extensive study of their properties in order to know in what cases they can
be applied, under what conditions they give reliable results, and what
corrections must be made under different circumstances. The physicochemical
part of this investigation will be presented here, while the analytical
significance of the work will be reserved for a future paper.
RESULTS:Knop' was the first to propose the use of diphenylamine as an indicatorin the titration of ferrous iron by potassium dichromate, whereas Cone andCady2 recommended either diphenylamine or diphenylbenzidine as internalindicators in the titration of zinc by ferrocyanide. Several workers3 havesince shown that these indicators are reliable and useful in oxidationreductiontitrations, but Sarver4 pointed out that end-points are oftenpassed without any color formation, whereupon the addition of a traceof ferrous iron will then produce it instantly. Moreover, Watsonb hasrecently shown that mercuric chloride has a powerful inhibiting effect onthe color production.Since diphenylamine and diphenylbenzidine now belong among thecommon analytical laboratory indicators it appeared desirable to make anextensive study of their properties in order to know in what cases they canbe applied, under what conditions they give reliable results, and whatcorrections must be made under different circumstances. The physicochemicalpart of this investigation will be presented here, while the analyticalsignificance of the work will be reserved for a future paper.
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