Mercuric diphenylcarbazide

Blue-violet mercuric diphenylcarbazide paper turns red in the presence of cyanide ions in neutral or weakly basic solution [Idn. Limit 0.25 y CN"). ... 

A method has been described [17] for the determination of chlorine in polymers containing chlorine, fluorine, phosphorus and sulfur, which involves oxygen flask combustion over water, addition of ethanol, and titration to the diphenylcarbazide indicator end point with 0.005 M mercuric nitrate ... 

This is Schales modification. Actually, in Dubsky s method, it would also be diphenylcarbazone that would give the same chelate as that obtained in Schales modification. The same diphenylcarbazone would form in situ by oxidization of diphenylcarbazide by mercuric ions. For some other authors, diphenylcarbazide would simply be an acid-base indicator. 

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