In serching for the literature on the method of estimation of hydroquinone content in commercial product, the author obtained five, but failed to find out the simple and sure method to estimate hydroquinone within the limit of past method.
The author proposed a new method of estimation of hydroquinone with diazotised solution of p nitro anilin, of which concentration was preliminary chequed with β-naphthol solution of known concentration.
Though the end points of titlation of hydroquinone with diazotised solution of p-nitro anilin and β-naphthol are both rather unconspecuous, they are made clear when take up small quantity of solution in a separate vessel at the end point of the reaction. The chemical reactions are as follows,
(1)_??_
(2) diazo nitro anilin chioride+hydrequinone
(3) or_??_
In case of neutral or acid solution be adopted (2) the reaction product is yellowish red but when rather alkaline solutzon be adapted by the addition of sodzum acetate, the reaction will be (3) and the colour of the reaction product is brown. The author recommezlds (2) method.

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