The reduction of diazotized aromatic amines has been observed to occur at the dropping mercury electrode. The reduction is irreversible and the polarographic waves are too complex to treat with electrochemical equations. Nevertheless distinct waves whose heights vary directly with concentration are obtained. One wave of the reduction occurs at a potential well below that of the azo or nitro groups or nitrite ion. Therefore, it is possible to use the dropping mercury electrode with an applied potential of 0.3 volt vs. the saturated calomel electrode as an indicator for the measurement of the concentration of diazotized amines. In this manner, amperometric coupling titrations, diazotization rates, coupling rates, etc., may be studied. The new technique is more generally applicable than either the gasometric or colorimetric methods of measuring the concentration of diazotized amines. In certain cases, such as measuring the rapid formation of an insoluble azo compound, the polarographic technique is the only practical method available.

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