AzoDyes

Determination of azo dyes is done most satisfactorily in the presence of sodium tartrate which prevents the precipitation of the difficultly solu­ble dye acids (e. g., benzopurpurin, see Knecht,105 pages 31-32). Yellow dyes cannot be easily titrated because titanium tartrate is strongly yellow in color.

The reduction takes place quantitatively according to the equation: R—N=N—R’ + 4 TiCls + 4 HC1 -» 4 TiCl4 + R—NH2 + R’—NH2

It is only necessary to know the molecular weight of the dye and the number of azo groups present. The titration is carried out exactly as described above.

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