The aggregation of colloidal electrolytes from transport number and conductivity measurements: some benzidine dyes

Abstract

In previous communications* from this laboratory some of the properties of benzopurpurine 4B and the isomer prepared from m-tolidine have been described. These two dyes (which will be referred to briefly as the " 4B " and " meta " dye, respectively) differ in chemical constitution only by the position of two methyl groups, but show striking differences in their colloidal properties.* Further, the 4B dye is a well-known cotton substantive dye, while the meta dye is not sufficiently substantive to be of any practical value. A comprehensive study of the solutions of these two substances is therefore of considerable interest, for it should not only extend our knowledge of colloidal electrolytes, but should throw some light on the theory of dyeing. In the previous communications it was shown that the viscosities, conductivities, and osmotic pressures of the half per cent. (N/70) solutions of the two dyes are about the same. On the other hand, the 4B dye was Found to be stopped by much coarser ultrafilters, and is flocculated completely by small concentrations of electrolytes, while the meta dye is never completely flocculated, even by very large concentrations.