The amount adsorbed of sodium dodecyl sulfate and dodecylammonium chloride on carbon black versus equilibrium concentration curves were measured and the results were correlated with the suspendability of the carbon black particles in the surfactants solutions under the same conditions. It is found that the correlation of the amount adsorbed with the suspendability is not necessarily valid. At the low equilibrium concentrations dodecylammonium chloride does not act to disperse the carbon particles, whereas the adsorption is fairly greater for dodecylammonium chloride than for sodium dodecyl sulfate. With both surfactants, the suspendability-concentration curves show a steeper increase immediately below the concentration at which adsorption attains saturation, and the formation of stable suspention of the carbon particles is observed in the range of saturation, probably owing to the effect of orientation of adsorbed ions at the solid surface. From the another measurement on the relationships between suspendability and concentration obtained in surfactants solution such as sodium dodecyl sulfate, dodecyl pyridinium bromide and dodecyltrimethylammonium chloride, it is evident that the suspending power of both anionic and cationic surfactants is rather reduced at their higher concentrations.
