AbstractThe deposition of carbon on cotton from solutions of sodium dodecyl sulfate of varying concentration was determined, together with the adsorption isotherms of NaDS on both cotton and carbon, and the aggregate size of the carbon in the suspensions.An optimum concentration for protection against deposition of carbon was found far below the critical micelle concentration, and not correlating with either the presumed values of the zeta‐potential nor the extent of surface coverage by adsorbed detergent. Various explanations were considered and rejected for accounting for the inflection in the adsorption isotherm of NaDS on carbon at the c.m.c., and the subsequent occurrence of a maximum in the isother