The controlled formation of stable dispersions of solid powders in liquids is of both theoretical and practical interest. The suspendibility of a powder depends upon and aids in the understanding of the surface properties of the disperse phase, as these affect, cohesion between particles in various media and as they result, in selective adsorption of ions or molecules from solution. Moreox-er many commercial products, such as paints and printing inks, consist of finely clix idecl solids dispersed in liquids. It also seems likely that the relative effectiveness of detergents may be closely related to their ability to stabilize suspensions of removed dirt.In the present work the effectixre particle-size distribution of powdered manganese dioxide was determined in a number of media to aid in ascertaining the mechanism whereby relat.ix'ely stable dispersions may be produced in aqueous solutions. The amounts remaining in suspension after a 4-hr. settling period xvere also determined as a function of concentration in aqueous solutions of Aerosol OT, Oronite, Hyamine 1622, Triton X-100, sodium oleate, and p-t.oluenesulfonic acid. Characteristically, the curxres of amount suspended vs. concentration of dispersing agent pass through a maximum at low concentrations. It seems likely that the shapes of these cuives, as well as the differences between different, detergents, are explicable in terms of varying effectix'eness in disgregation of the aggregates xvhich normally form on introducing a powder of given ultimate particle size into a pure liquid. The mechanism by xvhich this is accomplished appears to be through change in the zeta potential effected by adsorption of ions from solution. MATERIALS Baker's c.p. manganese dioxide powder was used throughout this work without further purification.Aerosol OT was obtained from the American Cyanamid Company in the form of "100%" pellets and used directly. It is the sodium salt of dioctylsulfosuccinic acid.Oronite Actix'e, made by the California Research Company, was a sample receix'ed through the courtesy of the Lever Brothers Company, and described as 1 ITesentcd at the Twenty-second National Colloid Symposium, which was held under the auspices of the Division of Colloid Chemistry of the American Chemical Society at Cambridge. Massachusetts, .June 23-2.5, 1948.

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