Influence of condensable vapor on strength of powders

Diametrically different influences of small moisture contents upon strength are often measured in beds of different kinds of particles. Here we explain such opposing trends in terms of capillary forces exerted by condensed liquid rings at the points of particle contact. The effects of such rings are opposite for different particle shapes at the point of contact, namely, at spherical or at sharp angular contact points. In addition to the theoretical development, data are given for two different illustrative types of particles.