Two aspects of the chemistry of dispersion of materials in fluids are studied, (1) the dispersion of fine powders in fluids to enhance reactivity and (2) the interaction between magnetic fields and charged species in fluids. The problems arising from a conflict between (i) the use of fine powders to optimize reactivity and (ii) the health hazards of fine powders and the decreased reactivity resulting from reaction of these powders with the atmosphere are considered for tin (II) carboxylate catalysts, calcium hydroxide-processing aids for fluoroelastomers and cobalt oxide ruminant feedstocks. Fine particle suspensions and crystal nuclei dispersed in fluids have high surface charges that can react with an applied magnetic field. The effects of magnetic fields on charged species are studied for precipitation reactions of calcium sulphate and calcium phosphate and for suspensions of cementaceous materials in water. The effects of magnetic fields on the solubility of barium sulphate and calcium phosphate in water are also reported. It is shown that the magnetic treatment of fluids can have a profound effect on the behaviour of charged species in fluids. Changes in particle size, morphology and solubility arising from the interaction between the field and the changes at the solid-fluid interface are discussed in terms of possible field-charge mechanisms. The major factors affecting the behaviour of species in magnetic fields are considered to be (i) the separation of positive and negative charges by opposite helical motion in the field and (ii) the direct interaction of the field with the highly charged surfaces of crystal nuclei and dispersed fine particles.