This invention discloses, as an article of manufacture, a capsule having a hollow interior and an enclosing wall, referred to as a membrane. The membrane is not soluble in water, but is permeable to water or an aqueous solution. The membrane is comprised of a first material and can also include a second material. When the membrane is comprised of the first material and the second material, then it is referred to as a composite material wherein the first material forms sporting matrix having the second material fixed in the matrix. The first material is a urethane/vinyl hybrid polymer and is not soluble in, reactive with or a solvent for the second material. The second material is a particulate solid, different from the first material, and is not soluble in, reactive with or a solvent for the first material. The capsule of this invention is useful to maintain in the hollow interior thereof a solid, water-soluble first chemical composition which is not soluble in, reactive with or a solvent for the enclosing wall of the capsule. In operation, the exterior of the capsule, having the first composition maintained in the interior thereof, is placed in contact with a water-soluble second chemical composition which is not soluble in, reactive with or a solvent for the enclosing wall of the capsule, but which is reactive with the first chemical composition.