Zero-order release method

Claim 1

Method for the automatic release at a desired substantially constant predetermined rate R of a diffusible solid into a fluid medium into which said solid has a propensity to diffuse wherein said solid has diffusion constant (D) and solubility (Cs) with respect to said medium which comprises 1. introducing said solid into a cavity within a container, said container being impervious to said solid and said medium during the period of delivery of said solid and having a slot-like port having uniform length and width and having two ends and two sides with the narrower dimension (a) at the ends and the longer dimension (L) at the sides, said port communicating in its entirety with said cavity, said cavity being defined by a rear wall, and a pair of parallel congruent planar end walls arranged at right angles to said slot and adjacent to the ends thereof, and a pair of inwardly extending congruent planar side walls adjacent the opposite sides of said slot and in substantially divergent radial relation to said slot and extending to said rear wall, said introduction being carried out so as to completely cover the rear wall of said cavity with said solid and seal said solid to the walls thereof, and expose a single surface thereof to the slot-like port in facing relation thereto for contact with said medium, and 2. immersing said container into said medium so that the medium enters the slot and contacts said exposed surface of said solid, and 3. adjusting the dimensions (a), (L), and ( Theta ), wherein ( Theta ) is the angle subtended by the side walls of said cavity, so that said rate R is achieved and is defined by the expression