Patent ID: 8376175

Claim:
A storage cap for use with a container, comprising: a first structure having a first wall at least partially defining an inner storage chamber operable for storing a first substance, the first wall also defining a first annular opening having a first annular convex surface facing toward the storage chamber and a diameter; and a second structure coupled to the first structure, the second structure including plunger element located within the storage chamber having a domed-end with a convex surface facing to the annular opening, the domed-end having a radius greater than one-half of the diameter of the first opening; wherein the second structure is configured such that the domed end is moveable to make and break contact with the annular opening, and wherein when the domed end is in contact with the first annular convex surface, a seal is formed between two convex surfaces along an annular path to seal the storage chamber.