Pressurized container providing for the separate storage of a plurality of materials

A container arrangement for separately storing a first liquid material and a second material in a container and providing for the automatic admixing of the first and second materials upon opening of the container, comprising, a container containing said first liquid material at superatmospheric pressure, with the pressure surrounding said container being atmospheric, a separate closed compartment arranged within said container and filled with said second material, said separate compartment being formed of a unitary piece of plastic molded as a clamshell shaped compartment with a first half of the unitary piece forming a first separable component of the compartment and a second half of the unitary piece forming a second separable component of the compartment, said first and second halves being hingedly joined along a common linear hinge wall which provides an opening force to bias the first and second halves apart toward an open position of the clamshell compartment, said second material being placed in the clamshell compartment at atmospheric pressure and the clamshell compartment then being closed against the opening force of the common linear hinge wall, and the clamshell compartment then being retained in a closed position by an adhesive material adhesively joining the separable halves of said clamshell compartment, said adhesive material being soluble in the first liquid material stored in said container, said clamshell compartment being placed, after being filled with said second material and then being adhesively joined, in the first liquid material in the container and the container then being sealed and attaining said superatmospheric pressure, after which said adhesive is dissolved by said first liquid material, leaving only the pressure differential between the superatmospheric pressure inside said container and the atmospheric pressure inside of said clamshell compartment to provide a closing force to hold the separable halves closed together in a compartment-sealing condition with the closing force provided by said pressure differential being greater than the opposed, opening force provided by said common linear hinge wall such that when the pressure differential between the compartment and container is removed, responsive to opening of said container, the compartment will be biased apart by the opening force provided by said linear hinge wall to empty the second material from said compartment into first liquid material in said container.