Abstract: A package for materials that are to be mixed shortly before use comprises a compartmented container and a device for rupturing a frangible partition member in the container. The device comprises a shaft having an upper end connected with a closure for a top opening in the container. Resilient arm-like vanes project radially from the shaft near a pointed lower end thereof and have their tips engage inner wall surfaces of the container under bias to hold the shaft coaxial. Downward movement of the device causes the point on the shaft and sharp bottom edges on the vanes to cooperate in completely rupturing the partition member, and the device then remains in a position in which the vanes break up and stir the materials as the container is shaken.