Abstract: A container having a first compartment configured to hold a first substance, a second compartment configured to hold a second substance, a frangible separator coupled to both the first and second compartments, and an actuator operably attached to the frangible separator. The second compartment is removably attached to the first compartment. The frangible separator forms a seal between the first compartment and the second compartment such that the first substance and the second substance do not mix. Actuating the actuator causes at least a portion of the frangible separator to rupture, which creates an opening in the frangible separator and allows the first substance and the second substance to mix. The actuator may be a string. The invention is particularly well-suited for mixing formula and water in baby bottles, but has many other uses.