of one material which material when it is pushed into the region of the bypass 3 expands and occludes the bypass 3 since the piston 5 is in constant contact with the product component 10 the piston 5 must be formed of a material that is not fluid absorbent suitable materials are those that due to their elasticity rest against the inner wall of the housing in a swelling or sealing manner and can penetrate expand or extend into the bypass 3 to occlude or block the latter by occupying at least a portion of it in one embodiment a sequence of use or function of an embodiment of a multichamber ampoule and administering device in accordance with the present invention comprises the following steps in the initial state fig1 of the two chamber ampoule the fluid solvent 10 is located between the closing piston 5 and the separating piston 4 the product component 9 to be dissolved is located between the separating piston 4 and the collar 2 through application of a force to the closing piston 5 the latter is moved during the mixing process in the discharge direction a in consequence of the incompressibility of the solvent 10 the movement is transferred to the separating piston 4 until the latter is axially located with its entire length in the region of the bypass 3 for this in some embodiments the separating piston 4 has a shorter axial length than the bypass 3 since the solvent 10 now flows past the separating piston 4 via the bypass 3 to the front product component 9 and can thus mix with it the separating piston 4 remains.