Abstract: A kit for mixing comprises a housing accommodating an ampoule containing a solid and a container containing a solvent which is either pre-pressurized or which may be pressurized when it is desired to mix to the liquid and solid components. A needle unit comprises a first needle, the opposite ends of which pierce rubber membranes closing the ampoule and the container, to establish a transport channel through which pressurized solvent flows from the container to the ampoule. The ampoule is vented through a second needle inserted through the membrane of the ampoule and provided with a micro-filter. In one embodiment, the needle unit is displaceable to cause the ends of the needles to pierce the respective membranes, and locked in place by a spring biased locking mechanism. A branch passage from the needle is connected to a cylinder containing a piston coupled to the locking mechanism. When the ampoule is full, pressure in the branch passage will rise, actuating the piston and releasing the locking mechanism.