Sample bottle, comprising a cylindrical sample chamber and a coaxial cylindrical displacement chamber, an axially movable piston sealingly separating said chambers, a feedthrough from the sample chamber to outside the sample bottle, a feedthrough from the displacement chamber to outside the sample bottle, and at least one end piece. The sample bottle is distinguished in that it comprises a mixing device, the mixing device is located in the sample chamber, the mixing device has the shape of a pipe section that closely fits into the sample chamber and it has end surfaces and a bore between said end surfaces, the piston and the end piece or sample bottle, on the sides facing the sample chamber, have shape and a protrusion coaxial to the mixing device bore, said shapes and protrusions are adapted to fit completely to the shape and bore of the mixing device, such that the mixing device is slideable in the sample chamber while providing mixing effect and the volume of the sample chamber can be reduced to contain only the mixing ring.