a continuous flow mixer includes an impeller assembly and a mixing chamber formed from concentric inner and outer tubes . the inner tube is radially constrained but is movable along the axis of the outer tube . the impeller assembly is at one end of the mixing chamber and draws fluid along the interior of the inner tube and discharges the fluid to the annular region between the inner and outer tubes . the fluids are introduced into the mixing chamber at the end remote from the impeller assembly and the mixed solution exits the mixing chamber substantially centrally of its length from the annular region .