Rates of free convection mass transfer inside cylindrical cavities were studied by measuring the limiting current for the cathodic deposition of copper from acidified copper sulphate solution using a cylindrical anode placed inside the cavity. Variables studied were cavity orientation (vertical with upward facing opening, vertical with downward facing opening and horizontal), physical properties of the solution and cavity dimensions (diameter and depth). For vertical cavities with upward facing openings the data were correlated by the equation Sh = 0.257 (Sc x Gr)(0.33) For horizontal cavities the data were correlated by the equation Sh = 0.139 (Sc x Gr)(0.33) For vertical cavities with downward facing openings the data were correlated by the equation Sh = 0.187 (Sc x Gr)(0.297) A comparison between the present data and the data obtained from other cavity geometries was made to shed light on the role of cavity geometry in thermosyphon design.