In the presence of oxygen, galena is oxidized in an aqueous medium containing ammonium acetate in accordance with the following reaction: $$PbS + 1/2\,{O_2} + 2\,N{H_2}Ac \to PbA{c_2} + S^\circ + 2\,N{H_2} + {H_2}O.$$ This reaction was studied in an autoclave under oxygen pressure by Polarographic measurement of the concentration of lead ion in solution. Oxidation rate is parabolic. The reaction products are lead acetate and elemental sulfur, the latter forming a film on the galena crystal. Reaction kinetics appear to be determined by the diffusion of lead from the galena phase to the solution interface through the film of sulfur.