Abstract: A series of double-jet silver halide emulsions are prepared with iodide ions incorporated at different instants of precipitation and thus presumed to locate at different distances from emulsion grain surface. "With iodide ions reaching the grain surface, the emulsion speed falls, the ionic conductivity of the grains rises and, in the case of sulphur-plus-gold sensitization, the drop in ionic conductivity otherwise caused by the sensitization is more than compensated. The desensitizing action of surface iodide, obviously partly due to development retardation, is thought to be connected in some way with the rise in ionic conductivity.