Abstract: A separating device for two liquids of different density, in particular for separating an oil layer floating on a liquid surface by means of an over flow edge on a weir, said edge being positioned in the area of the boundary layer of the two liquids. The separating wall provided with the over flow edge has an convex-concave shape in a vertical direction and seals against the inside of the convex weir whereby an improved sealing with less leakage is obtained.The separating wall is hollow and can be accurately positioned vertically by remote control by means of supplying more or less air under pressure to the inside of the separating wall so that the buoyancy thereof can be varied according to the thickness of the oil layer. For obtaining a quick response to wave action a float is positioned in front of the separating wall and controls the vertical position thereof starting from the adjusted nominal position reached by the remote control by air pressure.