This method is especially suitable for sulphide ores like zinc blende ( ZnS ), and copper pyrites. In this process a mixture of water , pine oil, detergent and powdered ore is taken in a tank. The whole mixture is then stirred vigorously by blowing compressed air. The oil forms a forth (foam) with air. The sulphide ore particles are wetted and rise up along with the forth. ( sulphides are more electronegative so it attracted by covalent oil molecules. The gangue particles wetted by water sink to the bottom of the tank. (The gangue particles are less electronegative so it attracted by water). The forth containing the sulphide ore is skimmed off, collected and allowed to subside, washed and dried to get concentrated ore. The forth flotation process is shown in the following figure.