In this method a capillary tube is first immersed in the liquid sample. subsequently constant flow of gas is purged through the tube forming small bubbles into the liquid.
The pressure needed to form a bubble is measured and the surface tension of the sample is calculated from the pressure difference between inside and outside the bubble and the radius of the bubble. This kind of tensiometers are used in many "on-line" measurements. However, the range of surface tensions accessible to this method is limited and cleaning of the system is difficult, resulting in deviation.