The foams are made using a foam generator consisting of a
closed cell with supply of both nitrogen gas and concentrated
surfactant solution (commercial detergent Fairy Liquid at a
volume fraction of 3%). The cell is about half filled with solution,
and the tip of a hollow needle is introduced through the bottom of
the cell, slightly below the gas/liquid interface. An overpressure of
the gas leads to a thin thread of gas, surrounded by liquid,
streaming through the needle into an attached tube. This thread is
unstable and breaks up, resulting in the formation of a very wet
foam (with estimated liquid fraction 33 ¡ 2%) of equal sized
bubbles. The bubbles are continuously expelled from the tube
which is positioned slightly above a liquid pool consisting of the
same surfactant solution.