Research & InnovationScience Insider
Have you seen the referee marks of free kick?
Vidunenahawula Website (National Institute of Fundamental Studies)
In a football match when there is a free kick you may have seen the referee marks where the wall should be using a small spray bottle. When the referee sprays the bottle there is a white line on the ground but after some time you may see that the line has vanished from the ground. Do you know what happens here? This vanishing spray contains a mixture of butane, a foaming agent and water with other chemicals. When sprayed liquefied butane expands. Then butane evaporates instantly, forming bubbles of gas in the water/surfactant mixture. The surfactant causes the bubbles to have stability and hence foam forms. This you see as a white line. The bubbles eventually collapse and the foam disappears, making the white line vanish.
