Some Experiments with Soap Films

There are a number of relatively simple experiments with soap films that illustrate beautifully some of the implications of the Young-Laplace equation. Two of these have already been mentioned. Neglecting gravitational effects, a film stretched across a frame as in Fig. II-1 will be planar because the pressure is the same as both sides of the film. The experiment depicted in Fig. II-2 illustrates the relation between the pressure inside a spherical soap bubble and its radius of curvature by attaching a manometer, AP could be measured directly. 

Returning to equilibrium shapes, these have been determined both experimentally and by solution of the Young-Laplace equation for a variety of situations. Examples 

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It was Joseph Plateau s experiments with soap films that provided mathematicians with renewed motivation to investigate the problems of minimum area surfaces. Some of these beautiful analogue solutions are examined in Chapter 4 with coloured plate illustrations. Although substantial efforts were made to obtain analytic solutions to these problems it was not until the 1930 s that significant progress was made by mathematicians such as Jesse Douglas, who obtained some general solutions, and Tibor Rado. " ... 

The decrease in the size of soap bubbles caused by air diffusion has been observed by some researchers [480]. Manegold et. al. [480] have determined gas permeability of bubble films with a diameter of 5 cm produced from a 2% Nekal solution and filled with hydrogen and carbon dioxide. These experiments can hardly be used to draw any definite conclusions on the effect of adsorption layer on the rate of diffusion transfer. 

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