Effect of surface tension on a thin plaquette

Let us consider the surface of a liquid whose surface tension is to be measured and let us put a clean platinum plaquette (1 x 1 x 10 2 cm3) vertically into contact with the liquid-air interface. The plaquette is suspended by a thread from a scale-pan of a balance, and one edge is in contact with the liquid (see Fig. 5.6). The liquid wets the platinum surface and a meniscus appears. The surface tension r exerts a downwards vertical force on the plaquette. This force is 

By performing the operation successively for pure liquid and for the liquid with an adsorbed layer, one obtains the surface tensions r0 and r0+1. 

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