Many of the macroscopic properties of foams and emulsions are controlled by the mesoscopic properties of the thin films separating the bubbles or droplets. The properties of these films depend on contributions (1) from the adsorbed surface layers and (2) from the liquid that separates these adsorbed layers. To separate in the experimental studies the effects of these two contributions, we developed a new modified version of the capillary cell for foam film studies (originally developed by Scheludko and Exerowa (Scheludko, A.; Exerowa, D. Kolloid Z. 1959, 165, 148-151), which allows exchange of the film-forming liquid between the air-water surfaces. This modified cell allows one to distinguish between the role of the adsorbed species (e.g., proteins, particles, or long-chain synthetic polymers) and the species present in the film interior (e.g., particles, electrolytes, or surfactants). The film properties that can be studied in this way include film stability, rate of film thinning, and surface forces stabilizing the film. These properties are of significant interest in understanding and controlling the stability of dispersed systems. The experimental procedure and the capabilities of the modified cell are demonstrated in several examples.