Response of a gas‐liquid interface to concentration pulses

Frequency response techniques have been applied to the study of the absorption of sulfur dioxide in water contaminated with surface‐active material. The response of a 0.004‐in. thick liquid film to a sinusoidally varying sulfur dioxide pressure was determined for frequencies ranging from 1 to 10 cycles/sec. The total quantity of sulfur dioxide dissolved was observed continuously by measuring the amount of light absorbed by the film, which contained a colored hydrogen ion indicator, cresol red. The experimental data indicate the presence of a surface phase of absorbed material through which sulfur dioxide molecules had to pass as they were transferred between gas and liquid. In addition to creating a resistance to the passage of the solute molecules, the surface phase apparently was capable of storing the molecules temporarily.