Effect of the precipitation of neutral-soap, acid-soap, and alkanoic acid crystallites on the bulk pH and surface tension of soap solutions.

The natural pH of sodium dodecanoate (laurate), NaL, and sodium tetradecanoate (myristate), NaMy, solutions is measured as a function of the surfactant concentrations at 25 degrees C, and at several fixed NaCl concentrations. Surface tension isotherms are also obtained. Depending on the surfactant concentration, the investigated solutions contain precipitates of alkanoic acid, neutral soap, and acid soaps.