The relative efficiencies of some of the common wetting agents have been determined by measuring the surface tension of five-minute-old surfaces of the solutions using the ring method in a modified form. Aqueous solutions giving a surface tension of 37 dynes per cm. may be considered to have good wetting properties. It is found that wetting power is not necessarily associated with detergent and emulsifying properties.
Salts greatly increase wetting power. Bivalent cations are more effective than univalent cations in increasing wetting power. A moderate degree of hardness in water employed in preparing solutions of wetting agents may be of advantage in the textile industry.
The maximum bubble pressure method is shown to be unsuitable for the measurement of surface tension of solutions which show a variation with time. A rough idea of the order of wetting efficiencies of wetting agents can however be obtained by measuring the surface tension of a five-second-old surface by this method.