Fundamental Studies on Interfacial Tensions in Flotation. IV : Suspended-Plate Method of Determining Wetting Tension and the Time Variation of Wetting Tension of Glass at Water-Air Interface

A new method of measuring wetting tension of solids with a suspended plate was developed. The method enables us the precise as well as rapid measurement of the wetting tension. In order to contribute to the study of the wettability of pure surface of minerals, the wettability of a glass plate, which was selected as an example because of its perfect wettability and ease of cleaning, was measured. The method of cleaning in which glass was immersed in an ethyl alcohol solution of sodium hydroxide and then washed with distilled water, was found to be simple and yet very effective. The wetting tension of crystal glass against pure water was measured to be 71.97 dynes/cm at 24.9℃, that is the contact angle was zero. The larger values of contact angle of glass given in literatures were discussed and the causes were summarized. The time variation of the wetting tension of a clean glass plate was measured precisely. It was assumed that the change of the wettability of clean glass surfaces on standing was due to the adsorption of air or vapour from the atmosphere. From the theoretical consideration of simple adsorption of gas on the surface of solids, the wetting tension-time equation was derived. It was verified that the equation held good. From the equation the characteristic values as the wetting tension at zero time, that at infinite time, the wetting velocity, that at zero time and the time required for the wetting tension to go half way to its final value was obtained. These values may be utilized for the investigation of wetting characteristics of solids.