The purpose of this standard is to establish a method for measuring the interfacial tension between two immiscible liquid phases, one aqueous and the other organic, that form an interface between them, based on the stretching of the interfacial film. The two phases may contain one or more surface agents. This standard is also applicable for the measurement of interfacial tension in systems of two immiscible liquid phases other than those indicated above. NOTE Various methods have been developed to determine interfacial tension. Among them are the following: a) Methods based on the stretching of a liquid film, by means of a stirrup or a ring; b) Drop volume method; c) Sessile drop method; d) Hanging drop method; e) Spinning drop method. Methods based on the stretching of liquid films have great advantages due to the simplicity of their operating procedure. NOTE The method described in this standard does not allow obtaining precise results. It is acceptable for laboratory controls.