Abstract: A liquid-liquid contactor comprised of a jet of fluid 1 flowing through a coaxial, cocurrently flowing stream of fluid 2 (fluid 1 and fluid 2 being immiscible), with one or both of the fluids being continuously recycled. This device is used as a scientific instrument to measure the rate of interphase transfer of material dissolved in or comprising one of the fluids. The device can also be employed to acquire data on chemical reactions occurring at the interface between the two fluids, in a film adjacent to the interface, or throughout the volume of one or both of the fluids.