Pierre Lecomte du Noüy's blood pressure monitor (1930)

This instrument quantifies the surface tension exerted at the air-liquid interface or between two immiscible liquids by measuring the force required to remove an immersed ring. Invented by Pierre Lecomte du Noüy, director of the biophysics section at the Institut Pasteur in Paris, this device, also called the Lecomte du Noüy ring, also measures the critical micellar concentration of surfactants. It is mainly used to evaluate manufacturer oils or surfactant solutions.