Coalescence times for air bubbles rising through hexadecane to an air-hexadecane interface are measured and compared with an analysis based upon our previous extension of continuum mechanics to the nanoscale [J.C. Slattery, E.-S. Oh, K. Fu, Chem. Eng. Sci. 59 (2004) 4621-4635] with the assumption of retarded dispersion forces. The relation between the retarded and non-retarded Hamaker constants proposed by Gomer and Pich [J. Aerosol Sci. 20 (7) (1989) 735-747] is tested for the first time. (c) 2007 Elsevier Inc. All rights reserved.