Experimental studies of light scattering in the tricritical region of mixtures of ethane with heavier hydrocarbons show that the intensities and correlation lengths do not satisfy the asymptotic form of the Griffiths first sum rule. Both sums increase sharply rather than approaching zero as the tricritical point is approached, indicating that either (a) there is a nonclassical divergence in the sums, or (b) many terms must be retained in a power series for the coupling "constant." Similar results have been found in a reanalysis of earlier experiments.

• Received 4 March 1985

DOI:https://doi.org/10.1103/PhysRevLett.54.2234