The solution of the Percus-Yevick (PY) equation for a binary mixture with a square well potential as a perturbation has been applied to the study of the Pb-Bi molten alloy system. The partial structure factors in the long wavelength limit is calculated and used to evaluate the long wavelength limit of the concentration-concentration fluctuationsScc(0). This has in turn been used to obtain the Warren-Cowley short range order parameter α1and the chemical diffusion D. The calculations indicate compound forming tendencies in Pb-Bi molten alloys with greater magnitude at low atomic fraction of Bismuth.