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By observing particles being pushed up an incline by an advancing solidification front, the repulsive force, FR, between the front and the particle is measured. This is done with three particle-melt systems, acetal particles in benzophenone, biphenyl, and salol, where the free energy of particle adhesion to the solidification front, ΔFadh, is known. A linear relationship is found to exist between FRand ΔFadhfor these three particle-melt systems. Having values for FRand ΔFadhit is possible to calculate the minimum separation distance, h, between the particle and the solidification front below which particle engulfment will occur. For all three particle-melt systems hwas found to be essentially the same, 20 nm. In particle-melt systems where his constant, theory would predict that a linear relationship exists between FRand ΔFadh. The fact that this relationship was found to exist between values of FRmeasured directly and ΔFadhcalculated from contact angle measurements using an equation of state for interfacial tensions provides strong support for the validity of the approach used to determine ΔFadh.