Unitarian entropy of dimerization (entropy corrected for the effect of the disappearance of a solute mole on dimerization) (15). This result is in good agreement with our previous results on acridine orange N-alkyl derivatives (6, 7) and is in favor of our suggestion, also proposed by other authors (16-20), on the dominant contribution of hydrophobic interactions to the association of these dyes in aqueous solution.