The activity coefficients of naphthalene in aqueous NaNO3, NaClO3, SrCl2, BaCl2, (NH4)2SO4, Na2SO4, K2SO4, and MgSO4 solns. were detd at 25癈 by using spectrophotometric method. The relations log absorbance-concn. are found to be all straight lines through the origin, in agreement with the Setschenow experimental formula. The slopes of the straight lines are the salting-out constants with the salting-out order Na2SO4 > K2SO4 > MgSO4 > (NH4)2SO4 > BaCl2 > SrCl2 > NaClO3 > NaNO3. The experimental results are compared resp. with the calculation results of Debye-McAulay and Conway-Desnoyers-Smith electrostatic theories, Masterton-Lee scaled particle theory, and McDevit-Long internal pressure theory. The numerical calculation of the modified internal pressure theory gives the best fit with the experimental data. All the experimental results once again confirm the van der Waals force salt effect mechanism.

Key words: ULTRAVIOLET SPECTROPHOTOMETRY, AQUEOUS SOLUTION, NITRATE, AMMONIUM SULFATE, PERCHLORATE, NAPHTHALENE, SODIUM SULFATE, POTASSIUM SULFATE, SALT EFFECT, MAGNESIUM SULFATE