Solubility and activity coefficients of acidic and basic nonelectrolytes in aqueous salt solutions. 1. Solubility and activity coefficients of o-phthalic acid and L-cystine in NaCl(aq), (CH3)(4)NCl(aq), and (C2H5)(4)NI(aq) at different ionic strengths and at t=25 degrees C

The solubility of o-phthalic acid and l-cystine was determined at following concentrations:  NaCl(aq) (0.1 to 4.5) mol·L-1, (CH3)4NCl(aq) (0.1 to 3) mol·L-1, (C2H5)4NI(aq) (0.1 to 1) mol·L-1 and in pure water. The solubility trend is (C2H5)4NI > (CH3)4NCl > NaCl for o-phthalic acid and NaCl > (CH3)4NCl > (C2H5)4NI for l-cystine. Setschenow constants and activity coefficients of neutral species were calculated from these data. The different trends shown by o-phthalic acid and l-cystine are discussed.