1299are the stoichiometric coefficients.of the ions upon ionization, then the activity of the electrolyte as a whole is where r = r1 + r2 and f, the mean activity coefficient, takes into account the possible deviation from free volume ideality. If the free volume fractions are now written in terms of the molality of the hydrated solute and if the average volume ratio of the electrolyte as a whole, (qsl + rZsz)/r, is denoted by s, then cy12 is given by a = alrz a2ra = f' alri o 1 2 r~ = f ' a i z (13) If one now applies (3), cancels all common terms, substitutes (l), and makes use of the same technique which led to ( 5 ) , one obtains the desired equationThere are some interesting special cases. If s = 1, mole fractions result, and (15) reduces For the ideal non-electrolytes, r and f' are both to (5).unity and (15) becomes( 1 6 ) If there is no solvation, (16) reduces to equation 9.21 of reference 4. Equation 16 has been fitted to the data for aqueous sucrose from 0.1 to 5m with h = 8.7, 'z = 2.7. The fit is about as good as that of 9.214 with h = 0, z = 5. If z were really proportional to the molal volume, it would have been larger than h. If the Debye-Hiickel equation is applied to the solvated ions as before, one obtains for aqueous solutions z+ z-A 4 1 + a~& + 2.303[1 -0.018(h -rs)m] logy = log [I -0.018(h -rs)m] Since a t present there is no a priori way to determine s, equation 17 remains a three parameter equation. Acknowledgment.-The author wishes to acknowledge conversations with Professor Joseph E. Mayer and Dr. Edward V. Sayre. He is indebted to Miriam Miller, Lorraine Fischer and Stuart Rideout for very generous aid with the computations.O.O18s(s -1)rm (17) The effects of a series of salts and acids on the melting points of gelatin gels have been studied. The effects of ions, of the same or opposite charge, are additive. There is a correlation between the binding of ions, as indicated by pH changes, and their effects 011 the melting point. However, by the use of amino-acetylated gelatin and a guanidino-nitrated, hydroxylsulfated gelatin, it is shown that binding of anions at amino, guanidino or hydroxyl groups is not responsible for melting point changes. B y the use of carboxyl-esterified gelatin and hydroxyl-acetylated gelatin, it is shown that binding of cations at carboxyl or hydroxyl groups is not the cause d melting point reduction. Iron (111) ion, at low concentration, raises the melting point by inter-or intramolecular cross-linking through the carboxyl groups, I n agreement with previous reports polarizable anions are effective melting point reducers with diiodosalicylate being the most potent observed.