Fig. 5. (a) Equivalent fraction of cations on the Soil 1 (S1), Soil 1 + bentonite (S1B), and Soil 1 + zeolite (S1Z) exchanger phases predicted from the Rothmund–Kornfeld equation and Gaines–Thomas convention vs. laboratory-measured equivalent fractions on the S1, S1B, and S1Z exchangers. (b) Also with Na added to the ternary solutions at 0.013 mol L^–1. Root-mean square (RMS) = [( predicted N – measured N)²/n]^0.5.