EXCHANGE_SPECIES
 0.618Ca+2 + 2KX = CaX2 + 1.236K+; -log_k -0.281
 -no_check
 -mole_balance CaX2
 -gamma 5.0 0.165
SOLUTION 1
 K 100                              # 100 mmol K/kg H2O
EXCHANGE 1
 KX 0.417                           # 417 mmol KX, total K in the system = 517 mmol
                                    # Remove 517 mmol K+, replace with 258.5 mmol Ca2+
REACTION
 K -1 Ca 0.5
 0.517 in 20 steps
USER_GRAPH                          # Plot isotherm...
 -head alpha_K beta_K
 -axis_titles "Solute K / (K + 2Ca)" "Exchangeable K / (K + 2Ca)"
 -axis_scale x_axis 0 1 0.2 0.1; -axis_scale y_axis 0 1 0.2 0.1
 -start
 10 graph_x tot("K") / 0.1
 20 graph_y mol("KX") / 0.417
 -end
END