Figure 3.

The m value v.s. pH. (black square) 0 M NaCl, (white square) 0.01 M NaCl, (black circle) 0.02 M NaCl, (white circle) 0.05 M NaCl, (black up-triangle) 0.1 M NaCl, (white up-triangle) 0.2 M NaCl. The experimental condition is in Figure 3.