1. The question of the critical pore diameter for streaming potential is discussed. 2. The surface charge is calculated for cellulose in contact with solutions of K3PO4, K2CO3, K2SO4, KCl, and ThCl4. 3. The surface charge of cellulose in contact with a solution of 2 x 10–4 N NaCl is calculated as a function of temperature and is found to show a sharp break at 39°. This is interpreted in terms of the change of the specific heat of water. 4. A marked ion antagonism is found in NaCl:KCl, KCl:MgCl2, NaCl:MgCl2, NaCl:CaCl2, KCl:CaCl2, CaCl2:MgCl2 mixtures when the surface charge is calculated as a function of concentration.