JACQUES LOEB 625 



contradict the idea that the p.d. increases inversely with the radius of 

 the three cations. 



It has already been stated in the preceding paper^ that atpH 3.0 only 

 the anion of the salt has any effect on the p.d between gelatin chloride 

 and the liquid with which it is in contact and that this effect is only 

 depressing. The cation of the salt has no effect. This is shown in 

 Fig. 3, where the influence of NaCl, CaCl2, and BaCU on the p.d, 

 between solid gelatin chloride and the liquid with which it is in equilib- 

 rium are plotted. The method of the experiments was the same as 

 in the experiments with LiCl and NaCl just described. The abscissae 

 in Fig. 3 are the chlorine ion concentrations (on the assumption of 

 complete ionization) and the ordinates are the p.d. The influence of 

 NaCl, CaCl2, and BaCl2 on the p.d. is, therefore, the same for the same 

 concentration of chlorine ions, which means that there exists at pH 3.0 

 only a depressing effect of the CI ions on the p.d., but no increase of the 

 p.d. through adsorption of cations. If this latter effect existed the curves 

 in Figs. 2 and 3 representing the influence of salts on the p.d. should 

 not be identical. The identity of the curves in Figs. 2 and 3 can only 

 mean that that ion of a salt which has the same sign of charge as the 

 protein ion has no effect on the p.d. between the particles of gelatin 

 chlorideof pH 3.0 and the liquid with which they are in equiHbrium. 

 It may be stated incidentally that this was to be expected if the 

 Donnan equilibrium is the cause of the p.d. 



If we now return to the interpretation of the influence of the radius 

 of the cation on the transport curves in anomalous osmosis in Fig. 1 , we 

 must infer that the difference in the transport curves for KCl, NaCl, and 

 LiCl is not due to any influence of the three cations on the electrical 

 double layer inside the pores of the membrane. We have seen in the 

 preceding paper that there exists a second p.d. which has an influence 

 on the transport curves, namely, the p.d. across the membrane, which 

 is essentially but not exclusively due to a difference in the mobility 

 of the oppositely charged ions. This p.d. was measured at the begin- 

 ning of each transport experiment and at the end, i.e., after 20 minutes. 

 By that time some of the salt had diffused from the salt solution into 

 the surrounding water. Table I gives the p.d. across the membrane 



* Loeb, J., J. Gen. Physiol., 1921-22, iv, 463. 



