JACQUES LOEB 671 



were dipped into beakers containing 350 cc. of HCl solution of pH 

 3.0. The HCl solutions in the beakers were made up in NaCl solu- 

 tions of different concentrations and the concentration of the NaCl 

 solution in the beaker was at the beginning of the experiment always 

 identical with the concentration of the NaCl in the gelatin solution 

 inside the collodion bag. The final measurements were made after 

 18 hours when the osmotic and the membrane equilibria were estab- 

 lished. The osmotic pressure was a maximum (about 425 mm. 

 water) in the gelatin chloride solution free from salt, and the osmotic 

 pressure was the lower the higher the concentration of the salt added. 

 This effect is represented in the upper curve of Fig. 1 . The abscissae 

 are the concentration of the NaCl solution and the ordinates the 

 osmotic pressure. The curve shows that the osmotic pressure drops 

 very rapidly with the increase in the concentration of NaCl. 



The potential differences at the boundary of the inside and outside 

 solutions were measured with a Compton electrometer as described 

 and the values found are plotted on the second upper curve in 

 Fig. 1. The scale for the ordinates was selected in such a way as 

 to make the osmotic pressure ordinate and the ordinate for the 

 p.D. coincide for a m/4,096 NaCl solution. The reader will notice 

 that the two curves for osmotic pressure and p.d. coincide practically 

 throughout which signifies that the p.d. and the osmotic pressure of 

 the gelatin chloride solution undergo a similar depression under the 

 influence of a neutral salt like NaCl. 



We stated in the last paper that the observed p.d. is always equal 

 to the P.D. calculated on the assumption that at equilibrium the p.d. 

 is due to the difference in the pH inside and outside the collodion bag. 

 The pH inside and outside were measured electrometrically and the 

 results are contained in Table I. 



On the assumption stated above we can calculate the p.d. in 

 millivolts by multiplying the value pH inside minus pH outside by 

 59, and the values so obtained should agree with the observed p.d. 

 Table II shows that this is true. 



The two lower curves of Fig. 1 give the depressing effect of different 

 concentrations of Na2S04 on the osmotic pressure and on the p.d. of 

 a 1 per cent gelatin chloride solution of pH 3.5. Everything was the 

 same as in the preceding experiment, except that Na2S04 was sub- 



