140 THEORY OF COLLOIDAL BEHAVIOR 



inside minus pH outside. It was possible to show that this is 

 true. 



Gelatin chloride solutions containing 1 gm. of originally iso- 

 electric gelatin in 100 c.c. solution and having a pH of 3.5 were 

 made up in different concentrations of NaNO 3 in water, the 

 concentration of NaNO 3 varying from M/4 ? 096 to M/32 NaNO 3 , 

 and all possessing a pH of 3.5. These mixtures were put into col- 

 lodion bags and the bags were put into HC1 solutions of pH 3.0 

 made up in different concentrations of NaNO 3 , also of pH 3.0. 

 These outside solutions contained no gelatin. The collodion bags 

 were put into these outside solutions free from gelatin in such a 

 way that the concentration of the NaNO 3 solution inside the 

 collodion bag was always the same as outside. 



When the P.D. across the collodion membrane was measured 

 after 18 hours (after equilibrium was established) it was found 

 that it was diminished upon the addition of neutral salt and the 

 more the higher the concentration of the salt. This shows that 

 the addition of neutral salt to a protein solution has a similar 

 depressing effect on the P.D. as on the osmotic pressure, swelling, 

 and viscosity of the protein solutions. 



The next fact of interest was that the values of pH inside 

 minus pH outside diminish in a parallel way with the diminution 

 of the P.D. and that the values of 59 (pH inside minus pH outside) 

 agree remarkably well with the observed P.D. (Table XVIII). 



We have seen in Chapter VI that the addition of a salt with 

 bivalent anion, e.g., Na 2 SO 4 , to a gelatin chloride solution has a 

 much greater depressing effect on the osmotic pressure, viscosity, 

 etc., of the solution than the addition of a salt with monovalent 

 anion, namely, NaNO 3 . It can be shown that the addition of 

 Na 2 SO 4 also has a greater depressing effect on the P.D. of a 

 gelatin chloride solution than has a NaNO 3 solution of the same 

 molecular concentration (Table XIX). 



We will consider as a third case the influence of CaCl 2 on the 

 P.D. of a gelatin chloride solution. It has been shown that the 

 depressing effect of CaCl 2 on the osmotic pressure of a gelatin 

 chloride solution is about twice as great as that of an equimolec- 

 ular concentration of NaCl. Table XX shows that the depress- 

 ing influence of CaCU on the P.D. is about twice as great as 

 that of NaNOs. The agreement between the observed P.D. and 



