406 ION SERIES AND PROTEINS. Ill 



above than the curve for the depressing effect of NaCl. Fig. 8 shows 

 that the curves for the depressing effect of these three salts are slightly- 

 lower than the curve for NaCl or NaH2P04. The greatest apparent 

 deviation from the valency rule occurs in the curve for Na acetate 

 whose depressing effect is of the order of that of Na2S04. 



In the colloidal literature it is always stated that Na acetate acts 

 like Na2S04 and this is interpreted to mean that the acetate anion 

 acts like the bivalent SO4 anion and not like the monovalent CI or 

 NO3 anion. Table I shows that Na acetate also depresses the hydro- 

 gen ion concentration more than NaCl or NaH2P04; m/64 Na acetate 

 brings the gelatin solution practically to the isoelectric point, and 

 at the isoelectric point the viscosity of gelatin solution is a minimum. 

 This lowering of the hydrogen ion concentration (and not the alleged 

 influence of the acetate anion) explains the excessive depressing effect 

 of Na acetate. That this interpretation is correct can be proved in 

 the following way. We prepare 1 per cent solutions of gelatin acetate 

 of pH 3.3 and gelatin chloride also of pH 3.3. The specific viscosity 

 of these two solutions was practically the same (both were 1 per cent 

 solutions in regard to originally isoelectric gelatin). The solution of 

 gelatin acetate of pH 3.3 was made up in various concentrations of 

 Na acetate of pH 3.3. The Na acetate solution of pH 3.3 was obtained 

 by dissolving m/16 Na acetate in 1^ m acetic acid and the various de- 

 grees of dilution of this m/16 Na acetate solution of pH 3.3 were 

 brought about by dilution with pure acetic acid of pH 3.3. The 

 non-dissociated molecules of acetic acid have no more depressing influ- 

 ence on the physical properties of proteins than have the molecules 

 of any non-electrolyte. Fig. 9 gives the curve representing the 

 depressing effect of Na acetate on gelatin acetate of pH 3.3 when the 

 pH is kept constant. 



The gelatin chloride solution of pH 3.3 was made up in different 

 concentrations of NaCl and the depressing effect of NaCl on the 

 viscosity of gelatin chloride is also plotted in Fig. 9. It is obvious 

 from Fig. 9 that the depressing effect of Na acetate and NaCl are 

 identical when the pH is kept constant and identical in both cases. 



The same fact was confirmed in a somewhat different way. A 2 

 per cent solution of gelatin chloride of pH 3.0 was made up in various 

 concentrations of Na acetate also of pH 3.0. In order to prepare Na 



