394 ION SERIES AND PROTEINS. Ill 



When, however, neutral salts are added to protein solutions we no 

 longer notice an opposite effect of the oppositely charged ions. When 

 neutral salts are added to isoelectric gelatin no effect is noticed as 

 long as the concentration of salt does not reach the value required for 

 precipitation. When neutral salt is added to a protein solution on 

 either side of its isoelectric point only a depressing action of that 

 ion which has the opposite sign of charge as the protein ion is ob- 

 served. No augmenting action of the ion with the same sign of charge 

 as the protein is noticeable. Thus if we add CaCl2 or Na2S04 to a 

 solution of gelatin chloride or gelatin nitrate we observe only a depres- 

 sing effect of the CI or SO4 ion but no augmenting eff'ect of the Ca or 

 Na ion ; while when we add these salts to a solution of a metal gelati- 

 nate we observe only a depressing effect of the Ca or Na ion but no 

 augmenting effect of the anion. We shall first show that this is the 

 correct expression for the difference in the action of acids and bases 

 on the viscosity of proteins on the one hand and of neutral salts on 

 the other. 



A 2 per cent solution of isoelectric gelatin is prepared and brought 

 to a pH of 4.0. The solution is made 1 per cent in regard to the orig- 

 inally isoelectric gelatin by adding to 50 cc. of the 2 per cent solution 

 either 50 cc. of H2O or of a salt solution, e.g. NaCl, of different molecu- 

 lar concentration, from m/8,192 to 1 m, taking care that the hydrogen 

 ion concentration remains the same. We determine the viscosity 

 (i.e. the time of outflow through a viscometer) in the way described 

 in a preceding publication and plot the reciprocal of time of outflow 

 (counting that of water as 1) as ordinates over the pH as abscissa 

 (lower curve, Fig. 1). For the sake of briefness we beg leave to des- 

 ignate this value as specific viscosity.^ The addition of the NaCl 

 causes only a drop, and no rise in the curve. 



If, however, we mix the 2 per cent gelatin solution of pH 4.0 with 

 various concentrations of HCl (upper curve. Fig. 1) instead of with 

 NaCl we do not notice a drop but at first a rise followed by a drop 

 when the concentration of the CI ion is a little above n/1,000. In 

 Fig. 1 the drop appears at a concentration of about n/256 FICl, but 

 the reader must remember that on account of the fact that part of 

 the acid combined with the gelatin the pH of the solution was about 

 3.0. In other words, while the addition of H ions increases the vis- 



