THE ACTION OF NEUTRAL SALTS 97 



of colloids that the opposite ions of a neutral salt affect the prop- 

 erties of a protein in an opposite direction. We made sure 

 that in all these cases the pH of the gelatin solution was not 

 altered by the addition of the salt. 



When 0.8 per cent solutions of gelatin chloride of pH 3.0 are 

 prepared in solutions of Na salts with the anion of a weaker 

 acid, e.g., Na2 oxalate, Na4Fe(CN) 6 , the pH is increased and 

 there exists the danger of erroneously attributing a depressing 

 effect to the anion which in reality is caused by the increase in 

 pH. In Fig. 31 the effects of the addition of equal concentrations 

 of Nad, Na 2 SO4, and Na 4 Fe(CN) 6 on gelatin chloride of pH = 

 3.0 are plotted. In the case of Na 4 Fe(CN) 6 only the lowest 

 concentrations, from M/8,192 to M/ 1,024, could be used, since 

 in these only did the pH of the protein solution remain = 3.0. 

 Figure 31 shows that the depressing effect of these salts increases 

 rapidly with the valency of the anion. When the concentration 

 of the salt was only M/ 1,024 a drop in the viscosity was already 

 noticeable. This drop was small in the case of NaCl (from 2.8 

 to 2.6), was greater in the case of Na 2 S0 4 (from 2.8 to 2.35), 

 and considerably greater in the case of Na 4 Fe(CN) 6 (from 2.8 

 to 1.5). The objection might be raised that since Na 2 SO 4 has 

 twice as many cations as NaCl of the same concentration and 

 Na 4 Fe(CN) 6 has four times as many cations, it was the difference 

 in the concentration of the cations which caused the difference 

 in the drop. This is refuted by the fact that Na2SO 4 causes a 

 drop in the specific viscosity to 1.8 at a concentration of M/256 

 while NaCl causes the same drop at a concentration of above 

 M/64 which is about four times as high. If the concentration 

 of the cation were responsible for the drop the two concentrations 

 should be more nearly as 1 : 2. Na 4 Fe(CN) 6 causes the same drop 

 of the viscosity to 1.8 at a concentration less than M/ 1,024. 

 Hence, the concentration of Na 4 Fe(CN) 6 required to cause the 

 same diminution of the specific viscosity as that caused by M/64 

 NaCl is less than one-sixteenth of the latter, while it should be 

 only one-fourth if the cation were responsible for the drop. 



Experiments on osmotic pressure and on swelling lead to the 

 same formulation of the difference in the effect of acids and salts 

 as the viscosity experiments. 



What has been shown for the effect of acids on the physical 



7 



