THE ACTION OF NEUTRAL SALTS 89 



by Lillie, is not entirely correct owing to the fact that the influence 

 of the hydrogen ion concentration of the gelatin solution was not 

 taken into consideration. It was shown in the preceding chapter 

 that if acid is added to a gelatin-acid solution of a pH of 3.0 or 

 below, the effect is practically the same as when we add a neutral 

 salt, namely, a diminution of the osmotic pressure of the solution; 

 and that when alkali, e.g., KOH, is added to a solution of a metal 

 gelatinate of pH 11.0 or above, the effect is also a similar depres- 

 sion of the osmotic pressure to that caused by the addition of 

 KC1. A depression is also noticed when some acid is added to a 

 solution of metal gelatinate or when some alkali is added to 

 gelatin-acid salts ; since in both cases the gelatin is brought nearer 

 to the isoelectric point. 



It is also incorrect to speak of an antagonism between the 

 effects of acids and salts, since the facts mentioned show that 

 there is also an antagonism between little and much acid; thus, 

 if the pH of a gelatin-acid salt is 3.0, a further addition of the 

 same acid depresses the osmotic pressure or viscosity. The 

 question then arises, What is the correct expression of the facts 

 in the case? 



The answer seems to be as follows: Suppose the pH is below 

 but near that of the isoelectric point of a protein and HC1 be 

 added. In this case the more acid is added the more non- 

 ionogenic protein is transformed into salt. This salt formation 

 raises the osmotic pressure, swelling, and viscosity of the protein. 

 This agrees with the views of Laqueur and Sackur, and of Pauli. 

 At the same time the anion of the acid has an opposite, namely 

 a depressing effect. The addition of acid has, therefore, two 

 opposite effects on the osmotic pressure, viscosity, and swelling 

 of protein, namely, first, an augmenting effect due to increasing 

 protein-salt formation with increasing hydrogen ion concentration, 

 and second, a depressing effect due to the anion, in our example 

 Cl. At first, the augmenting effect increases more rapidly than 

 the depressing effect. When, however, the pH of the protein 

 solution approaches the value 3.0 the augmenting influence due 

 to the formation of new gelatin chloride grows less rapidly with 

 a further decrease in pfi than does the depressing effect of the 

 anion, and hence, when the amount of acid added increases 

 still further, the depressing effect of the Cl ion prevails over the 



