392 ION SERIES AND PROTEINS. Ill 



at a pH < 4.7 only the anion of the neutral salt is capable of combin- 

 ing with the protein, forming gelatin-acid salts.^ 



Lillie has made the statement that while acids and alkalies increase, 

 salts depress the osmotic pressure of gelatin.^ This statement, while 

 it was the expression of facts actually observed by Lillie, is no longer 

 tenable owing to the fact that the influence of the hydrogen ion con- 

 centration of the gelatin solution was not taken into consideration. 

 If we add acid 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 when we add 

 alkali, e.g. KOH, to a solution of a metal gelatinate of pH 11.0 or 

 above, the effect is also a similar depression of the osmotic pressure as 

 that caused by the addition of KCi. We also get a depression when 

 we add some acid to a solution of metal gelatinate or when we add 

 some alkali 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 acid depresses the osmotic pressure 

 or viscosity. The question then arises, what is the correct expression 

 of the facts in the case? 



An analogy with another field of phenomena may be of service. 

 The writer has recently published a series of articles on the influence 

 of electrolytes on the rate of diffusion of water through collodion 

 membranes, which have shown that water diffuses through such a 

 membrane as if the particles of water were positively charged. When 

 pure water is separated from a solution of an electrolyte of not too 

 high a concentration, the positively charged particles of water diffuse 

 through the collodion membrane into the solution as if they were 

 attracted by the anion and repelled by the cation with a force increas- 

 ing with the valency of the ion. In this case the oppositely charged 

 ions of an electrolyte influence the rate of diffusion of water through 

 the membrane in an opposite sense. 



2Loeb, J., ./. Gen. Physiol., 1918-19, i, 237; Science, 1920, Hi, 449. 

 3 Lillie, R. S., Am. J. Physiol, 1907-08, xx, 127. 



