JACQUES LOEB 403 



the pH approaches 3.0 the addition of the same amount of acid which 

 near the isoelectric point caused a considerable change now causes 

 only a slight change, while when the pH falls below 3.0 the depressing 

 influence of the anion continues to increase with increasing concen- 

 tration of the electrolyte. 



//. Ion Series and the Action of Salts on Proteins. 



We have shown in preceding papers that, as long as the concentra- 

 tion of the electrolyte is not too high, only the sign of the charge and 

 the valency of an ion influence such physical properties as swelling, 

 viscosity, solubility in alcohol, and osmotic pressure of proteins; 

 while all the different ions of the same sign of charge and valency have 

 either the same effect or if there is a difference in effect it is too small 

 to be noticed with our present methods of work.^ This proof was 

 furnished for the action of acids and alkalies on the physical properties 

 of proteins just mentioned. We now wish to make the proof com- 

 plete by considering also the action of salts. To do this we are com- 

 pelled to compare the relative depressing action of low but equal con- 

 centrations of different salts upon the physical properties of a gelatin 

 salt, for example gelatin chloride of a definite pH; e.g., 3.0. As can 

 be easily surmised the addition of a salt will in many cases alter the 

 pH of the solution and this alteration will be larger in the case of cer- 

 tain salts, e.g. Na acetate, than in the case of others, e.g. NaCl. 

 Unless we take into consideration these variations in the pH caused 

 by the addition of salts we shall be in danger of erroneously ascribing 

 the influence of a variation in the hydrogen ion concentration to an 

 influence of the nature of the anion. The Hofmeister ion series are 

 due to this error. 



The method of our experiments was as follows. 50 cc. of a 2 per 

 cent solution of originally isoelectric gelatin were brought to a pH of 

 3.0 by the addition of HCl. To this were added 50 cc. of H2O or of 

 a salt solution of different molecular concentration, and the viscosity 

 of this mixture was measured using those precautions which were 

 described in a preceding paper. 



Fig. 8 gives the curves representing the depression of the specific 

 viscosity of a gelatin chloride solution of pH 3.0 by different concen- 

 trations of salts with monovalent anion; namely, NaCl, NaH2P04, 



