CHAPTER V 

 THE VALENCY RULE AND THE HOFMEISTER SERIES 



(A) OSMOTIC PRESSURE 



In this chapter it will be shown that the combining ratios of 

 acids and alkalies with proteins furnish the key for the under- 

 standing of the influence of ions on the physical properties of 

 proteins, inasmuch as only the sign of charge and the valency 

 but not the other properties of an ion influence such physical 

 qualities of proteins as osmotic pressure, viscosity, and, in the 

 case of gelatin, swelling. In this discussion only the monovalent 

 and bivalent ions will be considered. 



The fact to be proved is contrary to the statements current in 

 colloid chemistry according to which the chemical nature of the 

 ion is of as much importance as the valency. As already stated 

 in the first chapter, the ions have been arranged in series, 

 the so-called Hofmeister series, according to their relative in- 

 fluence on swelling, viscosity, and osmotic pressure of proteins. 

 It is perfectly true that the different ions of the same valency, 

 e.g., Li, Na, K, Rb, Cs, or Cl, Br, and I, have different chemical 

 properties according to their position in the periodic table, and 

 monovalent anions, such as NO 3 , CH 3 COO, also have definite 

 chemical characteristics different from those of I or Br or Cl. 

 These differences manifest themselves in many phenomena, 

 e.g., in solubility, but they are obviously of minor importance 

 in their influence on the physical properties of proteins alluded 

 to, for a reason which will become clear in the second part of the 

 book. For the present it will only be shown that the Hofmeister 

 ion series are largely the result of the same methodical error 

 which had prevented the recognition of the fact that acids and 

 alkalies combine with proteins stoichiometrically, namely, the 

 failure to measure the hydrogen ion concentration of the protein 

 solutions. If we wish to compare the relative efficiency of two 

 5 65 



