CHAPTER VI 



THE ACTION OF NEUTRAL SALTS ON THE PHYSICAL 

 PROPERTIES OF PROTEINS 



1. THE DIFFERENCE IN THE EFFECT OF ACIDS, ALKALIES, 

 AND SALTS ON PROTEINS 



The most striking proof for the alleged existence of specific 

 ion effects on proteins (aside from those due to valency of the 

 ion), seemed to have been furnished by experiments on the 

 influence of neutral salts on the osmotic pressure, swelling, and the 

 viscosity of protein solutions. 



It has been noticed by a number of authors that the influence 

 of neutral salts on the physical properties of proteins differs from 

 that of acids and bases, and various attempts have been made to 

 find an accurate expression for this difference. Some hold that 

 neutral salts form "adsorption compounds" with " electrically 

 neutral," i.e., non-ionized, protein molecules, in which both ions 

 of the salt were believed to be simultaneously adsorbed by the 

 "neutral" protein molecule. 1 This idea is no longer tenable for 

 salt solutions of low concentration since the experiments with 

 powdered gelatin discussed in Chapter II have shown that only 

 one (or practically only one) of the two ions of a neutral salt can 

 combine at one time with a protein. At the isoelectric point, 

 i.e., at pH 4.7, gelatin can combine with neither ion of a neutral 

 salt; at a pH > 4.7 only the metal ion of the neutral salt can com- 

 bine with the gelatin, forming metal gelatinate ; at a pH < 4.7 only 

 the anion of the neutral salt is capable of combining with the 

 protein, forming gelatin-acid salts. 



R. S. Lillie has made the statement that while acids and alkalies 

 increase, salts depress the osmotic pressure of gelatin. 2 This 

 statement, while it was the expression of facts actually observed 



1 PAULI, W., Fortschr. naturwiss. Forschung, vol. 4, p. 223, 1912. 



2 LILLIE, R. S., Am. J. Physiol.,vol. 20, p. 127, 1907-08. 



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