ION SERIES AND THE PHYSICAL PROPERTIES OF 



PROTEINS. 



III. The Action of Salts in Low Concentration. 



By JACQUES LOEB. 

 {From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, November 9, 1920.) 



/. The Difference in the Effect of Acids, Alkalies, and Salts on Proteins. 



The data concerning electrolytic dissociation and the behavior of 

 electrolytes in general suggest that it is well to discriminate between 

 solutions of electrolytes in low and in high concentrations. While 

 no sharp line of demarcation can h. drawn it will suffice for the prob- 

 lem we are discussing to designate a concentration of electrolytes 

 below m/16 as low and those near the solubility limit of one of the 

 components as high. In this paper we intend to deal with solutions 

 of low concentrations; i.e., m/16 or less. 



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 

 expression for this difference. Pauli^ states that while acids and 

 alkalies form salts with proteins, neutral salts form "adsorption com- 

 pounds" with "electrically neutral," i.e. non-ionized, protein mole- 

 cules, both ions of the salt being simultaneously adsorbed by the 

 protein molecule. This idea is no longer tenable for salt solutions of 

 low concentration since the writer has shown through his experiments 

 with powdered gelatin 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 combine with the gelatin, fomiing metal gelatinate; 



^ Pauli, W., Fortschr. naturwiss. Forschung, 1912, iv, 223. 



391 



