32 THEORY OF COLLOIDAL BEHAVIOR 



[R 



-NH ; 



COOH 



Such proteins behave as if they were simple (probably polybasic) 

 fatty acids, the rest of the molecule not participating in the reac- 

 tion. In the presence of a hydroxide, e.g., NaOH, sodium pro- 

 teinate is formed 



NH 



. COOH + NaOH " |_ 1X COONa + H 2 O 

 and the sodium proteinate dissociates electrolytically into a 

 protein anion and a Na ion 



- COONa L A " COO + Na" 



When other electrolytes are present they can of course exchange 

 their cation with the Na of the protein salt. Our symbol con- 

 siders only one COOH group, but it is probable that as a rule 

 more than one COOH group of a protein molecule combines 

 with alkali (Bugarszky and Liebermann, Sackur, Robertson, 

 S^rensen, Pauli, Northrop 1 ). 



On the acid side of the isoelectric point only the NH 2 groups of 

 the molecule are capable of reacting with other compounds and 

 we represent the protein molecule on this side in the following 

 form: 



[R 



_NH 2 



COOH 



In this form the proteins behave like NH 3 which according to 

 Werner 2 is capable of adding an acid, e.g., HC1, the H ion of the 

 acid being added directly to the N while the Cl remains outside 



H 



the ring of the 4H in the following way: HNHC1. It has been 



H 



1 NORTHROP, J. H., /. Gen. PhysioL, vol. 3, p. 715, 1920-21. 



2 WERNER, A., " Neuere Anschauungen auf dem Gebiete der anorganischen 

 Chemie, 3rd ed., Braunschweig, 1913. 



