PRECIPITATION AND COAGULATION 131 



H 



HzN.R.COH-t-^ + "^N-R-COOH + 2 NaNOa 



I 

 CI 



Na 

 I 

 = HaN.R.CONa = N.R.COOH + 2 HNO3 (i) 



I 



CI 

 H 



H2N.R.C0Na++ + "^N.R.COOH + NaCl 



I 

 OH 



Na 

 I 

 = H2N.R.C0Na = N.R.COOH + H2O (ii) 



I 

 CI 



Since proteins, dissolved in salt solutions, are electrically neutral 

 (Hardy), it appears probable that this compound undergoes 

 internal neutralization thus {vide Chap. I) : 



Na Na 



I I 



H2N.R.C0Na = N.R.COOH = H3N.R.C0Na = N.R.C00 (iii) 



I I I 



CI CI 



It will be observed that this hypothesis is a slight modification 

 of that advanced by Pauli and Handovsky (57) in that, in the 

 first place, cognizance is taken of the fact that the proteins ionize, 

 not at terminal — NH2 or — COOH groups but at internal enol 

 groups and, in the second place, the compounds which are formed 

 with acid- and alkali-protein respectively are symmetrical in 

 structure, so that the symmetry of the effects of salts in dissolv- 

 ing and coagulating these compounds, which has been observed 

 by Pauli, is readily accounted for. 



In dilute solutions, that is, solutions in which the active mass 

 of water is great, these compounds undergo hydrolytic dissocia- 

 tion in the following way: 



