n6 ALTERATIONS IN STATE OF THE 



An alteration of the freezing point depression with time can 

 be noted in such solutions when the alkali content is high. 

 This result corresponds to a decrease in total molecular con- 

 centration, and, like the fall in conductivity with time, probably 

 finds its explanation in the increased combination of alkali 

 with casein, as proved electrometrically. In any case, the 

 observation of a decrease in molecular concentration of the 

 alkali caseinates is evidence against the existence of any 

 considerable hydrolytic decomposition of the protein. 



These observed results can be considered from the chemical 

 point of view by dealing with the question of the structure 

 of the salts of proteins with bases. The earlier workers, par- 

 ticularly Liebermann and Bugarsky, held the view that proteins 

 form typical metallic salts with bases. This conception was 

 adhered to by W. B. Hardy and by Pauli, and expressed in the 

 following equation, in which the free carboxyl groups react as 

 acid valencies with formation of a negative protein ion : 

 NHo /NH 2 



+ NaOH > R/ + H 2 0. 



| X i| C*. \~S JL J. W AV \_ 



^COOH X COO . Na 



T. B. Robertson, also, is entitled to the credit of emphasising 

 the importance of the peptide linkage as the source of basic and 

 acid valencies, and bases his theory on the following scheme, in 

 which the peptide group reacts in its enol form : 

 ...... COH:N ...... + NaOH -- > ... CONa++ + N" ... 



OH H 



According to this scheme, the protein is ionised by rupture 

 at the peptide linkage with formation of two oppositely charged 

 protein fragments. Further, according to Robertson, diamino- 

 and dicarboxyl-groups play a leading part, so that, doubling 

 the previous equation, the formation of two quadrivalent 

 radicles from a double peptide linkage is seen to occur : 



X COH:N COK++ 



R/ +2KOH -- >R/ -f 



X COH:N \COK++ N" 



H /NX OH 



