ALKALI PROTEINS WITH LAPSE OF TIME 117 



Protein salts of the Robertson type, therefore, give no free 

 metal ions, but only equal numbers of oppositely charged 

 protein ions. When investigated in the electrophoresis appa- 

 ratus, however, the protein salts with alkali show only negative 

 protein ions, in the same way as wheji acid is added, migration 

 to the cathode alone occurs. In this place, without going into 

 the arguments which Robertson uses to support his theory, we 

 will give a summary of the facts which tend to show that alkalis 

 form regular salts with proteins, the latter behaving as polybasic 

 acids. 



1. The protein part of the alkali protein migrates to the 



positive pole, while the alkali content increases at the 

 negative pole. 



2. The viscosity of solutions of the protein salt passes through 



a maximum value corresponding to a repression of 

 the ionisation of the alkali protein in excess of alkali 

 a behaviour exactly parallel to that of acid albumin 

 in excess of acid. 



3. The difference in electrical conductivity between sodium 



caseinate and ammonium or potassium caseinate 

 corresponds to the difference in mobility of the 

 sodium ion compared with the ammonium or potas- 

 sium ion. This behaviour is compatible only with 

 the existence of free metal ions. 



4. When casein is added to sodium hydroxide solution a fall 



in the total molecular concentration of the latter 

 occurs which can be demonstrated by the diminution 

 of the freezing point depression. This effect is pro- 

 duced by the polyacid character of the casein, as a 

 result of which only one polyvalent casein ion appears 

 when several OH ions of the alkali are replaced. 

 In the proteins that have been studied the basic constant K 6 

 is large compared with the acid constant K a . In dialysis of 

 natural albumin the alkali is the more difficult to remove, so 

 much so that at one stage in the dialysis the protein reacts as an 

 alkali protein. 



The carboxyl-groups at the end of the chains in the protein 

 molecule primarily provide the acid valencies for combination 



