MIGRATION VELOCITY OF THE PROTEIN IONS 133 



the adhering precipitate of casein. The concentration of 

 casein in the solutions at the electrodes was found by determina- 

 tions of the alteration in refractive index with a refractometer. 

 A silver voltameter arranged for titrimetric estimation was 

 included in the circuit. The work was carried out at a tempera- 

 ture of 30. The liquid at the anode always became poorer in 

 casein but unchanged in reaction towards indicators, whereas 

 that at the cathode also became weaker in casein, but developed 

 a strongly alkaline reaction. This behaviour is easy to under- 

 stand from the conception of the structure of the casemates 

 which we have emphasised in the foregoing pages. 



When, on the other hand, we apply Robertson's conception, 

 difficulties arise at once with these results. He maintains that 

 the alkali enters the molecule at the peptide linkage, with 

 production of two oppositely charged protein ions : 

 H 



R.N"and KO . C . R+ + 



AH 



The former would move to the anode, the latter towards the 

 cathode. Robertson further assumes that the negative ion 

 reacts with water at the anode with liberation of oxygen and 

 formation of solid casein, and that the positive ion reacts with 

 water at the cathode, hydrogen being liberated and casein 

 formed. The casein at this pole dissolves at once in the potas- 

 sium hydroxide which is produced at the same time. Thus he 

 quite overlooks the fact that these protein products do not give 

 the original casein when they react with water, but can only 

 give a new protein product, which must be different at the two 

 electrodes, the new substances being fractional parts of the 

 casein. According to Robertson the secondary reaction at the 

 cathode must always lead to the saturation of the base with 

 protein, and thus even with varying proportion of alkali to 

 casein in the original solution, a constant electro-chemical 

 equivalent would be found for various casemates. The observed 

 values, however, show no such constancy, for with increasing 

 content of alkali the electro-chemical equivalent decreases. 



