184 ELECTROCHEMISTRY 



casein, i.e., a multiple of 4386, and the valency of the casein ions 



must be a multiple of oooc ■ ioo > i-^-, of 1.9 ± 0.15, or, in round 



Zooo ± loo 



numbers, 2. 



Since, as we have seen in the earlier part of this chapter, the 

 former of these two assumptions is inadmissible, we may con- 

 clude that the valency of the casein ions, in solutions of a base 

 "saturated^' with casein, is a multiple of 2. This obviously cor- 

 responds with the view that the caseinate dissociates into two 

 protein ions in accordance with the scheme: 



H 



I ++ 



Ri.N = C.R2 + KOH = RiN" + KOCR2 



I I 



OH OH 



3. The Relative Masses of Protein Anions and Cations. — 



From the above experimental results it appears that the masses 

 of the protein cation and anion must be nearly equal, for other- 

 wise the weight of one ion would not be one-half but some other 

 fraction of the entire molecule and the valency, deduced from 

 the above experimental data, would not be a whole number but 

 some fraction. Since the valency of an ion is necessarily a whole 

 number and not a fraction, the weights of the cations and anions 

 which the protein molecule yields must be nearly equal. The 

 above data do not enable us, however, to decide whether or not 

 the weights of the cations and anions are exactly equal, since the 

 precision attained in these experiments is not sufficient to reveal 

 with certainty a difference of less than 10 per cent between the 

 weights of the two ions. 



It has been shown by Bredig (3) that the equivalent migration- 

 velocities * of very heavy ions under unit potential gradient at 

 constant temperature tend to approach a minimal constant value 

 of about 20 X lO"^ cm. per sec. at 18° C. The conception de- 

 veloped above, therefore, of the mode of dissociation of the salts 

 of a protein leads to the conclusion that the velocities of migra- 

 tions of both the cation and the anion of a protein salt must be 



* That is, the migration-velocity under unit force. For a divalent ion 

 under unit potential gradient the force exerted is twice as great as that which 

 is exerted on a univalent ion; the absolute velocity is, therefore, twice as great 

 as that of a univalent ion, but the equivalent velocity is the same. 



