130 COLLOID CHEMISTRY OF THE PROTEINS 



protein is saturated in presence of excess of acid or of alkali 

 only the highest possible valency of the protein ion comes into 

 consideration. In all intermediate stages the protein salts with 

 acids or bases give mixtures of ions of differing valency and 

 mobility. This is why the mobilities of the protein ions, as 

 determined by Pauli and Oden for increasing addition of acid, 

 lie on a continuously rising curve. 



Henderson * has deduced a general formula on the basis of 

 Nernst's theory, for the diffusion potential which applies to any 

 ions or mixtures. Thus 



RT . (Ux-VJ-tUs-Vs) , U't + V'i 



F (U\ + V\) (U' 2 - V'3 e U' 2 + V 2 



in which 



Uj == %Cj -f u 2 C 2 + 



Y! == VjCj. + v 2 C 2 + 



U 7 ! = UjWjCj^ + U 2 W 2 C 2 + .... 

 V'j = V^C! -f V 2 W 2 C 2 -f- .... 



Whenwj, u 2 ,v lf v 2 .... are the mobilities, w lt w 2 ,w lt w 2 ...., 



are the valencies, and C lt C 2 ...., C 1; C 2 ... are the concentrations 

 of cations and anions respectively. 



Pauli and Matula have carried out experiments (not yet 

 published) with a view to determining the mobility of the 

 protein ions in this way. Various circuits, in which albumin 

 salts were included, were built up, the following being a typical 

 example. Solutions of the protein salt and of hydrochloric acid 

 were included between two normal calomel electrodes. In the 

 second circuit given below, concentrated potassium chloride 

 solution, which gives the equally mobile K* and Cl' ions, was 

 interposed to eliminate the diffusion potential. 



Circuit I. 



Hg/HgCl . N KCl/o-002 N HC1 + i per cent, albumin/ 

 0-002 N HC1/N KC1 . HgCl/Hg. 



* Zeitsch. physikal. Chem., 1907, 59, 118 ; 1908, 63, 325. 



