MIGRATION VELOCITY OF THE PROTEIN IONS 125 



composed of uniform particles necessitates special methods 

 (Zsigmondy, Oden). A separation of the particles according 

 to size, when an electric field is applied, is not found to occur, 

 because they all move with the same velocity in such circum- 

 stances. Now, according to Helmholtz's theory, equal mobility 

 is due to equal density of charge on the surface ; that is, the 

 number of charges on one particle increases in proportion to 

 the surface of the particle. Thus in the large complexes of the 

 globulin precipitate, a considerable polyvalent effect occurs by 

 each of the surface particles of the aggregates ionising as if it 

 were a free globulin ion. But the charged particles united into 

 aggregates, in spite of the unchanged masses of globulin 

 produced by hydrolysis and carried along therewith, have 

 actually a smaller total surface than the same number of globulin 

 ions. Hence such aggregates will transport an equal quantity 

 of electricity with less difficulty and more rapidly than the free 

 ions. In this way the remarkably high mobility found by 

 Hardy in very turbid globulin acetate can be explained. 



A similar effect which also bears on the question is the increase 

 in mobility of ions of the same size when the valency is increased. 

 We give here two examples * ; the analogous results for 

 albumin will be added later : 



v. 1 8. v. 1 8. 



I. H 2 P(V 26-3 II. H 2 P 2 O 7 " 41-6 



HP0 4 " 53-4 HP 2 7 "' 597 



PO 4 '" 69-0 P 2 O 7 "" 81-4 



If the charge on an ion is doubled while its surface remains 

 constant, the transport of the same quantity of electricity occurs 

 with doubled velocity. This actually happens, for example, in 

 the ions of pyrophosphoric acid shown in series II. above. 

 On the other hand, R. Wegscheider found that with organic 

 ions of the same number of atoms, the ratio of the mobilities 

 of di- and monovalent ions was not 2 but 1-8. Here the effect 

 is not merely due to the change, but also to the alteration of 

 hydration, an influence which is even more important in the case 

 of complex protein ions. The large number of atoms in the 

 molecule, and the heavy hydration have a retarding effect on 



* Abbot and Bray, /. Amer. Chem. Soc., 1909, 31, 729. 



