128 COLLOID CHEMISTRY OF THE PROTEINS 



Results for serum albumin are given in Table 49. The 

 limiting value as extrapolated from the curve of protein- 

 normality and ion mobility (Fig. 27) is about 33. 



The rise of the mobility of the protein ions to a maximum 

 corresponds to the increase in valency of the ions, which, as we 



have seen above in the case 

 of inorganic ions, causes a 

 proportional increase in the 

 migration velocity when the 

 size of the ions remains 

 the same. 



Addition of alkali causes a 

 # w '* gradual decrease in the charge 

 on the protein ions with a fall- 

 ing off in migration velocity 

 and finally a reversal with increasing mobility in the opposite 

 direction. A similar effect with inorganic colloids, to which we 

 can ascribe, as Zsigmondy has done, the multiple charge of a 

 single ion, has been described by Burton.* He measured the 

 rate of electrophoresis of gold and silver suspensions before and 

 after addition of increasing quantities of aluminium sulphate, 

 of which the trivalent metallic ion is the source of the positive 

 charge. The results of some of these experiments are given 

 below, the sign of the electric charge being stated as well as the 

 absolute migration velocity. 



Table 70. 

 Colloidal Silver treated with Aluminium Sulphate. 



FIG. 27. 



*** 



V. cm/fee, at i &. 



A comparison of the behaviour of a protein and a colloidal 

 metal is useful in spite of the apparent difference of the two 

 Phil. Mag., 1906 (6), 12, 472. 



