126 COLLOID CHEMISTRY OF THE PROTEINS 



the increase in mobility which the valency increase would 

 produce. 



Moreover, the formation of aggregates composed of both 

 albumin ions and albumin molecules occurs, the latter produced 

 by hydrolysis. In such complex ions (Hardy's pseudo-ions) 

 the mobility will be determined by the proportions by weight 

 and distribution of the component parts, and by other factors. 

 We have already seen that such large ions, together with the 

 metal or acid ions attached to them, will not pass through 

 membranes, and consequently produce a high pressure in the 

 osmometer.. 



The free diffusion of such ions, which has not, so far, been 

 investigated, presents points of considerable interest. Accord- 

 ing to Nernst's theory, the following relation holds between the 

 diffusion constant and mobility of ions : 



but in the case under consideration the high valency of the 

 aggregates makes it necessary to test Hevesy's expanded 

 formula. 



A knowledge of the mobility of the protein ions is important, 

 not only for the general chemistry of the proteins, but also for 

 the solution of many biological problems. A supplementary 

 exposition will therefore be devoted to it. In general, the 

 proteins react with acids and bases with variable valency, and 

 hence the number of possible protein ions is also variable. The 

 simplest case is when, as in sodium caseinate, or in the globu- 

 linates, a maximum quantity of protein is taken up by a given 

 quantity of alkali with formation of a definite neutral salt, 

 giving only one ion of definite and not very high valency. 



With increased addition of acid or alkali, however, new basic 

 or acid valencies of the protein molecule are activated, with 

 formation of ions of different valency ; and only after the maxi- 

 mum combination with acid or alkali can the existence of simple 

 positive or negative valencies be again assumed. Under such 

 conditions the maximum valency is exhibited. In this case 

 the mobility of the protein ions also reaches its highest value. 

 Between these points of saturation only the mean value of the 



