86 PROTOPLASMIC ACTION AND NERVOUS ACTION 



centrations. As Pauli^ also has pointed out, many 

 properties (viscosity, osmotic pressure, refractive index, 

 precipitability by alcohol) pass through a minimum 

 which is coincident with the isoelectric point. 



In all colloids the electrical factor plays a special 

 part in changes of aggregation state or dispersion. In 

 precipitation by electrolytes adsorption processes enter; 

 one or the other ion is adsorbed predominantly, i.e., 

 the ion of opposite sign to the colloidal particle; accord- 

 ingly this ion is the precipitant. In general the more 

 readily adsorbed an electrolyte is, the more effective it is 

 as a precipitating agent. Freundlich has shown this 

 clearly for the salts of a number of organic bases.^ 

 The relative precipitating effectiveness of the several 

 salts, with colloidal arsenious sulphide, is shown in the 

 following table: 



c , Precipitating 



^^*'' Concentration 



Aniline chloride 4.1 



P-chloraniline chloride 2.2 



Strychnine nitrate o. 39 



Morphine chloride o. 36 



Neufuchsin o. 30 



The order of precipitating concentrations is the 

 reverse of the order of relative adsorption. 



Theoretically the two ions of an electrolyte should 

 have different adsorption constants in relation to an 

 adsorbing surface. The nature and quantity of the 

 ions adsorbed will influence the electrical conditions at 

 the interface, and, secondarily, all processes in which 

 these conditions are a factor, such as colloidal stability, 



I Cf. W. Pauli, loc. cit. 



^ Kolloid-Z., I (1907), 328; Kapillarchemie, p. 351. 



