IONS GIVE THE ELECTRICAL CHARGE 93 



electrolytes (crystalloids) the substance dissociates 

 into ions which wander to the positive or negative 

 pole as they are negatively or positively charged. 

 But if a similar current is sent through a colloidal 

 solution the, particles all move in one direction and 

 accumulate upon the positive or negative electrode 

 according to the charge they have. This is con- 

 clusive that such particles have an electric charge. 

 The native protein has a negative charge, and its 

 particles collect about the cations or metallic ions, 

 which are miniature positive electrodes, and they 

 accumulate thereon until aggregates of sufficient 

 size are produced to cause precipitation. 



It has been shown, by Biltz and others, that there 

 is further a connexion between the electrical charge 

 and the precipitation. Oppositely charged colloids 

 mutually precipitate each other, and such precipi- 

 tated colloid has no electrical charge, i.e. it does 

 not move with the electric current. Pauli and Hoff- 

 meister demonstrated that the electrical charge 

 possessed by proteins is entirely due to their associa- 

 tion with ions. Hardy and Bredig endeavoured to 

 show that the electrical phenomena of colloidal par- 

 ticles were dependent upon an antagonism between 

 the surface tension and the electrical charge of the 

 colloidal particles. But Billitzer does not consider 

 that surface tension plays the part attributed to it 

 by the former. If oppositely charged ions are added 

 to a colloid, the colloidal particles collect about 

 those ions through electro-static attraction, the ions 

 acting as electrodes, and aggregates are formed 

 which are precipitated or go into solution according 

 to the nature of the ion. Pauli performed a number 



