26 THE .MECHANISM OF LIFE 



find that the metals or metallic radicals of the solution are 

 liberated at the negative pole, while the acid radicals of the 

 salts and acids and the hydroxyl of the bases are liberated at 

 the positive pole. The liberated substances may either be dis- 

 charged unchanged, or they may enter into new combinations, 

 causing a series of secondary reactions. 



Electrolytes. — Solutions which conduct electricity are called 

 Electrolytes, and the conducting metallic rods dipping into 

 the solution are the Electrodes. Faraday gave the names 

 of Ions to the atoms or atom -groups liberated at either 

 electrode. The ions liberated at the positive electrode are the 

 Anions, and those at the negative electrode are the Cations. 

 The only solutions which possess any notable degree of 

 electrical conductivity are the aqueous solutions of the various 

 salts, acids, and bases, and in these solutions only do we meet 

 with those phenomena of dissociation which are evidenced by 

 anomalies of osmotic pressure, freezing point and the like, 

 — anomalies which show that the solution contains a greater 

 number of molecules than that indicated by its molecular 

 concentration. These anomalies are due to dissociation, the 

 division of some of the molecules into fragments, each of 

 which plays the part of a separate molecule, contributing its 

 quota to the osmotic tension and vapour pressure of the 

 solution, in fact to all the phenomena which are dependent 

 on the degree of molecular concentration. The electrical 

 conductivity of a solution is therefore proved to be dependent 

 on its molecular dissociation. 



Arrhenius'' Theory of Electrolysis. — In 1885, Arrhenius 

 brought forward his theory of the transport of electricity by 

 an electrolyte. According to this hypothesis, the electric 

 current is tarried by the ions, the positive charges by the 

 cations, and the negative charges by the anions. In virtue 

 of the attraction between charges of different sign, and 

 repulsion between charges of like sign, the cations are 

 repelled by the positive charge on the anode, and attracted 

 by the negative charge on the cathode. Similarly the 

 anions are repelled by the cathode and attracted by the 

 anode. 



