10 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



deposited from a solution of a ferrous salt as from a solution of a 

 ferric salt, provided that the deposition is not complicated by 

 secondary reactions which cause the deposit to be redissolved 

 chemically. 



5. The dissociation theory of electrolysis. The molecules of 

 an electrolytic salt or acid when in solution, or when melted, are 

 thought to be more or less dissociated into what are called ions. 

 For example, the molecules of copper sulphate (CuSO 4 ) in a 

 dilute aqueous solution are all dissociated into Cu (cathions) and 

 SO 4 (anions) ; the molecules of sodium chloride (NaCl) in a 

 dilute aqueous solution are all dissociated into Na (cathions) 

 and Cl (anions). These ions are supposed to be electrically 

 charged* and to wander about through the solution. When an 

 electric current flows through the electrolyte, the positively 

 charged ions (cathions) move towards the cathode where they 

 part with their positive charges and are deposited as hydrogen 

 or metal, as the case may be, and the negatively charged ions 

 (anions) move towards the anode where they part with their 

 negative charges. This movement of positively and negatively 

 charged ions constitutes the electric current in the electrolyte. 



Conception of Faraday 's first law. All of the ions of a given 

 substance have the same electric charge so that the strength of 

 the current is proportional to the number of ions deposited per 

 second on one of the electrodes. 



Conception of Faraday's second law. All monovalent ions 

 carry the same amount of charge, the charge on a monovalent 

 cathion being positive and the charge on a monovalent anion 

 being negative. For example, the cathions in the following 

 series of chlorides are all monovalent, hydrochloric acid (HC1), 

 potassium chloride (KC1), sodium chloride (NaCl), and cuprous 

 chloride (CuCl), and the same number of atoms of H, K, Na, and 

 Cu are deposited from solutions of these chlorides in a given 

 time by a given current, so that the electrochemical equivalents 



* See Art 85 for definition of electric charge. 



