Theories of Electricity . 141 



trolysis of solutions. When an electric current is passed 

 through conducting chemical solutions, known as elec- 

 trolytes, chemical decomposition takes place, and the 

 products of the decomposition appear at the electrodes. 

 In the passage of a current through acidulated water, 

 for example, the components of the water molecule, 

 hydrogen and oxygen, are set free at the electrodes. 



Faraday supposed that the passage of electricity 

 through a solution resulted from a decomposition of the 

 chemical substance into positively and negatively charged 

 carriers or ions. Under the influence of the electric field 

 there was a migration of the positive and negative ions 

 in opposite directions, the positive ions moving to the 

 negative electrode and vice versa. 



Faraday observed that the weight of matter appear- 

 ing at the electrodes, for the passage of a definite quan- 

 tity of electricity through various chemical solutions, 

 bore a very simple and intimate relation to the atomic 

 weights of the elements. The weight of any element 

 set free was directly proportional to its atomic weight 

 divided by a whole number which might be i, 2, 3 or 

 more, depending on what is known as the " valency " of 

 the element. For example, the weight of gold deposited 

 for the passage of a given quantity of electricity was 65.5 

 times the weight of hydrogen. The atomic weight of 

 gold relative to hydrogen is 196.6, so that in this case 

 the dividing number was three. 



