232 THE DEVELOPMENT OF ELECTRICAL SCIENCE. 



to be found iu some text-books. Faraday's work is by far the most 

 valuable of the early contributions to the subject. He gave the fol- 

 io AYing laws: 



The amount of chemical decomposition in electrolysis is proportional 

 to the current and the time of its action. 



The mass of an ion liberated by a definite quantity of electricity is 

 directly proportional to its chemical equivalent weight. 



The quantity of electricity which is required to decompose a certain 

 amount of an electrolyte is equal to the quantity which would be pro- 

 duced by recombining the separated ions in a battery. 



These laws are all of the greatest importance, and the last one clearly 

 points out the reversibility of the electrical process. By forcing a current 

 through an electrolyte it is decomposed and the mutual potential energy 

 of the components consequently increased. By allowing the compo- 

 nents to recombine in a battery the mutual potential energy is reduced 

 and a current of electricity is the result. An excellent illustration of 

 this action is exhibited by the secondary battery. 



In 1857 Olausius gave a theory of electrolysis and at the same time 

 reviewed the weaknesses of the hypotheses of Grothuss and others. 

 Clausius assumes that the molecules of the liquid are in continual 

 motion ; that impacts frequently occur which produce temporary disso- 

 ciation, leaving atomic groups charged with opposite electricities, and 

 that during these separations any directive agency, such as an electro- 

 motive force, is able to cause a motion of these atoms in opposite 

 directions. This is probably the first indication of the idea of the 

 purely directive character of the applied electro-motive force taking 

 advantage of dissociation to produce chemical separation. 



The energy side of the problem now began to attract attention, and 

 the development of what may be called the thermodynamics of electro- 

 chemistry began. Among the most prominent workers in this field 

 have been Joule, Helmholtz, Gibbs, Kelvin, Boscha, and Favre. 



In 1853 Hittorf made quantitative determination of the change of 

 concentration near the electrodes when a current is passed through a 

 solution. This work is of historical interest, because it formed practi- 

 cally the starting point for what may be called the modern view of 

 electrolysis. Hittorf's experiments extended over several years and 

 served practically to establish the theory of the migration of the ions 

 in the solution. Hittorf communicated the following laws: 



The change in concentration due to current is determined by the 

 motion which the ions have in the unchanged solution. 



The unlike ions must have different velocities to produce such change 

 of concentration. 



The numbers which express ionic velocities mean the relative distance 

 through which the ions move between the salt molecules, or express 

 their relative velocities in reference to the solution, the change in con- 

 centration being a function of the relative ionic velocities. 



