510 



SCIENCE. 



[N. S. Vol. IV. No. 93. 



Important experimental contributions fol- 

 lowed one another rapidly, batteries were 

 perfected, many physical actions of the 

 electrical current were studied, the action 

 of the current upon magnets was discov- 

 ered, measuring instruments for quantita- 

 tive work were invented. Ohm's law was 

 enunciated, etc., so that when Michael 

 Faraday, Sir Humphrey Davy's man of all 

 work and his successor at the E-oyal Insti- 

 tute, with matchless experimental genius 

 and wonderful breadth of view, attacked 

 the problem of electro-chemical action, he 

 had at his command the means for quanti- 

 tative work in this field which enabled him 

 to discover and formulate one of the most 

 important laws of electrolysis. Faraday's 

 charming directness and clearness in the 

 exposition of his work and results con- 

 trast refreshingly with the prolix, flowery 

 and mystifying style of his immediate pred- 

 ecessors ; it at once stamped him a master 

 of the subject treated. Faraday's original 

 notes are well worth studying; they may be 

 taken as models to-day by many who essay 

 to record experimental results and conclu- 

 sions . Confusion in terms and errors in infer- 

 ences occurring in his work are well excus- 

 able ; from our more extended and accurate 

 knowledge, we are inclined to be unfairly 

 critical. A review of Faraday's work in 

 electrolysis alone would be interesting, for 

 in it we may see foreshadowed many impor- 

 tant points in the theories of to-day, though 

 Faraday himself scarcely appreciated them. 



The most important law Faraday con- 

 tributed to the behavior of electrolytes 

 acted upon by a current is stated thus : 



The amount of chemical decomposition 

 in electrolysis is proportional to the current 

 and time of its action. 



The mass of an ion liberated by a definite 

 quantity of electricity, is directly propor- 

 tional to its chemical equivalent weight. 



The quantity of electricity which is re- 

 quired to decompose a certain amount of a 



certain electrolyte is equal to the quantity 

 which would be produced by recombining 

 the separated ions in a battery. 



The latter law, clearly showing the rever- 

 sibility of the process, at once makes the 

 problem one capable of theoretical treat- 

 ment from the standpoint of conservation of 

 energy and has brought most abundant 

 fruit in later years. Faraday, in the main^ 

 accepted Grothuss' hypothesis, differing 

 from him in the conception of the character 

 and manner of action of the forces. Fara- 

 day showed experimentally, by measuring 

 the change of potential between the elec- 

 trodes, that Grothuss' conception of attract- 

 ing and repelling forces, varying inversely 

 as the square of the distance, was untena- 

 ble; he (Faraday) assumed that through 

 the action of the electrodes the chemical 

 afl&nities of the combined ions were so 

 changed or weakened that they acquired a 

 greater attraction for the plates and their 

 neighboring opposite ions ; that decompo- 

 sition and recombination occurred along 

 the entire line. With Grothuss, he as- 

 sumes that each liberated ion has a definite 

 quantity of electricity belonging to it. This 

 theory then demands that the action of the 

 constituent parts of the electrolyte extend 

 to considerable distance, and that the effect 

 of the electrode is to modify or weaken the 

 chemical affinity between the groups so that 

 decomposition results. Faraday leans to the 

 opinion that chemical and electrical forces 

 are identical, and in considering the reversi- 

 bility of the process becomes an advocate 

 of the chemical theory of the Voltaic cell. 



Faraday, though somewhat confused in 

 his nomenclature, brings out very clearly 

 the relations between quantity of electricity 

 and quantity of material separated, and 

 electrical potential and chemical affinity^ 

 though at that time the concept of energy 

 and work done, as a function of both poten- 

 tial and quantity of electricity, was not 

 clearly established. 



