MICHAEL FARADAY — HIS LIFE AND WORKS. 235 



been i^iven of this plicnomcnon, and concludes that it is much rather a chem- 

 ical plieuoraeuon than a truly electrical one. In other words, it is a peculiar 

 form of atlinitv which, under tho influence of electricity, is exerted between the 

 neighboring molecules, so that the decomposition is the easier in propoilion as 

 tho affinity is stronger. He shows that the transfer of the elements can only 

 take place between bodies the constituent parts of which have an affinity for 

 each other ; and if these elements separate in a free state against the surface of 

 the metallic poles of the pile, this is because they cannot comltine with the sub- 

 stance of these poles ; for whenever this combination is possible, they are no 

 longer set free. "Water in some cases, air in others, as we have already seen, 

 may serve as poles just as well as solid bodies. Faraday justly rejects the old 

 idea of certain physicists who attributed electro-chemical decompositions to the 

 ordinary electrical attractions and repulsions exerted upon the elements of a con- 

 ductive liquid by the voltaic poles immersed in it. The metallic wires, or other 

 conductors, which transmit electricity into a liquid, are merely, according to 

 him, the roads by which the electric cmTent passes into the liquid ; therefore, to 

 exclude any idea of electrical tension, which is more or less implied in the name 

 2)0le^ Faraday proposed to substitute for the denomination poles that of elec- 

 trodes. He liliewise applied the term electrolysis to the chemical decomposition 

 eflected l)y electricity, reserving that of analysis for the ordinary chemical 

 decompositions in which electricity does not assist. Lastly, he gives the name 

 of electrolytes to those compound bodies which are capable of being decom- 

 posed by the electric current. 



After this preliminary and general study of the subject, Faraday enumerates 

 the results which he obtained by submitting to electro-chemical decomposition a 

 very great number of compounds, some of them simple acids or simple bases, 

 others saline combinations. He dwells particularly on the secondary effects 

 often manifested in these decompositions, especially in tho case of aqueous solu- 

 tions, in which decomposition of the water and of the substance dissolved takes 

 place at the same time. But the essential point of his researches is the law at 

 which he arrived as to the definite nature of electro-chemical decomposition. 

 He demonstrates, relying solely upon experiment, that the quantity of chemical 

 action exerted by an electrical ciuTcnt is proportionate to the quantity of elec- 

 tricity constituting this current ; and, further, that the same quantity of elec- 

 tricity, or the same current, decomposes cliemically equivalent quantities of all 

 the compound bodies through which it is passed. Thus, if we place one after 

 the other in the circuit of a voltaic pile, several pieces of apparatus arranged 

 for the decomposition of water and for collecting the gaseous products of this 

 decomposition, we find that in all, even when the degree of acidity of the water 

 and the form and size of the electrodes are different in each, the same current 

 traversing them for a given time produces the same quantity of gas, and conse- 

 quently decomposes the same quantity of water. The quantity of water decom- 

 posed in a given time, appreciated by the quaiitity of gas evolved, is, therefore, 

 the exact measure of the quantity of electricity which has produced this effect. 

 Hence, like Faraday, we give the name of voliayneter to the very simple appa- 

 ratus which holds acidulated water destined to be decomposed by the current, 

 and by means of which the volume of gases set free by this current in a given 

 time may be exactly measured. 



Tho second principle, that the same quantity of electricity decomposes chem- 

 ically equivalent quantities of all compound bodies, was demonstrated by Fara- 

 day by placing several different electrolj'tes one after tho other in the same cir- 

 cuit ; as, for example, acidulated water in a voltameter, and protochlorido of tin 

 and chloride of lead in a state of fusion ; and ho obtains quantities of tin, lead, 

 chlorine, hydrogen, and oxygen, which are chemically equivalent. Then, rising 

 fi-om the effect to tho cause, ho comes to the conclusion that there is a perfect 

 equality between the electricity which decomposes a body and that which is 



