1174 The Galvanic Battery. [No. 108. 



the supply constituting the current was almost entirely derived from 

 that source, but whether metallic contact or chemical action originated 

 and determined the current, was by no means clear to him. To set 

 this point at rest, was therefore the first step in his investigations, and 

 seeing no reason if metallic contact was not essential, why true decom- 

 position by an electric current should not be produced without it, even 

 in a simple circuit composed of two pieces of metal and an interposed 

 fluid, he accordingly instituted some beautiful experiments under this 

 impression, and persevering, ultimately succeeded in obtaining the 

 most satisfactory evidence that metallic contact was not necessary to 

 the production of the Galvanic current. This was farther aptly proved 

 by referring to the spark which appears when the wires of a pair of 

 plates in vigorous action are brought in contact with each other. 

 This spark is occasioned by the electricity passing through a thin stra- 

 tum of air, and its production proves that electro-motion really occur- 

 red while the wires were separated, and anterior to any actual contact 

 between them being the result of the action of pure, unmixed chemical 

 forces. 



From his experiments, Faraday accordingly felt warranted in con- 

 cluding that the electricity of the Voltaic pile is not dependant, either 

 in its origin or its continuance, upon the contact of the dissimilar 

 metals with each other ; that it is entirely due to chemical action, is 

 proportionate in its intensity to the intensity of the affinities concern- 

 ed in its production, and in its quantity to the quantity of matter 

 which has been chemically active during its evolution. Thus when 

 zinc, copper, and dilute sulphuric acid are used, it is the union of the 

 zinc with the oxygen of the water which determines the current, and 

 though the acid is essential to the removal of the oxide so formed, in 

 order that another portion of zinc may act on another portion of water, 

 it does not, by combination with that oxide, produce any sensible 

 portion of the current of electricity which circulates : for the quantity 

 of electricity is dependent on the quantity of zinc oxidised, and in defi- 

 nite proportion to it ; its intensity is in proportion to the intensity of the 

 chemical affinity of the zinc for the oxygen under the circumstances, and 

 is scarcely, if at all, affected by the use either of strong or weak acid. 

 But in considering this oxidation or other direct action upon the metal 

 itself, as the cause and source of the electric current, it is of the utmost 



