



1 



GALVANISM. 361 



ferred to ; but, as has been already stated, the expressions are not so clear as 

 to remove all doubt of his exact meaning. 



Davy uses the term " electrical energy" apparently to express the same phe- 

 nomenon which Volta called " electro-motive action," and which had been also 

 called "Voltaic action." This term denotes the quantity of electricity evolved 

 upon the two metals on either side of their common surface, according to Vol- 

 ia's theory of contact. The act of conveying forward through the series in 

 each direction the electricity, positive and negative, thus propagated at the 

 common surface, is called by Davy the " restoration of the electrical equilib- 

 rium which was disturbed by the electrical energy of the metals." Strictly 

 speaking, there is no restoration whatever of electrical equilibrium during the 

 action of the pile. The electric fluids are never in a state of repose. Two 

 currents run in uninterrupted streams in opposite directions. When therefore 

 Davy says that " the chemical changes" produced by the liquid interposed be- 

 tween the metallic elements of the pile are "the causes that tend to restore 

 the equilibrium," he must, as we conceive, be understood to mean that these 

 changes are " the causes by which the electric currents are propagated toward 

 the poles of the pile." 



Having premised these explanations, let us now consider the reasoning and 

 the facts on which this theory of Davy has been based. He denies that the 

 liquid elements of the pile can act as an ordinary conductor of electricity > the 

 term conductor being used in the same sense as when applied to the metals 

 and other solid conductors, because, with regard to electricities of such very 

 low intensity, water (as well as liquids in general) is an insulating body. Be- 

 sides, there is every reason to believe that, " if the fluid medium were a sub- 

 stance incapable of decomposition (by the metallic elements), the motion of the 

 electricity would cease." When the liquid in a Voltaic arrangement of zinc 

 and copper is a solution of muriate of soda, decomposition ensues. The oxy- 

 gen and muriatic acid pass through the fluid from the copper toward the zinc, 

 transporting or transported by the negative current ; and the hydrogen and soda 

 pass from the zinc toward the copper, transporting or transported by the posi- 

 tive current. Whether the author considered that the transfer of the electricity 

 is effected by the locomotion of the decomposed elements through the fluid, or 

 by a series of decompositions and recompositions, in which there is no motion 

 of translation imparted to any of the elements resulting from the decomposi- 

 tion, and in which the electricities themselves are not transferred through the 

 fluid, but rendered alternately free and latent as the successive decompositions 

 and recompositions are effected, does not appear from the developments con- 

 tained in this paper. 



A pile of twenty-four pairs, in which the connecting fluid was water free 

 from air, had no Voltaic power. To determine whether another liquid with 

 superior conducting power, but still incapable of chemical action, would be af- 

 fected, concentrated sulphuric acid was tried. No permanent current was pro- 

 duced. Solutions of neutral salts render the pile active at first ; but when, by 

 continued decomposition, the solution in contact with the zinc becomes acid, 

 and that in contact with the copper alkali, the action ceases. Dilute acids 

 >3ing themselves easily decomposed, and promoting the decomposition of the 

 water, dissolving the oxide of zinc as fast as it is formed, and evolving gases 

 only on the copper side, are the most powerful and durable fluid elements for 

 a pile. All these facts supply converging evidence upon the position that 

 chemical action is essential to the vitality of the Voltaic apparatus. 



Against the hypothesis that chemical change is the primary source of the 

 action of the pile, it is contended that in a combination of zinc and copper 

 plates with dilute nitrous acid, the side of the zinc exposed to the acid is posi- 



