136 Analyses of Books. [Aug. 



concluded that the energy of the pile depends upon the chemical 

 action between the liquid conductor and the metals. This 

 liquid must be such as to be capable of oxidizing and dissolving 

 one of the metals ; while it is incapable of acting upon the other. 

 The galvanic energy continues as long as the oxidizementof the 

 metal ; but when this oxidizement is at an end, the energy like- 

 wise ceases to produce any sensible effect. Dr. Wollaston even 

 went so far as to infer, that the evolution of electricity in the 

 common electrical machine depends upon the oxidizement of the 

 amalgam attached to the rubber, and this oxidizement he consi- 

 dered as originating from the oxygen of the surrounding atmo- 

 sphere. Accordingly he found that the electrical machine lost 

 its energy when inclosed within the exhausted receiver of an 

 air-pump; but when the Rev. Mr. Wollaston, at that time 

 Professor of Chemistry at Cambridge, repeated this experiment, 

 the result was different. 



It would appear from the present state of our knowledge that 

 the essence of the galvanic battery is a series of metallic plates 

 so placed that one side is oxidized and dissolved by a liquid, 

 while the other side of each plate is completely screened from 

 the action of the liquid. The plates must all be connected with 

 each other by means of conductors of electricity. The only use 

 of the copper plates in the battery seems to be to protect one 

 side of the zinc plates from the chemical action of the liquid. 

 In what way it produces this effect is not very obvious, though 

 the fact is undoubted. If we were to adopt the notion of Ber- 

 zelius, and, I believe, of Davy, that chemical affinity and the 

 electric forces are merely different names for the same thing, 

 we might be able to form some notion how the effect is brought 

 about ; though not without adopting a theory of electric action 

 very different from the one hitherto adopted. Let us suppose 

 that dilute nitric acid is essentially negatively electric. In that 

 case it will act only on bodies which possess positive electricity, 

 and its action will be most powerful the greater the intensity of 

 the positive electricity in the substance on which it acts. Now it 

 appears from the experiments of Bennet, Cavallo, and Volta, 

 that when a plate of zinc is laid upon a plate of copper, if the 

 two plates be separated, we find the zinc in a plus, and the copper 

 in a minus electric state. If the zinc by this contact becomes 

 decidedly positive, and the copper decidedly negative, then it 

 follows that the diluted nitric acid will act with energy upon the 

 zinc, and not at all upon the copper. 



Sir H. Davy's pile, composed of one metal and two liquids, 

 one of which acted on the metal, while the other did not, shows 

 very obviously that two metals are merely necessary in the 

 galvanic battery in order to screen the one side of the most 

 easily oxidizable metal from being acted on ; while the action 

 goes pn freely on the other side. The sulphuret in Sir EL 



