adduced hy Prof. Faraday in support of Tie la Rive's Theory. 533 



deux lames homogenes de platine, et il est du aiix impuretes 

 dont il est impossible de preserver completement les surfaces 

 metalliques; aussi disparait-il trcs-promptement, et quoique 

 les deux melaux restent dans le liquide, on n'en voit bientot 

 plus aucune trace." 



Then also the learned Genevan sees the voltaic current on 

 immersing in the pure nitric acid the gold and the platina 

 fixed to the ends of the galvanometric wire : he observes that 

 the current itself is not stronger than that produced by the 

 two homogeneous plates of platina ; and he attributes it to 

 the impurities, from which he says it is impossible completely 

 to preserve metallic surfaces. And in proof that this and no 

 other is the cause of that current, M. de la Rive adduces the 

 fact that it disappears immediately, and that however long 

 the two metals may remain in the liquid, in a few moments 

 there is no more trace of it. 



The difference, then, is not in the fact, but in the manner of 

 studying and interpreting it. M. de la Rive not being able 

 to persuade himself that there can be an electric current with- 

 out chemical action, and insisting that neither the gold nor 

 the platina can be injured by the nitric acid, supposes it im- 

 possible entirely to purify the surfaces of the two metals. 

 Instead of this, I imagine that the current is produced because 

 the platina touches the gold metallically, by means of the 

 galvanometric wire, and is immersed with it in a liquid. If 

 the current is weak, it is because the metals are sufficiently 

 near in the voltaic scale; if it vanishes, or rather, if it becomes 

 sensibly weaker in a short time, it is because the current itself 

 increases the electromotive faculty of the gold, and diminishes 

 that of the platina, so that in a short time the two metals be- 

 come almost homogeneous in the voltaic sense of that term. 



M. de la Rive attributes the vanishing of the current to the 

 disappearance of the impurities from the surfaces of the two 

 metals. But I shall here ask if it is desired that the nitric 

 acid may destroy those impurities by means of the little cur- 

 rent which is developed, or that it may be destroyed inde- 

 pendently of it. In the first case, I shall inquire how it hap- 

 pens that if the gold is immersed in the acid a moment before 

 the platina, the galvanometric deviation is extremely weak, 

 and sometimes even nothing. In the second case, the current 

 which is observed when the two plates are allowed to remain 

 immersed in the acid for some time before putting them in 

 communication with each other by means of the wire of the 

 galvanometer, will have to be explained. 



There is still a remark to make respecting the disappear- 

 ance of the current, which M. de la Rive declares to happen 



