343 



communication had been made through water ; but, on the other hand, solu- 

 tions of the sulphurets were incapable of acting chemically on the zinc. If, 

 therefore, chemical action on the zinc be a necessary condition to ensure trie 

 activity of the pile, such an arrangement must be inactive. Twenty-five pairs 

 of silver and zinc plates, erected with cloths moistened in solution of sulphuret 

 of strontia, produced no sensible action, though the moment the sides of the 

 pile were moistened with nitrous acid, the ends gave shocks as powerful as 

 those of a similar pile constructed in the usual manner. 



The next question brought to the test of experiment was, whether the chem- 

 ical action which takes place between the liquid and the plates of the pile is 

 of the same kind as that which is manifested when water is decomposed by 

 its extreme wires ; that is, whether, when the oxygen is freed upon the surface of 

 the zinc, the remaining constituent of the solution decomposed is also liberated at 

 the surface of the zinc, as in ordinary oxydation ; or is transmitted invisibly through 

 the fluid to the surface of the silver, and there deposited, or otherwise liberated, 

 as in the decomposition between the positive and negative wires. An arrange- 

 ment of zinc and copper plates, in the form of the couronne des tosses, was 

 formed, and charged with spring water. The general result of these experi- 

 ments showed that the hydrogen liberated by the zinc was manifested not at the 

 zinc, but at the silver surface ; and, therefore, that the action in the cells is 

 similar to the decomposition of water at the extreme wires of the pile. The 

 phenomena were, however, rendered less decisive of the question by the mod- 

 ifications produced by the azote of the common air combined with the water, 

 and also by saline matter which it held in solution, effects which were then 

 imperfectly understood. 



The inventor of the pile maintained that, among the metals, those which 

 held the extreme places in the scale of electro-motive power were silver and 

 zinc ; and that, consequently, these metals, paired in a pile, would be more 

 powerful, coEteris paribus, than any other. But as he also showed that pure 

 charcoal was a good conductor of the electric current, and that the electro- 

 motive virtue depended on the different conducting powers of the metallic ele- 

 ments, it was consistent with analogy that charcoal, combined with another 

 substance of different conducting power, would produce Voltaic action. Dr. 

 Wells accordingly showed that a combination of charcoal and zinc produced 

 sensible convulsions in the frog ; and Davy, adopting this principle, constructed 

 a couronne des tasses, consisting of a series of eight glasses, with small pieces 

 of well-burned charcoal connected with zinc by pieces of silver wire, using a 

 solution of red sulphate of iron as the liquid conductor. This series gave 

 sensible shocks, and rapidly decomposed water. Compared with an equal and 

 similar series of silver and zinc, its effects were much stronger. Hence he 

 inferred that charcoal and zinc formed a combination equal, if not superior, to 

 any of the metals. 



Volta was understood to refer the electro-motive power of the metallic ele- 

 ments of the pile to the difference of their powers as conductors of electricity. 

 The experiments of Davy induced him to connect the electro-motive power 

 with the amount of chemical action on the more oxydable metal. These two 

 prii.dples might, nevertheless, be compatible, if it could be shown that the 

 oxydaiion was dependant on, and proportional to, the difference of conducting 

 power of the metals. To test this, it was only necessary to construct a pile 

 with metals of nearly equal conducting power. With this view, Davy con- 

 structed a pile with gold and silver plates, these metals being supposed to dif- 

 fer very little in their power of conducting electricity, interposing disks of cloth 

 moistened with dilute nitric acid. Voltaic action was produced. A similar 

 pile, formed of plates of silver and copper, and a solution of nitrate of mercury, 



