192 Sir H. Davy on the Relations 



If two, three, or four glasses are used, and two, three, or 

 four arcs of platinum and zinc, the extreme metals of which 

 are connected through the multiplier, a piece of platinum 

 used instead of one of the arcs will not now entirely destroy 

 the electro-motive effect : it will be diminished as if one arc 

 had been removed. The two will act as a single combina- 

 tion ; the three as two arcs, and the four as three ; and of 

 course in a voltaic combination of 100 arcs, a single piece of 

 platinum substituted for any one of the arcs, will diminish the 

 power of the apparatus only 1-lOOdth part. 



In attempting to protect copper by zinc, in a separate ves- 

 sel, from the action of sea-water, I found that when the two 

 vessels were connected by moist tow or vegetable substances, 

 or by a wire (even through fine) of any oxidable metal, the 

 protection was complete : but when even a thick wire of 

 platinum was employed, the copper, though in immediate con- 

 tact with the zinc, became corroded. After the experiment 

 had continued several days, the surface of the platinum op- 

 posite to the copper was found tarnished, as if it had been 

 slightly acted upon by the chlorine combined in the sea-water; 

 but this effect had been too feeble to be connected with any 

 sensible degree of electrical polarity in the platinum. 



This result, with those mentioned in the preceding pages, 

 seems to show that there can be no accumulation of electri- 

 city in voltaic combinations, unless the same or similar con- 

 ditions of chemical change exist in the elements or single cir- 

 cles composing them ; and that under other conditions, the 

 power generated in single circles is either destroyed or di- 

 minished according to the opposing nature, or want of con- 

 ducting power of the chain of intervening bodies. For instance, 

 in the arrangement (mentioned p. 191) of one piece of zinc 

 and one of platinum, the power is doubled by another series 

 of the same kind, destroyed by an arc of platinum, and di- 

 minished by an arc of zinc; by a second solution and a second 

 arc of zinc, it is diminished still more ; by a third it is nearly, 

 and by a fourth absolutely, destroyed. 



As the chemical changes always tend to restore the elec- 

 trical equilibrium destroyed by the contact of the metals with 

 each other in the fluids, it is evident that in cases in which 

 arcs primarily inactive are connected witli those primarily 

 active, the chemical changes produced by the electrical attrac- 

 tions must tend to produce in the primarily inactive parts of 

 the combination, an arrangement which must give it a power 

 in direct opposition to that of the primai'ily active circles ; so 

 that when separated, their actions, if any, must be directly the 

 reverse of the other. This result, which I anticipated, I have 



actually 



