Mr. W. K. Bridgman on the Theory of the Voltaic Pile. 381 



pairs of poles, namely, the metal B and the air above, and the 

 metal A and the acid below, or a voltaic series composed of one 

 metal and two fluids. 



But as the air is a non-conductor, no current can yet be ob- 

 tained. It is essential therefore to insert a conductor as its 

 representative which shall retain the same relative condition of 

 polarity, this polar condition being secured by its having a less 

 affinity for oxygen than the zinc or primary metal. 



A secondary plate of platinum, as in fig. 3, being substituted 

 for the acid and the air of fig. 2, gives 

 an arrangement of two equally polarized 

 plates with their alternate poles in oppo- 

 sition; and having their lower poles joined 

 by a conducting medium, they require only 

 to be connected by their upper poles or 

 electrodes to complete the circuit. 



While separate, the chemical action is 

 confined to the primary plate, and takes 

 place in an upward direction ; but imme- 

 diately the electrodes are put into commu- 

 nication with each other, the action is di- 

 verted to the negative opposed to it in the 

 conducting acid, and is now spread uni- 

 formly over the whole surface of the im- 

 mersed metal. The polarization of the electrodes is thus shown 

 to constitute an integral part of the battery itself; and these, by 

 the addition of conducting-wires, are only made to undergo an 

 extension of surface without alteration of electrical condition. 



It is now obvious that placing between the electrodes any con- 

 ducting substance capable of being decomposed must effect a 

 corresponding action to that which takes place in the exciting 

 fluid, and that an equal amount of chemical action will be effected 

 at either end of the metals. Metallic contact, however, will re- 

 duce the two pairs of poles to one, as in the case of the horse- 

 shoe magnet, and thus effect a concentrated action. 



In the first instance the secondary platinum plate only repre- 

 sents the polarity of the acid and the atmosphere ; but on im- 

 mersing the primary plate, and on this becoming equally polarized 

 and combining with the oxygen of the electrolyte, there is a de- 

 finite amount of hydrogen liberated, which retains its combining 

 force unbalanced, and which then augments the charge of the 

 secondary plate in an equal degree, and thus imparts to it a 

 feeble degree of tension additional to the first power of the com- 

 bination. 



The chemical action occurring with the single metal chiefly at 

 the surface of the fluid and but feebly within the acid lower 



