GALVANIC ELECTRICITY. 113 



composing the acid, are supposed to be arranged as rep- 

 resented in the figure. The alternation of positive and 

 negative, in copper, zinc, and the line of acid molecules 

 is analogous to the case of the sus- 

 pended keys. As long as the metals 

 are immersed, and made to touch, an 

 atom of zinc constantly combines 

 with an adjacent atom of chlorine. 

 It follows, that no chlorine is set at 

 liberty. As fast as each atom unites 

 with the zinc, its hydrogen combines 

 with the next chlorine, the hydrogen of this, with 

 the next, and so on, as before explained, in the de- 

 composition of water. Hydrogen is therefore con- 

 stantly given off at the surface of the copper. But 

 when the two metals are not in contact above the li- 

 quid, and the circuit is, consequently, not completed, 

 there is no negative influence exerted at the extremity 

 of the copper, and the series of decompositions, before 

 described, does not occur. 



272. A SALT EMPLOYED AS EXCITANT 



Explain how . -,, -iini 



a battery can It is not essential, that an acid shall be used 

 b amit? ed by as tlie excitm g liquid iii the galvanic bat- 

 tery. A metallic salt is sometimes em- 

 ployed. This may be best illustrated, by supposing 

 chloride of copper to be employed instead of hydrochlo- 

 ric acid, which is chloride of hydrogen. The chlo- 

 rine goes to the zinc, as in the previous case, and the 

 copper of the salt, to the strip of copper, placed in the 

 solution. Being a solid, it remains there, and en- 

 crusts the copper, instead of being evolved, as in the 

 case of hydrogen. 



