210 INDUCTIVE AFFINITY. 



be like a piece of iron connecting two like magnetic poles, 

 which itself is not then polarized. 



But if one of the two zinc plates were less disposed to dis- 

 solve in the acid than the other, from the physical condition 

 of its surface, from the acid being weaker there, or from any 

 other cause, then the plate so situated might become negative 

 to the other, and a voltaic circle of weak power be established, 

 in which both metals were zinc. 



If zinc is alone in the acid, and every superficial particle of 

 the metal equally disposed dissolve, then the zinc every- 

 where exposes a surface in a state of zincous polarity; and an 

 inductive circle in the liquid, starting from one particle of the 

 zinc and returning upon another, cannot be established, as this 

 requires that a part of the zinc surface be chlorous. But if the 

 FIG. 12. zmc contains on its surface a single particle of 

 copper, F (Fig. 12.), a chlorous pole is created 

 upon which an inductive circle starting from 

 an adjoining particle of zinc, A, and passing 

 through the liquid, may return as shewn in the 

 figure. It is the formation of such circles that 

 causes impure zinc, which is contaminated by 

 other metals, to dissolve so much more quickly 

 in an acid than the pure metal. Why such 

 circles are not formed when the positive metal 

 in combination with the zinc is mercury, which 

 forms a fluid alloy, has already been accounted for ; and the 

 nature of the evil which might otherwise attend the amalga- 

 mation of the zinc is now evident. 



The whole chain polarized molecules in the voltaic circle 

 admits of a natural division into two segments, the acid or 

 liquid segment, BCD (Fig. 10.), and the metallic segment, 

 A K F, each of which has a pair of poles, the unlike poles 

 of the two segments being opposed to each other. The pole at 

 B of the acid portion is chlorous, and is opposed to the 

 zincous pole at A of the metallic segment ; while the pole of the 

 liquid segment at D is zincous, and is opposed to the chlo- 

 rous pole of the metallic segment at F. The distribution of 

 polarity in these two segments is, therefore, the same as in 

 two magnets with their unlike or attracting poles in contact. 



Such, then, is the action of affinity by induction, which the 

 mere introduction of zinc and copper in contact into the same 



