218 INDUCTIVE AFFINITY. 



the acid fluids commonly employed in the voltaic battery. 

 Each metal is positive to any one below it in the table,, and 

 negative to any one above it. 



Most positive. 



Potassium. 



Sodium. 



Manganese. 



Zinc. 



Cadmium. 



Iron. 



Nickel. 



Cobalt. 



Lead. 



Tin. 



Bismuth. 



Copper. 



Silver. 



Mercury. 



Palladium. 



Platinum. 



Rhodium. 



Iridium. 



Gold. 

 Most negative. 



Zinc which stands high in the list, is the only metal which 

 can be used with advantage in the voltaic battery, as the posi- 

 tive metal. Although closely approaching zinc in the strength 

 of its affinities, iron is ill adapted for the purpose, from the 

 impossibility of amalgamating its surface, the irregularity of 

 its structure, and certain peculiarities of this metal in reference 

 to chemico-polarity. Platinum forms an excellent negative 

 metal from the weakness of its affinities, and is generally used 

 for the plates in the cell of decomposition. Silver also is 

 highly negative, but copper is the only negative metal, which 

 from its cheapness can be used in the construction of active 

 cells of ordinary magnitude. 



But although the difference between two metals in point of 

 affinity be very small, yet their association in the same acid 

 always gives a decided predominance to the affinity of the more 

 positive, by causing the surface of the other to become chlorous, 



