198 



INDUCTIVE AFFINITY. 



FIG. 



substitution for hydrogen,, as in this experiment, is attended 

 by a train of extraordinary phenomena, which become apparent 

 when a second metal, such as copper, silver, or platinum is 

 placed in the same acid fluid, and allowed to touch the zinc, 

 the second metal being one upon which the fluid exerts no sol- 

 vent action, or a less action than upon zinc. 



The zinc plate being connected by a me- 

 tallic wire with a copper plate, as repre- 

 sented in the figure, and both dipped to- 

 gether in the hydrochloric acid, the zinc 

 copper only is acted upon, and dissolves as rapidly 

 as before ; but much of the hydrogen gas 

 now appears upon, and is discharged from 

 the surface of the copper plate, and not from 

 the zinc. The hydrogen, being produced by 

 the solution of the zinc, thus appears to 

 travel through the liquid from that metal to 

 the copper. But no current or movement in the liquid is 

 perceptible, nor any phenomenon whatever to indicate the 

 actual passage of matter through the liquid in that direction. 

 The transference of the hydrogen must take place by the pro- 

 pagation of a decomposition through a chain of particles of 

 hydrochloric acid extending from the zinc to the copper, and 

 may be conceived by the diagram on the margin, in which 



each pair of associated circles 

 marked cl and h represents a 

 particle of hydrochloric acid. 

 The chlorine cl of particle 1 in 

 contact with the zinc combining 

 er with that metal, its hydrogen 

 h combines, the moment it is 

 set free, with the chlorine of 

 particle 2, as indicated by the 

 connecting bracket below, and liberates the hydrogen of 

 that particle, which hydrogen forthwith combines with the 

 chlorine of particle 3, and so on through a series of particles 

 of any extent till the decomposition reaches the copper plate, 

 when the last liberated atom of hydrogen (that of particle 3 in 

 the diagram) not having hydrochloric acid to act upon, is evolved 

 and rises as gas in contact with the copper plate. 



It is to be observed that this succession of decompositions 

 and recombinations leading to the discharge of the hydrogen at 



FIG. 2. 



zinc 



