460 



Prof. Williamson on the Dynamics 



arrangement of atoms which I would gladly have spared you had 

 it been possible to do so. 



It will be most convenient for our purpose to select for con- 

 sideration the very simple case of a cell containing a zinc plate and 

 a copper plate immersed in hydrochloric acid. The zinc dis- 

 solves by taking chlorine away from the hydrogen, and hydrogen 

 is evolved from the surface of the copper plate. It is generally 

 admitted that the first step of the process is the establishment of 

 a polar arrangement of the molecules of hydrochloric acid of such 

 kind that the chlorine atoms are turned towards the zinc, the 

 hydrogen atoms towards the copper. The atom of chlorine next 

 to the zinc then combines with it, forming chloride of zinc, and 

 at the same time the atom of hydrogen next to the copper is set 

 free and escapes. But the chlorine cannot combine with the 

 zinc without getting rid of its hydrogen at the same time to the 

 next atom of chlorine in the chain ; and this second atom of 

 chlorine must combine with another of hydrogen instead of the 

 one which is thus taken from it. This goes on till, at the end 

 of this chain of particles, we have in this manner an atom of 

 hydrogen which loses its chlorine, and cannot get another in 

 exchange, hut escapes uncombined on receiving the necessary 

 impulse from the copper plate. In the annexed diagram, Z re- 

 presents the zinc plate, 

 C represents the copper 

 plate, and between them 

 we have the chain of mo- 

 lecules of hydrochloric 

 acid arranged in polar 

 order from zinc to cop- 

 per. If we remove from 

 our diagram the chlorine 

 from one end and the 

 hydrogen from the other, 

 we have a chain of mole- 

 cules in the order in which they are kept after the first action, 

 an order which we may call antipolar. If matters remained 

 in this order, there could be no further combination of zinc 

 with chlorine, no further liberation of hydrogen on the cop- 

 per. We see that there can be no continuous current without 

 a motion of the atoms : the atoms of chlorine must come in 

 contact with the zinc to combine with it, and the atoms of 

 hydrogen in contact with the copper to escape from it, and the 

 original polar arrangement must re-establish itself throughout 

 the whole liquid from the zinc to the copper before the next 

 decomposition ensues. It would be unnecessary to discuss at 

 present the particular manner in which this atomic motion takes 



C1H,C1H,C1H,C1H,C1H,C1H 



