1902.] on the Electronic Theory of Electricity. 175 



Voltaic Action. 



Any theory of electricity must in addition present some adequate 

 account of such fundamental facts as voltaic action and magneto- 

 electric induction. Let us briefly consider the former. Suppose a strip 

 of copper attached to one of zinc and the compound bar immersed in 

 water to which a little hydrochloric acid has been added. 



All chemical knowledge seems to point to the necessity and indeed 

 validity of the assumption that the work required to be done to remove 

 an electron from a neutral atom varies with the atom. Conversely the 

 attraction which exists between a free electron and an atom deprived 

 of an electron also varies. Accordingly the attraction between atomic 

 ions, that is, atoms one of which has gained and one of which has lost 

 electrons, is different. Upon this specific attraction of an atomic 

 ion for electrons or their relative desire to form themselves into 

 neutral molecules depends what used to be called chemical affinity. 

 Mr. Rutherford has shown that negative ions gave up their charges 

 more readily to some metals than others, and most readily to the 

 electro-positive metals. Hence a zinc atomic ion is more ready to 

 take up electrons and again become neutral than a copper ion. 



Consider then the simple voltaic couple above described. In the 

 electrolyte we have hydrogen ions which are H atoms minus an 

 electron, and chlorine ions which are chlorine atoms plus an electron. 

 These are wandering about in a menstruum which consists of water 

 molecules and hydrochloric acid molecules. Then in the metal 

 bar we have zinc and copper divalent ions which are these atoms each 

 minus two electrons, and also an equivalent number of free and mobile 

 electrons. 



If we adopt Volta's original view of contact electricity, we must 

 assume that at the surface of contact of the metals there is some action 

 which drives electrons across the boundary from the zinc to the 

 copper. This may be due to the neutral copper atom having a slightly 

 greater attraction for electrons than the neutral zinc atom. The zinc 

 is therefore slightly electrified positively and the copper negatively. 

 Accordingly in the electrolyte the negative chlorine ions move to 

 the zinc and combine with positive zinc ions, forming neutral zinc 

 chloride, two chlorine ions going to one zinc ion. The hydrogen 

 ions therefore diffuse to the copper side and each takes up a free 

 electron from the copper, becoming neutral hydrogen atoms and 

 there escape. 



In proportion as the zinc atomic ions are removed from the zinc 

 bar and the corresponding free electrons from the copper, so must there 

 be a gradual diffusion of electrons from the zinc bar to the copper bar 

 across the metallic junction. But this constitutes the voltaic current 

 flowing in the circuit. It is a current of negative electricity flowing 

 from zinc to copper and equivalent to a positive current from copper 

 to zinc. The energy of this current arises from the differential 

 attraction of zinc and copper ions for chlorine ions, and is therefore 



