1 8 POPULAR SCIENCE MONTHLY. 



ford 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 hydrochloride 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 atoms having a slightly greater 

 attraction for electrons than the neutral zinc atom. The zinc is there- 

 fore slightly electrified positively and the copper negatively. Accord- 

 ingly 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 there- 

 fore 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 the equivalent 

 of the exhaustion of the chemical potential energy of the cell. Thus 

 the electronic theory outlines for us in a simple manner the meaning 

 of voltaic action. Even if we do not admit the existence of a metallic 

 junction volta contact force, the theory of the cell may be based on 

 the view that the movement of the saline ions in the electrolyte is 

 determined by the law that that motion takes place which results in 

 the greatest exhaustion of potential energy. Hence the chlorine ions 

 move to the zinc and not to the copper. 



In the same manner the electronic theory supplies a clue to the 

 explanation of the production of an electric current when a conductor 

 is moved across a magnetic field. Every electron in motion creates a 

 magnetic force. Hence a uniform magnetic field may be considered as 

 if due to a moving sheet of electrons. The ' cutting' of a conductor 



