522 Prof. J. J. Thomson on the Relation between the 

 the increment when Q is increased by 8Q is equal to 



SQ|q — (°"a _(7 b) j j 



or, if Y is the difference of potential between A and B, the 

 increment of the potential energy is equal to 



SQ{V-K-<r E )}. 



Thus so long as V is less than o" A — <r B , an increase in Q 

 w 7 ill be accompanied by a decrease in the potential energy, so 

 that Q will tend to increase; while, on the other hand, when V 

 is greater than <r A — er B , an increase in Q will be accompanied 

 by an increase in the potential energy, so that Q will tend to 

 diminish : there will be equilibrium when V = <r A — (T B . 



We see from this that if an atom of A has a unit negative 

 charge, an atom of B a unit positive one, these atoms will retain 

 their respective charges even though connected by a conductor, 

 unless the potential of B exceeds that of A by more than 

 <r A — (r B , If, on the other hand, A had a positive charge, B a 

 negative one, they would, if connected by a conductor, inter- 

 change their charges unless the potential of B exceeded that 

 of A by more than <7 A — cr B . 



Thus, assuming that 0" is positive for chlorine and negative 

 for hydrogen, an atom of hydrogen could retain a positive 

 charge, and an atom of chlorine a negative one, even though 

 the two were immersed in a conductor, provided the potential 

 of the hydrogen atom did not exceed that of the chlorine 

 atom by more than a certain limit ; whereas if the hydrogen 

 were negatively electrified and the chlorine positively, they 

 would, if immersed in a conductor, interchange their charges 

 unless the potential of the hydrogen atom exceeded that of 

 the chlorine by the same limit as before. 



Chemical Combination. 



Thus, if we have a number of hydrogen atoms and an equal 

 number of chlorine atoms immersed in a conductor, and if 

 initially half of both the hydrogen and chlorine atoms were 

 positively and half negatively electrified, interchange of 

 charges between the atoms would go on until all the hydrogen 

 atoms were positively and all the chlorine atoms negatively 

 electrified. 



For this interchange of charges to go on, however, it would 

 seem necessary that a negatively electrified hydrogen atom 



