DIELECTRIC CONSTANT 59 



at different concentrations ; tlic more HCl present, the greater the 

 diffnsion potential. This is due, of course, to the relatively greater 

 speed of the hydrogen ion. The K ions move at about the same 

 speed as the CI ions, while the H ions move about five times as fast. 

 The boiuidary surface previously charged negatively with a low 

 E.M.F. would take on a positive charge with a higher E.M.F. It 

 is imperative to note that unless the electrostatic force mutually 

 exerted between anion and cation is overcome, these ions though 

 separated will never be far apart. 



In ordinary solutions the " metal " ion, no matter what its 

 relative speed, cannot be separated from its " acid " ion by mere 

 diffusion. The disturbance of electrical equilibrium caused by the 

 introduction of electrodes into the solution will produce a separation 

 of the salt into metal and acid. 



Now, if there exist equal and opposite 

 charges on an- and cat-ions, tending to draw 

 them together, why, in the first instance, did 

 they separate, and what keeps them apart ? 

 This brings us to the discussion of the 

 dielectric constant. To put a name on a 

 thing or on a process does not explain it. 

 Neither is it sufficient to say that the 

 dielectric constant or specific inductive 

 capacity of any medium is a measure of the cation anion 



capacity of that medium to act as a dielectric fig. 14.— Model ot anion 



^ •" . . and cation. Two pith balls 



(non-conductmg) substance ot an electric suspended by siik threads 



1 • 1 PI attract one another if carrv- 



condenser. The higher the value of the ing opposite charges, when 



. PI *'i^ charges are of the same 



constant, the greater is the value ot the sign, the bails diverge, i.e., 



repel one another. 



condenser. 



According to the electron theory, an atom is composed of 



protons and electrons. Electrons are all similar, and are supposed 



to be not sensible matter, but the smallest possible unit of negative 



electricity. Atoms of different substances owe their different 



qualities to the varying number of electrons they contain and to 



the diversity of their arrangement. These electrons are supposed 



to exercise an obstructing influence on the passage of an electric 



charge due to their tendency to move in the direction opposite 



to the direction of the current. The larger the number of the 



electrons, therefore, the greater the obstruction. Now it can be 



show^n that when two small electrically charged bodies (charges e 



and e' respectively) are immersed in a medium at a distance r 



ee' 

 apart, the force they exert on each other equals ^r-g, where K is a 



constant for the medium and is known as the dielectric constant. 



