THE ALUMINUM ELECTROLYTIC CONDENSER 



43 



upwards of 300 volts, at least for limited periods. If a film is formed 

 on a piece of aluminum to this maximum voltage and the metal is 

 then made the anode in an electrolytic cell across which variable 

 potential can be applied, a current corresponding to a density of less 

 than a microamp. per sq. cm. of filmed surface will flow when a 

 potential of one tenth the maximum voltage is impressed. 



LJ 



'-'3 



tr-i 



§- 

 o 



3. 



ALUMINUM ASYMMETRICAL CELL IN 

 AMMONIUM BORATE ELECTROLYTE 

 350 VOLT FILM 



80 



ALUMINUM 

 NEG. 



80 



160 



240 



ALUMINUM POSITIVE 

 POTENTIAL ACROSS FILM -VOLTS 



320 



400 



480 



Fig. 2 — Influence of potential on the current through an electrolytic cell with a 

 film-coated aluminum electrode 



As the potential is increased this "leakage" current will increase 

 at a rate somewhat greater than proportionate to the voltage. As 

 the maximum or breakdown potential is approached it will be noticed, 

 if the room is darkened, that the anode begins to glow uniformly over 

 the surface with a pale light and with further increases in voltage 

 sparks begin to scintillate over the entire electrode, being noticed 

 first at the surface of the electrolyte. The current through the cell 

 becomes appreciable under this condition and increases more rapidly 

 until at voltages slightly above the sparking potential the cell acts 

 virtually as a short circuit. 



