42 



BELL SYSTEM TECHNICAL JOURNAL 



used in direct-current telephone power plant equipment ^ utilizes the 

 dielectric property of the film to provide electrostatic capacity. 



Electrical Qualities of Films on Aluminum 



There are a number of electrolytes, including various concentrations 

 of phosphates, borates, tartrates, carbonates and others in which 

 films can be formed on aluminum to withstand maximum potentials 



100 100 200 300 



ALUMINUM NEGATIVE ALUMINUM POSITIVE 



POTENTIAL ACROSS THE FILM -VOLTS 



400 



Fig. 1 — Influence of impressed potential upon the electrical resistance of the film 

 on an aluminum electrode 



^ Young, R. L., Bell System Techn. J., 6, 708 (1927). 



