392 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Some of these factors appear to have a more definite influence, or 

 rather a less complicated influence, than others. Temperature, for 

 example, must be considered a more general factor than the others. 

 They are, however, apparently all independent variables within certain 

 limits, and a complete expression for the action of an aluminium anode 

 must include all of them. 



It may be of interest to attempt to segregate the effects produced by 

 variation of these factors. 



1. Formation voltage may determine — 



(a) Thickness of an oxide or hydroxide film. 



(b) Density and thickness of a gas film. 



(c) The perfection of a semi-permeable membrane. 



2. Time of formation (and history of formation in general). 

 Same as 1. 



3. The applied voltage may determine — 



(1 (a) should remain constant for various applied voltages below 

 the voltage of formation unless solution by the electrolyte or 

 other disintegrating action takes place) 



(a) Thickness and density of a gas film. 



(b) Ionic concentration within the active layer of the film. 



4. Time of charge (complete formation assumed) may determine — 



(a) The thickness (distributed) of an insulating or other active 

 ' film. 



(b) The ionic concentration within the active layer of the film. 



5. Insulation time may determine the rate of return to the un- 

 charged condition — 



(a) By disintegration of an insulating solid film. 



(b) By gas diffusion. 



(c) By ionic diffusion. 



6. Time of discharge may determine — 



Factors similar to those in 5, but under conditions varying with 

 the electrical constants of the discharge circuit. 



7. The electrolyte may determine the entire activity or non-activity 

 of the anode — 



(a) By the ions it furnishes, which may or may not be able to 



pass the film it forms (semi-permeable film theory). 

 (h) By its solvent action on the film. 



8. Temperature affects all the above. 



9. Electrical constants of the circuit can affect 4 and 6 especially. 

 All of the effects enumerated are quite open to study, and some of 



them have already been investigated. The authors hope to offer 

 further data on some of these variables in the near future. 



