Pure aluminum specimens were anodically oxidized in 13M and 1.5M sulfuric acid solutions at constant c. ds, and measurements were made of the amount of Al
3+ ions accumulated in the formed oxide (W
f), the amount dissolved in the solution (W
d), and the coating ratio of the film. It was found that the sum of W
f and W
d was always equal to the total amount of oxidized aluminum (W
T) as calculated from the quantity of electricity. The amounts of W
f and W
d increased almost linearly with anodization time t
a. For any given value of W
T, the value of W
d obtained was smaller for the 13M solution than for the 1.5M solution, suggesting that the dissolution of the barrier layer at the pore-base proceeds more slowly in the 13M solution than in the 1.5M solution. This concept explains the high voltages and high current efficiencies observed for the formation of 13M films. Since the 13M films had smaller values of W
d and larger amounts of SO
42- ions compared to the 1.5M films, their weights and coating ratios were always larger. In the case of the 13M films, η and CR decrease appreciably with the lapse of anodizing time. This is due to the marked chemical dissolution of the pore walls during anodization.
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