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684 LEVENSON December
in autoxidation rate occurred beyond the 1000-cubic-centimeterper-minute stage. At pR 10.5 (10.45 in Fig. 11), however, the rate of autoxidation appeared to reach no limit within practical rates of air flow and increased steadily up to the maximum measurable airflow rate of 2000 cubic centimeters per minute. On increasing the rate of air flow to the maximum that could be tolerated without blowing the developer out of the oxidation tube (about 5000 cubic centimeters per minute), it was found that the hydroquinone was completely oxidized in the 30-minute run. The experiment was repeated, this time reducing the time of aeration to 10 minutes, and the results, after multiplying the actual hydroquinone losses by 3, are shown by the broken line and agree very well with the results obtained previously.
From these results it may be concluded that at pR levels up to 10.0 (at 20 degrees centigrade) the rate of oxidation of the developing agents will increase on increasing the degree of aeration until the concentration of oxygen in solution is sufficiently high to ensure that the autoxidation of the developing agents can take place at the maximum rate permissible under the given conditions of temperature, pK, and sulfite concentration. Increasing the degree of aeration beyond this point has no further influence on the autoxidation rate.
Factors Influencing Autoxidation
Further study of this point might show that the factor setting the level of the maximum rate of autoxidation is the solubility of oxygen in the developer, the maximum being reached at the degree of aeration that is sufficient to maintain the developer saturated with oxygen. Some experiments were made in the hope that this point might readily be cleared up, but the results were ambiguous. Briefly, it was found that adding quantities of potassium chloride up to 200 grams per liter to the following developer:
Elon 2.0 grams
Hydroquinone 5.0 grams
Sodium sulfite, anhydrous 20.0 grams
Borax 2.0 grams
Water to 1 liter
7>H adjusted with sodium bisulfite to 8.7
reduced the percentage of hydroquinone oxidized in a 15-minute run from 5 per cent to 4 per cent (air flow of 1250 cubic centimeters per minute). This evidence tended to favor the oxygen-saturation the