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1949
SPRAY PROCESSING
683
Fifty milliliters of the developer under test were placed in a tube 52 centimeters long and of 2.0 centimeters internal diameter. Compressed air, metered by a Rotameter flowmeter, was moistened by bubbling it through a flask of water packed with marble chips, and was injected at the bottom of the oxidation tube through a 0.71-mmdiameter jet. The pressure of the air at the flowmeter was measured by a mercury manometer. The oxidation tube was placed in a water jacket which was set at 20 degrees before each run. Unless otherwise stated, each sample of developer was aerated for 30 minutes. Only the hydroquinone content of the developer was determined, since the relation between the rates of Elon and hydroquinone oxidation, at a given pH, did not seem likely to vary with the general rate of oxidation.
The results for the negative and positive developers are shown in Fig. 11. They are not corrected for the change in pressure of the air (7.5 centimeters mercury at 2000 cubic centimeters per minute) at the measuring point. At pH 8.7 the rate of autoxidation of hydroquinone reached a maximum at an air-flow rate of less than 250 cubic centimeters per minute. Increasing the air flow up to 2000 cubic centimeters per minute produced no increase in the rate of loss of
AIR FlOW IN
Fig. 1 1 — The course of the autoxidation of 50-milliliter samples of the developers, as the degree of aeration was increased.
hydroquinone. The addition of tolusafranine (1 drop of a 1 per cent solution in 50 milliliters of developer) was made in another run, the dye being used as a substitute for the sensitizing dyes, likely to be picked up by a negative developer, which might affect the rate of oxidation. The results, shown by the broken line, indicated no significant change. Neither did the addition of one drop of a 1 per cent copper (sulfate) solution affect the results.
At pR 10.0 (9.97 in Fig. 11) the positive developer showed what was substantially the same mode of behavior, the practical limit to the rate of oxidation of hydroquinone being reached at an air flow of about 1500 cubic centimeters per minute, although very little further increase