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086
LEVENSON
December
To examine the effect of varying the sulfite concentration at pH 10.0, a range of solutions was prepared by mixing solutions A and B in varying proportions:
B
Elon T... .
1.72 grams 3.30 grams 10 . 0 grams 21.2 grams 1 liter
1.72 grams 3.30 grams 200 . 0 grams 21.2 grams 1 liter
10.00 9.98
Hydroquinone
Sodium sulfite, hydrated, analytical reagent . . Sodium carbonate, anhydrous
Water to make
1 Ordinary electrode
pH adjusted to < J 1 ALKI electrode..,
9.94
CM/LITRE N.ZSO,
Fig. 12— The influence of sulfite concentration on the rate of autoxidation of hydroauinone from the Elon-hydroquinone developers.
Because of the wide range in sodium ion concentration, it was deemed unsafe to level the pR values using the ordinary glass electrode. Solution B was brought to pR 10.00 using the ordinary glass electrode; the pR value of the solution as given by an ALKI (high pR) electrode was 9.98. The pR of solution A and the pR values of the intermediate solutions were then measured with the ALKI electrode. All the pR readings fell within the range of 9.94 to 10.00, which may be taken to mean that the pR's of the intermediate solutions were probably intermediate between those of the extreme solutions.
Fifty-milliliter samples of these solutions were aerated at 20 degrees centigrade, using an air flow of 1250 cubic centimeters per minute. The percentage losses of hydroquinone, plotted in Fig. 12, agree with the results of James and Weissberger,12 who found that the initial rate of autoxidation of hydroquinone was inversely proportional to the sulfite concentration. The log-log plot, inset in Fig. 12, shows a reasonably linear relationship over a sulfite concentration range of 20:1.
The conclusion to be drawn from these results is that 40 grams per