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July, 1943] REMOVAL OF HYPO AND SILVER SALTS 33
F-5 without alum for 10 minutes.* These operations were then reversed and a comparison made with an emulsion processed (/) in F-5 and (2) with a chrome alum hardening stop bath (SB-3) in combination with a bisulfite-sulfite non-hardening fixing bath (F-24).
The analyses indicated that in the case of potassium alum hardening baths hardening should take place before fixation to obtain the best conditions for effective hypo removal. The most effective combination was the chrome alum hardening bath (SB-3) followed by the bisulfite-sulfite non-hardening fixing bath but this combination was no better than the use of a chrome alum fixing bath (F-23) alone. However, tests with shorter times of washing in a less effective washing system than that illustrated in Fig. 1 showed that the SB-3: bisulfite-sulfite fixing bath combination was more effective than F-23 alone. When exhausted fixing baths were used, the retention of silver paralleled that of the hypo.
(4) Temperature of Processing. — The results of several experiments with various films indicated that for a fixed washing temperature large temperature differences between the developer or fixing bath and the wash water resulted in only small differences in the rate of elimination of hypo and no differences in the rate of elimination of silver.
WASHING
(1) Effect of Nature of Water: (a) pH of the Wash Water.— The pH of the wash water has a very definite effect upon the rate of removal of hypo as shown in Table V. Eastman Fine-Grain Release Positive Film, Type 1302, was developed, fixed, and washed for 5 minutes at 65°F in tap water at a />H of approximately 7.0, and then further washed by bathing in trays of water at different pH values.
TABLE v
Effect of pH of Wash Water on Rate of Removal of Hypo (Potassium Alum Fixing
Bath) Eastman Fine Grain Release Positive Film, Type 1302
Concentration of Hypo (Mg per Sq-In) £H 2 Min Washing 5 Min Washing
3.4 0.13 0.07
5.4 0.09 0.05
8.0 0.04 0.02
10.0 Nil Nil
* Formulas of this type are necessary because those similar to the non-hardening F-24 fixing bath sludge when only one-half exhausted.