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July, 1943] REMOVAL OF HYPO AND SILVER SALTS 19
The film was developed in D-76, rinsed 5 seconds in running water, fixed for 20 minutes, and washed for 10 and 25 minutes in the experimental washing device shown in Fig. 1. In order to maintain constant the quantity of fixing bath lost by carry-over when the film samples were transferred to the washing apparatus, the films were first suspended until the residual fixing bath began to drain drop wise.
It was found that the slight increase in pH (approximately 0.5 unit) of the F-5 fixing bath during exhaustion under these conditions was not sufficient to effect any appreciable change in the rate of removal of hypo. However, when the ^>H of F-6 or F-10 was increased by 0.5 unit, the hypo contents of the films decreased as shown below:
Time of
Washing F-10 F-10 F-6 F-6
(Min) 0H-4.6 0H-5.1 0H-4.9 . PH.-5A
10 0.12 0.02 0.02 Nil
25 0.06 Nil Nil Nil
The £H of the F-23 chrome alum bath increased by 3 units. Removal was very rapid after fixation in chrome alum baths at the £H of the fresh solution and more rapid at higher pH values. It should be remembered that with chrome alum baths the initial hardening and non-sludging properties are retained for not more than 24 hours.10
If no rinse was used between development and fixation with F-5, the pH increased more rapidly and effected somewhat greater
TABLE in
Effect of Exhaustion of Fixing Baths on Rate of Removal of Hypo
Comparison of "Rinse" and "No Rinse" Between Development and Fixation
Eastman Super -XX Panchromatic Negative Film, Type 1232
Hypo Content (Mg per Sq-In) Wash, Wash,
Bath pH 10 Min 20 Min
F-5, fresh unused 4.1 0 . 18 >0 . 04
F-5, exhausted to 400 ft per gallon with
rinse 4.60 0.14 0.34
F-5, exhausted to 400 ft per gallon, no rinse 5.45 <0.005 <0.005 F-5, exhausted to 400 ft per gallon with
rinse, pH adjusted 4.1 0.18 0.04
F-5, exhausted to 400 ft per gallon, no
rinse, pH adjusted 4.1 0.18 0 . 04