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July, 1943]
REMOVAL OF HYPO AND SILVER SALTS
21
Negative Film, Type 1232, was developed as recommended and then fixed for four times the apparent "time to clear" (see "Time of Fixation," p. 25) in the Kodak F-5 potassium alum fixing bath without the use of a rinse between development and fixation. The fixing baths used were both fresh and exhausted to 100, 200, 300, and 400 feet per gallon. Similar tests were made with Eastman Motion Picture Positive Film, Type 1301, and all tests with both emulsions duplicated in the Kodak F-23 chrome alum fixing bath and in the Kodak F-24 bisulfite-sulfite non-hardening fixing bath.
5 10 2.0 50
WASHING (MINUTES) 68°F
I 5 10 20 5O
WASHING (MINUTES) <be°p
FIG. 4. Effect of exhaustion of fixing bath on rate of removal of hypo by washing. Eastman SuperJO" Panchromatic Negative Film, Type 1232. Fixed in Kodak F-5.
Curve A— Fresh bath, pR = 4.1.
B — Exhausted to 100 feet per gallon, pR = 4.3. C— Exhausted to 200 feet per gallon, pR = 4.7. D — Exhausted to 300 feet per gallon, pR = 5.1. E — Exhausted to 400 feet per gallon, pR = 5.5.
(a) pR maintained at 4.1.
(b) pR increased with exhaustion from 4.1 to 5.5 as shown above.
The curves in Figs. 3, 4, and 5 illustrate the effects of the degree of exhaustion and changes of pH. of the F-5 fixing bath on the rates of removal by washing of hypo and silver from processed Motion Picture Negative Film, Type 1232.
Fig. 3 illustrates two important relationships between the hypo and silver contents of the film after a given washing time of 5 minutes, namely:
(1) If the pH of the fixing bath was maintained during exhaustion at the pH of the fresh bath, the residual hypo content was essentially constant while the silver content increased appreciably.
(2) If the £H of the fixing bath was allowed to increase (4.1 to 5.5) by carry-over of developer during exhaustion, the residual