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May, 1930]
STOP BATHS AND FIXING BATHS
503
acid after processing 150 feet of film per gallon, was capable of treating 250 feet of film per gallon before a decrease in the hardening properties occurred. The hardening action was restored by the addition of acid but decreased on further exhaustion up to 380 feet per gallon. The original degree of hardening was again obtained after the addition of acid and the hardening action again decreased after processing 500 feet of film per gallon. After revival with acid the hardening properties increased but decreased rapidly on further exhaustion
g'30 -90
3.0
4.0
3.0
4-0
2 % CHROME ALUM TOT
O MELTING RREVIVAL
\$— 4
FRESH
epH
FRESH
I WEEK
FEET PER GALLON
I WEEK
100 200 300 4OO 3OO 60O 7OO QOO
FIG. 9. Effect of exhaustion with acid revival on the hardening properties of a plain 2 per cent chrome alum stop bath (D-16 developer, 70 °F.).
when they were not satisfactorily revived by the addition of acid. The hardening action of the samples was again determined after storing for one week. With the samples taken before revival a minimum degree of hardening was obtained except in the case of the sample taken at 150 feet when the hardening action was satisfactory. This indicates that the bath should be revived more frequently if uniform hardening properties are desired.
With D-16 at 70°F., the 3 per cent bath, when exhausted and revived in a manner similar to that employed for the 2 per cent bath, showed more uniform hardening properties (Fig. 10). A maximum degree of hardening was maintained throughout the ex