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June, 1930]
STOP BATHS AND FIXING BATHS
681
exhausted to 750 feet per gallon, with acid revival after processing 590 feet and 750 feet, respectively. At these revival points the hardening properties had again decreased but were increased by the addition of acid. The film processed in the samples taken before revival and stored one week reticulated at a low temperature, which indicates that the bath should have been revived more frequently. A comparison between the acidity curve of the fresh bath and the one after storing for one week indicates that the acidity tends to come to
10 170
m u
V30
4.0
•0/70
4.0
FIXING* BATH NO.TL
P-lfe 65 °F R
O MELTING
9 RETICULfCTIQH
5 -SULPHURIZED OH ADDING flC'D
R-R.EV/1/AL.
FR.ESH
100
200
300
400
SOO
600
500
FIG. 4. Effect of exhaustion with acid revival on the hardening properties of chrome alum fixing bath No. II (D-16 developer at 85° F.).
a constant pH value and that satisfactory hardening is produced when the pH of the bath is inaintained between a value of 3.0 and 3.8.
With D-16 (Fig. 4) more uniform hardening properties of the fixing bath No. II were obtained at 85°F. than at 70°F. which indicates that an increase in the temperature increases the hardening action. However, this advantage is offset by the fact that the bath tends to sulfurize more readily at 85°F. than at 70°F. The bath produced a satisfactory degree of hardening up to 600 feet per gallon, but was not exhausted beyond this point because it sulfurized on the addition of acid. No decrease in hardening properties was observed after the samples had stood one week.