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J. I. CRABTREE AND H. D. RUSSELL [ j. S. M. p. E.
TABLE VIII
Effect of Prolonged Washing at Various Temperatures on Film Hardened by Different
Hardening Agents
Temperature and Duration of Washing
Condition of Gelatin or M. P.* °F. after Test
Film No. 1
Film No. 2
Film No. 3
Film No. 4
48hrs. at60°F.
108 °F.
170 °F.
95 °F.
212 °F.
48hrs. at70°F.
104°F.
150 °F.
Slight swell
212°F.
ing -95°F.
24 hrs. at 75 °F.
110°F.
165 °F.
Slight swell
212 °F.
ing -95°F.
24hrs. at80°F.
Soft after 1V<
Soft after 5
Soft — reticu
212 °F.
hrs. -95°F.
hrs. -170°F.
lated 15 min.
212 °F.
24 hrs. at 90 °F.
Reticulated
Reticulated
Reticulated
212 °F.
8 min.
30 min.
2 min.
24 hrs. at 100 °F.
Reticulated
Reticulated
212 °F.
2 min.
5 min.
24 hrs. at 150 °F.
212 °F.
Initial hardness de
termined in usual
way
135 °F.
180 °F.
95 °F.
212 °F.
* M. P. — Melting Point.
Film No. 1 Film hardened in potassium alum hardening fixing bath. Film No. 2 Film hardened in potassium alum hardening fixing bath. Film No. 3 Unhardened. Film No. 4 Hardened in fresh chrome alum fixing bath.
From these results it is seen that chrome alum produces a more rugged type of hardening than aluminum alum. Also, chrome alum hardening is more stable than potassium alum hardening with respect to the action of acids and alkalis. Strips of film were hardened in each of the two types of fixing baths, washed for five minutes in running water, and then placed in solutions of varying concentrations of sodium hydroxide for five minutes. It was found that the hardening produced by both chrome alum and potassium alum is readily destroyed by alkali but the hardening produced by chrome alum is more resistant to the action of acetic acid and sodium hydroxide than that produced by potassium alum.
THE RELATIVE MERITS OF CHROME ALUM AND POTASSIUM ALUM STOP BATHS AND FIXING BATHS
A choice between the use of potassium alum and chrome alum in fixing baths for motion picture work depends upon the particular requirements involved. Usually excessive hardening of motion pic