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374 Transactions of S.M.P.E., Vol. XIII, No. 38, 1929
not affect tjae time of fixation and state that in the case of hardened film which does not melt at 212° F. as compared with a film melting at 105° F., the time of fixation is the same in both cases. Experiments by the authors have indicated that although an excessive quantity of the hardened constituents retards fixation, for all practical purposes when using normal hardening baths with motion picture film, the hardener does not materially affect the time of fixation.
Strauss^^ and Lehmann and Busch^^ have observed that the accumulation of potassium iodide in a fixing bath used for fixing bromo-iodide emulsions has a considerable retarding effect on the rate of fixation. Experiments by Crabtree and Ross^^ indicate that the addition of 3 grams per liter of potassium iodide to a 30% hypo solution doubles the time to clear a negative emulsion at 70° F.
(3) The effect of temperature on the time of fixation is likewise shown in Fig. 2. With positive motion picture film an increase in temperature from 55° to 75° F. changes the time of fixation from 50 seconds to 30 seconds in a 30% hypo solution, while with negative film the same temperature change alters the time of fixation from 3 to 2 minutes in a 40% hypo solution. For maximum efficiency it is therefore necessary to maintain the temperature of the fixing bath not lower than 60° F.
(4) The effect of agitation on the rate of fixation is shown in the following table.
Table I
Effect of Agitation on the Time to Cleai
at 65° F.
Hypo
No
Agitation
Continuous
Brush
Cone.
Nature of Film
Agitation
every SO sec.
Agitation
Treatment
35%*
Eastman Panchromatic Negative
120 sec.
120 sec.
105 sec.
90 sec.
35%
Eastman Motion Picture Positive
35 sec.
35 sec.
30 sec.
10%
Eastman Motion Picture Positive
150 sec.
120 sec.
90 sec.
75 sec.
* Crystalline liypo was used. A
35% solution
was prepar
ed by dis
solving 35 grams in water and then adding water to make 100 c.e. of solution.
It is seen that with motion picture negative film a very thorough renewal of the fixing bath at the surface of the film by brushing causes the emulsion to clear in 90 seconds at 65° F. as compared with