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SYMBOLS
Symbol Definition
A Rate of carry-over of liquid into tank
B Rate of loss of solution from tank
Bc Rate of loss of solution from tank by carry-over
B0 Rate of loss of solution from tank by overflow
C Concentration
C0 Desired concentration of constituent in processing
solution
Cr Concentration of constituent in replenisher solution +jO Rate of removal of constituent from solution due to
chemical reaction — D Rate of addition of constituent to solution due to
chemical reaction / Quantity of leader or film
R Rate of addition of replenisher solution
T Tank capacity
V Rate of passage of film through machine W Quantity of constituent in tank W0 Initial quantity of constituent in tank Wr Quantity of constituent in replenisher
Units
Gallons per foot Gallons per foot Gallons per foot Gallons per foot Grams per liter Grams per liter
Grams per liter Grams per foot
Grams per foot
Feet
Milliliters per minute
Gallons
Feet per minute
Grams
Grams
Grams
however, is often wet when it reaches the developer, and the amount of liquid carried in by the entering film does affect the formulation of the replenisher and the rate at which it should be pumped into the developer tank.
Empirical methods have generally been used in establishing replenishment formulas and rates. In commenting on a paper by Evans1 dealing with calculation of developer concentrations, Townsley2 reported that the "cut and try" method of establishing a replenishment technique had worked well in his laboratory. Townsley indicated that over 25,000 ft of 16mm film had been processed weekly for 18 months, and required no adjustments in developing time or replenishment rate. Baumbach3 described replenishment techniques which had also proved quite workable. He reported that occasionally, in an unpredictable way, processing solutions strayed from the desired concentration levels, so that they had to be readjusted. Baumbach also indicated that close sensitometric and chemical control had to be employed in order to detect trends away from gamma and density standards.
Bates and Runyan4 described replenishment techniques which "were formulated using solution-analysis techniques" and proved successful "when used in combination with photographic and analysis tests." The schedule of analyses listed by Bates and Runyan included sensitometric tests every 15 min; temperature and pH checks every hour; bromide analyses every 4 hr; ferrocyanide analyses, specific gravity and silver analyses every 8 hr; and complete developer analyses every 48 hr.
Empirical methods have proved unsuccessful in some respects. A replenishment technique developed empirically will always work well for the particular operating conditions under which it was developed. When small changes in operating procedure, such as a readjustment of machine speed, are made, uncertainty about the effects makes it necessary to follow closely with control tests. New situations, such as a change from original negative to dupe negative, require that the trial-and-error process of finding a new replenishment rate start again right from the beginning. Also, empirical methods tend to be
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January 1954 Journal of the SMPTE Vol.62