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678
LEVENSON
December
Running Cost
In order to illustrate the relative cost in developing agents of running the various systems, without processing film, the values from Table II are shown pictorially in Fig. 8, 1 .0 gram of Elon being taken as equal in cost to 2.0 grams of hydroquinone*
At pH. 8.7, in the case of D76d, the loss of developing agent is negligible in the quiet circulation system. The cost of running the S-R Spray system is about one third of that for the air-trapping and about one fourth of that for the air-bubbling system. The cost of running the L-R Spray system is far greater than any of the others.
-H SPRAY QUIET
AIR-TRAPPING
COSTS IN GRAMS HYDROOUINONE PCH HOUR
Fig. 8 — Diagrammatic representation of the data given in Table II. The values refer only to the cost of chemicals wasted by aerial oxidation.
At pH 10.5 both the spray systems are more costly to run than the other systems. The quiet-circulation system loses an insignificant quantity of developing agent. The air-trapping and air-bubbling systems cost about two thirds as much as the S-R Spray system, and about one sixth as much as the L-R Spray system.
At pH 10.0 the cost of running the two spray systems is roughly two thirds of the cost at pH. 10.5.
The presence of colloidal silver made no significant difference to the cost of running, and in the diagram the best value for a particular system is probably the mean between the figures shown for the rates with and without the colloidal silver.
The minimum cost of running a bath depends upon the amount of silver that is to be reduced to form the image. Evans8 quotes figures for the silver content of 1000 feet of motion picture positive image;
* Based on prices in Great Britain.