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Fine-Grain D§velope?\s — Carlton and Crahtrcc 429
carbonate were added to a developer in which 40 feet of motion picture film per gallon had been processed. Most of them gave no practical increase in film speed and some of them gave a decrease in speed. Four grams of borax per liter added to an exhausted developer increased the speed of the film by about 50 per cent. Further tests are in progress to determine if there is a practical method of increasing the life of the developer.
4. Effect of Use on the Fogging Properties. The table in Fig.l gives the fog values for fresh borax developer over a wide range of degrees of development. With use, the amount of fog decreases for a constant degree of development on account of the accumulation of bromide ions liberated by the development process. A fog value of 0.20 for a given" degree of development in a fresh developer drops to 0.12 by the time 80 feet of motion picture film have been processed per gallon.
The above values are given for fresh film. Under working conditions the fog depends upon a number of factors which include : (1) the age of the film; (2) the amount of light scatter during exposure in the camera; and (3) the amount of exposure which the film may receive during handling in the darkroom. The fog density obtained in actual practice includes that caused by the developer plus the fog accumulated in the process of handling.
C. Revival of tJie Borax Developer
The equation representing the chemical reactions occurring during development shows that the developing agents, the alkali and sodium sulfite, are used up in the process of development, although the quantity of sulfite which is used up is relatively small. It is obvious therefore that a solution for reviving the developer should at least contain all these ingredients. In practice it was found with the rack and tank method of development that the developer could be revived by adding half the original quantity of Elon, hydroquinone, and borax, together with a small quantity of sulfite after 80 feet of film per gallon had been processed. These were dissolved in as small a volume as possible of a 10 per cent sodium sulfite solution before adding to the developer.
Curve C (Fig. 6) shows the effect of such revival. (Compare with curve B.) The condition of the developer after 160 feet of film had been processed is shown by curve D. (See also Fig. 7)