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134
CINEMATOGRAPHIC ANNUAL
alkalinity increases to a limiting value such that further sulfite additions leave it unchanged.
An increasing solvent action also accompanies increase of sulfite concentration. This solvent action has been known for may years and C. E. K. Mees* and C. W. Piper (I) published data on the quantities of silver bromide necessary to saturate aqueous solution
Fig. 1. Eight minute developments with:
Sodium sulfite, varied ; metol, 2 g /l. Hydro
quinone, 5 g/1; borax 2 g /l. Emul. No. 1612.
Curve Sulfite Fog
1 1 (approx.) .01
2 10 .06
3 50 .13
4 100 .14
of sodium sulfite. Under developing conditions saturation may not be reached and the rapidity of solution may be affected by the other chemicals present. To test this solvent action in developers, test series were mixed differing only in sulfite content. Equal quantities of film were developed for equal times determined. Fig. 2 shows the change of silver content with increase of sulfite concentration. The slope of this curve is increasing rapidly, showing that a markedly greater effect of the solvent action is to be expected at the higher sulfite concentrations. The actual amount of silver observed in the developer was only a small porportion of the silver on the film, so small in fact that we hope to test more fully this solvent action to see if it really is a sufficient cause for the decrease of density observed.
The two effects just cited appear to be sufficient to account for the maximum development produced with increasing sulfite concentration. At low concentrations the increased alkalinity appears to be predominant, while at high concentrations the solvent action seems more important.
Other workers have shown that high sulfite concentration tends to produce fine grained images. From a practical point of view a developer which gives a satisfactory fine grain with maximum effective emulsion speed is to be desired. A sulfite concentration of 75 grams per liter was found to give satisfactorily grain free images, and at the same time to give a high effective emulsion speed.