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150 CINEMATOGRAPHIC ANNUAL
However, in the case of developers containing borax, which are very sensitive to slight changes in alkalinity, the presence of an appreciable quantity of calcium salts would be sufficient to lower the alkali content and due allowance for this should be made.
Salts liable to be present other than the above are chlorides and bromides of the alkali metals which exert a restraining action. Sodium carbonate which is present in certain alkaline waters tends to speed
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Fig. 1
Photomicrograph of developer sludge (calcium sulfite) caused by
presence of calcium salts in water supply.
up the action of a developer weak in alkali, although with the average developer the concentration of the alkali in the water used for mixing is insufficient to exert any appreciable effect.
Developers mixed with water containing sodium or potassium sulfides will give bad chemical fog even if the sulfides are present in very small quantities.
It is customary to add copper sulfate to certain water supplies at periodic intervals in order to kill vegetable and biological growths. While the presence of 1 part in 10,000 of the copper salt in a developer will cause aerial fog,4 the concentration of the copper salt in the water supply usually is much lower than this.
2. A. Dirt and iron rust suspended in the developer solution often produce spots and stains. In the case of a pyro developer the iron is apt to combine with the pyro forming an inky compound which imparts a bluish red color to the solution although photographically it is harmless.
Particles of finely divided sulfur which give the characteristic opalescence to sulfur waters will cause fog owing to the formation